Volume 23, Issue 1 e13263
COMPREHENSIVE REVIEW
Open Access

Comprehensive review of clean-label antimicrobials used in dairy products

Dasol Choi

Dasol Choi

Department of Food Science, University of Wisconsin–Madison, Madison, Wisconsin, USA

Food Research Institute, University of Wisconsin–Madison, Madison, Wisconsin, USA

Department of Bacteriology, University of Wisconsin–Madison, Madison, Wisconsin, USA

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Wendy Bedale

Wendy Bedale

Food Research Institute, University of Wisconsin–Madison, Madison, Wisconsin, USA

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Suraj Chetty

Suraj Chetty

Food Research Institute, University of Wisconsin–Madison, Madison, Wisconsin, USA

Department of Bacteriology, University of Wisconsin–Madison, Madison, Wisconsin, USA

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Jae-Hyuk Yu

Corresponding Author

Jae-Hyuk Yu

Food Research Institute, University of Wisconsin–Madison, Madison, Wisconsin, USA

Department of Bacteriology, University of Wisconsin–Madison, Madison, Wisconsin, USA

Correspondence

Jae-Hyuk Yu, Department of Bacteriology, University of Wisconsin–Madison, 1550 Linden Drive, Madison, WI 53706, USA.

Email: [email protected]

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First published: 13 December 2023

Abstract

Consumers expect safe, healthy, natural, and sustainable food. Within the food industry, ingredient use is changing due to these consumer demands. While no single agreed-upon definition of clean label exists, a “clean label” in the context of food refers to a product that has a simplified and transparent ingredient list, with easily recognizable and commonly understood components to the general public. Clean-label products necessitate and foster a heightened level of transparency between companies and consumers. Dairy products are vulnerable to being contaminated by both pathogens and spoilage microorganisms. These microorganisms can be effectively controlled by replacing conventional antimicrobials with clean-label ingredients such as protective cultures or bacterial/fungal fermentates. This review summarizes the perspectives of consumers and the food industry regarding the definition of “clean label,” and the current and potential future use of clean-label antimicrobials in dairy products. A key goal of this review is to make the concept of clean-label antimicrobial agents better understood by both manufacturers and researchers.

1 INTRODUCTION

The dairy industry needs to ensure that its products are safe and maintain quality throughout their shelf lives. In the recent years, the industry has also faced pressure from consumer demands for minimally processed foods with easy-to-recognize ingredients. For most consumers, ingredients with chemical names are intimidating and considered “unclean” (Shoup, 2019). Often, these ingredient names are long and scientific, which may make the consumer less likely to purchase a product or apprehensive while eating products with such ingredients. A “clean label” in the context of food refers to a product that has a simplified and transparent ingredient list, with easily recognizable and commonly understood components without showing chemical, long, and scientific names (Innova Market Insights, 2016).

Clean-label products create a new level of transparency between the food company and the consumer. According to a survey performed by the Kerry company, 60% of 2100 US consumers interviewed were familiar with the term “clean label,” with more than 76% of consumers believing that “clean-label foods are healthier than traditional foods” (Kerry, 2019). Another survey of 1300 consumers across three continents (Europe, North America, and Asia-Pacific), conducted by Ingredient Communications, found that a significant majority of consumers (76%) indicated a higher likelihood of purchasing a product that contains ingredients they have confidence in. Additionally, almost one in five respondents (18%) said that they would pay 75% or more for a natural ingredient over a synthetic one (Harman, 2016). A separate survey of 1000 respondents from the United States and the United Kingdom by SurveyGoo found that 36% were less likely to buy a product containing an unfamiliar ingredient (Marrapodi, 2020), while 54% of US respondents in a similarly sized survey by International Food Information Council (IFIC) said that it was “important that ingredients do not have chemical-sounding names” (International Food Information Council, 2021). The 2021 IFIC survey indicated that nearly 50% of consumers in the United States considered chemicals in their food a top food safety concern (International Food Information Council, 2021). Clean labeling is clearly a significant factor considered by the consumers when purchasing foods.

While no single agreed-upon definition of “clean-label” products exists, part of discerning what “clean label” means is assessing what level of chemical manipulation of ingredients in a food product is tolerated by consumers. Preservatives are chemicals that are necessary to ensure the quality and safety of many foods, especially dairy foods that are prone to be contaminated by both pathogenic and spoilage microorganisms. However, the presence of synthetic antimicrobials or preservatives created by humans, rather than occurring naturally, in foods (and on its label) may present concerns for some consumers. Consumers do, of course, expect their food to be safe and free from pathogenic microorganisms, but they sometimes take food safety for granted (Food Safety News, 2019). Furthermore, consumers and retailers are both fiscally and increasingly environmentally conscious and do not want to waste food (Tromp et al., 2016). Complicating the picture further, consumers do not always consume foods, including dairy foods, by a “best by” date, and they may store foods at improper temperatures (Daelman et al., 2013). Given these requirements, it might seem paradoxical that consumers have negative views of synthetic ingredients intended to enhance food safety and extend the shelf life of food products. Food producers are challenged to produce foods that are fresh, healthy, safe, and sustainable with a long shelf life, while avoiding the use of synthetic chemicals. However, traditional synthetic preservatives can be replaced with clean-label ingredients—even sometimes delivering the same active substance—that function as antimicrobials to maintain food safety, shelf life, and the overall quality of dairy products. For instance, citric acid, although it can be artificially synthesized through human processes, can also be naturally derived from citrus fruits or by the fermentation products of Generally Recognized as Safe (GRAS) organisms; the natural alternative will represent probiotics. In this case, the latter will represent products with a clean label to consumers. The objective of this review is to provide insight into the concept of clean-label ingredients, especially those potentially applicable to the protection and preservation of dairy products.

2 DEFINITION OF CLEAN LABEL

The definition of “clean label” varies among consumers and within the food industry and is continuing to evolve (Asioli et al., 2017). Clean-label foods can be identified in part by their ingredients, which usually include natural preservatives, colors, and flavors (Cassiday, 2017) and exclude artifical preservatives and additives (Asioli et al., 2017) as well as unintentional contaminants (Bowen, 2019). Both consumers and industry agree that clean-label foods consist of easy-to-recognize, natural ingredients that are made with little to no chemical processing, but nuances in their perspectives exist (Figure 1). The term “clean label,” as outlined in various sources listed in Table 1, is also being increasingly associated with foods that are labeled natural or organic or are produced in a way consistent with certain values, for example, no bioengineered ingredients, no added hormones or antibiotics, sustainably raised, plant-based, fair trade, minimal and/or environmentally friendly packaging, and so on (Asioli et al., 2017; Janjarasskul & Suppakul, 2018).

