Model Cheese Research Articles

High voltage pre-treatment on cheddar cheese for model cheese feed preparation

The growing consumer demand for clean label food products has led to the search for alternatives to calcium-chelating salts in cheese powder production. Pulsed electric field (PEF) technology presents a promising green processing approach with its ability to disrupt casein networks. This study investigated the impact of PEF treatment on Cheddar cheese properties and the resulting model cheese emulsion. Response surface methodology revealed that pulse repetition and electric field strength are the primary parameters influencing the solubilization of calcium and phosphorus from the cheese matrix. Texture profile analysis indicated a notable reduction in cheese hardness with the application of PEF. Despite the significant impact of PEF on cheese structure, our study found no substantial alterations in the emulsion stability of cheeses treated with the applied PEF parameters. These promising results highlight the need for further exploration of alternative PEF parameters, such as different waveforms (i.e. exponential) or shorter pulse durations (nanoseconds), to unlock the full potential of PEF for clean label cheese powder production.

Fermented food consumption modulates the oral microbiota

Fermented food consumption is recommended for health and environmental purposes. While it is known to impact gut microbiota, further investigation is needed to establish connections with the oral microbiota. For this purpose, we investigated the effect of daily consumption of a model cheese containing 3 Lactic Acid Bacteria (LAB) species on the oral microbiota of rats following a 3-week diet. Cheese consumption transiently modifies the oral microbiota and leads to a transient persistence of LAB in the oral cavity of 1/3 of the animals. The origin of this variability was partly explained by an overrepresentation of salivary proteins involved in the response to oxidative stress in animals without LAB persistence. These findings highlight the significance of fermented foods in shaping the diversity of the oral microbiota. Additionally, they suggest that variations in the salivary proteome among individuals may influence the permissiveness of the oral microbiota towards exogenous microorganisms.

Formation of cheese pattern when using monospecies cultures

The article presents the results of a study of the influence of monospecies gas-aroma-forming cultures Lactococcus lactis subsp. lactis biovar. diacetylactis (L. diacetylactis) and Leuconostoc subsp. on the peculiarities of pattern formation in cheeses with a low second heating temperature molded from a layer. The studied cultures were used at a dose of 0.6% of the total milk volume as as single starter microflora in the model cheeses (1-M and 2-M) and additional microflora along with the main lactococcal microflora (Lactococcus lactis subsp. lactis; Lactococcus cremoris) in the control cheeses (1-K and 2-K). The model and control cheeses were subjected to microbiological tests (total number of lactic acid microorganisms, number of L. diacetylactis and Leuconostoc subsp.), physicochemical (mass fraction of moisture, pH), biochemical (mass fraction of lactose) and organoleptic studies after pressing and during ripening at the age of 15, 30, 45, 60 days. It has been established that the use of a culture of citrate-fermenting lactococci L. diacetylactis ensures a stable lactic acid fermentation process during the production and ripening of the model and control cheeses, the formation of an elastic consistency and the desired pattern with eyes of a regular round shape. The use of the hetero-fermentative culture Leuconostoc subsp., as single starter microflora, does not guarantee the required level of lactic acid fermentation during cheese production and leads to an increase in the moisture content of the cheese mass after pressing and overacidification of the cheese in the first stages of ripening, which together contributes to the formation of an overly plastic consistency and an overdeveloped pattern in the form of cracks. The use of Leuconostoc subsp. as a gas-aroma-forming component of a traditional starter culture for semi-hard cheeses, also consisting of mesophilic lactococci Lc. lactis subsp. lactis and Lc. cremoris, causes the development of a nest-like pattern, which does not fully ensure the formation of the desired pattern with regular rounded eyes.

