Spoilage yeasts: What are the sources of contamination of foods and beverages?

Effect of the cleaning and disinfection methods on the hygienic conditions of fermentation tanks of table olives (Olea europaea L.) Negrinha de Freixo cultivar

This study aimed to evaluate and identify the microbial community attached to the surfaces of fermenter tanks used in table olive Negrinha de Freixo cultivar processing through molecular analysis and verify if the cleaning/disinfection was done correctly. Four fermentation tanks previously used in table olive processing were sampled at three different inside areas: upper, middle, and lower. Before sampling, four cleaning/disinfection methods were applied to the tanks, including (i) pressurised water; (ii) a disinfectant product used to clean bowls (Vasiloxe); (iii) 10% sodium hydroxide solution (caustic soda liquid); and (iv) a disinfectant product used by the wine industry (Hosbit). For each sample collected, mesophilic aerobic bacteria, yeast and moulds (YMC), lactic acid bacteria (LAB), as well as total coliforms (TC) and Pseudomonas aeruginosa were evaluated. The results showed significant differences between the different cleaning/disinfection methods applied. The fermenter sanitised with only pressurised water showed a greater abundance of microorganisms than the others. Mesophilic aerobic bacteria were the predominant population, with counts ranging between 2.63 and 5.56 log10 CFU/100 cm2, followed by the moulds (3.11-5.03 log10 CFU/100 cm2) and yeasts (2.42-5.12 log10 CFU/100 cm2). High diversity of microbial communities was observed between the different fermenter tanks. The most abundant species belonged to Aureobasidium, Bacillaceae, Cladosporium, and Rhodotorula genera. LAB, TC, and P. aeruginosa were not detected. This study hopes to improve hygienic conditions and increase the quality assurance and safety of the final product.

Microbial food spoilage: impact, causative agents and control strategies

Microbial food spoilage is a major contributor to food waste and, hence, to the negative environmental sustainability impacts of food production and processing. Globally, it is estimated that 15-20% of food is wasted, with waste, by definition, occurring after primary production and harvesting (for example, in households and food service establishments). Although the causative agents of food spoilage are diverse, many microorganisms are major contributors across different types of foods. For example, the genus Pseudomonas causes spoilage in various raw and ready-to-eat foods. Aerobic sporeformers (for example, members of the genera Bacillus, Paenibacillus and Alicyclobacillus) cause spoilage across various foods and beverages, whereas anaerobic sporeformers (for example, Clostridiales) cause spoilage in a range of products that present low-oxygen environments. Fungi are also important spoilage microorganisms, including in products that are not susceptible to bacterial spoilage due to their low water activity or low pH. Strategies that can reduce spoilage include improved control of spoilage microorganisms in raw material and environmental sources as well as application of microbicidal or microbiostatic strategies (for example, to products and packaging). Emerging tools (for example, systems models and improved genomic tools) represent an opportunity for rational design of systems, processes and products that minimize microbial food spoilage.

Wheat Bread Enriched with House Cricket Powder (Acheta domesticus L.) as an Alternative Protein Source

The house cricket (Acheta domesticus L.) is one of four edible insect species introduced to the EU market as a novel food and alternative protein source. Innovative products, such as cricket flour, are increasingly appearing on supermarket shelves and can offer an alternative to traditional cereals, while providing the body with many valuable nutrients of comparable quality to those found in meat and fish. The aim of this study was to investigate the possibility of using cricket powder as a substitute for wheat flour in the production of bread. The physicochemical properties of cricket powder were evaluated in comparison to wheat flour. As a result of technological studies, bread compositions with 5%, 10% and 15% replacements of wheat flour by cricket powder were designed and their quality characteristics (physicochemical, sensory and microbiological) were evaluated. Cricket powder was characterised by a higher protein (63% vs. 13.5%) and fat (16.3% vs. 1.16%) content and a lower carbohydrate (9.8% vs. 66%) and fibre (7.8% vs. 9.5%) content as compared to wheat flour. The tested preparations had a similar pH (6.9 and 6.8, respectively, for cricket powder and flour) and fat absorption capacity (0.14 vs. 0.27 g oil/g powder, respectively, for cricket powder and flour) but different water holding capacities and completely different colour parameters. All breads had good microbiological quality after baking and during 7 days of storage. In instrumental tests, the 10 and 15% replacements of wheat flour by cricket powder affected the darker colour of the breads and caused a significant increase in the hardness of the breads. The research has shown that the optimal level of replacement, which does not significantly affect the physiochemical and sensory characteristics, is 5% cricket powder in the bread recipe. Considering the results obtained and the fact that insects provide a sufficient supply of energy and protein in the human diet, are a source of fibre, vitamins and micronutrients, and have a high content of monounsaturated and polyunsaturated fatty acids, the suitability of cricket powder for protein enrichment of bakery products is confirmed.

Exploring the potential of probiotic-enriched beer: Microorganisms, fermentation strategies, sensory attributes, and health implications

Probiotic-enriched beers have emerged as an innovative solution for delivering beneficial microorganisms, particularly appealing to consumers seeking non-dairy options. However, navigating the complex beer environment presents challenges in effectively cultivating specific probiotic strains. This review aims to promote innovation and distinctiveness within the brewing industry by providing insights into current research on the integration of probiotic microorganisms into beer production, thereby creating a functional beverage. The review explores the effects of probiotic incorporation on the functional, technological, and sensory attributes of beer, distinguishing contributions from bacterial and yeast, as well as potential health benefits. Probiotic microorganisms encounter hurdles during beer production, including ethanol, hops, CO2 levels, pH, oxygen, and nutrients. Ethanol tolerance mechanisms vary among bacteria and yeasts, with specific lactic acid bacteria showing resistance to hop compounds. Hops, crucial for beer categorization, exert a timing-dependent impact on probiotics-early isomerization impedes growth, while late additions yield non-isomerized antibacterial properties. Effective probiotic integration necessitates precise post-fermentation addition stages to ensure viability and flavor. The sensory impact and consumer reception of probiotic-enriched beers require further exploration. Probiotics must endure storage conditions to qualify as functional beer, while limited research investigates health advantages, urging enhanced production techniques, sensory optimization, and clinical validation.

