Invited review: Redefining raw milk quality-Evaluation of raw milk microbiological parameters to ensure high-quality processed dairy products

Raw milk typically has little bacterial contamination as it leaves the udder of the animal; however, through a variety of pathways, it can become contaminated with bacteria originating from environmental sources, the cow herself, and contact with contaminated equipment. Although the types of bacteria found in raw milk are very diverse, select groups are particularly important from the perspective of finished product quality. In particular, psychrophilic and psychrotolerant bacteria that grow quickly at low temperatures (e.g., species in the genus Pseudomonas and the family Enterobacteriaceae) and produce heat-stable enzymes, and sporeforming bacteria that survive processing hurdles in spore form, are the 2 primary groups of bacteria related to effects on processed dairy products. Understanding factors leading to the presence of these important bacterial groups in raw milk is key to reducing their influence on processed dairy product quality. Here we examine the raw milk microbiological parameters used in the contemporary dairy industry for their utility in identifying raw milk supplies that will perform well in processed dairy products. We further recommend the use of a single microbiological indicator of raw milk quality, namely the total bacteria count, and call for the development of a whole-farm approach to raw milk quality that will use data-driven, risk-based tools integrated across the continuum from production to processing and shelf-life to ensure continuous improvement in dairy product quality.

Development of a risk assessment model to predict the occurrence of late blowing defect in Gouda cheese and evaluate potential intervention strategies

Late blowing defect (LBD) is an important spoilage issue in semi-hard cheese, with the outgrowth of Clostridium tyrobutyricum spores during cheese aging considered to be the primary cause. Although previous studies have explored the microbial and physicochemical factors influencing the defect, a risk assessment tool that allows for improved and rational management of LBD is lacking. The purpose of this study was to develop a predictive model to estimate the probability of LBD in Gouda cheese and evaluate different intervention strategies. The spore concentration distribution of butyric acid bacteria (BAB) in bulk tank milk was obtained from 8 dairy farms over 12 mo. The concentration of C. tyrobutyricum from raw milk to the end of aging was simulated based on Gouda brined for 2 d in saturated brine at 8°C and aged at 13°C. Predicted C. tyrobutyricum concentrations during aging and estimated concentration thresholds in cheese at onset of LBD were used to predict product loss due to LBD during a simulated 1-yr production. With the estimated concentration thresholds in cheese ranging from 4.36 to 4.46 log most probable number (MPN)/kg of cheese, the model predicted that 9.2% (±1.7%) of Gouda cheese showed LBD by d 60; cheeses predicted to show LBD at d 60 showed a mean pH of 5.39 and were produced with raw milk with a mean BAB spore count of 143 MPN/L. By d 90, 36.1% (±3.4%) of cheeses were predicted to show LBD, indicating that LBD typically manifests between d 60 and 90, which is consistent with observations from the literature and the cheese industry. Sensitivity analysis indicated that C. tyrobutyricum maximum growth rate as well as concentration threshold in cheese at onset of LBD are the most important variables, identifying key data needs for development of more accurate models. The implementation of microfiltration or bactofugation of raw milk (assumed to show 98% efficiency of spore removal) in our model prevented occurrence of LBD during the first 60 d of aging. Overall, our findings provide a framework for predicting the occurrence of LBD in Gouda as well as other cheeses and illustrate the value of developing digital tools for managing dairy product quality.

Antifungal Metabolites as Food Bio-Preservative: Innovation, Outlook, and Challenges

Perishable food spoilage caused by fungi is a major cause of discomfort for food producers. Food sensory abnormalities range from aesthetic degeneration to significant aroma, color, or consistency alterations due to this spoilage. Bio-preservation is the use of natural or controlled bacteria or antimicrobials to enhance the quality and safety of food. It has the ability to harmonize and rationalize the required safety requirements with conventional preservation methods and food production safety and quality demands. Even though synthetic preservatives could fix such issues, there is indeed a significant social need for "clean label" foods. As a result, consumers are now seeking foods that are healthier, less processed, and safer. The implementation of antifungal compounds has gotten a lot of attention in recent decades. As a result, the identification and characterization of such antifungal agents has made promising advances. The present state of information on antifungal molecules, their modes of activity, connections with specific target fungi varieties, and uses in food production systems are summarized in this review.