Details are in the caption following the image
Description of similarities between industry and consumer regarding “clean-label” products (Asioli et al., 2017; Askew, 2021; Bowen, 2019; California Walnuts, 2020; Cassiday, 2017; Innova Market Insights, 2016; Williams, 2021). GMO: Genetically Modified Organism
TABLE 1. List of some definitions of “Clean Label” given in the literature and other publications.
Definition of “Clean Label” Source Reference
“…industry defines clean label as removing artificial additives, ingredients and preservatives. Meanwhile, consumers relate the term to foods made from natural, recognizable and safe ingredients. Matching all these different expectations is challenging for the industry” Food Ingredients First Durrell, 2020
“Fresh, real, and less processed are certainly words that consumers use interchangeably when they are seeking that clean ideal and ‘kitchen level’ ingredients” Food Navigator Shoup, 2019
“Clean label means making a product using as few ingredients as possible, and making sure those ingredients are items that consumers recognize and think of as wholesome—ingredients that consumers might use at home. It seeks out foods with easy-to-recognize ingredients and no artificial ingredients or synthetic chemicals, and it has become associated with trust with manufacturers of food” IFT Velissariou, 2018
“Clean labels can be defined in a broad (front-of-package, including textual and visual claims, ‘free from’ statements) and strict (back of package information, including an ingredient list with short, simple, not artificial, expected and familiar ingredients) sense” Food Research International Asioli et al., 2017
“Clean labeling is a consumer-driven initiative that encourages food developers to create products with easy-to-understand labels, listing natural ingredients and minimal artificial additives” UGA Cooperative Extension Bulletin 1476 Shangci Wang, 2017

“Clearer and simpler claims and packaging for maximum transparency and necessitating an industry response in terms of reformulation and new communication strategies”

“Shorter and more recognizable ingredients lists”

Innova Market Insights Innova Market Insights, 2016
“A clean label typically means foods with fewer ingredients, preservatives or artificial flavors, colors or sweeteners. Consumers also crave authentic, ethical, simpler alternatives to conventional fast-and-mass production processes. Transparency in the food chain involves many different domains.” Food Processing Magazine Hartman, 2016

2.1 Consumer perspective of clean label

In general, consumers want to feel at ease when buying food as they realize eating, while necessary, can involve risks. Clean-label products help consumers achieve that goal by including ingredients that are familiar, natural, and minimally processed. Artificial ingredients do not generate that same familiarity with the buyer, and foods with bioengineered ingredients are considered by consumers to be highly processed and potentially unsafe, making the consumer more hesitant to purchase them.

To consumers, “clean label” is loosely defined as close to its natural state (Askew, 2021). Natural ingredients are generally regarded as safe to eat by consumers. This usually means fresh, minimally processed foods that are made with “kitchen-level” ingredients (Shoup, 2019). Ingredients that consumers would use in their own cooking are generally acceptable as clean-label ingredients, and consumers are more likely to purchase foods containing such ingredients. However, consumers, without significant supporting evidence, feel that foods that make overt clean-label claims or foods free of bioengineered ingredients are healthier (Bowen, 2019; California Walnuts, 2020; Williams, 2021). Similarly, consumers frequently assume, without substantiation, that foods with clean-label ingredients are better for them than other foods (Asioli et al., 2017).

Consumers are wary of synthetic and unfamiliar ingredients because they perceive those compounds as potentially unsafe. These misconceptions may stem from a lack of understanding of how the US government oversees the safety of food additives, whether they are synthetic or clean label. A regulatory pathway for food additives exists that allows companies to introduce new ingredients into food products without undergoing the lengthy, expensive preapproval process (Neltner, 2021; Quinn & Young, 2015). The US Food and Drug Administration (FDA) has shifted the responsibility of ensuring food additive safety to companies, based on a debatable interpretation of a legal exemption for GRAS substances. Consequently, the FDA does not perform a pre-review of food additives if a company classifies them as GRAS, although it can request documentation regarding their GRAS determination. Clean-label ingredients, which companies themselves designate as GRAS, may be subject to less oversight than new chemical food additives.

2.2 Industry perspective of clean label

The food industry's and consumers’ definitions of “clean label” share common themes. One major commonality is that the ingredients in clean-label products are easily recognizable to the consumer. The food industry deems recognizable ingredients as those with easily pronounced names and those that consumers could purchase at a local grocery store to stock their kitchen cupboards (Cassiday, 2017; Williams, 2021). Clean-label products also tend to have shorter ingredient lists (Innova Market Insights, 2016). In response to the consumer's demand, food companies are increasingly using ethically and naturally sourced ingredients in their formulations.

3 CURRENT STATUS OF COMPANIES AND CLEAN-LABEL FOODS

With a $180 billion global market for clean-label foods (Brewster, 2021), food manufacturers and retailers in the United States are embracing “clean eating.” On the retail side, Whole Foods created its own list of “unacceptable ingredients for food” in 2019, banning more than 235 ingredients from its foods (Whole Foods Market, 2020). Other retail food establishments including Panera, Trader Joe's, Aldi, and Kroger have joined the movement toward clean-label ingredients and foods free from artificial preservatives (BevSource, 2018). On the manufacturing side, large food companies such as Nestle, General Mills, and Kraft have simplified product ingredient lists and continually seek ways to offer “cleaner” ingredients (Taparia, 2015).

The demand for clean-label foods has resulted in an increasing market for clean-label ingredients, which is expected to top $64 billion by 2026 (Brewster, 2021). To meet consumer demand for clean-label foods without jeopardizing shelf life or food quality, food manufacturers and foodservice brands need alternative ingredients to replace synthetic food additives that have long been implemented and demonstrated to be effective. Clean-label preservatives and/or clean-label antimicrobials are being developed or are already being marketed by several companies, including Kerry, Dupont, A & B Ingredients, Corbion, and PhageGuard as described in Table 2.

TABLE 2. List of companies developing or marketing clean label preservatives/antimicrobials.
Clean label preservatives/antimicrobials Description Company
Accel, DuraFresh, and UpGrade
  • A line of cultured celery, cultured sugar, and buffered vinegars from fermentation.
  • Replaces sodium nitrite, lactates, and diacetates in cured meat products.
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Verdad Ferments
  • Blends of cultured corn sugar and vinegar for use as a preservative by the meat industry.
  • Controls Listeria growth in cooked meats and extends shelf life in both fresh and cooked meats.
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BioVia, MicroGARD, Natamax, Nisaplin, and NovaGARD
  • GRAS components including metabolites produced during microbial fermentation, starter cultures, and other microorganisms such as Streptomyces natalensis.
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CytoGuard LA
  • Contains lauric arginate, which is synthesized from lauric acid (a natural fatty acid found in coconuts), and arginine (an essential amino acid).
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PhageGuard Listex, PhageGuard E, and PhageGuard S
  • PhageGuard is committed to clean label antimicrobial solutions using phages.
  • FDA-approved PhageGuard solutions as new food processing aid against Listeria monocytogenes, E. coli O157, and Salmonella.
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4 THE NEED FOR CLEAN-LABEL ANTIMICROBIALS IN DAIRY PRODUCTS

Antimicrobials are employed in the dairy industry for a multitude of reasons, including enhancing the safety, quality, and nutritional benefits of dairy products. They are also utilized to prolong the shelf life of dairy items by impeding the growth of spoilage bacteria, yeasts, and molds, thereby preventing spoilage (Ibarra-Sánchez et al., 2020; Ledenbach & Marshall, 2009). Although extending shelf life and improving quality are important, microbiological safety is more critical, and it is essential that the antimicrobial used does not compromise safety for other gains. Table 3.

Preventing the growth of harmful bacteria that may lead to foodborne illness is a major reason for taking precautions with milk and milk products like cheese, yogurt, and ice cream. According to the National Outbreak Reporting System (NORS) of the Centers for Disease Control and Prevention (CDC) report, nearly all dairy-related outbreaks in the United States are associated with the consumption of raw and unpasteurized milk (Centers for Disease Control & Prevention, 2022). As shown in Figure 2 and Mungai et al. (2015), the top three pathogens responsible for raw milk outbreaks in the United States between 2010 and 2018 were Salmonella enterica, Campylobacter jejuni, and Shiga toxin-producing Escherichia coli (STEC). Consumption of unpasteurized milk has been linked to various health hazards, particularly these three pathogens, which are commonly found in cattle.

