Mesophilic Starter Research Articles

Impact of microbial milk quality on mesophilic starter culture metabolism: A metaproteomics approach

Using a metaproteomics approach, we showed that the initial milk quality impacts the proteome allocation of starter cultures used in cheese production and can be considered a fundamental source of cheese quality batch-to-batch variation. Raw milk was spiked with a highly proteolytic strain of Pseudomonas trivialis, previously isolated from raw milk, and incubated for 1, 3, and 6 days at refrigerated temperature. After incubation, the milk was heat-treated and then fermented with a mesophilic starter culture commonly used to produce Gouda-type cheeses. The development of metabolites was analyzed and a taxonomical and functional characterization of the starter culture was performed. Milk storage time impacted both the metaproteome of the starter culture, consequently affecting metabolite levels after fermentation and the level of protein expressed by the different taxa; Lactococcus protein was more abundant in samples made from milk stored longer with Pseudomonas while proteins expressed by Leuconostoc spp. decreased in abundance.

Crafting Algerian “Jben”: a traditional soft cheese enhanced by locally derived starters

The global dairy industry faces challenges in sourcing cost-effective and suitable lactic starters for traditional cheese production. This study investigates the use of locally selected lactic starters in crafting Algerian Jben cheese, aiming to provide a sustainable alternative to imported starters. Local lactic starters comprising Lactococcus lactis, Leuconostoc mesenteroides, and Enterococcus durans were characterized by their technological properties when applied to cow's milk. The resulting cheese was compared with another cheese produced under similar conditions but using an industrial mesophilic starter, including strains of Lactococcus and Leuconostoc. Physicochemical and microbiological analyses were conducted on both cheeses, followed by sensory evaluations using the triangular and classification tests. Microbiological analyses revealed the absence of pathogenic germs or spores in both types of cheese. However, the cheese made with the industrial starter exceeded the standards for fecal coliforms and total coliforms. Titratable acidity measurements indicated comparable levels in both cheeses. Interestingly, there were no discernible differences in taste or aroma between the two types, with both being well received by tasters. In conclusion, our findings suggest that local lactic starters have the potential to replace the commercial starters currently employed in the Algerian dairy industry.

Increasing Nutritional Value of Cottage Cheese Products by the Rúbus idáeus Fortification

The cottage cheese and cottage cheese products introduction in the diet enables to compensate the protein deficiency observed in a significant part of the population. A man can increase cottage cheese product consumer supply by the non-dairy component use, in particular fruit ones. The research aims at cottage cheese product development with the introduction of raspberry fruits Rubus idaeus processing product for the finished product fortification with biologically active substances and organoleptic properties improvement. To amplify the cottage cheese product produced by the cow milk fermentation with a mesophilic starter culture Chr.Hansen CHN-22 (50U) by the thermoacid method (control sample), a man used flour obtained by drying fresh raspberry fruits of the variety “Vislucha” in a dehydrator to a final moisture content of 2–5 % followed by grinding in a dry grinding mill (sample 1); and fruits dried in a freeze dryer to a final moisture content of 2–5 % (sample 2). A man introduced fruit ingredients in the amount of 4 % by weight of the cottage cheese at the time of its semi-readiness with the removal of most of the whey. The authors evaluated organoleptic properties of the cottage cheese product samples using a developed score scale. During the tasting, the sample 2 (with freeze-dried fruits added) scored the maximum possible 15 points, whereas sample 1 (with fruit flour added) – 12. The research demonstrates that the consumption of 100 g of the developed cottage cheese product will satisfy the daily need for vitamin C: for an adult – by 28 %, for a child – by 83 %. A man developed technological process for the manufacture of the cottage cheese product with a functional fruit component.

A multifaceted investigation of lactococcal strain diversity in undefined mesophilic starter cultures.