Innovative Biobased and Sustainable Polymer Packaging Solutions for Extending Bread Shelf Life: A Review

Sustainable packaging has been steadily gaining prominence within the food industry, with biobased materials emerging as a promising substitute for conventional petroleum-derived plastics. This review is dedicated to the examination of innovative biobased materials in the context of bread packaging. It aims to furnish a comprehensive survey of recent discoveries, fundamental properties, and potential applications. Commencing with an examination of the challenges posed by various bread types and the imperative of extending shelf life, the review underscores the beneficial role of biopolymers as internal coatings or external layers in preserving product freshness while upholding structural integrity. Furthermore, the introduction of biocomposites, resulting from the amalgamation of biopolymers with active biomolecules, fortifies barrier properties, thus shielding bread from moisture, oxygen, and external influences. The review also addresses the associated challenges and opportunities in utilizing biobased materials for bread packaging, accentuating the ongoing requirement for research and innovation to create advanced materials that ensure product integrity while diminishing the environmental footprint.

Study of chemical constituents, antioxidants and antimicrobial activities of Tamarindus indica L. seed

The fruits of Tamarindus indica L. are consumed worldwide, with various parts of the plant being used for medicinal purposes. The residues (pericarp and seeds) generated during cellulose processing are of significant value as they contain bioactive compounds with diverse biological activities. The objective of this study was to evaluate the chemical constituents of the ethyl acetate fraction as possible substitutes for synthetic compounds with biological properties using ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS/MS) analysis and the evaluation of the antioxidant activity (ferric reducing antioxidant power [FRAP], 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid [ABTS], and 1-diphenyl-2-picrylhydrazyl [DPPH]), total phenolic compounds (TPC), and antimicrobial activity of the hydroalcoholic extract and tamarind seed fractions were also performed. The chemical investigation of the acetate fraction using UHPLC-HRMS/MS resulted in the putative identification of 14 compounds, including flavonoids, (+)-catechin/(-)-epicatechin, procyanidin B2, procyanidin C2, isoquercetin, quercetin, luteolin, rutin, taxifolin, eriodictyol, kaempferide, hydroxybenzoic acid, protocathecuic acid, and protocathecuic acid methyl and ethyl esters derivatives. The crude hydroalcoholic extract exhibited the best results in terms of TPC: 883.87 gallic acid equivalent (GAE; mg/g) and antioxidant activity: FRAP: 183.29 GAE (mg/g), ABTS: 39.67%, and DPPH: 91.08%. The extract exhibited excellent antibacterial activity against gram-positive bacteria, specifically Staphylococcus aureus minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC; 62.5/125 g/mL) and Bacillus cereus MIC/MBC (125/250 g/mL), and gram-negative bacteria, specifically Aeromonas hydrophila MIC/MBC (125/250 µg/mL) and Pseudomonas aeruginosa MIC/MBC (250/500 g/mL). Morphological damage to cells was observed using flow cytometry and scanning electron microscopy. Tamarind seeds contain unique bioactive compounds that should be explored for their use as novel food preservatives. PRACTICAL APPLICATION: Original data were obtained regarding the Tamarindus indica L. seed extract and the ethyl acetate and hexane fractions. This research aimed to investigate the potential of these for food preservation and as alternatives to additives and synthetic compounds added to cattle feed. This paper reports novel findings regarding the chemical composition of the extract and its antioxidant activity, along with its antimicrobial activity against bacteria (gram-positive: Staphylococcus aureus, Bacillus cereus, and gram-negative: Salmonella enterica serovar Enteritidis, Escherichia coli, Pseudomonas aeruginosa, and Aeromonas hydrophila) and yeasts (Candida albicans and Saccharomyces cerevisiae).

Spices as Sustainable Food Preservatives: A Comprehensive Review of Their Antimicrobial Potential

Throughout history, spices have been employed for their pharmaceutical attributes and as a culinary enhancement. The food industry widely employs artificial preservatives to retard the deterioration induced by microbial proliferation, enzymatic processes, and oxidative reactions. Nevertheless, the utilization of these synthetic preservatives in food products has given rise to significant apprehension among consumers, primarily stemming from the potential health risks that they pose. These risks encompass a spectrum of adverse effects, including but not limited to gastrointestinal disorders, the disruption of gut microbiota, allergic reactions, respiratory complications, and concerns regarding their carcinogenic properties. Consequently, consumers are displaying an increasing reluctance to purchase preserved food items that contain such additives. Spices, known for their antimicrobial value, are investigated for their potential as food preservatives. The review assesses 25 spice types for their inherent antimicrobial properties and their applicability in inhibiting various foodborne microorganisms and suggests further future investigations regarding their use as possible natural food preservatives that could offer safer, more sustainable methods for extending shelf life. Future research should delve deeper into the use of natural antimicrobials, such as spices, to not only replace synthetic preservatives but also optimize their application in food safety and shelf-life extension. Moreover, there is a need for continuous innovation in encapsulation technologies for antimicrobial agents. Developing cost-effective and efficient methods, along with scaling up production processes, will be crucial to competing with traditional antimicrobial options in terms of both efficacy and affordability.

Exploring yeast-based microbial interactions: The next frontier in postharvest biocontrol

Fresh fruits and vegetables are susceptible to a large variety of spoilage agents before and after harvest. Among these, fungi are mostly responsible for the microbiological deteriorations that lead to economically significant losses of fresh produce. Today, synthetic fungicides represent the first approach for controlling postharvest spoilage in fruits and vegetables worldwide. However, the emergence of fungicide-resistant pathogen biotypes and the increasing awareness of consumers toward the health implications of hazardous chemicals imposed an urgent need to reduce the use of synthetic fungicides in the food supply; this phenomenon strengthened the search for alternative biocontrol strategies that are more effective, safer, nontoxic, low-residue, environment friendly, and cost-effective. In the last decade, biocontrol with antagonistic yeasts became a promising strategy to reduce chemical compounds during fruit and vegetable postharvest, and several yeast-based biocontrol products have been commercialized. Biocontrol is a multipartite system that includes different microbial groups (spoilage mold, yeast, bacteria, and nonspoilage resident microorganisms), host fruit, vegetables, or plants, and the environment. The majority of biocontrol studies focused on yeast-mold mechanisms, with little consideration for yeast-bacteria and yeast-yeast interactions. The current review focused mainly on the unexplored yeast-based interactions and the mechanisms of actions in biocontrol systems as well as on the importance and advantages of using yeasts as biocontrol agents, improving antagonist efficiency, the commercialization process and associated challenges, and future perspectives.

Nanostructured Hybrid BioBots for Beer Brewing

The brewing industry will amass a revenue above 500 billion euros in 2022, and the market is expected to grow annually. This industrial process is based on a slow sugar fermentation by yeast (commonly Saccharomyces cerevisiae). Herein, we encapsulate yeast cells into a biocompatible alginate (ALG) polymer along Fe₃O₄ nanoparticles to produce magneto/catalytic nanostructured ALG@yeast-Fe₃O₄ BioBots. Yeast encapsulated in these biocompatible BioBots keeps their biological activity (growth, reproduction, and catalytic fermentation) essential for brewing. Catalytic fermentation of sugars into CO₂ gas caused a continuous oscillatory motion of the BioBots in the solution. This BioBot motion is employed to enhance the beer fermentation process compared to static-free yeast cells. When the process is finished, magnetic actuation of BioBots is employed for their retrieval from the beer samples, which avoids the need of additional filtration steps. All in all, we demonstrate how an industrial process such as beer production can be benefited by miniaturized autonomous magneto/catalytic BioBots.