Effect of chymosin/pepsin ratio on milk coagulation and physical properties of model cheese

Chymosin and pepsin are the two major enzymes in coagulants for the cheese industry. They affect milk coagulation properties, curd composition, casein hydrolysis and the consequent development of cheese texture. Limited knowledge is available on the effect of the chymosin/pepsin ratio on the mentioned factors. This study aimed (1) to better understand the effect of chymosin/pepsin ratio on milk coagulation properties, casein hydrolysis, rheological and textural properties of model cheese during storage, and (2) to link casein hydrolysis to the rheological and textural properties. For this purpose, coagulants were prepared in which the ratio between the two enzymes was systematically varied. Our results showed that even when milk clotting activity was standardized, coagulants with different chymosin/pepsin ratios had a significant effect on curd firming rate and final firmness, which could be attributed to the different specificity of chymosin and pepsin for hydrolyzing κ-CN. During 4 weeks of storage, the chymosin/pepsin ratio influenced the hydrolysis of αs1-CN, and the subsequent properties of the protein network and the cheese texture. For coagulants with a higher proportion of pepsin, less intact αs1-CN and a higher degree of casein hydrolysis (expressed as protein fraction soluble at pH 4.6) were found. Correspondingly, the cheese had a weaker and less brittle network, and was softer, less elastic and more sticky. Commercial calf rennet showed more extensive hydrolysis of αs1-CN than other coagulants, which led to the weakest protein network and the softest cheese. The present study's findings can be used to control and design cheese with desired textures. For example, coagulants with varying chymosin/pepsin ratio or from a specific source can be used to modulate the casein hydrolysis.

Sheep's Second Cheese Whey Edible Coatings with Oregano and Clary Sage Essential Oils Used as Sustainable Packaging Material in Cheese.

Sheep's second cheese whey (SCW), the by-product resulting from whey cheese production, was used as a component of cheese coatings containing oregano (Origanum compactum) and clary sage (Salvia sclarea) essential oils (EOs). SCW powder was obtained by the ultrafiltration/diafiltration of SCW followed by reverse osmosis and freeze drying. The coatings were produced with a mixture of SCW and whey protein isolate (WPI) using glycerol as plasticizer. Model cheeses were produced with cow´s milk and those containing SCW:WPI coatings; those with and without EOs were compared to controls without coating and with a commercial coating containing natamycin. At the end of ripening (28 days), the cheeses containing EOs presented higher water activity (ca. 0.930) and moisture content, as well as lower titratable acidity. Concerning color parameters, significant differences were also observed between products and as a result of ripening time. However, the use of SCW:WPI coatings did not significantly influence the color parameters at the end of ripening. Regarding texture parameters, the cheeses containing SCW:WPI coatings presented significantly lower values for hardness, chewiness, and gumminess. Significant differences were also observed for all microbial groups evaluated either between products and as a result of ripening time. In all cases, lactobacilli and lactococci counts surpassed log 7-8 CFU/g, while the counts of yeasts and molds increased steadily from ca. log 3 to log 6 CFU/g. The lowest counts of yeasts and molds were observed in the samples containing natamycin, but nonsignificant differences between products were observed. In conclusion, SCW:WPI cheese coatings can successfully substitute commercial coatings with the advantage of being edible packaging materials manufactured with by-products.

Phage resistance mutations affecting the bacterial cell surface increase susceptibility to fungi in a model cheese community.

Diverse populations of bacteriophages infect and coevolve with their bacterial hosts. Although host recognition and infection occur within microbiomes, the molecular mechanisms underlying host-phage interactions within a community context remain poorly studied. The biofilms (rinds) of aged cheeses contain taxonomically diverse microbial communities that follow reproducible growth patterns and can be manipulated under laboratory conditions. In this study, we use cheese as a model for studying phage-microbe interactions by identifying and characterizing a tractable host-phage pair co-occurring within a model Brie-like community. We isolated a novel bacteriophage, TS33, that kills Hafnia sp. JB232, a member of the model community. TS33 is easily propagated in the lab and naturally co-occurs in the cheese community, rendering it a prime candidate for the study of host-phage interactions. We performed growth assays of the Hafnia, TS33, and the fungal community members, Geotrichum candidum and Penicillium camemberti. Employing Random Barcode Transposon Sequencing experiments, we identified candidate host factors that contribute to TS33 infectivity, many of which are homologs of bacterial O-antigen genes. Hafnia mutants in these genes exhibit decreased susceptibility to phage infection, but experience negative fitness effects in the presence of the fungi. Therefore, mutations in O-antigen biosynthesis homologs may have antagonistic pleiotropic effects in Hafnia that have major consequences for its interactions with the rest of the community. Ongoing and future studies aim to unearth the molecular mechanisms by which the O-antigen of Hafnia mediates its interactions with its viral and fungal partners.

