Degree Of Proteolysis Research Articles

Enhancing the functionality of yogurt: Impact of exotic fruit pulps addition on probiotic viability and metabolites during processing and storage

The effect of exotic fruit pulp (araçá, cagaita, cambuci, grumixama, blueberry, and uvaia) on probiotic viability during storage and after gastrointestinal tract (GIT) simulation, in vitro biological activity, total phenolics (TPC) and flavonoids content, and the production of metabolic products of microbial in probiotic yogurt were investigated. During the storage period (28 days), probiotic strain populations remained high (above 6 log CFU/g), while after the GTI simulation, L. acidophilus and B. animalis survival rates were higher when adding grumixama, blueberry, and uvaia pulp. Fermentation increased the antioxidant activity of yogurt containing araçá (12.87 ± 0.32 to 17.46 ± 1.79 μg Trolox/mg) and blueberry pulp (12.05 ± 1.43 to 17.49 ± 1.68 μg Trolox/mg) for ORACH for example. However, the total phenolic content increased in all samples after fermentation (ranging from 1.80 ± 0.26 μg gallic acid/mg (Uvaia) to 2.42 ± 0.08(Grumixama)), and there was no significant difference among treatments for total flavonoids. Thirty-eight metabolic compounds, mainly free amino acids, were detected, indicating a high degree of proteolysis in samples. Exotic fruit pulps positively impacted the probiotic yogurt parameters and are a potential alternative in functional food processing.

Effect of different thermal processing methods and thermal core temperatures on the protein structure and in vitro digestive characteristics of beef

This study aimed to investigate the effect of different thermal processing treatments on the protein digestion characteristics of beef. The beef samples were subjected to different cooking methods, namely steaming, boiling, and roasting, and different core temperatures (75 °C, 80 °C, 85 °C, and 90 °C), and were subjected to in vitro gastrointestinal digestion simulation. All the thermal processing treatments increased the protein digestibility; the samples that were steamed at 85 °C (S85), boiled at 80 °C (B80), and roasted at 80 °C (R80) showed the biggest gains. The S85 released more peptide species after gastrointestinal digestion, according to peptididomic studies. These differences were closely related to protein structure. Thermal processing treatments resulted in a higher degree of proteolysis and looser protein conformation, as evidenced by decreased intrinsic fluorescence and electrophoretic band intensity, increased surface hydrophobicity, and the change in protein secondary structure from α-helix to β-sheet and random coil. Based on the results, S85 was identified as the optimal thermal processing treatment for enhancing the digestibility of beef protein. The results provide valuable insights into the nutritional qualities and digestion of heat-processed beef protein.

The Effects of Substrates and Sonication Methods on the Antioxidant Activity of Kefir Postbiotics

Sonoporation stimulates cell growth as it improves the permeability of the membrane and increases the uptake of impermeable molecules in the extracellular matrix. We evaluated the effects of substrates (whey, whole, and skim milk) and ultrasonic treatments (ultrasonication and thermosonication) on the antioxidant activity (AA) of water-soluble kefir postbiotics (WSKPs). The samples were evaluated in terms of antioxidant activity (ABTS, DPPH, FRAP, and ORAC), water-soluble protein content, proteolysis (SDS-PAGE profiles), and cell membrane permeability. The levels of AA in all WSKPs depended on the substrate and method of obtaining them. However, the WSKPs from whey had higher antioxidant activity with DPPH (11.11 mg TE/100 mL), ABTS (12.77 mg TE/100 mL), and FRAP (5.18 mg TE/100 mL). Also, the WSKPs from whey had the highest values for water-soluble protein (1.45–1.32 mg/mL) and proteolysis degree and the lowest percentage of dead cells (11.4–28%). These results suggest that the production of WSKPs from whey might add value to whey production. Furthermore, WSKPs have potential as a functional ingredient in the production of beverages or foods with antioxidant activity.