This study reports on the development of a combined culture-based analysis and metagenomics approach to evaluate the composition of two undefined mesophilic starter cultures. In addition, a novel qPCR-based genotype detection assay, capable of discerning nine distinct lactococcal genotypes (based on lactococcal cell wall polysaccharide biosynthesis gene clusters), was used to monitor compositional changes in an undefined starter culture following phage attack. These analytical approaches facilitate a multifaceted assessment of starter culture compositional stability during milk fermentation, which has become an important QC aspect due to the increasing demand for consistent and high-quality dairy products.

Changing some parameters in the production technology of camambre cheese

One of the exclusive European products is camembert cheese. This is a soft cheese with a current consistency, rich taste, and aroma, with a characteristic crust, on top of which the white mould Penicillium camembert grows. However, the organoleptic characteristics of the classic camembert are particular and differ from the taste habits of Russians. Russian consumers do not like too fluid cheeses and flavorful. This has caused a lot of problems with its sale. In this regard, the purpose of the research was to adjust the primary operations in the technological map related to the processing of cheese grains and moulding, as well as the selection of starter cultures. In our research, we suggest that after cutting the clot, the cheese grain should be set and the moulds filled utterly, reducing the cost of cheese moulding. The second factor that we propose is the use of domestic mesophilic starter culture MN (AltaLact). Organoleptic, physicochemical and microbiological parameters were determined in the finished cheese samples. So, the cheese taste was creamy when using the domestic starter culture MN (AltaLact) and setting the cheese grain after cutting the clot. The mushroom had no bitterness on the aftertaste and no "ammonia" taste. Using a stabilised technology, we increased the concentration of dry substances due to the production of cheese grains, which allowed us to slow down the proteolytic activity of microorganisms. Thus, the fat content in the dry matter was 59%, which is more by 2% than with traditional moulding and by 3-1% relative to the starter Danisko MM101, depending on the processing of the clot and the moulding method. The stabilised technology will increase the nutritional value by increasing the protein content in cheese; in our study, the protein content increased by 0.4 – 0.9%. Thus, the research results substantiate the practicality of making adjustments to the production technology of camembert cheese.

Quarg Cheese: The Impact of Fat Content Change on its Microstructure, Characterization, Rheology, and Textural Properties

This study aimed to investigate the impact of different levels of fat content on the microstructure, rheology, and textural characteristics of Quarg cheese. Quarg is a soft unripened cheese variety made by the addition of mesophilic starter cultures (Lactococcus lactis subsp. lactis, Leuconostoc citrovorum) and a trace of rennet. The fat levels of cheese were; 6.0 ± 0.01 (QC1), 3.5 ± 0.03 (QC2), 1.5 ± 0.03 (QC3), and 0.5 ± 0.02 (QC4). Statistically significant changes (p< 0.05) were observed in the values of textural parameters. Furthermore, rheological investigations indicated a positive correlation between the reduction in fat percentages and an increase in the hardness of the cheese. The characterization of the sample was conducted using Fourier Transform Infrared (FTIR) and Ultraviolet-Visible (UV-Vis) spectrophotometric techniques. The microstructure of quarg cheese was analyzed using fluorescence microscopy and helped depict the distribution of fat and protein in the cheese matrix. Sensorial properties were superior in cheese samples with higher fat percentages as a virtue of fat content.

Fabrication of UF-white cheese: Obtaining a different proteolysis rate, texture, and flavor via using combinations of mesophilic starter culture and Lactobacillus helveticus.

The effect of using mesophilic starter culture (Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris) and Lactobacillus helveticus (L. helveticus) at different ratios (100:0, 75:25, 50:50, 25:75, and 0:100) on the quality properties of UF-white cheese during 90 days of ripening was studied. The results revealed that an increase in L. helveticus ratio caused a significant decrease in the pH and total protein contents of the cheeses (p < .05). No significant changes were observed in the dry matter content of the cheeses (p > .05). The use of higher ratios of L. helveticus led to a noticeable increase in proteolysis and lipolysis indices in the cheeses (p < .05). The cheese produced with higher ratios of L. helveticus had less storage (G') and loss (G″) moduli compared to other cheeses. The more open structure was seen in the cheeses produced using higher ratios of L. helveticus. Regarding sensory properties, lower scores of body and texture, and higher scores of odor and flavor were assigned to the cheeses produced using higher ratios of L. helveticus. In conclusion, the use of combinations of mesophilic starter culture and L. helveticus at specific ratios (75:25 and 25:75) led to improve quality characteristics of UF-white cheese.