Unveiling the hidden potential of nisin-permeabilized Streptococcus thermophilus as proteolysis accelerant during cheese ripening

Proteolysis is the most significant primary ripening process in cheese, as it produces amino acids that serve as precursors for various flavor compounds. Therefore, the degree of proteolysis is an important indicator of cheese ripening. Here, the potential of nisin-permeabilized lactic acid bacteria as proteolysis accelerant during cheese ripening was explored. Both nisin-permeabilized Lactococcus lactis and Streptococcus thermophilus cells could hydrolyze peptidase substrates lysyl–p-nitroanilide (Lys–pNA) and glycyl–pro–pNA [Gly–Pro–pNA] efficiently. The overall proteolytic capacity of permeabilized cells depended on nisin concentration, strain used, temperature, and pH. The best candidate, S. thermophilus ST057-1, could hydrolyze 80% Lys–pNA and 94% Gly–Pro–pNA at 30 °C and pH 7 when treated with 5 μg/mL nisin. Permeabilized ST057-1 cells, when used as a starter adjunct, led to a significant increase in free amino acid content in model cheeses, up to 1.5 times that of the reference cheese, within 80 days of cheese ripening. This study highlights the potential of utilizing nisin-permeabilized S. thermophilus cells as an adjunct to accelerate proteolysis during cheese ripening.

Cows’ and buffalo milk for cooked fresh cheese: preliminary comparison of the cheese-making efficiency and quality of griddled acid/heat-coagulated Paneer and rennet-coagulated Tosella/Schiz

Milk from cows and buffaloes represents the major source of dairy products worldwide. Cheese is consumed fresh, ripened, cooked, or as recipe ingredient in many different types. Using Paneer and Tosella/Schiz model cheeses as a case study of cooked cheeses, in this short communication we evaluated the cheese yield and quality of fresh cheese before and after cooking comparing the two major dairy species (cows and buffaloes). A total of 75 model cheeses (37 Paneer and 38 Tosella/Schiz) were made. Slices of all the cheeses were cooked on a griddle at 130 °C. Milk, whey, and cheese composition traits, cheese-making efficiency traits, and cooked cheese quality traits were evaluated using a mixed model that included the fixed effects of cheese type and animal species, and their interaction, and the random effects of session, animal within species, and the residual. Higher cheese yields are obtained from the buffalo milk not only because more concentrated in nutrients, but also for the greater recovery of nutrients in cheese. There was a greater recovery of protein with the acid/heat Paneer procedure than the rennet Tosella/Schiz procedure, but we found a species × cheese type interaction for fresh cheese yield. The interaction was related mainly to the higher water retained in the Tosella/Schiz curd rather than to total solids. This led also to greater cooking weight-loss compared with Paneer. The qualitative traits of cheese were highly affected by griddling. Future research on the sensorial perception of cooked cheeses from the two major dairy species is needed to predict consumer response.

Determination of the effects of proteolysis-based changes by adjunct lactobacilli on the bioactivity (ACE-inhibitory and antioxidant activities) of cheese: a model cheese study.