Evolution of bacterial flora in raw yak milk and its effect on quality characteristics during frozen storage

Due to the scarcity of yak milk in Tibetan areas, local herders primarily use traditional freezing methods for preservation. However, the extent of microbial contamination in raw yak milk during frozen storage and its impact on milk quality remains largely unexplored. This study analyzed the changes in bacterial populations and quality of raw yak milk stored at −18 °C for 6 months. The results indicated that, compared to fresh milk, the freshness of yak milk showed no significant change after 2 months of frozen storage (P > 0.05). After 4 months, the bacterial diversity of flora in yak milk increased significantly, with Pseudomonas and Acinetobacter emerging as the dominant psychrophilic bacteria. Correspondingly, the expression of metabolic pathways related to quality deterioration increased, with a significant increase in physicochemical indicators such as acidity, proteolysis degree, acid value and fat oxidation degree (P < 0.05). Extending the frozen storage to 6 months resulted in a slight but no significant decrease in bacterial diversity, with no significant difference in quality deterioration compared to the 4-month group (P > 0.05). Correlation analysis further revealed that Acinetobacter and Psychrobacter were significantly positively correlated with quality deterioration of frozen milk (P < 0.05). In summary, when frozen for more than 4 months, raw yak milk exhibited the highest bacterial diversity and predicted the most abundant metabolic pathways, with dominant psychrophilic bacteria massive proliferation leading to a decline in quality and safety.

Human milk vs. Infant formula digestive fate: In vitro dynamic digestion and in vivo mini-piglet models lead to similar conclusions

Infant formula (IF), the only nutritionally adequate substitute for human milk (HM), still needs to be improved to be more biomimetic with HM, including in terms of digestive fate. The latter can be explored using different digestion models. The present study aimed to compare IF and HM digestion using in vivo (mini-piglet) and in vitro (dynamic system, DIDGI®) models. Fresh mature HM was collected and compared with a standard bovine IF. In vivo, 18 Yucatan mini-piglets (24-day-old) received HM or IF and were euthanized 30 min after the last meal. The entire digestive content was collected from the stomach to the colon. In vitro, the same meals were fed to an in vitro dynamic digestion model simulating the term infant at four weeks of age. Digesta were sampled regularly in the gastric and intestinal compartments. Structure (confocal microscopy and laser light scattering) and proteolysis (SDS-PAGE for residual intact proteins, OPA for hydrolysis degree, LC-MS/MS for peptides) were investigated along digestion. The digesta microstructure differed between HM and IF in a similar way between in vitro and in vivo digestion. In vitro gastric proteolysis of caseins and α-lactalbumin was significantly slower for HM than for IF, such as for the early intestinal proteolysis degree. In vitro bioaccessibility of free AAs explained only 30 % of the true ileal digestibility of AAs. Peptide mapping of caseins differed between HM and IF along their digestion. The relative peptide mapping data over six proteins from HM and IF were highly correlated between in vitro and in vivo digestion, particularly at 80 and 120 min of in vitro gastric digestion vs. in vivo stomach data and at 20 and 40 min of in vitro intestinal digestion vs. in vivo proximal jejunum data (r = 0.7–0.9, p < 0.0001, n = 1604). 40 to 50 % of the bioactive peptides identified in vivo were also found in vitro, with a good correlation of their abundances (r = 0.5, p < 0.0001, n = 61). Overall, in vitro and in vivo digestion were in good agreement, both indicating a different digestive fate for HM and IF.

The promotion and inhibition of proteolysis in silages during ensiling of citrus waste