Simple & better – Accelerated cheese ripening using a mesophilic starter based on a single strain with superior autolytic properties

In the manufacture of rennet-coagulated cheese, autolysis is a rate-limiting step for ripening. Previously, a highly autolytic and thermotolerant Lactococcus lactis strain, RD07, was generated, which in preliminary laboratory cheese trials demonstrated great potential as a cheese ripening accelerant. RD07 is proteinase positive (Prt+) and capable of metabolizing citrate (Cit+). In this study, we obtained two derivatives of RD07: EC8 lacking the citrate plasmid, and EC2 lacking the proteinase plasmid. EC2 and EC8 retained the autolytic properties of RD07, and autolyzed 20 times faster than Flora Danica (FD) and SD96, where the latter is the parent of RD07. The three strains EC2, EC8 and RD07 were used in a ratio of 90:8:2, to create a simple starter termed ERC. ERC was less sensitive to cooking when cultured in milk and autolyzed well after entering the stationary phase upon facing sugar starvation. The ERC starter was benchmarked against FD and SD96 in laboratory cheese trials. The free amino acid content in cheese prepared using the ERC culture was 31 % and 34 % higher than in cheese prepared using FD and SD96, respectively. Overall, the ERC culture resulted in a more rapid release of free amino acids. A large-scale (5000 L) Gouda cheese trial at a Danish dairy demonstrated that the single strain ERC starter was comparable in performance to FD + an adjunct Lactobacillus helveticus culture. Furthermore, a large-scale Danbo cheese trial demonstrated that ERC could reduce the ripening period by 50 % for long-term ripened (25 weeks) cheese, resulting in better cheese.

Analyzing the genetic diversity and biotechnological potential of Leuconostoc pseudomesenteroides by comparative genomics.

Leuconostoc pseudomesenteroides is a lactic acid bacteria species widely exist in fermented dairy foods, cane juice, sourdough, kimchi, apple dumpster, caecum, and human adenoid. In the dairy industry, Ln. pseudomesenteroides strains are usually found in mesophilic starter cultures with lactococci. This species plays a crucial role in the production of aroma compounds such as acetoin, acetaldehyde, and diacetyl, thus beneficially affecting dairy technology. We performed genomic characterization of 38 Ln. pseudomesenteroides from diverse ecological niches to evaluate this species' genetic diversity and biotechnological potential. A mere ~12% of genes conserved across 38 Ln. pseudomesenteroides genomes indicate that accessory genes are the driving force for genotypic distinction in this species. Seven main clades were formed with variable content surrounding mobile genetic elements, namely plasmids, transposable elements, IS elements, prophages, and CRISPR-Cas. All but three genomes carried CRISPR-Cas system. Furthermore, a type IIA CRISPR-Cas system was found in 80% of the CRISPR-Cas positive strains. AMBR10, CBA3630, and MGBC116435 were predicted to encode bacteriocins. Genes responsible for citrate metabolism were found in all but five strains belonging to cane juice, sourdough, and unknown origin. On the contrary, arabinose metabolism genes were only available in nine strains isolated from plant-related systems. We found that Ln. pseudomesenteroides genomes show evolutionary adaptation to their ecological environment due to niche-specific carbon metabolism and forming closely related phylogenetic clades based on their isolation source. This species was found to be a reservoir of type IIA CRISPR-Cas system. The outcomes of this study provide a framework for uncovering the biotechnological potential of Ln. pseudomesenteroides and its future development as starter or adjunct culture for dairy industry.