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Number of outbreaks in dairy-related products caused by key pathogens in the United States between 2000 and 2018. Data obtained from CDC's National Outbreak Reporting System (NORS).

Dairy products overall are also associated with 37.1% of Listeria monocytogenes illnesses (IFSAC, 2022). Additionally, thermophilic spores of Bacillus species including Bacillus licheniformis, Bacillus cereus, Bacillus subtilis, Bacillus mycoides, and Bacillus megaterium are frequently found in dairy products. These spores are capable of surviving pasteurization and high temperatures, leading to spoilage and some foodborne illnesses (Kalogridou-Vassiliadou, 1992; Ledenbach & Marshall, 2009).

Compared to other foods like fruits and vegetables, the acidic pH of dairy products makes them less prone to fungal spoilage (Garnier et al., 2017;  Schnürer & Magnusson, 2005). Nevertheless, fungal contamination of dairy products remains a possibility, and various genera, such as Aspergillus, Byssochlamys, Cladosporium, Eupenicillium, Fusarium, Hamigera, Neosartorya, Penicillium, and Talaromyces, have been detected in the contaminated dairy products (Pitt & Hocking, 2022).

As the need for antimicrobials in food industry has evolved, the use of antimicrobials in dairy products is strictly regulated by government agencies to ensure the safety of the final product. Certain types of preservatives such as natamycin, potassium sorbate, and selected organic acids are approved for use in dairy products, which must be used according to specific guidelines to ensure adequate microbial safety of the foods. In response to concerns about these non-clean-label antimicrobials, the demand for “consumer-friendly” clean-label antimicrobials is on the rise. The potential benefits of clean-label antimicrobials in dairy products, including improved safety and stability, are discussed in the following section.

5 POTENTIAL CLEAN-LABEL ANTIMICROBIALS IN DAIRY PRODUCTS

5.1 Food cultures

Food cultures used in food production affect physicochemical, sensory, and nutritional properties of foods in addition to impact their safety and shelf life (Bourdichon et al., 2012). The dairy industry greatly benefits from food cultures, as the quality and sensory appeal of certain dairy products are significantly influenced by the use of dairy starter cultures (Hati et al., 2013). Bacteria, introduced naturally or through the addition of starter cultures, are the dominant microorganisms involved in food fermentation (Voidarou et al., 2020).

The long history of the addition of “good” and “safe” microorganisms to ferment foods provides ample evidence of the many benefits that fermentation can bring to a finished food product (Soemarie et al., 2021; Tamang et al., 2016). The fermentation of milk to make cheese, for example, results in a new and valuable product. Importantly, fermentation also preserves and protects perishable products (Bourdichon et al., 2012; Mannaa et al., 2021). Microorganisms such as bacteria, molds, and yeasts present in fermented foods, either through intentional addition or by their serendipitous presence, have demonstrated antimicrobial effects. For example, lactic acid bacteria (LAB)-fermented cultures show a wide range of antifungal properties against various spoilage fungi, Penicillium and Mucor species (Shi & Maktabdar, 2021). Additionally, the use of LAB cultures in dairy products has the potential to reduce the risk of foodborne diseases caused by bacteria such as Staphylococcus aureus and L. monocytogenes (Arqués et al., 2015). Microbial cultures added to foods explicitly for their antimicrobial properties are commonly referred to as protective cultures.

The use of food cultures, including protective cultures, in foods is generally viewed as a “clean-label” addition. However, the guidelines governing the use of food cultures in foods differ from region to region (Laulund et al., 2017). In 2010, the European Food and Fermentation Cultures Association (EFFCA) defined “microbial food cultures” as “characteristic food ingredients they should be listed on the ingredients label of the final food when they are used in the manufacture or preparation of a foodstuff unless exempted by other regulation” (Bourdichon et al., 2012; Herody et al., 2010). As of now, there remains a lack of dedicated regulations for microbial food cultures. Some species such as many LAB species are regarded as “safe and suitable” for human consumption as food additives, while others have GRAS status (Laulund et al., 2017).

5.1.1 Protective cultures

Protective cultures are the subcategory of food cultures that consist of living microorganisms specifically selected to produce metabolites with antimicrobial properties within a food, usually without changing the physicochemical, sensory, or nutritional properties of the food (Medina & Nuñez, 2011). Due to their GRAS status and Qualified Presumption of Safety (QPS) status in the United States and the European Union, respectively, LAB are commonly used as protective cultures in the dairy industry. LAB are Gram-positive organisms that do not form spores and can be rod shaped (bacilli), spherical (cocci), or a combination of both (coccobacilli) (Quinto et al., 2014). Among LAB, certain species within the Lactococcus, Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus genera have been used in dairy foods to control food pathogens in milk, yogurt, and cheeses. Cheeses produced with bacteriocin-producing strains of Lactococcus lactis and Enterococcus faecalis were able to suppress the growth of L. monocytogenes (Silva et al., 2018). Interestingly, the sensory quality of cheeses that were inoculated with bacteriocin-producing LAB exhibited no significant differences in comparison to control cheeses (Table 3; Coelho et al., 2014). In addition, fermentation of milk using Lactobacillus rhamnosus and Lactobacillus fermentum demonstrated activity of protease, suggesting their potential suitability for the development of dairy products enriched with bioactive peptides (Table 3; Moslehishad et al., 2013).

Dairy product labeling may indicate the presence of such microorganisms as protective cultures or probiotic cultures, that is, “live microorganisms that offer a health benefit to the host when ingested in sufficient amounts” (Gaggia et al., 2011; Morelli & Capurso, 2012). Both protective and probiotic cultures are versatile and can be utilized in various fermented dairy products. These cultures exhibit efficacy across a broad spectrum of pH and temperature conditions and have been shown to combat numerous foodborne pathogens (Ahmad et al., 2017; Arqués et al., 2015). As a result, LAB cultures themselves can serve as desirable “clean-label” antimicrobial agents.

5.1.2 Fermentates generated by LAB

Antimicrobial properties of LAB present in protective cultures are conferred by inhibitory metabolites such as organic acids, bacteriocins, and other antimicrobial substances that the living bacteria produce (Vieco-Saiz et al., 2019). An alternative approach to using live bacteria is to employ fermentates, which, in this case, are products derived from bacterial cultures that contain the organic acids and bacteriocins produced by the bacteria (Engstrom et al., 2021). Cultured sugar products are one category of fermentates that are extensively used within the food industry. Fermentates function similarly to protective cultures (both of which are sometimes referred to as “biopreservatives”) in terms of the microorganisms they protect against. The advantages of a fermentate over a protective culture include better consistency and control over the timing and levels of antimicrobial activities present. Furthermore, there is no requirement for the food product to allow the growth of the protective culture, so fermentates can be used in a wider variety of products with different compositions and varying storage conditions.

Fermentates produced by microorganisms are now commonly used as biopreservatives in dairy products, particularly cheeses (Engstrom et al., 2021; Naldini et al., 2009; VytřaSoVá et al., 2010). Careful selection of fermentates will prevent interference with desirable fermentation by starter cultures without affecting the sensory properties of foods. Numerous commercial fermentates are now available for a wide range of applications. These ingredients are often listed as “cultured sugar,” “cultured milk,” or similar names on food product labeling and are generally recognized as “clean-label” ingredients (Engstrom et al., 2021; Yacoubo, 2015).