Development of predictive models evaluating the spoilage-delaying effect of a bioprotective culture on different yeast species in yogurt

Yeast spoilage of fermented dairy products causes challenges for the dairy industry, including economic losses due to wasted product. Food cultures with bioprotective effects are becoming more widely used to help ensure product quality throughout product shelf life. To assist the dairy industry when evaluating product quality throughout shelf life and the effect of bioprotective cultures, we aimed to build stochastic models that provide reliable predictions of yeast spoilage in yogurt with and without bioprotective culture. Growth characterizations of Debaryomyces hansenii, Yarrowia lipolytica, Saccharomyces cerevisiae, and Kluyveromyces marxianus at storage temperatures of 7, 12, and 16°C during a 30-d storage period were conducted in yogurt with and without a bioprotective culture containing Lacticaseibacillus rhamnosus strains. The kinetic growth parameters were calculated using the Buchanan growth model, and these parameters were used as baseline values in Monte Carlo models to translate the yeast growth into spoilage levels. The models were developed using 100,000 simulations and they predicted yeast spoilage levels in yogurt by the 4 yeast types. Each modeled yogurt batch was set to be contaminated with yeast at a concentration drawn from a normal distribution with a mean of 1 log₁₀ cfu/mL and standard deviation of 1 log₁₀ cfu/mL and stored for 30 d at a temperature drawn from a normal distribution with a mean of 6.1°C and a standard deviation of 2.8°C. Considering a spoilage level of 5 log₁₀ cfu/mL, the predicted number of spoiled samples was reduced 3-fold during the first 10 d and by 2-fold at the end of shelf life when a bioprotective culture was added to the yogurt. The models were evaluated by sensitivity analyses, where the main effect factors were maximum yeast population, storage temperature, and yeast strain. The models were validated by comparing the model output to actual observed spoilage data from a European dairy using the bioprotective culture. When the model prediction, based on a mixture of the 4 specific yeast strains, was compared with spoilage data from the European dairy, the observed effect of bioprotective cultures was considerably higher than predicted, potentially influenced by the presence of contaminating strains more sensitive to a bioprotective culture than those characterized here. The developed Monte Carlo models can predict yeast spoilage levels in yogurt at specific production settings and how this may be affected by various parameters and addition of bioprotective cultures.

Evolving challenges and strategies for fungal control in the food supply chain

Fungi that spoil foods or infect crops can have major socioeconomic impacts, posing threats to food security. The strategies needed to manage these fungi are evolving, given the growing incidence of fungicide resistance, tightening regulations of chemicals use and market trends imposing new food-preservation challenges. For example, alternative methods for crop protection such as RNA-based fungicides, biocontrol, or stimulation of natural plant defences may lessen concerns like environmental toxicity of chemical fungicides. There is renewed focus on natural product preservatives and fungicides, which can bypass regulations for 'clean label' food products. These require investment to find effective, safe activities within complex mixtures such as plant extracts. Alternatively, physical measures may be one key for fungal control, such as polymer materials which passively resist attachment and colonization by fungi. Reducing or replacing traditional chlorine treatments (e.g. of post-harvest produce) is desirable to limit formation of disinfection by-products. In addition, the current growth in lower sugar food products can alter metabolic routing of carbon utilization in spoilage yeasts, with implications for efficacy of food preservatives acting via metabolism. The use of preservative or fungicide combinations, while involving more than one chemical, can reduce total chemicals usage where these act synergistically. Such approaches might also help target different subpopulations within heteroresistant fungal populations. These approaches are discussed in the context of current challenges for food preservation, focussing on pre-harvest fungal control, fresh produce and stored food preservation. Several strategies show growing potential for mitigating or reversing the risks posed by fungi in the food supply chain.

Effect of Commercial Protective Cultures and Bacterial Fermentates on Listeria monocytogenes Growth in a Refrigerated High-Moisture Model Cheese