Storage related changes in short-set cream cheese manufactured using thermophilicstarter culture and direct acidification technique

Cream cheese is a fresh acid curd variety with semi-soft body, manufactured by the gradual, quiescent acid gelation of milk. The typical flavour profile of cream cheese is cultured diacetyl with little bit lactic acid flavour as well as aroma. It is envisaged that demand of cream cheese will increase in upcoming years due to its application as spread and it having higher nutritional value compared to similar products available in the market. The purpose of the study was to observe changes in sensory, physicochemical and microbial quality during storage in short-set cream cheese samples manufactured by using thermophilic starter culture and direct acidification technique and was compared with control cream cheese manufactured using mesophilic starter culture. All the three samples i.e., control cream cheese made using mesophilic culture (MC), cream cheese made using thermophilic culture (TC) and cream cheese made using laboratory grade lactic acid (SLA) were stored in re-closable polypropylene tubs at 7 ± 2°C. During storage study, flavour score, FFA, tyrosine value were significantly affected by storage period (P), treatment (T) and the interaction of T × P. Moisture, pH, titratable acidity, sensory parameters (except flavour) were significantly affected only by storage period (P) and treatment(T). All the three samples had storage stability up to 15 days at 7± 2°C.

Quality and Functional Parameters of Fermented Milk Obtained from Goat Milk Fed with Broccoli and Artichoke Plant By-Products.

Large amount of vegetal by-products are generated during production and processing steps. Introducing silage from vegetable by-products into dairy goat feed would be of great interest from the point of view of reducing costs and supporting the circular economy. The aim of this research was to study the effect of 40% inclusion of silage broccoli by-products and artichoke plant by-products in the diet of Murciano-Granadina goats throughout the lactation to establish milk suitability for fermented milks production. The novelty of this study is the use of milk from goats fed for a long term with a high inclusion of silages from artichoke plant and broccoli by-products, being the first one on broccoli inclusion. Two starter cultures thermophilic (YO-MIXTM300), and, mesophilic (MA400) were used and fermented milks were analyzed at two storage times after fermentation. Fermentation enhances antioxidant properties of fermented milks from all diets (p < 0.05), especially when mesophilic starter cultures are used. The main findings are that long term inclusion of 40% silage from broccoli and artichoke plant by-products in balanced diets of dairy goats yields milk suitable for fermentation by yogurt and cheese cultures, the inclusion of broccoli silage enhances antioxidant properties (p < 0.05), and, the inclusion of plant artichoke enhances fatty acids health indexes (p < 0.05).

The Antithrombotic Potential of Bioactive Peptides Induced by Buffalo Milk Probiotic Cheddar Cheese

Cheddar cheese undergoes significant changes resulting in numerous microbiological and biochemical processes called glycolysis, lipolysis, and proteolysis, accountable for a unique texture, aroma, appearance, and taste. Specific bioactive peptides developed during these biochemical reactions impart health benefits. Addition of probiotics boots the development of bioactive peptides in foods. Objective: The current research investigated the therapeutic potential of water-soluble peptides (WSPs) extracts from buffalo milk probiotic Cheddar cheese regarding anti-thrombic facets. Methods: The appropriateness of Buffalo milk for Cheddar manufacturing was assessed by analysing its pH, acidity, fat, protein, and total solids content. Two batches of Cheddar cheese were produced, one having a mixture of Probiotic microorganisms and commercially available mesophilic cheese starter and the second containing only commercially available cheese starters. Both of the cheese batches were analysed for their physicochemical properties. Water-soluble extract of Cheddar cheese samples was analysed for anti-thrombic effects after two-month intervals during ripening. Results: Three concentrations of WSE of buffalo milk cheddar cheese were used to assess the antithrombotic effect during 60, 120, and 180 days of ripening at 4°C. Antithrombotic activity increased with the ripening period for both control and probiotic cheddar cheese samples Conclusion: A significantly increased effect of antithrombotic activity was observed by Probiotic adjunct on control cheddar cheese.

Spirulina platensis Extract Nanoliposomes: Preparation, Characterization, and Application to White Cheese.