Bioactive properties, proteolysis and microbiology of model cheeses with and without adjunct lactobacilli (Lactobacillus helveticus, Lactiplantibacillus plantarum, Lactobacillus bulgaricus and L. casei) were studied during 120 days of storage at 8 or 16°C. Bioactive properties were observed in peptide fractions (< 3kDa, 3-10kDa, < 10kDa) separated using ultrafiltration membranes. Antioxidant activity of these fractions was determined by radical scavenging assays as ABTS [2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)]. Angiotensin-converting enzyme-inhibitory (ACE-i) activity (% and IC50) and peptide profiles of 70% ethanol-soluble and -insoluble fractions were determined by RP-HPLC. Use of lactobacilli as an adjunct culture significantly changed the RP-HPLC peptide profiles of the cheeses; however, slight changes were observed in the patterns of urea-polyacrylamide gel electrophoresis. Fractions smaller than 3kDa had higher ACE-i and antioxidant activities for all cheese samples. In conclusion, this study indicates that the addition of lactobacilli as an adjunct culture contributed to the formation of bioactive compounds in the model cheeses and also changed the proteolysis levels.

Linking casein hydrolysis by chymosin and plasmin to the rheological and textural properties of model cheese

The texture of cheese highly depends on the structure of its network, which develops during ripening due to the enzymatic degradation of caseins. However, the influence of the hydrolysis of individual casein fractions (αs1-and β-CN) on specific textural properties remains unclear. In this study, we aimed to link the breakdown of individual casein fractions by chymosin and plasmin to different rheological and textural properties used to characterize cheese texture. Model cheeses with two plasmin levels (active and inactive) and three chymosin levels (20, 50, and 80 IMCU/kg milk) were prepared.Our results showed that the hydrolysis of αs1-and β-CN by chymosin and plasmin played different roles in the rheological and textural properties of the samples. The hydrolysis of αs1-CN predominantly led to a decrease in G′ and Young's modulus, parameters related to the strength of the protein network. The hydrolysis of β-CN was more associated with changes in critical strain, resilience and cohesion, which were linked to rearrangements within the protein network resulting from hydrophobic interactions among hydrolyzed products. Hardness_40% (stress at a strain of 40%) was related to hydrolysis of both αs1-CN and β-CN, although the effect of αs1-CN degradation seemed more pronounced. The obtained knowledge offers new insights into the mechanisms behind cheese texture development.

Zein improves desirable melt-stretch properties in plant-based cheeses made from pea protein

Plant-based model cheeses made from pea protein isolate (PPI), zein and zein/PPI blends, were made in combination with corn starch, sunflower oil, different levels of κ-carrageenan (κC) and CaCl2 (CC), and glycerol as a zein-plasticizer. Their viscoelastic properties at ambient temperature and upon heating, as well as their lubrication properties were analyzed. The properties of all plant-based formulations were compared to two dairy cheeses of reference: mozzarella and raclette. Formulations containing PPI formed a gel, whose network structure did not weaken upon heating. In contrast, zein-based cheeses showed potential for structure weakening during heating, as observed during the rheological temperature sweep. The latter observation increased in zein/PPI-combinations with increasing zein content, even though the melting behaviour of any of the plant-based formulations was not fully comparable to the one of raclette cheese. All of the examined formulations reduced the friction coefficient by a factor between 2 and 10 in the boundary regime, compared to HEPES-buffer. In zein-containing formulations, the friction coefficients decreased to a lesser extent the higher the zein proportion was. Finally, the inclusion of κC or CC did not have a significant influence in the lubrication properties of PPI-formulations. In summary, particularly zein/PPI-combinations made of a total protein content of 30% in the formulation showed good potential in mimicking the melting of conventional cheese, opening prospect for the development of formulations with improved sensory characteristics in future works.

The impact of Brevibacterium aurantiacum virulent phages on the production of smear surface-ripened cheeses

Phages are ubiquitous and are particularly abundant in environments where their bacterial hosts thrive, such as those in the cheese industry. Although it is well documented that phages infect lactic acid bacteria, their impact has been notably overlooked on cheese ripening strains, such as Brevibacterium aurantiacum. Here, we aimed to study the impact of B. aurantiacum phages on the production of smear-ripened cheeses. We used model cheeses in industrial settings to monitor the development of the color of the cheese rind as well as of its microbial composition in presence or absence of virulent B. aurantiacum phages. Our results showed that the presence of B. aurantiacum phages significantly slowed down the development of the orange rind color in the model cheeses. In the final days of cheese ripening, phages were also detected in the control curds. By analyzing a hypervariable region of B. aurantiacum phage genomes, we detected phages with tandem repeat patterns that were different from those used in the phage-inoculated cheeses. Our results highlight the risks of using a phage-sensitive strain in smear-ripened cheese production. This is the first study to report on the impact of B. aurantiacum phages on smear-ripened cheeses.