ABSTRACT

Biopreservatives are clean-label ingredients used to control pathogenic and spoilage microorganisms in ready-to-eat foods, including cheese. In a first set of experiments, the efficacies of six commercial biopreservatives in controlling Listeria monocytogenes growth at 4°C were tested in a high-moisture model cheese (pH 6.00, 56% moisture, and 1.25% salt) made of cream, micellar casein, water, salt, lactose, lactic acid, and a single protective culture (PC-1, PC-2, or PC-3 at 106 CFU/g [target]) or bacterial fermentate (CM-1 or CM-2 [cultured milk] or CSV-1 [cultured sugar-vinegar blend], 0.5 or 1.0% target level). Cheeses were inoculated with 3 log CFU/g L. monocytogenes (5-strain cocktail), after which 25-g samples were vacuum sealed and stored at 4°C for 8 weeks. L. monocytogenes populations from triplicate samples were enumerated weekly on modified Oxford agar in duplicate trials. L. monocytogenes growth (≥1-log increase) was observed in approximately 1 week in control cheese and those formulated with 106 CFU of PC-1 or PC-2 per g. Growth was delayed to 2.5 weeks in model cheeses formulated with 106 CFU of PC-3 per g or 0.5% CM-2 and to 3 weeks with 0.5% CM-1 or CSV-1. Growth was further delayed to 6.5 to 7.5 weeks in model cheeses formulated with 1.0% CM-1 or CM-2, while formulation with 1.0% CSV-1 inhibited L. monocytogenes growth for 8 weeks. In a second set of experiments, the combined effects of pH and 0.5% CSV-1 on L. monocytogenes inhibition were investigated. Incorporation of 0.5% CSV-1 delayed L. monocytogenes growth to 3, 6, and >10 weeks in cheeses of pH 6.00, 5.75, and 5.50, respectively, versus growth observed in 1, 1, and 3.5 weeks in control cheeses. These data suggest that certain fermentates have greater antilisterial activity than protective cultures in directly acidified cheeses with direct biopreservative incorporation and refrigerated storage. Further research is needed to optimize the conditions to prevent listerial growth by utilizing protective cultures in fresh, soft cheeses.

HIGHLIGHTS

Evaluation of the efficacy of commercial protective cultures to inhibit mold and yeast in cottage cheese

Biopreservation is defined as using microbes, their constituents, or both to control spoilage while satisfying consumer demand for clean-label products. The study objective was to investigate the efficacy of bacterial cultures in biopreserving cottage cheese against postprocessing fungal contamination. Cottage cheese curd and dressing were sourced from a manufacturer in New York State. Dressing was inoculated with 3 different commercial protective cultures-PC1 (mix of Lacticaseibacillus spp. and Lactiplantibacillus spp.), PC2 (Lacticaseibacillus rhamnosus), and PC3 (Lactic. rhamnosus)-following the manufacturer recommended dosage and then mixed with curd. A control with no protective culture was included. Nine species of yeast (Candida zeylanoides, Clavispora lusitaniae, Debaryomyces hansenii, Debaryomyces prosopidis, Kluyveromyces marxianus, Meyerozyma guilliermondii, Pichia fermentans, Rhodotorula mucilaginosa, and Torulaspora delbrueckii) and 11 species of mold (Aspergillus cibarius, Aureobasidium pullulans, Penicillium chrysogenum, Penicillium citrinum, Penicillium commune, Penicillium decumbens, Penicillium roqueforti, Mucor genevensis, Mucor racemosus, Phoma dimorpha, and Trichoderma amazonicum) were included in the study. Fungi strains were previously isolated from dairy processing environments and were inoculated onto the cheese surface at a rate of 20 cfu/g. Cheese was stored at 6 ± 2°C. Yeast levels were enumerated at 0, 7, 14, and 21 d postinoculation. Mold growth was visually observed on a weekly basis through d 42 of storage and imaged. Overall, the protective cultures were limited in their ability to delay the outgrowth in cottage cheese, with only 8 of the 20 fungal strains showing an effect of the cultures compared with the control. The protective cultures were not very effective against yeast, with only PC1 able to delay the outgrowth of 3 strains: D. hansenii, Tor. delbrueckii, and Mey. guilliermondii. The efficacy of these protective cultures against molds in cottage cheese was more promising, with all protective cultures showing the ability to delay spoilage of at least 1 mold strain. Both PC1 and PC2 were able to delay Pen. chrysogenum and Pho. dimorpha outgrowth, and PC1 also delayed Pen. commune, Pen. decumbens, and Pen. roqueforti to different extents compared with the controls. This study demonstrates that commercial lactic acid bacteria cultures vary in their performance to delay mold and yeast outgrowth, and thus each protective culture should be evaluated against the specific strains of fungi of concern within each specific dairy facility.