5.1.3 Antimicrobial components of protective cultures and fermentates

Microbial metabolites, especially organic acids and bacteriocins, play a major role in the efficacy of protective cultures and fermentates against spoilage and pathogenic microorganisms. The following sections will discuss the mechanisms of these agents and clean-label approaches toward their use, especially in dairy products.

Organic acids

The efficacy of organic acids such as lactic acid, acetic acid, and propionic acid in inhibiting the growth of pathogenic bacteria and spoilage organisms is well established, and chemically synthesized organic acids are widely used in the food industry to control microbial growth. However, in their purified forms, organic acids are not usually considered to be “clean label” (Punia Bangar et al., 2022; Rattanachaikunsopon & Phumkhachorn, 2010). The antimicrobial effect of these acids is not simply a result of the reduction in pH that they cause; it also appears to be partially dependent on the type of acid that is present (Adams & Nicolaides, 1997; Engstrom et al., 2021). Organic acids are typically weak acids with relatively high pKa values. When the pH falls below an acid's pKa, the organic acid is mostly present in an undissociated (protonated) form, which lacks a charge. In this uncharged state, most organic acids possess some degree of fat solubility and can permeate bacterial (and fungal) cell membranes, entering the cell's cytoplasm. Once inside, due to neutral pH of the cytoplasm, the organic acid dissociates and releases a hydrogen ion (proton). The release of free hydrogen ions will lead to a decrease in pH within the cell's cytoplasm. Furthermore, the conjugate base of the organic acid that has entered the cell may exhibit some inherent toxicity, which can vary depending on the specific organic acid. The bacterial cell will have to work to maintain its normal intracellular pH, which decreases the ability of the cell to put resources into growth. Consequently, all organic acids are more effective at lower pH values, as a greater proportion of the acid exists in the undissociated form. Organic acids with higher pKa values will have more undissociated molecules at a given pH and are generally more effective antibacterial agents (Figure 3; Adams & Nicolaides, 1997).

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Mode of action of certain “clean-label” antimicrobials and organic acids (Adams & Nicolaides, 1997; Bouyahya et al., 2019; Brötz et al., 1998; Fernández et al., 2017; Jarudilokkul et al., 2000; Juneja et al., 2012; Lunde et al., 2005; McAuliffe et al., 2001; Nguyen et al., 2011). Created with Biorender.com. EO, essential oil.

LAB fermentations generate a wide range of organic acids as end-products of carbohydrate metabolism. Lactic, succinic, and propionic acids are the most commonly produced organic acids by LAB strains, while acetic acid was the least produced (Özcelik et al., 2016). Acetic and propionic acids, which have higher pKa values (4.75 and 4.87, respectively) and a greater proportion of undissociated acids at a given pH, are typically more potent antimicrobials among the organic acids generated by LAB than other acids, such as lactic acid (pKa = 3.08). Despite this, lactic acid, which is primarily produced by LAB, and the concentration of organic acids produced by LAB depend on the strain and the growth medium/food matrix. For instance, Özcelik et al. (2016) found that the production of lactic acid was highest in anchovy infusion broth with L. lactis subspecies (2403 mg/L) and Pediococcus acidilactici (2345 mg/L). A study on Halloumi cheese found that the levels of lactic and acetic acids significantly increased during the cheese ripening process, causing the cheese to become more acidic in flavor (Table 3; Kaminarides et al., 2007).

In cultures, lactic acid has demonstrated significant efficacy in inhibiting growth of L. monocytogenes, with a minimum inhibitory concentration (MIC) of 1.25 mg/mL. For S. aureus, B. cereus, and E. coli, the MIC of lactic acid ranged from 0.9 to 3.6 mg/mL, with the minimum bactericidal concentration (MBC) ranging from 1.8 to 7.2 mg/mL (Stanojević-Nikolić et al., 2016). In addition, for S. cerevisiae, the MIC of lactic acid was 278 mM (Narendranath et al., 2001). Lactic acid has been shown to be more effective against Gram-positive bacteria compared to Gram-negative bacteria, except for S. enteritidis and Pseudomonas aeruginosa, which displayed MIC concentrations of 1.25 mg/mL (Stanojević-Nikolić et al., 2016). Various factors can influence the MIC and MBC values, such as the type and sensitivity of the bacterial strain, the volume of the bacterial inoculum, the incubation time and temperature, among others.

The utilization of organic acids and their salts in diverse food products, including dairy, is permitted under the GRAS list (21 CFR 184). While the names of some of these compounds such as citric acid or acetic acid may make them less acceptable to consumers, clean-label ingredients that contain some of these agents can be easily used instead. For example, lemon juice is a mixture of organic acids—primarily citric acid (4%−7%, or 60%−70% of the total soluble solids) and smaller amounts of malic acid (0.2%−0.4%)—and amino acids as well as phenolics, with a pH of about 2.0–2.2 (Ladaniya, 2010; Penniston et al., 2008; Vandercook et al., 1966). These components, which may vary because it is a natural product that may be produced in various ways, are likely the main contributors to lemon juice's antimicrobial activity. Another example is vinegar, which generally contains 4%−10% acetic acid (Younes et al., 2022). Dried and buffered vinegar ingredients to use for preserving food products are commercially available.

Bacteriocins

For centuries, various types of food, including cheeses and yogurts, have naturally contained bacteriocins, which are antimicrobial peptides produced by bacteria (O'Connor et al., 2020; Yang et al., 2012). Despite the fact that several microorganisms produce bacteriocins, the dairy industry has shown particular interest in bacteriocins produced by LAB, as they are highly suitable and safe for use in food products (Egan et al., 2016). More than 230 bacteriocins, which are produced by LAB, have been identified (Alvarez-Sieiro et al., 2016). Bacteriocins may exhibit either a wide or limited range of antimicrobial activity but are generally more active against Gram-positive bacteria (And & Hoover, 2003; O'Connor et al., 2020), with certain bacteriocins demonstrating efficacy against foodborne pathogens including Gram negatives such as methicillin-resistant S. aureus (MRSA) and L. monocytogenes and Gram positives such as Shiga toxin-producing E. coli (STEC) and enterotoxigenic E. coli (ETEC) (Cotter et al., 2005; Grinter et al., 2012).

Although numerous bacteriocins are efficacious in controlling foodborne pathogens, the only bacteriocin that is commercially available and marketed in terms of active units for use in foods in the United States is nisin. Besides being GRAS listed (21 CFR Part 184.1538) for use in foods within the United States and considered safe for use in certain foods by the European Food Safety Agency (EFSA; Younes et al., 2017), nisin is licensed as a food additive in more than 50 countries and has a long and widespread history of use in foods as an antimicrobial (Alvarez-Sieiro et al., 2016; O'Connor et al., 2020). Nisin is a bacteriocin produced by L. lactis to fend off other bacteria (Juneja et al., 2012). Discovered in the late 1920s as a substance in milk that prevented cheese starter cultures from working properly, it has been used in processed cheese since the 1950s (Delves-Broughton et al., 1996; Rogers & Whittier, 1928). In more recent years, nisin has found applications in ready-to-eat (RTE) meat products, prepared salads, and other types of foods, while continuing to be commonly used in various dairy products. Nisin A is the most common form of the peptide, but variants with enhanced solubility or with other improved characteristics have been developed (O'Connor et al., 2020). The antimicrobial efficacy of nisin is believed to be due to its ability to bind to Lipid II, a crucial precursor for bacterial cell walls; when nisin attaches to Lipid II, it leads to the formation of sizable aggregates of nisin–Lipid II within the bacterial membrane, leading to the creation of pores in the cytoplasmic membrane and cell death (Figure 3; Brötz et al., 1998; McAuliffe et al., 2001). When combined with other antimicrobials, nisin may facilitate the entry of the other antimicrobials into cells, producing a synergistic effect (Zhao et al., 2020).