Cheese yield and nutrients recovery in the curd predicted by Fourier-transform spectra from individual sheep milk samples

The objectives of this study were to explore the use of Fourier-transform infrared (FTIR) spectroscopy on individual sheep milk samples for predicting cheese-making traits, and to test the effect of the farm variability on their prediction accuracy. For each of 121 ewes from 4 farms, a laboratory model cheese was produced, and 3 actual cheese yield traits (fresh cheese, cheese solids, and cheese water) and 4 milk nutrient recovery traits (fat, protein, total solids, and energy) in the curd were measured. Calibration equations were developed using a Bayesian approach with 2 different scenarios: (1) a random cross-validation (80% calibration; 20% validation set), and (2) a leave-one-out validation (3 farms used as calibration, and the remaining one as validation set) to assess the accuracy of prediction of samples from external farms, not included in calibration set. The best performance was obtained for predicting the yield and recovery of total solids, justifying for the practical application of the method at sheep population and dairy industry levels. Performances for the remaining traits were lower, but still useful for the monitoring of the milk processing in the case of fresh curd and recovery of energy. Insufficient accuracies were found for the recovery of protein and fat, highlighting the complex nature of the relationships among the milk nutrients and their recovery in the curd. The leave-one-out validation procedure, as expected, showed lower prediction accuracies, as a result of the characteristics of the farming systems, which were different between calibration and validation sets. In this regard, the inclusion of information related to the farm could help to improve the prediction accuracy of these traits. Overall, a large contribution to the prediction of the cheese-making traits came from the areas known as "water" and "fingerprint" regions. These findings suggest that, according to the traits studied, the inclusion of water regions for the development of the prediction equation models is fundamental to maintain a high prediction accuracy. However, further studies are necessary to better understand the role of specific absorbance peaks and their contribution to the prediction of cheese-making traits, to offer reliable tools applicable along the dairy ovine chain.

Identification of Marker Peptides for the Whey Protein Quantification in Edam-Type Cheese.

Several technologies are available for incorporating whey proteins into a cheese matrix. However, there is no valid analytical method available to determine the whey protein content in matured cheese, to date. Consequently, the aim of the present study was to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of individual whey proteins based on specific marker peptides ('bottom-up' proteomic approach). Therefore, the whey protein-enriched model of the Edam-type cheese was produced in a pilot plant and on an industrial scale. Tryptic hydrolysis experiments were performed to evaluate the suitability of identified potential marker peptides (PMPs) for α-lactalbumin (α-LA) and β-lactoglobulin (β-LG). Based on the findings, α-LA and β-LG appeared to be resistant to proteolytic degradation during six weeks of ripening and no influence on the PMP was observed. Good levels of linearity (R2 > 0.9714), repeatability (CVs < 5%), and recovery rate (80% to 120%) were determined for most PMPs. However, absolute quantification with external peptide and protein standards revealed differences in model cheese depending on the PMP, e.g., 0.50% ± 0.02% to 5.31% ± 0.25% for β-LG. As protein spiking prior to hydrolysis revealed differing digestion behavior of whey proteins, further studies are required to enable valid quantification in various cheese types.

Effects of calcium chloride substitution on the physicochemical properties of Minas Frescal cheese.