Evaluation of the inhibitory activity of essential oils against spoilage yeasts and their potential application in yogurt

Yeasts are the leading cause of spoilage in yogurt. Considering the high demand from consumers to use natural products as an alternative to additives, essential oils (EOs) could be a promising solution to guarantee high microbiological standards. The present study highlighted the in vitro antifungal potential of cinnamon, ginger, lemongrass, mandarin, orange, lemon and lime EOs against spoilage yeasts isolated from yogurts prepared with pasteurized buffalo milk. A total of 74 isolates represented by 14 different species of Candida, Rhodotorula, Debaryomyces, Kluyveromyces and Yarrowia genera were subjected to a disc diffusion assay, showing lemongrass EO to have the highest antifungal activity (40.97 ± 9.86 mm), followed by cinnamon (38.46 ± 6.59 mm) and orange (12.00 ± 4.52 mm) EOs. Yarrowia lipolytica was less susceptible to lemongrass EO than Candida sake and Yarrowia deformans isolates. Ginger EO exhibited the lowest efficacy. A minimum inhibitory concentration (MIC) assay showed the ability of lemongrass and cinnamon EOs to inhibit the growth of all selected isolates at concentrations between ≤0.31 and 1.25 μL/mL. Therefore, for the first time, the two best-performing EOs (lemongrass and cinnamon) based on in vitro assays were assessed for their potential roles as preservatives in an in vivo yogurt model prepared at the laboratory scale. Since some limitations, such as the inhibition of lactic acid bacteria by cinnamon EO, consequently leading to fermentation failure as well as species-specific antifungal activity of lemongrass EO, were observed, further studies are needed to explore the possibility of using a slightly higher concentration of lemongrass EO and/or combinations of different EOs and/or their components. Finally, since yogurt spoilage could also be prevented by correct sanitation procedures of the production environment, the sanitizers commonly used in the food industry were tested against all isolates, showing the high efficiency of alcohol-based sanitizers and the ineffectiveness of chlorine-based sanitizers.

Invited review: Controlling dairy product spoilage to reduce food loss and waste

Food loss and waste is a major concern in the United States and globally, with dairy foods representing one of the top categories of food lost and wasted. Estimates indicate that in the United States, approximately a quarter of dairy products are lost at the production level or wasted at the retail or consumer level annually. Premature microbial spoilage of dairy products, including fluid milk, cheese, and cultured products, is a primary contributor to dairy food waste. Microbial contamination may occur at various points throughout the production and processing continuum and includes organisms such as gram-negative bacteria (e.g., Pseudomonas), gram-positive bacteria (e.g., Paenibacillus), and a wide range of fungal organisms. These organisms grow at refrigerated storage temperatures, often rapidly, and create various degradative enzymes that result in off-odors, flavors, and body defects (e.g., coagulation), rendering them inedible. Reducing premature dairy food spoilage will in turn reduce waste throughout the dairy continuum. Strategies to reduce premature spoilage include reducing raw material contamination on-farm, physically removing microbial contaminants, employing biocontrol agents to reduce outgrowth of microbial contaminants, tracking and eliminating microbial contaminants using advanced molecular microbiological techniques, and others. This review will address the primary microbial causes of premature dairy product spoilage and methods of controlling this spoilage to reduce loss and waste in dairy products.

Control of spoilage fungi in yogurt using MicroGARD 200™, Lyofast-FPR2™ and HOLDBAC-YMC™ as bioprotectants

The aim of this study was to assess the inhibitory effect of three commercial bioprotectant agents on the growth of yogurt-spoiling fungi. Mucor circinelloides, Mucor racemosus, Penicillium spp., Saccharomyces exiguus, and Candida intermedia, commonly involved in the spoilage of dairy products, were isolated from spoiled yogurt and were fully characterized using molecular and phenotypic methods. HOLDBAC-YMC™, Lyofast-FPR2™ and MicroGARD 200™ were used as antifungal products. An optimized experimental mixture design was applied to determine the proportion of each bioprotectant in terms of growth-inhibition response against the fungal strains in standard laboratory media. The results of the challenge tests showed that the application of bioprotectants inhibited the growth of the moulds in the range of 85–100% and the growth of yeast between 1.23 and 5.40 log cycles. The optimal combination of the bioprotectants was determined, tested in standard laboratory media and found to inhibit fungal growth. The antifungal effect of the optimal combination of the bioprotectants was validated in yogurt against the most resistant fungal species of the study, M. circinelloides and C. intermedia. The bioprotectants elicited antifungal effect in yogurt by completely inhibiting all of the tested fungi compared to controls. To the best of our knowledge, this is the first time a mixture of commercial bioprotectants has been tested on yogurt as a potential alternative for the biopreservation of yogurt in order to reduce spoilage of fermented dairy products and economic losses.