Activity of Binary Combinations of Natural Phenolics and Synthetic Food Preservatives against Food Spoilage Yeasts

Natural compounds are a suitable alternative to synthetic food preservatives due to their natural origin and health-promoting properties. In the current study, phenolic-phenolic and phenolic-synthetic combinations were tested for their antibiofilm formation, anti-planktonic growth, and anti-adhesion properties against Debaryomyces hansenii, Wickerhamomyces anomalus (formerly Pichia anomala), Schizosaccharomyces pombe, and Saccharomyces cerevisiae. The phenolics were vanillin and cinnamic acid, while the synthetic preservatives were sodium benzoate, potassium sorbate, and sodium diacetate. The vanillin-cinnamic acid combination had synergistic effect in all the tested yeasts for the biofilm inhibition with a fractional inhibitory concentration index (FICI) of ≤0.19 for W. anomalus, 0.25 for S. pombe, 0.31 for S. cerevisiae, and 0.5 for D. hansenii. Most of the phenolic-synthetic combinations had indifferent interaction regarding biofilm formation. The vanillin-cinnamic acid combination also had higher activity against spoilage yeasts adhesion on the abiotic surface and planktonic growth compared to the phenolic-synthetic combinations. For the phenolic-synthetic anti-planktonic activity, synergistic interaction was present in all the vanillin-synthetic combinations in S. pombe, vanillin-sodium benzoate and vanillin-potassium sorbate in S. cerevisiae, vanillin-sodium benzoate in W. anomalus, and cinnamic acid-sodium diacetate in S. pombe. These results suggest a novel antimicrobial strategy that may broaden the antimicrobial spectrum and reduce compound toxicity against food spoilage yeasts.

Mycological evaluation of frozen meat with special reference to yeasts

Background and Aim

Fungi can play beneficial and detrimental roles in meat products; however, the diversity and significance of fungi in meat products are poorly understood. This study aimed to isolate and characterize fungal species from frozen beef samples collected from retail stores in the Qena Governorate, Egypt.

Materials and Methods

A total of 70 frozen beef samples were collected from retail stores in Qena, Egypt. All samples were subjected to mycological examination. Fungal colonies were identified using conventional approaches, as well as the VITEK 2 system and DNA sequencing of the internal transcribed spacer region. Analyses of enzymatic activity, biofilm formation ability, and the antimicrobial resistance profiles of the isolated yeasts were also conducted.

Results

Molds and yeasts were isolated from 40% and 60% of meat samples, respectively. Mold isolates were dominated by Aspergillus, Penicillium, and Cladosporium spp., whereas yeast isolates were identified as Candida albicans, Candida parapsilosis, Yarrowia lipolytica, Saccharomyces cerevisiae, and Rhodotorula mucilaginosa. Compared to other yeast species, the highest production of lipase and protease was observed in Candida species. The strongest ability to form biofilms was observed in Candida spp., followed by S. cerevisiae, Y. lipolytica, and R. mucilaginosa. The results of antimicrobial susceptibility testing revealed that all yeast isolates showed notable resistance to fluconazole and itraconazole.

Conclusion

A significant correlation between antimicrobial resistance and biofilm formation was observed in several species. This study highlights the importance of the dangers of yeasts in food products and the extent of their impact on public health.

Fruit-Based Fermented Beverages: Contamination Sources and Emerging Technologies Applied to Assure Their Safety

The food and beverage market has become broader due to globalization and consumer claims. Under the umbrella of consumer demands, legislation, nutritional status, and sustainability, the importance of food and beverage safety must be decisive. A significant sector of food production is related to ensuring fruit and vegetable conservation and utilization through fermentation. In this respect, in this review, we critically analyzed the scientific literature regarding the presence of chemical, microbiological and physical hazards in fruit-based fermented beverages. Furthermore, the potential formation of toxic compounds during processing is also discussed. In managing the risks, biological, physical, and chemical techniques can reduce or eliminate any contaminant from fruit-based fermented beverages. Some of these techniques belong to the technological flow of obtaining the beverages (i.e., mycotoxins bound by microorganisms used in fermentation) or are explicitly applied for a specific risk reduction (i.e., mycotoxin oxidation by ozone). Providing manufacturers with information on potential hazards that could jeopardize the safety of fermented fruit-based drinks and strategies to lower or eliminate these hazards is of paramount importance.

Rapid evaluation of ergosterol to detect yeast contamination in fruit juices

Foods and beverages are nutrient-rich systems prone to a rapid development of microorganisms that hamper their long-period storage. Particularly, yeasts are strong fermenters of fresh and processed fruits and vegetables; hence, they are often accountable for their spoilage and production of off-flavor. This work provides a quick and easy tool to recognize and count the spoilage of juices with ergosterol as distinctive biomarker of molds and yeasts. Melon juice was reconstituted at natural physical–chemical parameters according to legislation, and Saccharomyces cerevisiae was selected as yeast to contaminate the juice. Chemical and enzyme tests were performed on the fresh juice to ensure its authentic properties. Ergosterol was then evaluated using a spectrophotometric method that was proven against the official plate count test. The study showed linear and consistent results and, therefore, the ergosterol molecule may be indicated for testing molds and yeasts in contaminated beverages, replacing the common and time-consuming analysis.

Exploring Biocontrol of Unwanted Fungi by Autochthonous Debaryomyces hansenii Strains Isolated from Dry Meat Products

The exploration of alternatives to the use of chemical preservatives in food is a topic that has attracted great attention. The implementation of regulations associated with the reduction of these elements directly affects the production of cured meat products, with the premise of looking for more “natural” alternatives. From a previously identified collection of 24 strains of Debaryomyces hansenii, isolated from dry meat products of the “Valle de los Pedroches” (Córdoba), a screening was carried out to determine which strains had inhibitory potential against a battery of fungi belonging to the genera Aspergillus, Penicillium, and Candida. After a series of general trials, four strains showing the greatest potential were selected by a streak inhibition assay performed at several concentrations of NaCl. The inhibitory activity of the selected D. hansenii strains was later evaluated by measuring their fungal antagonistic diffusible and volatile compound production following radial inhibition and mouth-to-mouth approaches, respectively. Growth aspects, sporulation, and morphology changes were also considered during these assays. The results support ideas already raised in previous studies, such as the presence of D. hanseniii could imply a reduction of pathogenic fungi in food. Autochthonous yeast strains inhibited not only the mycelial growth, but also sporulation, which strengthens the biocontrol activity of this yeast. Our results show that, under certain conditions, all tested D. hansenii strains were able to alter the growth/development of fungi, being especially evident in the cases of Penicillium expansum and Aspergillus niger. Finally, our research can facilitate the future comparison of results in this area, since we contributed to standardize the methodology described to date, we quantified the number of yeast cells and spores used during the experiments, we homogenized growth conditions for both, yeasts, and molds, and applied an image analyzer software to quantify the growth of the studied microorganisms in solid media.