For food applications, nisin is commonly added as a culture or fermentate to a product, although it could be used on product surfaces, encapsulated, or used in films or in active packaging (Bahrami et al., 2019; Hassan & Cutter, 2020; Marcos et al., 2013). EFSA has evaluated the safety of nisin as food additive and concluded that it can be utilized safely in matured and processed cheese, with an allowable maximum concentration of 12.5 mg/kg. (Younes et al., 2017). Nisin's efficacy has been demonstrated in managing foodborne pathogens such as L. monocytogenes and S. aureus within dairy products (Ibarra-Sánchez et al., 2020). For example, the use of L. lactis, a bacterium that produces nisin, as a starter culture to produce fresh cheese resulted in a 2-log reduction of L. monocytogenes within 7 days of storage (Kondrotiene et al., 2018). Moreover, Felicio et al. (2015) demonstrated that the use of 500 IU nisin/mL in skim milk led to a reduction in S. aureus numbers of approximately 2 log in both the whey and curd of Minas Frescal cheese. Nisin suppresses spore formation across various Bacillus and Clostridium species present in dairy products, yet its impact on Gram-negative bacteria, yeasts, and molds is relatively limited (Cao-Hoang et al., 2010; de Arauz et al., 2009). Consequently, nisin has been widely employed as a replacement for nitrate in cheese and pasteurized cheese spreads.

According to Choyam et al. (2019), nisin has little to no effect on the flavor or texture of food products. Additionally, Saad et al. (2019) found that the use of nisin in pasteurized milk to mitigate the post-pasteurization contamination led to a higher overall sensory score, including higher ratings for appearance, odor, and flavor, than the control group (Table 3). However, Kallinteri et al. (2013) reported that while the inclusion of nisin at 100 and 200 IU/g in cheese extended its shelf life by 7 days, the sensory panels found the flavor and texture of the products containing nisin to be undesirable, stating that they had a “yeasty flavor and watery texture” (Table 3).

According to Ibarra-Sánchez et al. (2020), nisin can be utilized alone or generated by starter culture bacteria to enhance the safety, extend the shelf life, and ensure quality of food products. However, the production and efficacy of nisin can be affected by several food characteristics such as pH, temperature, composition, and the physical properties of the food matrix (Zhou et al., 2014). For instance, nisin is effective as a preservative in dairy products when the pH is below 7, as its antimicrobial activity decreases significantly at higher pH values. In particular, dairy products made with whole milk and a neutral pH are generally not good candidates for the use of nisin, as nisin is not effective under these circumstances (And & Hoover, 2003; Delves-Broughton et al., 1996).

In the United States, other bacteriocins besides nisin can be introduced into foods in the form of fermentates or protective cultures (O'Connor et al., 2020). In addition to nisin, pediocin PA-1 is available commercially in the form of a fermentate under the name Alta 2341 or Microgard (Garsa et al., 2014). Enterocin AS-48 shows broad activity against most Gram-positive bacteria including L. monocytogenes (Grande Burgos et al., 2014; Khan et al., 2010). Other bacteriocin preparations, including natural and bioengineered variants of nisin with enhanced potency, will likely find utility in the food industry in coming years (Choyam et al., 2019; Garcia-Gutierrez et al., 2020; O'Connor et al., 2020). The most ideal bacteriocins for use as food biopreservatives are those that are safe for humans to consume, do not significantly alter the human microbiota, are effective against foodborne pathogens and spoilage microorganisms, remain heat stable and pH tolerant in the food in which they are used, and do not negatively impact the sensory characteristics of the food (Johnson et al., 2018; Mills et al., 2011; O'Connor et al., 2020). Consumers may not view bacteriocins as “clean label” even if they are derived from natural sources (Labs, 2017); however, the use of bacteriocins does appear to be relatively well accepted by US and European consumers (Choyam et al., 2019).

5.1.4 Fermentates of yeasts and filamentous fungi

Fungi have been utilized extensively in the food industry and other fields for many years, including the manufacture of food additives, enzymes, pharmaceuticals, and nutraceuticals. Their capacity to decompose biomass and produce desirable flavors, colors, and textures has made fungi valuable in the production of different food items, as highlighted by Barzee et al. (2021). Although certain fungi such as Saccharomyces spp. are unicellular yeasts, the majority of fungi are filamentous and have hyphae, also known as molds.

Fungi play a crucial part in the manufacturing of various food products. Fungal species that are categorized as GRAS have a firmly established history of safe use within the food industry and are considered safe. Examples of GRAS fungal species include Aspergillus niger, Aspergillus oryzae, Agaricus bisporus, S. cerevisiae, Tolypocladium niveum, Rhizopus oligosporus, Trichoderma reesei, and Penicillium camemberti (Boratyński et al., 2018; Sewalt et al., 2016; Singh & Gaur, 2021). For thousands of years, fungi such as A. oryzae and Aspergillus sojae have been utilized in the production of doenjang, miso, makgeolli, sake, koji, and soy sauce, while S. cerevisiae has been an essential component in baking, brewing, and winemaking. This is due to their capacity to produce enzymes that decompose ingredients and contribute unique flavors to the final products (Bamforth & Cook, 2019).

Filamentous fungi are renowned for their capacity of producing substances with antimicrobial properties. A prominent example of this is penicillin, discovered as the first antibiotic compound by Alexander Fleming in 1928 and was derived from the mold Penicillium notatum (Ligon, 2004; Svahn et al., 2012). Numerous strains of Aspergillus have been demonstrated to be effective in hindering the growth of antibiotic-resistant microorganisms such as MRSA, extended-spectrum beta-lactamase-producing E. coli, vancomycin-resistant E. faecalis, and Candida albicans (Jakubczyk & Dussart, 2020; Svahn et al., 2012).

The most desirable yeasts for food fermentation are typically those belonging to the Saccharomyces family, particularly Saccharomyces cerevisiae and S. boulardii. In the dairy industry, yeasts are important because their enzymes catalyze desirable biochemical processes including the generation of ethanol in koumiss and kefir and the coagulation of milk in cheese (Kaur & Dua, 2022). Moreover, some studies have found that S. cerevisiae and S. boulardii possess antimicrobial characteristics against pathogenic microorganisms, notably L. monocytogenes, S. aureus, S. typhimurium, P. aeruginosa, E. coli, and E. faecalis (Rajkowska & Kunicka-Styczyńska, 2012; Roostita et al., 2011; Syal & Vohra, 2013). According to a study by Younis et al. (2017), milk is a suitable environment for the growth of yeasts capable of fermenting lactose; their research discovered that yeasts extracted from various dairy products, such as fruit yogurt, Kareish cheese, processed cheese, and butter, had potent antimicrobial effects against S. aureus, E. coli, and P. aeruginosa. However, yeast causes the production of alcohol and CO2 in many dairy products, contributing to a yeasty taste (Haasum & Nielsen, 1998; Moubasher et al., 2018). Rather than utilizing live yeast, fungal fermentates can be employed to enhance the flavor, texture, and nutritional value of dairy products, which may help alleviate sensory issues. Analogous to bacterial fermentates, fungal fermentates are complex mixtures of substances produced during fermentation, and they may comprise various biologically active compounds that could have antimicrobial effects but might pose a potential health risk to consumers.