The aim in this research paper was to investigate the effect of using calcium monophosphate (MCP) and MCP mixed with commercial phosphates salts, in total or partial replacement of calcium chloride (CaCl2) in the manufacture of Minas Frescal cheese. Initially, model cheeses were made to perform the rheological analysis during the coagulation process. Of these, the five best treatments were chosen to carry out the production of Minas Frescal cheese, used only CaCl2 and MCP, and partial replacements of MCP + polyphosphate, MCP + potassium monophosphate (MKP) and MCP. The cheeses showed no significant difference in physicochemical composition, yield and syneresis, however, the cheese with partial replacement of CaCl2 by MCP + polyphosphate and MCP + MKP showed the highest hardness values, like the control. This demonstrates that it is possible to replace calcium chloride without significant changes in the physicochemical characteristics and yield of Minas Frescal cheese, and it is still possible to modulate the hardness of the cheese produced according to the type of calcium/phosphate source used. This allows the industry to replace the source of calcium in the manufacture of Minas Frescal cheese according to the desired hardness.

Elaboration and characterisation of a miniature soft lactic goat cheese model to mimic a factory cheese

Although soft lactic goat cheeses are widely produced in France, there is little information available in the literature about them and no miniature model for this kind of cheese has yet been proposed. In this study, a miniature soft lactic goat cheese model was compared with equivalent factory cheese to use it as a reliable model for this cheese family. The composition of the cheeses was compared at four key stages of the production process using microbiological, physicochemical and Sift-MS volatilome analysis. The compositions of the model and factory cheeses were found to be similar until the ripening step, but some differences were observed on ripened cheeses. Moreover, under carefully monitored laboratory conditions, the variability across batches of the model cheese was reduced. This miniature soft lactic goat cheese could therefore be used as a reliable model to study the aspects of the same cheese type.

Improvement of Caciotta-like cheese nutritional value by means of enrichment with blackcurrant (Ribes nigrum) and Cornelian cherry (Cornus mas).

In this study, we supplemented models of Caciotta-like cheese with blackcurrant (Ribes nigrum) and Cornelian cherry (Cornus mas), as they have a high content of polyphenols, known as phytochemicals associated with health benefits. We evaluated the microbial composition, organoleptic aspects, total phenolic content, and chemical composition of model cheeses enriched with blackcurrant and Cornelian cherry. Two different suppliers have been tested: a conventional and an organic one. Two different conditions of preparation (freeze-dried and not freeze-dried) were tested in two different amounts (0.3 and 0.6% dry weight w/v milk volume). Polyphenols were determined using Folin-Ciocalteu reaction and spectrometry; microbial community was determined with selective 24 media and plate counts; composition was determined using nuclear magnetic resonance spectrometry. Organoleptic tests with an untrained panel have been performed. The enrichments with blackcurrant and Cornelian cherry increased the total polyphenol content in model cheeses, in particular, when blackcurrant and Cornelian cherry were from conventional farming. Blackcurrant-enriched cheeses showed higher counts of lactic acid bacteria, higher levels of organic acids, amino acids, gamma-aminobutyric acid, histamine, and lower amount of monosaccharides deriving from bacterial lactose fermentation in cheese, suggesting a positive effect of blackcurrant compounds on the growth and activity of lactic acid bacteria. The enrichments did not affect the acceptance of the cheese, neither by blackcurrant nor by Cornelian cherry incorporation, with the exception of the appearance. Overall, we showed that cheeses enriched with blackcurrant or Cornelian cherry from conventional farming increased the bioactive potential of the dairy product without having an adverse effect on the microbial community, physiochemical properties, or organoleptic properties.