Although waste generated from the production of citrus fruit juice is a suitable raw material for ensiling, excessive proteolysis greatly reduces the quality of silages and economic benefits. The driving force and factors influencing proteolysis during ensiling remain poorly understood. In this study, the degree of silage proteolysis was systematically evaluated through the analysis of silage composition, proteolysis promotion and inhibition under various ensiling factors were quantified, and the causes of proteolysis were explored through changes of microbiome. A reduction in soluble protein (SP) and in-solution protein (ISP) contents coupled with an increase in NH3-N were found after ensiling. A decrease in free amino acid content was evident in upper and middle sections, whereas there was an increase in the bottom section. The strongest proteolysis of silages was observed in the middle section. The main factor accelerating hydrolysis of protein into amino acid (the first stage of proteolysis) was acid protease activity (APA). The hydrolysis of amino acid into NH3-N (the second stage of proteolysis) was principally inhibited by lactic acids, acetic acids, pH, and soluble carbon, and accelerated by APA, moisture and total carbon. Acid protease was probably constituted mainly microbial protease, able to tolerate a pH range of 3.44–3.77. Bacterial coupled colony (B-CC), Trichocomaoute, and Trichocomaceae-1 presumably promoted the production and activity of acid protease. As inferred, the first stage of proteolysis was promoted by B-CC and fungal coupled colony (F-CC), and inhibited by Trichocomaoute. While the second stage of proteolysis was likely promoted by P. kudriavzevii and F-CC, and inhibited by B-CC and Trichocomaoute. Thus, the use of homofermentative lactic acid bacteria in raw materials is recommended to reduce the degree of proteolysis, particularly in the middle section of the silo.

Influence of thermophilic and mesophilic cultures blended with buffalo milk on camel milk cheese quality and proteolysis

SummaryCamel milk and its products are gaining higher demand due to their attractive nutritional and therapeutic profile. However, manufacturing of camel milk cheese (CMC) is a challenging task. This study aimed to compare the quality of camel milk cheese made using different starter cultures. Four groups CM (camel milk + mesophilic cultures), CT (camel milk + thermophilic cultures), CBM (camel milk + 10% buffalo milk using mesophilic cultures), and CBT (camel milk + 10% buffalo milk using thermophilic cultures) were created. The cheeses were stored for 60 days at 4 °C to assess their physicochemical, sensory, and proteolytic properties. Results indicated highest moisture content in CM (70.19%) as opposed to the lowest moisture in CBT (55.19%). In addition, CM and CBM revealed lower acidity (0.63% and 0.66%) in contrast with CT and CBT (0.78% and 0.83%, respectively). On the other hand, CBM and CBT exhibited higher contents of protein (21.04, 21.57%) and fat (17.65, 17.70%) during storage. All quality indices of cheese samples significantly declined (P &lt; 0.01) during storage excluding acidity. Sensory analyses revealed that panellists highly preferred CBT treatment followed by CBM and CT. Furthermore, urea‐PAGE and RP‐HPLC were performed for the proteolytic study of cheese samples. The study revealed that the presence of buffalo milk and thermophilic cultures in cheese resulted in a decrease concentration of intact caseins (αs1, β‐, and κ‐caseins) as storage days passed. The degree of proteolysis was found to be higher in CBT compared to CBM, CT, and CM. Based on the results, it was concluded that the use of pasteurisation at 65 °C for 30 min, pH of 5.5, 0.06% CaCl2, and the incorporation of 10% buffalo milk using thermophilic cultures (Lactobaccilus bulgaricus and Streptococcus thermophilus) resulted in desirable quality characteristics.

Effect of Air Classification and Enzymatic and Microbial Bioprocessing on Defatted Durum Wheat Germ: Characterization and Use as Bread Ingredient.

Its high dietary fiber and protein contents and nutritional quality make defatted wheat germ (DWG) a valuable cereal by-product, yet its negative impact on food structure limits its use as a food ingredient. In this research, DWG underwent air classification, which identified two fractions with high fiber (HF) and low fiber/high protein (LF) contents, and a bioprocessing protocol, involving treatment with xylanase and fermentation with selected lactic acid bacterial strains. The degree of proteolysis was evaluated through electrophoretic and chromatographic techniques, revealing differences among fractions and bioprocessing options. Fermentation led to a significant increase in free amino acids (up to 6 g/kg), further enhanced by the combination with xylanase. When HF was used as an ingredient in bread making, the fiber content of the resulting bread exceeded 3.6 g/100 g, thus reaching the threshold required to make a "source of fiber" claim according to Regulation EC No.1924/2006. Meanwhile, all breads could be labeled a "source of protein" since up to 13% of the energy was provided by proteins. Overall, bioprocessed ingredients lowered the glycemic index (84 vs. 89) and increased protein digestibility (80 vs. 63%) compared to control breads. Technological and sensory analysis showed that the enzymatic treatment combined with fermentation also conferred a darker and more pleasant color to the bread crust, as well as better crumb porosity and elasticity.