Distribution of psychrophilic microorganisms in a beef slaughterhouse in Japan after cleaning

The purpose of this study was to investigate the abundance and distribution of psychrophilic microorganisms associated with spoilage in beef slaughterhouse environments after cleaning. The processing lines and equipment used in slaughtering and boning were swabbed, and the microbial count was determined using a TSA and MRS medium and Chromocult^® Coliform agar incubated at 15ºC and 37ºC, respectively. As a result, the brisket saw (handle side) and trolley hook were the most heavily contaminated with microorganisms, with each having a microbial adhesion rate of 66.7%. The microbial adhesion rates of the apron and milling cutter (edge side) were 50%, respectively, and those of the foot cutter (edge and handle side), splitting saw (edge side), and knife (handle side) were 33.3%, respectively. Next, four colonies were randomly isolated from the petri dish used for the bacterial count measurement to identify the predominant microbial species of the microorganisms attached to each equipment. As a result of Sanger sequencing analysis, yeasts such as Candida zeylanoides and Rhodotorula sp. and bacteria including Pseudomonas sp. and Rhodococcus sp. were identified from the equipment used in the slaughtering line, and it was assumed that these microorganisms were of environmental origin. In contrast, only Pseudomonas sp. and Candida zeylanoides were isolated from the boning line. Despite the use of cleaning operations, this study identified some equipment was contaminated with microorganisms. Since this equipment frequently comes into direct contact with the carcass, it is critical to thoroughly remove the microorganisms through accurate cleaning to prevent the spread of microbial contamination on the carcasses.

Microbiota Survey of Sliced Cooked Ham During the Secondary Shelf Life

Sliced cooked ham packaged in a modified atmosphere is a popular ready-to-eat product, subjected to abundant microbial contamination throughout its shelf life that can lead to deterioration of both sensorial properties and safety. In this study, the microbial load and the chemical–physical features of cooked ham of five producers were monitored for a period of 12 days after the opening of the packages (i.e., the secondary shelf life), during which the products were stored in a domestic refrigerator at 5.2 ± 0.6°C. The sensorial properties presented a perceivable decay after 8 days and became unacceptable after 12 days. High-performance liquid chromatography analysis and solid-phase microextraction coupled with gas chromatography profiling of volatile metabolites indicated that lactic acid, ethanol, acetic acid, acetoin, 3-methyl-1-butanol, and 2-3 butanediol were the main metabolites that characterized the evolution of the analyzed cooked ham. The microbiota was monitored by 16S ribosomal RNA gene profiling and culture-dependent techniques. Already at the opening of packages, all the products presented high microbial load, generally dominated by lactic acid bacteria, with evident differences among the products. The increase of lactic acid bacteria somehow protected samples from abundant contamination by other bacteria, concurring with the evolution of more safe products. This role was exerted by numerous Latilactobacillus, Leuconostoc, and Carnobacterium species, among which the most frequently detected were Latilactobacillus sakei, Latilactobacillus sakei carnosum, Leuconostoc mesenteroides, and Carnobacterium divergens. Some products presented more complex communities that encompassed Proteobacteria such as Moellerella wisconsensis, Proteus hauseri, Brochothrix thermosphacta, and less frequently Pseudomonas, Erwinia, and Massilia. Opportunistic pathogenic bacteria such as Escherichia coli and Vibrio sp. were found in small quantities. The yeasts Kazachstania servazzii and Debaryomyces hansenii occurred already at 0 days, whereas various species of Candida (Candida zeylanoides, Candida sake, Candida norvegica, and Candida glaebosa) were abundant only after 12 days. These results indicated that the microbiological contaminants overgrowing during the secondary shelf life did not derive from environmental cross-contamination at the opening of the tray but were already present when the packages were opened, highlighting the phases of production up to the packaging as those crucial in managing the safety risk associated to this product.

Antimicrobial Activity of Slow Pyrolysis Distillates from Pine Wood Biomass against Three Pathogens

The aim of this study was to evaluate the antimicrobial activity of wood distillates obtained from Scots pine (Pinus sylvestris) sawdust in order to explore new alternatives for the utilization of wood industry by-products. The distillates were produced by slow pyrolysis thermal conversion in three process phases with increasing temperatures, namely drying, torrefaction and pyrolysis, and three cooling units with different temperatures to condensate the distillates. This yielded nine different liquid fractions. The food-related pathogens, Salmonella, Listeria monocytogenes and Candida albicans, were evaluated for their susceptibility to the distillate fractions using an agar diffusion test. The antimicrobial activity was estimated by measuring the formed inhibition zones after the incubation period. In addition, the minimum inhibitory concentration (MIC) and microbicidic concentration were assayed for a selected fraction (T2) from the torrefaction phase with Bio-screen C. The results indicated that the distillates from the torrefaction and pyrolysis phases had antimicrobial activity against the tested microbes. The MIC value of the T2 fraction for all tested microbes was 0.83% (v/v). Furthermore, the T2 fraction was microbicidic for Salmonella and Listeria strains in 0.83% (v/v) solution and Candida strain in 1.67% (v/v) solution. In conclusion, Scots pine wood distillates obtained from slow pyrolysis have the potential to be developed as antimicrobial agents against pathogenic microbes. Next, research is needed to investigate the chemical composition of the distillates and to assess their safe use.

Factors That Affect the Microbiological Stability of Chicha Morada during Its Production on an Industrial Scale: A Review

ABSTRACT

Chicha morada, also known as purple corn drink (PCD), is a traditional noncarbonated beverage commonly prepared at homes and restaurants in Peru. However, in recent years, it is being produced at an industrial scale aiming to extend its shelf life, expand its marketing, and make it known worldwide. Traditionally, this beverage, whose main component is purple corn (Zea mays L.), was made and consumed quickly and in some cases, stored under refrigeration until consumption, but never beyond 24 to 48 h. With its industrialization, factories are presented with challenges to design and provide adequate protection of the beverage, assuring its quality and safety. Although its production at an industrial level is similar to that of other noncarbonated drinks containing fruit juice, several processing factors could affect the microbiological stability desired for this beverage, such as the storage of the purple corn drink extract. In this document, a critical review of the production process (raw materials, production stages, and forms of commercialization) that can directly affect the contamination of the beverage is made. Recommendations are made for improving the control points in the industrial process and to avoid potential microbiological problems.