The use of fungal and yeast fermentates as viable clean-label preservation tools in the food industry has gained significant attention due to their potential to extend the shelf life of food products while also serving as a source of nutraceuticals. In recent decades, commercial availability of “cultured materials” or “fermentates” utilizing molds and yeasts has emerged, with some marketed as “clean label” or “label-friendly” solutions for increasing the shelf life of bakery products (Samapundo et al., 2016). More comprehensive research is necessary to fully understand the safety and potential of mold and yeast fermentates as preservatives in dairy products (Singh & Gaur, 2021).

5.2 Plant-based compounds and essential oils

Essential oils (EOs) are combination of aromatic, volatile natural compounds derived from plants (Bhavaniramya et al., 2019; Burt, 2004; Wińska et al., 2019). They have been linked to potent antimicrobial properties. The chemical constituents of EOs (largely phenolics and terpenoids) likely play a role in the plant's defense against microorganisms, and the presence of these varied chemicals in plants might be argued to function as their own natural “hurdle” approach against plant pathogens.

Many EOs are considered GRAS by the FDA when used as flavorings (21 CFR Part 182.20). EOs have been shown to be effective against pathogenic fungi and bacteria and can be used as natural preservatives in food. The hydrophobic nature of EOs enables them to effectively permeate the lipid cell membranes of bacteria and fungi, disrupting the cell wall (Figure 3; Bouyahya et al., 2019). Phenolic compounds present both in oregano and thyme EOs destabilize the cytoplasmic cell membrane, thus increasing its permeability (Moreira et al., 2005). However, the mechanism by which they operate against microorganisms has not been completely explained and cannot be attributed to a single mechanism (Khorshidian et al., 2018).

Oregano, thyme, and black cumin EOs exhibit antimicrobial activity against L. monocytogenes and E. coli O157:H7 in various types of cheeses. When 0.1% of oregano and thyme EOs were added to feta cheese, the growth of L. monocytogenes was inhibited effectively. Similarly, incorporation of 0.1%–0.2% black cumin seed EOs into soft cheese significantly reduced the presence of both L. monocytogenes and E. coli O157:H7 (Govaris et al., 2011; Hassanien et al., 2014). Sagdic et al. (2010) observed that black cumin EOs exhibited potent anti-yeast activity, causing a 3-log reduction in Candida zeylanoides and Candida lambica in butter. As a result, black cumin is frequently used as both flavoring ingredient and antimicrobial agent in cheese and butter in many countries (Govaris et al., 2011; Hassanien et al., 2014; Sagdic et al., 2010). Balaguer et al. (2013) demonstrated that applying cinnamon EOs containing 5% cinnamaldehyde to cheeses can effectively inhibit the growth of food-contaminating fungi, such as A. niger and P. expansum. Additionally, incorporation of 0.1% of EOs derived from cumin, rosemary, and thyme, either individually or in combination, in ultrafiltrated soft cheese was found to significantly reduce the growth of various microorganisms, including E. coli, S. typhimurium, S. aureus, B. subtilis, B. cereus, and A. niger (Table 3; EL-Kholy & Aamer., 2017). Moreover, thyme and cumin EOs have shown to have natural preservative or antioxidant properties in butter (Farag et al., 1990). Khorshidian et al. (2018) thoroughly described the research on the use of EOs in various type of cheeses.

The FDA's classification of EOs as GRAS flavoring compounds coupled with consumers’ belief in their health benefits has resulted in EOs being recognized and perceived as safe by the general public (MarketsandMarkets, 2022). Consequently, EOs have been identified as a promising group of clean-label preservatives due to their natural origin and antimicrobial properties (Burt, 2004). Although EOs have demonstrated efficacy in preventing the growth and survival of microorganisms in cheese, their use is constrained by certain limitations. These limitations include interactions between the constituents of EOs and food components like fats, carbohydrates, and proteins, which can reduce the antimicrobial effects of the oils. In addition, sensory defects may occur when EOs are used at levels needed for antimicrobial activity (Khorshidian et al., 2018). Nonetheless, there is considerable ongoing research on EOs, including work to better understand their activities as antimicrobials, to develop strategies to mitigate undesirable aromas and flavors, and to identify ways to increase delivery efficacy such as nanoencapsulation systems (Burt, 2004; Khorshidian et al., 2018).

5.3 Bacteriophages

Bacteriophages, which are viruses capable of infecting and, under specific circumstances, causing the demise of bacteria, have gained recognition as an environmentally friendly and natural approach to control microorganisms. Bacteriophage biocontrol or phage biocontrol harnesses lytic bacteriophages to selectively target specific pathogenic or spoilage bacteria through the lytic process, thus preserving the quality and sensory properties of food. Unlike certain antimicrobial agents, bacteriophages do not indiscriminately eliminate other microorganisms, including beneficial bacteria and starter cultures (Moye et al., 2018). Additionally, environmental stressors like heat, salts, and bacteriocins produced by other bacteria can trigger the induction and production of prophages, leading to the lytic cycle and death of the bacterial host cells (Figure 3; Fernández et al., 2017; Lunde et al., 2005).

The FDA has granted GRAS status to bacteriophages, particularly for Listeria-specific bacteriophage preparations, for use in foods in accordance with the guidelines specified in 21 CFR Part 172.785. Back in 2006, the FDA authorized the usage of Listex P100, which is a bacteriophage preparation containing six individually purified phages, developed by EBI Food Safety, as an antimicrobial agent against L. monocytogenes in RTE foods (Guenther et al., 2009). Over the past few years, numerous phages have been successfully commercialized and are used in a variety of food products (Cristobal-Cueto et al., 2021; Endersen & Coffey, 2020; Połaska & Sokołowska, 2019). Bacteriophage-based antimicrobial strategies have been shown to be effective in dairy products (Fernández et al., 2017). For instance, S. aureus bacteriophages obtained from cheese and milk prevented the growth of S. aureus in ultrahigh-temperature and pasteurized whole milk (García et al., 2009). Additionally, Bao et al. (2015) reported a reduction of 3.89-log CFU of Salmonella enteritidis in milk containing S. enteritidis phage within 1 h at 25°C, while Soffer et al. (2017) observed a 1.0-log CFU/g reduction of Shigella strains in yogurt after a 5-min exposure to ShigaShield. Nevertheless, the properties of food products, such as elevated pH, reduced storage temperature, higher mineral content, and higher bacterial counts, may influence the activities of bacteriophages. These factors could also alter the survival of phages within food products (Lewis & Hill, 2020), presenting a challenge when considering the use of phages as biocontrol agents in specific types of foods.

While numerous studies have demonstrated the effectiveness and cost-efficiency of bacteriophages in controlling foodborne pathogenic bacteria, fewer studies have explored their use as preservatives in dairy products. The hesitation to explore this area arises from the concerns regarding the potential impact on the quality of these products (Ge et al., 2022; Połaska & Sokołowska, 2019). The dairy industry has traditionally been cautious about employing bacteriophages due to the risk of fermentation failure and financial losses resulting from phage infection of dairy starter cultures (Samson & Moineau, 2013). As a result, EFSA remains cautious about the practical implementation of phages, including the incorporation of phage preparations on an industrial scale within the food industry (EFSA Panel on BIOHAZ, 2016). Certainly, several bacteriophage-derived products have been authorized for clean-label processing in the United States, Canada, Israel, Australia, New Zealand, Switzerland, Norway, and the European Union (Fernández et al., 2017).