Ultrafiltration cheese is produced in large scale from treated pasteurized milk with mesophilic starter, and to expand its shelf life, preservatives addition is needed. The purpose of the present study was preparation of encapsulate Spirulina platensis algae nanoliposomes to evaluate the characteristics of the nanoliposomes loaded with Spirulina extract (SE-NLs). In addition, the chemical and microbiological properties of white cheese produced with SE-NLs were studied. Nanoliposomes are composed of lecithin and cholesterol, used for the encapsulation of SE. The SE-NLs were prepared using the thin-layer hydration method. The characteristics of produced SE-NLs including particle size, zeta potential, morphology, and the encapsulation efficiency were studied during 4 weeks in different storage conditions (4°C and 25°C). In addition, the effect of SE and SE-NLs on the chemical and microbiological properties of white cheese was evaluated during 60 days of ripening. The results showed that the nanoliposomes loaded with 3 mg/g of SE had the optimum formulation due to the higher EE, smaller particle size, and higher negatively charged zeta potential. The quality of the produced nanoliposomes decreased by increasing the time of storage, but the SE-NLs stored at 4°C were more stable and possessed higher EE and smaller particle sizes. While the chemical composition of the cheeses manufactured by the nanoliposome loaded with 3 mg/g SE-NLs were comparable to that of control cheese at 60 days of ripening, it showed a significant inhibitory effect on Staphylococcus aureus and Listeria monocytogenes after 30 days. The utilization of SE-NLs can be considered a natural antimicrobial and an alternative to the use of synthetic preservatives in the production of white cheese. Nanoliposomes of Spirulina platensis extracts were prepared. Ultrafiltration white cheese prepared by nanoliposomes then was evaluated.

Adaptive Laboratory Evolution as a Means To Generate Lactococcus lactis Strains with Improved Thermotolerance and Ability To Autolyze.

Lactococcus lactis subsp. lactis (referred to here as L. lactis) is a model lactic acid bacterium and one of the main constituents of the mesophilic cheese starter used for producing soft or semihard cheeses. Most dairy L. lactis strains grow optimally at around 30°C and are not particularly well adapted to the elevated temperatures (37 to 39°C) to which they are often exposed during cheese production. To overcome this challenge, we used adaptive laboratory evolution (ALE) in milk, using a setup where the temperature was gradually increased over time, and isolated two evolved strains (RD01 and RD07) better able to tolerate high growth temperatures. One of these, strain RD07, was isolated after 1.5 years of evolution (400 generations) and efficiently acidified milk at 41°C, which has not been reported for industrial L. lactis strains until now. Moreover, RD07 appeared to autolyze 2 to 3 times faster than its parent strain, which is another highly desired property of dairy lactococci and rarely observed in the L. lactis subspecies used in this study. Model cheese trials indicated that RD07 could potentially accelerate cheese ripening. Transcriptomics analysis revealed the potential underlying causes responsible for the enhanced growth at high temperatures for the mutants. These included downregulation of the pleiotropic transcription factor CodY and overexpression of genes, which most likely lowered the guanidine nucleotide pool. Cheese trials at ARLA Foods using RD01 blended with the commercial Flora Danica starter culture, including a 39.5°C cooking step, revealed better acidification and flavor formation than the pure starter culture. IMPORTANCE In commercial mesophilic starter cultures, L. lactis is generally more thermotolerant than Lactococcus cremoris, whereas L. cremoris is more prone to autolysis, which is the key to flavor and aroma formation. In this study, we found that adaptation to higher thermotolerance can improve autolysis. Using whole-genome sequencing and RNA sequencing, we attempt to determine the underlying reason for the observed behavior. In terms of dairy applications, there are obvious advantages associated with using L. lactis strains with high thermotolerance, as these are less affected by curd cooking, which generally hampers the performance of the mesophilic starter. Cheese ripening, the costliest part of cheese manufacturing, can be reduced using autolytic strains. Thus, the solution presented here could simplify starter cultures, make the cheese manufacturing process more efficient, and enable novel types of harder cheese variants.