In vitro gastrointestinal digestion of cow’s and sheep’s dairy products: Impact of species and structure

Sheep’s milk (SM) is known to differ from cow’s milk (CM) in nutritional composition and physicochemical properties, which may lead to different digestion behaviours. This work aimed to investigate the impact of the species (cow vs sheep) and the structure (milk vs yogurt) on the digestion of dairy products. Using an in vitro static gastrointestinal digestion model, CM, SM, cow’s milk yogurt (CY) and sheep’s milk yogurt (SY) were compared on particle size evolution, microscopic observations, degree of lipolysis, degree of proteolysis, specific protein degradation and calcium bioaccessibility. Species and structure affected particle size evolution during the gastric phase resulting in smaller particles for yogurts compared to milks as well as for CM products compared to SM products. Species impacted lipid composition and lipolysis, with SM products presenting higher short/medium-chain fatty acids content and higher intestinal degree of lipolysis. Proteolysis was influenced by structure, with milks showing higher intestinal degree of proteolysis compared to yogurts. Caseins were digested faster in CM, ⍺-lactalbumin was digested faster in SM despite its higher concentration, and during gastric digestion β-lactoglobulin was more degraded in CM products compared to SM products and more in yogurts compared to milks. Lastly, SM products released more bioaccessible calcium than CM products. In conclusion, species (cow vs sheep) impacted more the digestion compared to the structure (milk vs yogurt). In fact, SM was different from CM mainly due to a denser protein network that might slow down the accessibility of the enzyme to its substrate which induce a delay of gastric disaggregation and thus lead to slower the digestion of the nutrients.

Study of the possibility of producing brine-ripened cheeses from frozen sheep’s milk

The article presents the results of a study of the quality indicators of brine-ripened cheeses produced from defrosted sheep’s milk. The objects of the study were natural and defrosted sheep’s milk, brine-ripened cheeses from this milk. The study of defrosted sheep’s milk (experiment) was carried out after 10 days of its storage at a temperature of –18 °C followed by defrostation at a temperature of 20 ± 2 °C. The composition of natural sheep’s milk (control) was examined after storage for 24 ± 12 hours at a temperature of 4 ± 2 °C. It has been found that the freezing of milk and its subsequent defrostation did not have a significant effect on the milk solids content, the mass fraction of protein and fat, titrated acidity; however, the mass fraction of calcium decreased, on average, by 20%. Freezing milk did not significantly affect the total number of micro- organisms, including spore aerobic microorganisms and molds. A decrease in the number of somatic cells (from 3.0 to 4.5 times) was found. There were no differences between the control and experimental milk samples in the renneting ability. The level of syneresis of clots in the control sample was 16 ± 1% higher compared to the experimental sample. The cheeses were produced according to the traditional technological scheme of brine-ripened cheese using a production mesophilic bacterial starter culture. The control and experimental cheeses did not differ significantly in physical and chemical parameters. According to the degree of proteolysis, there were no significant differences between the control and experimental variants. In the experimental sample, a decrease in the buffer capacity of the cheese mass was noted in comparison with the control cheeses. The freezing of milk did not have a significant effect on the taste characteristics of the cheeses: in both variants, the cheeses were characterized by a weakly expressed cheese, fermented milk taste with original taste of sheep’s milk. More noticeable differences were found in the consistency of the cheeses. In the control version, the consistency was characterized as tender, slightly brittle; in the experimental version, it was less tender, but brittle and slightly powdery. The greatest deterioration in consistency was observed in the samples of frozen cheese made from natural milk after defrosting; it was characterized as brittle, powdery, crumbly.