5.4 Animal-derived antimicrobial agents

Antimicrobials originating from animals are primarily obtained from vertebrate sources. These animal-derived antimicrobials, including lysozyme, lactoferrin, chitosan, lactoperoxidase, and ovotransferrin, have undergone extensive research and demonstrated effectiveness against various foodborne pathogens and spoilage microorganisms (Arias-Rios et al., 2017; Gyawali & Ibrahim, 2014). The upcoming sections will delve into the mechanisms of naturally occurring animal-derived antimicrobial agents found in dairy products, specifically lysozyme and milk-based peptides. Additionally, a clean-label approach will be discussed in relation to their utilization.

5.4.1 Lysozyme

Lysozyme, a small protein, is present in various forms across different sources such as milk, eggs, saliva, and other materials mostly derived from animals (Wu et al., 2019). It is a naturally occurring antimicrobial enzyme that can be found in animal-derived products like raw milk and egg whites (Jarudilokkul et al., 2000; Ragland & Criss, 2017). In bovine milk, lysozyme is found in low concentrations, ranging from 50 to 220 μg/mL, with approximately 3%−5% of the lysozyme located in the cream fraction. On the other hand, chicken egg white contains approximately 2500−3500 μg/mL of lysozyme, while duck egg white contains around 1000−1300 μg/mL (Chandan et al., 1964; Nawaz et al., 2022). Lysozyme production in milk is enhanced by employing high-temperature and short-time pasteurization methods, such as 75°C for 15 s or 85°C for 1 s. In contrast, its production is reduced when subjected to low-temperature and long-time pasteurization procedures such as 65°C for 30 min (Abd El-Aziz, 2006).

Hen egg white-derived lysozyme is recognized by the FDA as a GRAS ingredient for use in food applications to prevent late blowing of cheese caused by Clostridium tyrobutyricum, as stated in 21 CFR 184. As a result, it is commercially available as a food additive.

Lysozyme's antimicrobial activity is attributed to its capacity to break down the β-1,4- linkage within the peptidoglycan of the microbial cell wall, which eventually leads to cell death (Figure 3; Jarudilokkul et al., 2000; Juneja et al., 2012). Gram-negative bacteria, in contrast to Gram-positive bacteria, typically exhibit resistance to lysozyme due to the presence of a lipopolysaccharide layer rendering them less susceptible to the antimicrobial effects of lysozyme (Tiwari et al., 2009). Egg white lysozyme exerts strong antimicrobial activity against some Gram-positive bacteria including C. tyrobutyricum, Clostridium thermosaccharolyticum, Bacillus stearothermophilus, and Bacillus coagulans (Davidson et al., 2005; Feng et al., 2017). Listeria innocua and S. cerevisiae displayed the greatest susceptibility to lysozyme (Rawdkuen et al., 2012). Saad et al. (2019) found that lysozyme at concentrations of 500 IU/mL in freshly pasteurized milk reduced 99% of total bacterial, aerobic spore-forming, and psychrotrophic bacterial counts; furthermore, the sensory characteristics of the milk samples treated with lysozyme maintained their acceptability for a prolonged duration in contrast to the control samples (Table 3). Lysozyme's stability and antimicrobial activity are significantly reduced by heat treatments exceeding 85°C. In particular, subjecting lysozyme to heat treatment at 85°C decreased lysozyme levels by 60% (Ozturkoglu-Budak, 2018). A more effective antimicrobial approach involves applying a 1200-μs high-intensity pulsed electric field treatment to milk supplemented with 300 IU/mL of lysozyme. This combined treatment demonstrated a significant reduction of over 6.2-log units in S. aureus levels. Notably, this combinational approach holds promise for preserving the sensory properties of the milk with minimal alterations (Sobrino-López & Martín-Belloso, 2008).

Lysozyme, being a naturally derived ingredient, possesses characteristics that make it suitable for clean-label products. It aligns with consumers’ preferences for natural ingredients in food products. Lysozyme can serve as a preservative, extending the shelf life of certain foods, especially those prone to bacterial spoilage. Nevertheless, some consumers may be put off by the presence of “lysozyme” on the ingredient list. To address this, alternative terminology such as “egg white extract” or “egg white albumin” or even “lysozyme (egg-white)” could be employed to make it more appealing to consumers; however, some consumers may object to the presence of animal-product-derived ingredients or unfamiliar words such as “lysozyme” or “albumin.”

5.4.2 Casein and whey protein-derived peptides

Extensive research has been conducted on the functional properties of bioactive constituents present in milk and dairy products (Phelan et al., 2009). Bovine milk consists of approximately 3.5% protein, with casein and whey proteins comprising 80% and 20% of the total protein content, respectively (Davoodi et al., 2016). While casein and whey protein themselves do not exhibit antibacterial effects, bioactive peptides derived from casein and whey proteins through enzymatic digestion have been found to possess antimicrobial properties (Phelan et al., 2009). The antimicrobial activity of these peptides relies on their cationic charge and a substantial presence of hydrophobic residues, which contribute to their amphipathic characteristics. The amphipathic and cationic characteristics of these peptides make them highly inclined to engage with cell membranes, leading to the disruption of membrane integrity and subsequent cell leakage (Figure 3; Nguyen et al., 2011).

Various types of casein, such as αS1-casein, αS2-casein, β-casein, and κ-casein, have been found to yield antimicrobial peptides through hydrolysis (Park & Nam, 2015). Most of antibacterial peptides have been specifically isolated from αS1-casein and αS2-casein. In particular, the hydrolysis product of αS2-casein has demonstrated antibacterial properties against S. aureus, Sarcina spp., B. subtilis, Diplococcus pneumoniae, and Streptococcus pyogenes (Lahov & Regelson, 1996; Silva & Malcata, 2005; Zucht et al., 1995). MIC values of additional αS2-casein-derived peptides ranged from 8.6 to 15.6 μg/mL against B. subtilis and from 62.5 to 68.8 μg/mL against E. coli (Khan et al., 2018).

Some of the known bioactive peptides obtained from whey include α-lactalbumin, β-lactoglobulin, lactoferrin, and lactoferricin (Park & Nam, 2015). Håkansson et al. (2000) found that a distinct form of α-lactalbumin found in human milk exhibits bactericidal properties against antibiotic-resistant strains of Streptococcus pneumoniae. Peptides derived from β-lactoglobulin showed notable antibacterial activity against L. monocytogenes and S. aureus, inhibiting their growth by about 90% at concentrations of 10−20 mg/mL (Demers-Mathieu et al., 2013). Lactoferrin exhibited MIC values of 125, 250, 125, 500, and 2.5 mg/mL against E. coli, S. typhimurium, S. enteritidis, Citrobacter freundii, and C. albicans, respectively (Khan et al., 2018). Furthermore, lactoferrin exhibits antifungal activity against C. albicans, Candida krusei, Aspergillus fumigatus, and Cryptococcus neoformans (Al-Sheikh, 2009; Lai et al., 2016; Zarember et al., 2007). Shashikumar and Puranik (2011) investigated the effects of lactoferrin (10–20 μg/mL) incorporation in paneer cheese and found that incorporating 20 μg/mL lactoferrin into the cheese reduced bacterial, yeast, and mold growth at both room and refrigerated temperatures. As the concentration of lactoferrin increased, the cheese exhibited decreased levels of hardness, cohesiveness, springiness, and chewiness without altering overall acceptability of the paneer in sensory evaluation (Table 3; Shashikumar & Puranik, 2011).