HIGHLIGHTS

Ultrasound assisted modulation of yeast growth and inactivation kinetics

The yeast Saccharomyces cerevisiae is well known for its application in the food industry for the purpose of developing fermented food. The ultrasound (US) technology offer a wide range of applications for the food industry, including the enhancement of fermentation rates and inactivation of microbial cells. However, a better understanding and standardization of this technology is still required to ensure the scaling-up process. This study investigated the effect of the US technology on the growth of S. cerevisiae using frequencies of 20, 25, 45 and 130 kHz, treatment periods from 2 to 30 min. Furthermore, yeast kinetics subjected to US treatments were evaluated using modelling tools and scanning electron microscopy (SEM) analysis to explore the impact of sonication on yeast cells. Yeast growth was monitored after different US treatments plotting optical density (OD) at 660 nm for 24 h at 30 ⁰C. Growth curves were fitted using models of modified Gompertz and Scale-Free which showed good parameters of the fit. In particular, US frequencies of 45 and 130 kHz did not have a disruptive effect in lag phase and growth rate of the yeast populations, unlike the frequency of 20 kHz. Moreover, inactivation curves of yeast cells obtained after exposure to 20 and 25 kHz also observed the best fit using the Weibull model. US frequency of 20 kHz achieved significant reductions of 1.3 log cfu/mL in yeast concentration and also induced important cell damage on the external structures of S. cerevisiae. In conclusion, the present study demonstrated the significant effect of applying different US frequencies on the yeast growth for potential application in the food industry.

Εvaluation of the microbial stability and shelf life of 50% NaCl-reduced traditional Greek pork meat product "Syglino of Monemvasia" stored under vacuum at different temperatures

Nowadays, consumers are increasingly concerned about nutrition and health issues. "Syglino of Monemvasia" is a traditional Greek cooked and smoked, sliced pork meat product. Although this is a nutritious food, its consumption should be done in moderation due to the pickling process of its preparation. This product was thus here optimized to contain half salt (NaCl) amount and its microbial stability and shelf life was then assessed in comparison to the already available commercial product. For this, the total viable counts (TVCs) and some critical specific spoilage associations were enumerated at each product type during vacuum incubation at four different temperatures (0, 5, 10, and 15 °C). The alterations in pH, a_w, color, and some other crucial sensory attributes of each product were also periodically monitored. The new low-salt product was found to remain microbiologically stable under refrigerated vacuum storage for approximately two weeks, being finally spoiled by Brochothrix thermosphacta grown above 10⁷ CFU/g, ultimately resulting in the deterioration of taste, odor, and overall appearance of the product, and thus leading to its subsequent organoleptic rejection. Despite its limited shelf life, the 50% NaCl-reduced "Syglino" could be released in the local market provided that the cooling chain is maintained throughout its distribution (≤5 °C) and at the same time consumers are willing to accept its milder taste. Although salt replacers could have been used to improve its flavor and at the same time increase its shelf life, the product here developed without the use of such alternatives will hopefully contribute to the taste training of its consumers for less salt in their diet, keeping in parallel its clean label with no added preservatives and other food additives.

Development of quantitative real-time PCR and digital droplet-PCR assays for rapid and early detection of the spoilage yeasts Saccharomycopsis fibuligera and Wickerhamomyces anomalus in bread

In the present study, for the first time, high sensitive quantitative polymerase chain reaction (qPCR) and digital droplet polymerase chain reaction (ddPCR) assays were developed to detect and quantify total eumycetes with potential application in several food matrices and to specifically determine the level of contamination by Saccharomycopsis fibuligera and Wickerhamomyces anomalus cells directly in bread. Among the candidate target genes used to develop the assays, car1 gene was chosen to detect the two spoilage yeasts S. fibuligera and W. anomalus. The specificity of the PCR assays was tested using purified genomic DNA from 36 bacterial and fungal strains. The sensitivity of the assays was defined by using tenfold serial dilutions of genomic DNA starting from 10⁶ cfu/mL to 1 cfu/mL of S. fibuligera and W. anomalus. Validation of the assays was achieved by enumeration of S. fibuligera and W. anomalus DNA copies from samples of artificially contaminated bread homogenates detecting up to 10 cfu/mL (0.06 ± 0.01 copies/μL) of W. anomalus by using ddPCR. In conclusion, the developed qPCR and ddPCR assays demonstrate strong performance in the early detection of S. fibuligera and W. anomalus in bread, representing promising tools for applying high-throughput approaches to regularly monitor bread quality.

Microbial characterization of the Japanese traditional pickle senmaizuke produced by two different manufacturing processes

Senmaizuke, a traditional turnip pickle, prepared in Kyoto, Japan, is produced via two types of manufacturing processes: with and without vinegar for fermentation. The aim of this study was to reveal the microbial community and growth behavior in the products and manufacturing processes of two types of senmaizuke. Microbial growth analysis of commercial senmaizuke products showed that both types harbored 102-108 colony forming units (CFU)/g of lactic acid bacteria (LAB) and 102-104 of yeast. The fermented-type products showed successive growth of LAB during the pickling and ripening processes, whereas LAB in vinegar-type products showed growth only at the preliminary pickling step before vinegar addition; however, the bacteria were viable at the ripening step. LAB in the vinegar-type products showed growth when the pH of the pickle was neutralized, indicating that acidification via vinegar retards LAB growth. Metagenomic sequencing showed that the fermented-type products harbored Lactobacillus, Leuconostoc, and other halophilic and psychrophilic bacteria, with a higher bacterial diversity than in the vinegar-type products. In the vinegar-type products, Lactobacillus, Leuconostoc, or both were predominant. Culture tests using LAB isolates and turnip medium suggested that a change in the dominance of Leuconostoc to Lactobacillus members observed in the fermented-type products during pickling and ripening processes was attributed to the low pH sensitivity of Leuconostoc as well as a relatively long lag phase of growth for adapting to the pickling environment. The findings of this study will be useful for the appropriate quality control and assurance procedure of senmaizuke.