Autochthonous Fermentation as a Means to Improve the Bioaccessibility and Antioxidant Activity of Proteins and Phenolic Compounds of Yellow Pea Flour.

This study focused on evaluating the potential of the natural fermentation of pea flour to improve the release of antioxidant compounds. Preliminary fermentations of 36.4% w/w flour dispersions were performed in tubes under different conditions (24 and 48 h, 30 and 37 °C). Finally, fermented flours (FFs) were obtained in a bioreactor under two conditions: 1: 36.4% w/w, 24 h, 30 °C (FF1); 2: 14.3% w/w, 24 h, 37 °C (FF2). The pH values decreased to 4.4-4.7, with a predominance of lactic acid bacteria. As in the fermentations in tubes, an increment in the proteolysis degree (TNBS method) (greater for FF2), polypeptide aggregation and a decrease in their solubility, an increase in <2 kDa peptides, and an increase in the Oxygen Radical Absorption Capacity (ORAC) potency of PBS-soluble fractions after fermentation were demonstrated. Also, fermentation increased the proteolysis degree after simulated gastrointestinal digestion (SGID, COST-INFOGEST) with respect to the non-fermented flour digests, with some differences in the molecular composition of the different digests. ORAC and Hydroxyl Radical Averting Capacity (HORAC) potencies increased in all cases. The digest of FF2 (FF2D) presented the greater ORAC value, with higher activities for >4 kDa, as well as for some fractions in the ranges 2-0.3 kDa and <0.10 kDa. Fermentation also increased the 60%-ethanol-extracted phenolic compounds, mainly flavonoids, and the ORAC activity. After SGID, the flavan-3-ols disappeared, but some phenolic acids increased with respect to the flour. Fermentation in condition 2 was considered the most appropriate to obtain a functional antioxidant ingredient.

Performance, Carcass Composition, and Meat Quality during Frozen Storage in Male Layer-Type Chickens

An experiment was carried out in the Institute of Animal Science—Kostinbrod, Bulgaria, to investigate the growth performance of male layer-type chickens (Lohmann Brown Classic), raised to 6 and 9 weeks of age, to evaluate the economic aspects of this rearing, as well as to present changes in the quality characteristics of the meat during frozen storage. The chickens were reared in a controlled microclimate with an initial stocking density of 9 birds/m2. After 6 weeks of age, fragmentation of the stocking density was applied, and then it diminished to 3 birds/m2. The chickens were slaughtered at 6 and 9 weeks of age. Ten 9-week-old chickens were subjected to carcass analysis. Meat quality parameters (pH, color), degree of proteolysis (free amino groups), and lipid oxidation (content of peroxides and TBARS) were assessed in fresh breast and thigh meat (0 d) and in samples stored for 60 and 120 days at −18 °C in chickens slaughtered at 6 and 9 weeks old. The mean live weight of the male layer-type chickens at 6 weeks was 608.81 g, while the 9-week-old chickens reached 1115.93 g. The feed conversion ratio (FCR) for the whole period of rearing was 2.75. There were no considerable deviations in the meat traits, indicating quality deterioration over the course of the frozen storage. There was a significant increase in the pH of the breast and thighs, reaching maximum values for 60 days of storage in the 6-week-old chicks, while in the 9-week-old birds, pH peaked in the samples stored for 120 days. The changes in the dynamics of pH corresponded to those of proteolysis. There was an increase in lightness (L*), allowing for higher values in the samples stored for 60 days to be reached regardless of the type of meat and age of the chickens. The content of the peroxides increased considerably for 60 days of frozen storage and decreased afterwards. During storage, there was a constant increase in the secondary products of lipid oxidation. Our results indicated that the application of practices such as the fragmentation of stocking density and finding the suitable age for slaughter have significant importance for the profitability of producing meat product from male layer-type chickens. We found that rearing this type of bird until 9 weeks of age resulted in lower costs and higher economic efficiency.

Effects of Animal Diet and Processing Methods on the Quality Traits of Dry-Cured Ham Produced from Turopolje Pigs.