TABLE 3. Challenge studies of “clean-label product” in dairy products.
Antimicrobial Dairy products Intrinsic properties Target Results Reference
LAB protective cultures Cheese

pH ↓

Sensory evaluation (n = 50) ↑

Listeria monocytogenes
  • LAB strains used in this study can produce lactic acid and bacteriocins.
  • Two-log reduction and 3- to 4-log reduction of L. monocytogenes growth was observed with L. lactis and E. faecalis strains, respectively.
Coelho et al., 2014
Cow and camel milk Sensory evaluation (n = 30) ↑ NR
  • Among LAB, high sensory evaluation was observed with Lactobacillus rhamnosus PTCC 1637 and Lactobacillus fermentum PTCC 1638 in fermented cow's and camel's milk.
Moslehishad et al., 2013
Organic acid Ovine Halloumi cheese Sensory evaluation (n = 10) ↓ NR
  • Reduction of lactose followed by significantly gradually increase in lactic and acetic acids
  • Ethanol and acetic acid were the dominant volatile aromatic compounds
Kaminarides et al., 2007
Nisin Soft acid-curd cheese (Galotyri cheese)

pH ns

Sensory evaluation ↓

Yeast
  • Nisin-treated cheese, at about 100 and 200 IU/g, extended shelf life about 7 more days compared to control.
  • Nisin-treated cheese lowered overall acceptability with undesired aroma and watery texture including control.
Kallinteri et al., 2013
Pasteurized milk Sensory evaluation (n = 9) ↑

Unknown total bacterial counts

Psychrotrophic bacteria

  • Nisin-treated milk, at about 500 IU/mL, significantly lowered the aerobic spore-forming bacterial populations.
  • Overall sensory assessment of treated group was high.
Saad et al., 2019

Thyme EO

Cumin EO

Rosemary EO

Ultrafiltrated soft cheese

Moisture ns

Protein ns

Fat ↓

Total volatile fatty acids ↓

pH ↑

Rheological properties

(Hardness, cohesiveness, springiness, gumminess, and chewiness↓ but adhesiveness ↑)

Sensory evaluation (n = 10) ↑

Escherichia coli

Bacillus subtilis

Bacillus cereus

Salmonella typhimurium

Staphylococcus aureus

Aspergillus niger

  • EO-treated cheese (0.1%) enhanced the shelf life and overall acceptability to consumers preference.
  • Thyme EO had the strong antifungal activity and antibacterial activity compared to other EO.
EL-Kholy & Aamer, 2017
Lysozyme Pasteurized milk Sensory evaluation (n = 9) ↑

Unknown total bacterial counts

Psychrotrophic bacteria

  • Lysozyme-treated milk, at about 500 IU/mL, significantly lowered the aerobic spore-forming bacterial populations.
  • Slow acid development was observed.
  • Overall sensory assessment of treated group was high.
Saad et al., 2019
Lactoferrin Cheese (from Indian traditional milk)

Protein ns

Moisture ns

Fat ns

Rheological properties ↓

(Hardness, cohesiveness, springiness, and chewiness)

Sensory evaluation (n = 5) ns

Unknown total bacterial counts, coliform, yeast, and mold counts
  • Bactericidal effect from 20 μg/mL of lactoferrin-treated cheese
  • There was no significant difference of overall acceptability between lactoferrin-treated paneer and control.
Shashikumar & Puranik, 2011
  • Abbreviations: EO, essential oil; LAB, lactic acid bacteria; NR, not reported; ns, not significant compared to control.

Milk-derived bioactive peptides have garnered considerable attention as clean-label antimicrobials. Cow milk lactoferrin is well tolerated by humans and has been allowed by both US and European regulatory agencies for use in food products including infant formula (Ashraf et al., 2023). Both casein- and whey protein-derived antimicrobial peptides fall into the “clean label” category, as “milk proteins.” Their utilization as natural alternatives to conventional antimicrobial agents aligns with clean-label preferences, as they stem from a natural source but still effectively inhibit the growth of diverse pathogens. By incorporating casein- and whey proteins-derived bioactive peptides into food products, manufacturers can improve safety, prolong shelf life, and satisfy consumer demands for clean and natural ingredients.

6 CONCLUSION

Numerous natural antimicrobials are recognizable by consumers and can serve as substitutes for synthetic ingredients in dairy products. However, when attempting to develop or reformulate to create clean-label products by replacing synthetic antimicrobials, several challenges must be addressed. A SWOT (strengths, weaknesses, opportunities, threats) analysis of the use of innovative clean-label antimicrobials as opposed to conventional antimicrobials when formulating food items is outlined in Figure 4. In terms of strengths, consumer awareness has created strong demand for high-quality, clean-label foods with ingredient lists that are transparent and easily recognized by consumers. A key weakness of clean-label antimicrobial ingredients is the lack of uniformity as well as few regulatory or other standards for these products. Novel clean-label antimicrobial agents may require safety and efficacy testing as well as validation of their performance in each new food product, leading to an increase in expenses. In addition, manufacturers sometimes use hurdle approaches in their antimicrobial strategies for food products, combining thermal or nonthermal processes with conventional methods to maximize microbial control. The stability of many of the clean-label antimicrobials to both thermal and nonthermal physical processing technologies is not always understood and may be less than conventional antimicrobials. Some of the clean-label antimicrobials could benefit from the use of genetically modified organisms to produce the agents economically or to improve their effectiveness, but the use such modifications would likely taint clean-label status of the products. In terms of opportunities, when companies offer “clean-label food products,” they have the opportunity to establish a clean and fresh brand image, as these products facilitate a heightened level of transparency between the food company and the consumer. As a result, the increasing availability of clean-label products can reshape the perception of the “clean label” concept. Additionally, there remains a need for research regarding the replacement of conventional antimicrobials in existing commercial products, as such substitutions may significantly alter the physicochemical, sensory, or nutritional characteristics of the foods. For example, some plant-based clean-label antimicrobials have potent flavors or aromas that can impact product quality and limit consumer acceptance of a new or modified formulation. Clean-label antimicrobials may also be expensive or may deliver subpar shelf lives compared to conventional antimicrobials. Emerging nonthermal technologies such as high-pressure processing may also represent a clean-label alternative to conventional antimicrobials that could challenge the use of clean-label antimicrobials used in product formulations. To strike a balance between consumer acceptance of new additives and manufacturers’ pursuit of clean labels, a compromise must be reached, but this compromise must not sacrifice product safety.

Details are in the caption following the image
SWOT (strengths, weaknesses, opportunities, threats) analysis for employing clean-label antimicrobial ingredients in food products.

AUTHOR CONTRIBUTIONS

Dasol Choi: Conceptualization; investigation; writing—original draft; visualization; validation; data curation. Wendy Bedale: Writing—original draft; writing—review and editing; validation; conceptualization; data curation; visualization. Suraj Chetty: Writing—original draft; data curation. Jae-Hyuk Yu: Conceptualization; funding acquisition; writing—review and editing; validation; supervision; project administration; resources.

ACKNOWLEDGMENTS

This work is supported by the Michael and Winona Foster Predoctoral Fellowship to D.C., the National Institute of Food and Agriculture, United States Department of Agriculture, Hatch project 7000326 to J.H.Y., and the Food Research Institute of UW–Madison.

    CONFLICT OF INTEREST STATEMENT

    The authors declare no conflicts of interest.