In Vitro Activity of Selected Phenolic Compounds against Planktonic and Biofilm Cells of Food-Contaminating Yeasts

Phenolic compounds are natural substances that can be obtained from plants. Many of them are potent growth inhibitors of foodborne pathogenic microorganisms, however, phenolic activities against spoilage yeasts are rarely studied. In this study, planktonic and biofilm growth, and the adhesion capacity of Pichia anomala, Saccharomyces cerevisiae, Schizosaccharomyces pombe and Debaryomyces hansenii spoilage yeasts were investigated in the presence of hydroxybenzoic acid, hydroxycinnamic acid, stilbene, flavonoid and phenolic aldehyde compounds. The results showed significant anti-yeast properties for many phenolics. Among the tested molecules, cinnamic acid and vanillin exhibited the highest antimicrobial activity with minimum inhibitory concentration (MIC) values from 500 µg/mL to 2 mg/mL. Quercetin, (-)-epicatechin, resveratrol, 4-hydroxybenzaldehyde, p-coumaric acid and ferulic acid were also efficient growth inhibitors for certain yeasts with a MIC of 2 mg/mL. The D. hansenii, P. anomala and S. pombe biofilms were the most sensitive to the phenolics, while the S. cerevisiae biofilm was quite resistant against the activity of the compounds. Fluorescence microscopy revealed disrupted biofilm matrix on glass surfaces in the presence of certain phenolics. Highest antiadhesion activity was registered for cinnamic acid with inhibition effects between 48% and 91%. The active phenolics can be natural interventions against food-contaminating yeasts in future preservative developments.

Gold-Polyoxoborates Nanocomposite Prohibits Adsorption of Bacteriophages on Inner Surfaces of Polypropylene Labware and Protects Samples from Bacterial and Yeast Infections

Bacteriophages (phages) are a specific type of viruses that infect bacteria. Because of growing antibiotic resistance among bacterial strains, phage-based therapies are becoming more and more attractive. The critical problem is the storage of bacteriophages. Recently, it was found that bacteriophages might adsorb on the surfaces of plastic containers, effectively decreasing the titer of phage suspensions. Here, we showed that a BOA nanocomposite (gold nanoparticles embedded in polyoxoborate matrix) deposited onto the inner walls of the containers stabilizes phage suspensions against uncontrolled adsorption and titer decrease. Additionally, BOA provides antibacterial and antifungal protection. The application of BOA assures safe and sterile means for the storage of bacteriophages.

GABA enhancement by simple carbohydrates in yoghurt fermented using novel, self-cloned Lactobacillus plantarum Taj-Apis362 and metabolomics profiling

This study aimed to enhance natural gamma aminobutyric acid (GABA) production in yoghurt by the addition of simple sugars and commercial prebiotics without the need for pyridoxal 5′-phosphate (PLP) cofactor. The simple sugars induced more GABA production (42.83–58.56 mg/100 g) compared to the prebiotics (34.19–40.51 mg/100 g), with glucose promoting the most GABA production in yoghurt (58.56 mg/100 g) surpassing the control sample with added PLP (48.01 mg/100 g). The yoghurt prepared with glucose also had the highest probiotic count (9.31 log CFU/g). Simulated gastrointestinal digestion of this GABA-rich yoghurt showed a non-significant reduction in GABA content and probiotic viability, demonstrating the resistance towards a highly acidic environment (pH 1.2). Refrigerated storage up to 28 days improved GABA production (83.65 mg/100 g) compared to fresh GABA-rich yoghurt prepared on day 1. In conclusion, the addition of glucose successfully mitigates the over-use of glutamate and omits the use of PLP for increased production of GABA in yoghurt, offering an economical approach to produce a probiotic-rich dairy food with potential anti-hypertensive effects.

Nonionizing Electromagnetic Field: A Promising Alternative for Growing Control Yeast

In the food industry, some fungi are considered to be common spoilage microorganisms which reduce the shelf life of products. To avoid this outcome, different technologies are being developed to control their growth. Electromagnetic fields (EMF) have been used to combat bacterial growth, but there are few studies on yeasts and their possible action mechanisms. For this reason, we studied the effect of EMF between 1 to 5.9 GHz bands on the growth of Saccharomyces cerevisiae yeast and observed that all the frequencies of the band used cause the reduction of the viability of this yeast. In addition, we observed that the distance between the antenna and the sample is an important factor to consider to control the growing yeast. By using transmission electron microscopy, we found that the EMF caused a loss of continuity of the yeast cell membrane. Therefore, EMF may be used as a control method for yeast growth.

Use of metabarcoding and source tracking to identify desirable or spoilage autochthonous microorganism sources during black olive fermentations

This study aimed at investigating the influence of the process environment and raw materials as sources of microorganisms during Nyons black table olive fermentations. Fermented olives and/or brine from spoiled fermentation tanks were analyzed and compared to good quality samples from fermentations collected during 3 consecutive harvest years. Fresh olives, salt and different process environment samples were also analyzed. Microbial diversity of all samples was analyzed using 16S and ITS2 amplicon sequencing and SourceTracker tool was used to investigate links between environment, raw materials and fermentation samples. First, comparison of microbial diversity in control and most spoiled fermentations revealed striking differences in bacterial composition with an overall higher diversity in spoiled fermentations especially for lactic acid bacteria with Lentilactobacillus buchneri, Lentilactobacillus parafarraginis dominating in brine and Pediococcus parvulus, Pediococcus ethanolidurans dominating in olive fruits. Fungal communities were similar in composition although higher abundances of Pichia membranifaciens and Penicillium carneum/roqueforti were observed in spoiled samples. Secondly, process environment samples were characterized by high bacterial and fungal diversity, especially compared to fresh olive fruits. Overall, dominant fungal species in control fermentations were also found in most environmental samples revealing a "house mycobiota". SourceTracker analysis further highlighted the contribution of brine and water from the optical sorter as a source of fungi. Most interestingly, spoilage fungi and most bacteria were retrieved in brine and environmental samples while others such as P. ethanolidurans were only found in environmental samples indicating that the studied spoilage originated from a fermentation deviation rather than a punctual contamination. Taken altogether, these results highlighted the positive and negative influence of the process environment and emphasized the relevance of studying it to better understand microbial vectors occurring during food fermentations, especially natural ones.