The Turopolje pig (TP) is a local Croatian pig breed that almost became extinct in the second half of the 20th century. Today, the TP is still endangered, and a new conservation strategy based on products with higher added value is needed to preserve the breed. There is little information on the quality of TP meat products such as smoked and dry-cured ham, including the impact of natural feeds or processing innovations such as smoke reduction. This study, therefore, investigated the effects of the animal's diet (either conventionally fed or acorn-supplemented) and the processing method (standard or lightly smoked) on the quality traits of dry-cured TP ham. Twenty hams, evenly distributed among the treatments, were processed for 15 months and then analysed for physicochemical and textural traits, volatiles and sensory profile. The hams from acorn-supplemented pigs lost less weight during processing (p ≤ 0.05). Otherwise, the diet had no significant effect on most examined ham traits. The exceptions were protein content and the texture parameter hardness, which decreased (p ≤ 0.05), and the degree of proteolysis and colour parameters, which increased (p ≤ 0.05) as a result of acorn supplementation. However, these effects were generally small and varied between the inner (m. biceps femoris) and outer (m. semimembranosus) muscles. Furthermore, acorn supplementation was associated with less typical ham odour and lower sensory scores for sweetness and colour uniformity (p ≤ 0.05). The smoke reduction had no effect on the physicochemical and colour properties but resulted in a significant reduction (p ≤ 0.05) in the volatile phenolic compounds and an improved texture to the hams. This was reflected both in reduced (p ≤ 0.05) hardness, identified in the instrumental analysis, and in an increased (p ≤ 0.05) softness, solubility and moistness, identified in the sensory evaluation. To summarize, the quality of the TP ham under the conditions studied was only slightly affected by acorn supplementation, whereas reduced smoking had a more significant effect, which was mainly reflected in an improved texture.

Influence of different milk-clotting enzymes on the quality and shelf life of semihard cheeses

The study examined semi-hard cheeses made with milk-clotting enzymes (MCEs) of animal origin (Naturen Extra with a mass fraction of chymosin 95%, “Bovine Pepsin” with a mass fraction of chymosin 10%), microbial origin (Fromase 750 XLG) and recombinant origin (Chy-max Extra and Chy-max Supreme), at an introduction dose of MCE of 1,500 to 6,000 IMCU per 100 kg of milk. In cheeses at the age of 7, 60, and 150 days, pH, the degree of proteolysis, the content of peptides with a mass of 1–5 kDa, and the compressive stress at fracture were determined. Cheeses produced with a dose of MCE of 5,000–6,000 IMCU/100 kg of milk had a substantially (p&lt;0.05) lower pH compared to cheeses made with doses of MCEs of 1,500–3,000 IMCU/100 kg of milk. At the same time points, there were no significant differences (p&gt;0.05) in the degree of proteolysis between cheeses made using diverse types of MCEs at the same dose. The exceptions were cheeses produced with Chy-max Supreme, which had a substantially (p&lt;0.05) lower level of proteolysis. Sensory assessment of the bitter taste intensity in cheeses is proportional to the content of peptides with a molecular weight of 1–5 kDa. With an increase in the MCE dose, the content of peptides with a molecular weight of 1 to 5 kDa increases in cheese. Chy-max Supreme forms the least number of bitter peptides in cheeses (p&lt;0.05). There are no significant differences (p&lt;0.05) in the magnitude of the compressive stress at fracture between the cheese variants produced with the same MCE doses of diverse types at the same time points.

A comparative analysis of cooked smoked cockerel products derived from male layer-type chickens (Lohmann Brown Classic hybrid) and dual-purpose cocks (based on Bresse Gauloise)

Breeding of chickens is divided in two categories: meat production with focus on the males, and egg production – targeting the females. Culling of male layer-type chickens is a long-standing practice but is now ban some European countries. The dual-purpose cocks (based on Bresse Gauloise) are potential solution to the problem with banned culling practices. The aim of this work is to compare the cooked smoked cockerel products derived from male layer-type chickens (MLC) and dual-purpose cocks (DPC). The highest sensory scores were awarded to the thighs and fillets of the DPC. The hardness, springiness, gumminess, and chewiness, were greater in the thighs of the MLC. In contrast, these parameters were lower in the fillets. The degree of proteolysis in the thighs and fillets of the MLC was greater. The protein content in the tight was not affected by the breed of the cockerels. In contrast higher protein content in MLC fillets was found. Fat or ash content was not affected significantly by the breed of the cockerels. Overall, both breeds of cockerels used for the production of cooked smoked products had a similar and sufficiently high yield, establishing an opportunity for their industrial utilization.