Effect of Probiotic Strains on Sensory Attributes of Buffalo Milk Cheddar Cheese

Probiotics are living micro-organisms which impart certain health benefits like anti-oxidant, anti-hypertensive, immune-modulatory, opioid, anti-inflammatory, anti-microbial and consumer related inherit nutrition with the utilization in recommended quantity. The study aimed to determine the effect of Lactobacillus acidophilus, Bifidobacterium bifidum and Lactobacillus helveticas and their adjuncts on sensory attributes of cheddar cheese. The cheddar cheese having commercially available mesophilic starter cultures and with probiotics strains were prepared and assessed for acetic acid production, proteolysis and descriptive sensory analysis. The probiotics adjuncts Lb. acidophilus + Bifidobacterium bifidum (La + Bb) and Lb. acidophilus + Bifidobacterium bifidum + Lb. helveticus (La + Bb + Lh) showed remarkable results in production of acetic acid 489.33 (ppm) and as compared to control respectively. Among probiotic strains, the probiotic strain Lactobacillus helveticas showed the highest water-soluble nitrogen as 28.50 (%) and free amino acid 5220 µg/g. non-significant effect was observed for overall acceptability for control and probiotic adjuncts. Higher rates of organic acids and proteolysis was observed in probiotic adjuncts as compared to control samples. The current study reveals that the addition of probiotics adjuncts to cheddar cheese does not affects its overall acceptability.

Study of the influence of the composition of mold and starter microflora on the formation of organoleptic characteristics of soft-ripened cheeses

The article presents the results of a study of the characteristics of growth, incl. joint, mold cultures of Penicillium camembеrti and yeast-like fungi of Geotrichum candidum on a dense nutrient medium and the regularities of changes in the organoleptic, physicochemical and microbiological characteristics of Camembert-type cheeses in the process of production, ripening and storage, depending on the combinations of bacterial and mold starter microflora. The objects of the study were the cultures of Penicillium camembеrti and Geotrichum candidum, cheeses with white mold, made according to the type of “Camembert” cheese, produced from cow’s milk with mesophilic and thermophilic fermenting microflora, mold cultures of Penicillium camembеrti and yeast-like fungi of Geotrichum candidum. The study of cheeses was carried out in the process of ripening and storage after 15, 30, 60 days from the date of manufacture. It was found that when Penicillium camembеrti and Geotrichum candidum were co-cultivated on Petri dishes, visual assessment showed a symbiotic effect of culture development, which manifests itself in the stimulating effect of yeast-like fungi on the growth of mold fungi compared to the cultivation of each culture separately. Under the conditions of the experiment carried out, the main mold culture influencing the organoleptic characteristics of the cheese was the mold culture of Penicillium camemberti. The combination of mold cultures did not affect the improvement of the organoleptic characteristics of the cheeses. It is shown that the composition of the main acid-forming starter microflora, both mesophilic and thermophilic, has a significant effect on the lactic acid process and flavoring of Camembert-type cheese. The cheeses produced on the basis of mesophilic starter microflora were distinguished by an accelerated ripening process and less storage capacity due to deeper proteolysis. At the same time, cheeses produced on the basis of thermophilic fermenting microflora retained quality stability for up to 60 days. Thus, the use of various combinations of starter cultures will make it possible to create a flavor line of cheeses with white mold, depending on consumer preferences with different storage capacity.

Effect of selected starter cultures on production, properties and shelf life of fresh type cheese

The aim of this study was to examine the influence of different starter cultures including protective culture on the production and properties of fresh cheese. Fresh cheeses were produced from pasteurized milk by adding mesophilic starter cultures, mesophilic cultures and liquid rennet and by adding protective culture. All samples were analysed for acidity (active and titratable), microbiological quality, texture, colour and sensory properties during 21 days of cold storage. Additionally, milk fat, the total dry matter, total proteins and mineral content were determined in all cheese samples on the first day of storage. It could be observed that the used mesophilic culture in general did not affect chemical composition of cheese. As expected, during the storage period acidity in all cheeses decreased, while the number of microorganisms increased, whereby that changes were significantly slowed down in cheese produced by adding protective culture. Scores of sensory evaluation were high during the entire storage period for all cheeses, but samples containing and cheese protective cultures achieved the highest score (18.56) at the first as well as at the last day of storage (17.98). According to all analyses, it is evident that the shelf life of cheese produced by adding protective culture has been prolonged for 12 days in comparison to samples produced without protective culture, and accounted 21 days when properly cool stored. In conclusion, the addition of protective culture might be useful for extending the shelf life and maintaining sensory properties as well as colour of fresh cheese.