Adhesion Properties, Biofilm Forming Potential, and Susceptibility to Disinfectants of Contaminant Wine Yeasts

In this study, yeasts isolated from filter membranes used for the quality control of bottled wines were identified and tested for their resistance to some cleaning agents and potassium metabisulphite, adhesion to polystyrene and stainless-steel surfaces, and formation of a thin round biofilm, referred to as a MAT. A total of 40 strains were identified by rRNA internal transcribed spacer (ITS) restriction analysis and sequence analysis of D1/D2 domain of 26S rRNA gene. Strains belong to Pichia manshurica (12), Pichia kudriavzevii (9), Pichia membranifaciens (1), Candida sojae (6), Candida parapsilosis (3), Candida sonorensis (1), Lodderomyces elongisporus (2), Sporopachydermia lactativora (3), and Clavispora lusitaniae (3) species. Regarding the adhesion properties, differences were observed among species. Yeasts preferred planktonic state when tested on polystyrene plates. On stainless-steel supports, adhered cells reached values of about 6 log CFU/mL. MAT structures were formed only by yeasts belonging to the Pichia genus. Yeast species showed different resistance to sanitizers, with peracetic acid being the most effective and active at low concentrations, with minimum inhibitory concentration (MIC) values ranging from 0.08% (v/v) to 1% (v/v). C. parapsilosis was the most sensible species. Data could be exploited to develop sustainable strategies to reduce wine contamination and establish tailored sanitizing procedures.

Fungal diversity of "solom" a Ghanaian traditional beverage of millet (Pennisetum glaucum)

The association of cereals with fungi cannot be disregarded as their manifestation in our foods poses serious health risks. The aim of this study was to investigate the mycofloral (fungal) and chemical (pH) qualities of the "solom" (beverage of millet) available for consumption from their respective sales points in Ho. "Solom" a cereal beverage of millet was sampled from ten (10) different locations in the Ho Municipality of Ghana and evaluated for their pH, fungal counts, and species diversity. Mycological analyses were done on Oxytetracycline Glucose Yeast Extract (OGYE) and Dichloran Rose Bengal Chloramphenicol (DRBC) media from three (3) points per location using serial dilution. A total of fourteen (14) fungal species belonging to eight (8) genera were isolated on both media; Aspergillus (A. niger, A. flavus, A. fumigatus, A. parasiticus, A. alutaceaus, A. terreus), Rhizopus (R. stolonifer), Mucor (M. racemosus), Fusarium (F. oxysporum), Penicillium (P. digitatum, P. verucosum), Cladosporium (C. cladosporoides), Curvularia (C. lunata), and Rhodotorula sp. were recorded. Fungal counts on both media ranged between 1.68 ± 0.8 and 4.11 ± 0.9 log10 CFU/ml. There were statistically significant (p < .05) differences observed in the samples from different locations. The values of pH recorded were in the range of 3.03 ± 0.09-4.03 ± 0.23 and showed no significant differences (p > .05) among them. All samples were found to be in the acceptable range of values prescribed by the International Commission for Microbiological Specification of Foods (ICMSF, 1998). Good Manufacturing Practices (GMP) and Good Hygiene Practices (GHP) should be employed to enhance food safety.

The Important Contribution of Non-Saccharomyces Yeasts to the Aroma Complexity of Wine: A Review

Non-Saccharomyces yeast plays an important role in the initial stages of a wild ferment, as they are found in higher abundance in the vineyard than Saccharomyces cerevisiae. As such, there has been a focus in recent years to isolate these yeast species and characterize their effect on wine fermentation and subsequent aroma. This effect on wine aroma is often species and strain dependent, as the enzymatic profile of each yeast will determine which aroma compounds are formed as secondary metabolites. Semi-fermentative yeast, such as Hanseniaspora spp., Candida spp. and Metschnikowia pulcherrima, are commonly in high abundance in fresh grape must and have diverse enzymatic profiles, however they show a weak tolerance to ethanol, limiting their impact to the initial stages of fermentation. Fully fermentative non-Saccharomyces yeast, characterized by high ethanol tolerance, are often found at low abundance in fresh grape must, similar to Saccharomyces cerevisiae. Their ability to influence the aroma profile of wine remains high, however, due to their presence into the final stages of fermentation. Some fermentative yeasts also have unique oenological properties, such as Lanchancea thermotolerans and Schizosaccharomyces pombe, highlighting the potential of these yeast as inoculants for specific wine styles.

Guidance on date marking and related food information: part 1 (date marking)

A risk-based approach was developed to be followed by food business operators (FBO) when deciding on the type of date marking (i.e. 'best before' date or 'use by' date), setting of shelf-life (i.e. time) and the related information on the label to ensure food safety. The decision on the type of date marking needs to be taken on a product-by-product basis, considering the relevant hazards, product characteristics, processing and storage conditions. The hazard identification is food product-specific and should consider pathogenic microorganisms capable of growing in prepacked temperature-controlled foods under reasonably foreseeable conditions. The intrinsic (e.g. pH and aw), extrinsic (e.g. temperature and gas atmosphere) and implicit (e.g. interactions with competing background microbiota) factors of the food determine which pathogenic and spoilage microorganisms can grow in the food during storage until consumption. A decision tree was developed to assist FBOs in deciding the type of date marking for a certain food product. When setting the shelf-life, the FBO needs to consider reasonably foreseeable conditions of distribution, storage and use of the food. Key steps of a case-by-case procedure to determine and validate the shelf-life period are: (i) identification of the relevant pathogenic/spoilage microorganism and its initial level, (ii) characterisation of the factors of the food affecting the growth behaviour and (iii) assessment of the growth behaviour of the pathogenic/spoilage microorganism in the food product during storage until consumption. Due to the variability between food products and consumer habits, it was not appropriate to present indicative time limits for food donated or marketed past the 'best before' date. Recommendations were provided relating to training activities and support, using 'reasonably foreseeable conditions', collecting time-temperature data during distribution, retail and domestic storage of foods and developing Appropriate Levels of Protection and/or Food Safety Objectives for food-pathogen combinations.

Chemometric Screening of Fourteen Essential Oils for Their Composition and Biological Properties

Essential oils (EOs) obtained from aromatic plants are widely used worldwide, especially in cosmetic and food products due to their aroma and biological properties and health benefits. Some EOs have significant antimicrobial and antioxidant activities, and thus could effectively increase the shelf lives of foodstuff and beverages. In this study, fourteen essential oils (clove, eucalyptus, fennel, lavender, oregano, palmarosa, pepper, star anise, tea tree, turmeric, Chinese yin yang, Japanese yin yang, and ylang ylang) from different medicinal plant families were screened by gas-chromatography-mass spectrometry (GC-MS) for their different chemical profiles and bioassays were performed to assess their antifungal and antioxidant activities. The results obtained were assessed by principal component analysis (PCA). PCA distinguished six groups characterized by different terpene chemotypes. Amongst the EOs studied, the clove EO showed the strongest antioxidant activity characterized by an EC50 of 0.36 µL/mL. The oregano EO had the greatest antiyeast activity characterized by a minimal inhibitory concentration of 10 µL/mL. In conclusion, clove and oregano EOs are strong antifungal and antioxidant agents, respectively, with great potential in the food industry to avoid spoilage and to increase shelf life.