Acceleration of proteolysis, flavour development and enhanced bioactivity in a model cheese using Kuflu cheese slurry: An optimisation study

This study aimed to use Kuflu (a mould-ripened cheese) cheese slurry to accelerate ripening, improve biological activity and flavour development in a model cheese in terms of proteolysis and volatile compounds. Response surface methodology (RSM) was employed for the model cheese to determine higher proteolysis and volatile development level during ripening as a function of Kuflu cheese slurry addition level (0–5 %), salt concentration (1–3 %) and ripening temperature (5–15 °C). The highest aminopeptidase activities (0.140 and 0.187 OD/g per hour) were determined in 15-day-old samples containing 3 % and 5 % Kuflu cheese slurry, respectively. Also, the use of Kuflu cheese slurry, regardless of ripening, caused an increase in ABTS*+ antioxidants, angiotensin-converting enzyme (ACE)-inhibition activity and volatile compounds in model cheeses. The sensory evaluation indicated that the use of 3 % (w/w) Kuflu cheese slurry, storage temperature 10 °C for 15 days provided better flavour, odour, texture, colour, appearance and overall acceptability. In conclusion, using Kuflu cheese slurry for model cheese production enhanced the level of proteolysis and volatile flavour composition with shortened ripening time.

Milk metagenomics and cheese-making properties as affected by indoor farming and summer highland grazing.

The study of the complex relationships between milk metagenomics and milk composition and cheese-making efficiency as affected by indoor farming and summer highland grazing was the aim of the present work. The experimental design considered monthly sampling (over 5 mo) of the milk produced by 12 Brown Swiss cows divided into 2 groups: the first remained on a lowland indoor farm from June to October, and the second was moved to highland pastures in July and then returned to the lowland farm in September. The resulting 60 milk samples (2 kg each) were used to analyze milk composition, milk coagulation, curd firming, and syneresis processes, and to make individual model cheeses to measure cheese yields and nutrient recoveries in the cheese. After DNA extraction and Illumina Miseq sequencing, milk microbiota amplicons were also processed by means of an open-source pipeline called Quantitative Insights Into Microbial Ecology (Qiime2, version 2018.2; https://qiime2.org). Out of a total of 44 taxa analyzed, 13 bacterial taxa were considered important for the dairy industry (lactic acid bacteria, LAB, 5 taxa; and spoilage bacteria, 4) and for human (other probiotics, 2) and animal health (pathogenic bacteria, 2). The results revealed the transhumant group of cows transferred to summer highland pastures showed an increase in almost all the LAB taxa, bifidobacteria, and propionibacteria, and a reduction in spoilage taxa. All the metagenomic changes disappeared when the transhumant cows were moved back to the permanent indoor farm. The relationships between 17 microbial traits and 30 compositional and technological milk traits were investigated through analysis of correlation and latent explanatory factor analysis. Eight latent factors were identified, explaining 75.3% of the total variance, 2 of which were mainly based on microbial traits: pro-dairy bacteria (14% of total variance, improving during summer pasturing) and pathogenic bacteria (6.0% of total variance). Some bacterial traits contributed to other compositional-technological latent factors (gelation, udder health, and caseins).

Effect of plasmin on casein hydrolysis and textural properties of rennet-induced model cheeses

Plasmin plays an important role in casein hydrolysis during cheese ripening, which may influence the properties of the casein network and the texture of the final product. In view of this, the relation between plasmin-induced casein hydrolysis and textural changes of cheese during ripening was investigated in this study. Four batches of model cheese with different concentrations of added plasmin (0, 0.4, 0.6 and 1.0 μL/g milk) were prepared, and were stored for 12 weeks at 16 °C. During this period, plasmin activity, casein hydrolysis, textural properties and other compositional characteristics (pH, dry matter) were determined. Our results show that the addition of plasmin had significant effect on both the degree and the pattern of proteolysis. As a result, cheeses with different plasmin content showed different textural properties. With increased plasmin concentration, Young’s modulus, hardness, resilience and cohesion decreased, while brittleness increased. All textural properties showed linear relations with the degree of casein hydrolysis, and logarithmic relations with the percentage of intact casein fractions. At the beginning of ripening, only slight changes in textural properties were found, although a substantial part (40–60 %) of the casein fractions was already been broken down. When ripening progressed, ongoing proteolysis significantly weakened the protein network and consequently led to noticeable textural changes. Model cheeses became softer, more brittle and less elastic. The knowledge gained from this study provide new insights in the changes of different textural parameters of model cheese. This will help to optimize the existing products and create new ones.