Diversity in NaCl tolerance of Lactococcus lactis strains from dl-starter cultures for production of semi-hard cheeses

Mesophilic starter cultures, such as Lactococcus lactis, are exposed to NaCl stress during brining of cheeses influencing their viability. We investigated the effect of NaCl water solutions, used at concentrations of 3.4%, 8.0% and 15% (w/v), on viability of Lc. lactis subsp. cremoris, Lc. lactis subsp. lactis biovar. diacetylactis and Lc. lactis subsp. lactis isolated from commercial dl-starter cultures. Viability was assessed by plate counts and flow cytometry. Bacterial viability decreased with increased concentration of NaCl in a strain-dependent manner (between 0.02% and 62% cfu at 15% (w/v) NaCl, compared with controls at 0.85% (w/v) NaCl), whereas no significant differences were detected between the subspecies. Viability levels determined by plate counts were generally lower than by flow cytometry, indicating the presence of viable but not culturable cells. Knowledge of salt tolerance of Lc. lactis strains would enable rational selection of starter cultures targeting production of cheeses with different NaCl content.

Predicting the antimicrobial effect of probiotic lactic acid bacteria against Staphylococcus aureus in white cheeses, using Fourier series modeling method

AbstractIn this study, it was aimed to design the time‐predicted inactivation model for various growth curves and the growth parameters representing the changes in the inactivation of Staphylococcus aureus in probiotic white cheese. For this purpose, S. aureus were inoculated in the pasteurized milk and the production of probiotic white cheese was performed in five different groups, and then samples were matured for 60 days at 4°C. S. aureus, Lactobacillus rhamnosus, Lactobacillus casei Shirota, and mesophilic starter culture levels of the samples were analyzed on the 1st, 4th, 7th, 10th, 15th, 30th, and 60th days of maturation. The inactivation model evaluation was performed by using the number of microorganisms counted with Fourier modeling method. In determining the model to be applied, the coefficient of determination (R2) and the sum of squared errors (SSE) for the mean number of microorganisms detected via modeling method were used. As conclusions, the number of S. aureus has decreased by approximately 5 logarithmic units at the end of the storage period by using probiotics together with the starter culture. It was determined that the Fourier modeling method is a suitable inactivation model with R2 values of 0.9847–0.9986 and SSE values of 0.094–0.510.

Power ultrasound as a tool to improve the processability of protein-enriched fermented milk gels for Greek yogurt manufacture

One approach to avoid production of acid whey during the manufacture of high-protein yogurt and related products is to concentrate the milk before fermentation. However, the resultant gels are firm so that stirring in the tank and further processing are difficult on an industrial scale. We hypothesize that power ultrasound (US) during fermentation softens the gel because sound waves cause cavitation and strong shear forces in the fluid. Skim milk was standardized to different protein contents up to 12%, heated (85°C, 30 min), and acidified with thermophilic or mesophilic starter cultures. An excessive increase in gel firmness as a function of protein content was detected. In the next series of experiments, US was applied during fermentation. Milks (10% protein) were acidified at 43.5°C and sonicated from pH 5.8 to 5.1 with a sonotrode (20 kHz, 20 W). Immediately after fermentation, gels were agitated using a rheometer with a vane geometry. The maximum torque required to break the gel was reduced by 75% following US, and gel firmness was reduced by 80%. Gels were then processed into stirred yogurt and analyzed. Sonicated samples were smoother with fewer large aggregates. Confocal laser scanning microscopy images suggested a less cohesive structure and more compact microgel particles, resulting in reduced viscosity. We concluded that US is a promising tool to weaken the gel and facilitate further processing. This enables new approaches for the manufacture of Greek yogurt, particularly in regard to avoiding production of acid whey and developing products with novel textures.