Gaps in the assortment of rapid assays for microorganisms of interest to the dairy industry

This review presents the results of a study into the offering of rapid microbial detection assays to the Irish dairy industry. At the outset, a consultation process was undertaken whereby key stakeholders were asked to compile a list of the key microorganisms of interest to the sector. The resultant list comprises 19 organisms/groups of organisms divided into five categories: single pathogenic species (Cronobacter sakazakii, Escherichia coli and Listeria monocytogenes); genera containing pathogenic species (Bacillus, Clostridium, Listeria, Salmonella; Staphylococcus); broad taxonomic groupings (Coliforms, Enterobacteriaceae, fecal Streptococci, sulfite reducing bacteria/sulfite reducing Clostridia [SRBs/SRCs], yeasts and molds); organisms displaying certain growth preferences or resistance as regards temperature (endospores, psychrotrophs, thermodurics, thermophiles); indicators of quality (total plate count, Pseudomonas spp.). A survey of the rapid assays commercially available for the 19 organisms/groups of organisms was conducted. A wide disparity between the number of rapid tests available was found. Four categories were used to summarize the availability of rapid assays per organism/group of organisms: high coverage (>15 assays available); medium coverage (5-15 assays available); low coverage (<5 assays available); no coverage (0 assays available). Generally, species or genera containing pathogens, whose presence is regulated-for, tend to have a good selection of commercially available rapid assays for their detection, whereas groups composed of heterogenous or even undefined genera of mainly spoilage organisms tend to be "low coverage" or "no coverage." Organisms/groups of organisms with "low coverage" by rapid assays include: Clostridium spp.; fecal Streptococci; and Pseudomonas spp. Those with "no coverage" by rapid assays include: endospores; psychrotrophs; SRB/SRCs; thermodurics; and thermophiles. An important question is: why have manufacturers of rapid microbiological assays failed to respond to the necessity for rapid methods for these organisms/groups of organisms? The review offers explanations, ranging from the technical difficulty involved in detecting as broad a group as the thermodurics, which covers the spores of multiple sporeforming genera as well at least six genera of mesophilic nonsporeformers, to the taxonomically controversial issue as to what constitutes a fecal Streptococcus or SRBs/SRCs. We review two problematic areas for assay developers: validation/certification and the nature of dairy food matrices. Development and implementation of rapid alternative test methods for the dairy industry is influenced by regulations relating to both the microbiological quality standards and the criteria alternative methods must meet to qualify as acceptable test methods. However, the gap between the certification of developer's test systems as valid alternative methods in only a handful of representative matrices, and the requirement of dairy industries to verify the performance of alternative test systems in an extensive and diverse range of dairy matrices needs to be bridged before alternative methods can be widely accepted and adopted in the dairy industry. This study concludes that many important dairy matrices have effectively been ignored by assay developers.

Potential of natamycin to control growth of Zygosaccharomyces spp. in apple juice during storage

In this research, anti-yeast activity of natamycin in apple juice inoculated with both Zygosaccharomyces rouxii and Z. bailii during the storage at different temperatures was investigated. For this purpose, a response surface methodology approach was used to test and optimize effects of some processing variables; storage time (1, 21 and 41 days), storage temperature (4, 12 and 20 °C), sodium benzoate as a positive control (0, 0.05 and 0.1%) and natamycin concentration (0, 30 and 60 mg/L) on several physicochemical and bioactive properties of the apple juice samples. The results showed that the natamycin performed a remarkable anti-yeast effect on Z. bailii rather than on Z. rouxii. The brix levels of the samples decreased and so the turbidity values increased significantly due to the yeast activity during the storage. Bioactive properties were also significantly affected by the natamycin which was also revealed to increase the antioxidant capacity of apple juice during storage. Using multiple response optimization technique, it was calculated that minimum yeast count (YC) values would occur at storage time = 38.64 and 40.9 days, storage temperature = 19.81 and 14.4 °C, sodium benzoate level (fixed to 0%) and natamycin concentration = 40 and 51.9 mg/L for the samples inoculated with Z. bailii and Z. rouxii, respectively. It was concluded that the bioactive properties of apple juice could be preserved by addition of natamycin which is suggested to be a natural inhibitor during the storage.

Strain variability in biofilm formation: A food safety and quality perspective

The inherent differences in microbial behavior among identically treated strains of the same microbial species, referred to as "strain variability", are regarded as an important source of variability in microbiological studies. Biofilms are defined as the structured multicellular communities with complex architecture that enable microorganisms to grow adhered to abiotic or living surfaces and constitute a fundamental aspect of microbial ecology. The research studies assessing the strain variability in biofilm formation are relatively few compared to the ones evaluating other aspects of microbial behavior such as virulence, growth and stress resistance. Among the available research data on intra-species variability in biofilm formation, compiled and discussed in the present review, most of them refer to foodborne pathogens as compared to spoilage microorganisms. Molecular and physiological aspects of biofilm formation potentially related to strain-specific responses, as well as information on the characterization and quantitative description of this type of biological variability are presented and discussed. Despite the considerable amount of available information on the strain variability in biofilm formation, there are certain data gaps and still-existing challenges that future research should cover and address. Current and future advances in systems biology and omics technologies are expected to aid significantly in the explanation of phenotypic strain variability, including biofilm formation variability, allowing for its integration in microbiological risk assessment.

Fungistatic and Fungicidal Capacity of a Biosurfactant Extract Obtained from Corn Steep Water

Biosurfactants are surface-active compounds that are produced by microorganisms, which in addition to their surfactant capacity, can possess interesting antimicrobial activities that are used in their incorporation into the agrifood industry. In this work, the preservative capacity of a novel biosurfactant extract obtained from a residual stream of the corn-milling industry was evaluated against two different fungi (Aspergillus brasiliensis and Candida albicans) under different biosurfactant concentrations (0.33–0.99 mg/mL), temperatures (4–40 °C), and incubation times (5–11 days). All the assays started with the same concentration of fungi (2 × 10⁶ CFU/mL). The results showed that temperature played an important role in the bactericidal and fungistatic effects of this biosurfactant extract. It was observed that at a low biosurfactant concentration (0.33 mg/mL) and low or high temperatures in the range tested, this biosurfactant extract possessed an important fungicidal effect (complete inhibition) on A. brasiliensis, while at intermediate temperatures, it achieved a fungistatic effect (50% of inhibition). Regarding C. albicans, it was observed that this strain was more resistant than A. brasiliens, although it was possible to achieve growth inhibitions of 76.3% at temperatures of 40 °C after 8 days of incubation with a biosurfactant concentration of 0.99 mg/mL. This work supports the possible application of biosurfactants extracted from corn steep water as preservatives and antimicrobial agents against fungal contaminations on agrifood products.