A model to reduce tyrosine crystallization in Chinese fermented soybean curd by adjusting NaCl, ethanol and temperature during fermentation

Abstract Objectives White spots, mainly consisting of tyrosine, refer to small white particles that exist on the surface of mature Chinese fermented soybean curd or in the fermentation broth and have affected the appearance of Chinese fermented soybean curd. Materials and Methods The study determined the composition of the white spots throughout mass spectrometry and high-performance liquid chromatography and investigated the relationship between tyrosine content, amino acid nitrogen content, depth of the proteolysis index and protease activity to interpret the mechanism of white spot formation during fermentation. Results In this study, the results confirm that tyrosine accounts for 78.22% of the white spots. Excessive tyrosine content can promote the formation of white spots during fermentation. Free tyrosine content, amino acid nitrogen content, depth of the proteolysis index and protease activity during the fermentation process increased during fermentation. Correlation analysis results show that free tyrosine content was positively correlated with amino acid nitrogen content, depth of the proteolysis index and protease activity, which showed that the production of tyrosine is related to the degree of proteolysis. Solubility studies show that high concentrations of NaCl and ethanol affect the production of tyrosine and reduce its solubility, while the increase in temperature increases the solubility of tyrosine. Taking NaCl, ethanol and temperature as influencing factors, a mathematical model of tyrosine solubility was established. Conclusion This study lays the groundwork for understanding the mechanism of white spot formation during Chinese fermented soybean curd fermentation and provides solutions for controlling white spot formation.

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.

Proteolytic Changes During Ripening Of Kučki Cheese

Summary Production of various traditional dairy products, particularly cheese, has a long history in Montenegro. White-brined cheeses are the most well-known. One of them is Kučki cheese, with distinct flavor and higher level of proteolysis. The aim of this research was to analyze the proteolysis process during ripening of Kučki cheese. The cheese is produced using traditional technology. FTIR Spectrophotometry was used to calculate the amount of total protein in cheese (IDF141C: 2000). The degree of proteolysis was determined by SDS PAGE (Laemmli, 1970). The cheese was examined for their water-soluble nitrogen (WSN) content using Kuchroo and Fox’s method from 1982, as well as their 5% phosphotungstic acid soluble nitrogen (PTAN) content using Stadhouser’s method from 1960. The results were expressed as percentages of WSN and PTAN of the total nitrogen matter (WSN/TN and PTAN/TN), as well as PTAN as a percentage of WSN (PTAN/WSN). All analyses were done on 10th, 20th and 30th day of cheese ripening. Four samples of cheese were analyzed for each ripening period. The content of proteins increased during the ripening period. The parameters that determine the process of proteolysis increased during the first 30 days of ripening. The WSN/TN ranged from 13.33 to 44.32%. Also, PTAN/WSN varied from 3.79 to 21.57%. The initial results show that uneven ripening conditions have a direct impact on how proteolytic changes develop throughout ripening. Due to the absence of established cheese-making procedures, Kučki cheese has a considerable degree of heterogeneity in their protein content and proteolysis parameters. However, it is not possible to strictly define the optimal values of the degree of ripening for Kučki cheese. In order to reach certain conclusions, it is necessary to carry out further studies focusing on analyzing a larger number of samples.

Changes in Composition of Some Bioactive Molecules upon Inclusion of Lacticaseibacillus paracasei Probiotic Strains into a Standard Yogurt Starter Culture.

Incorporation of probiotic Lacticaseibacillus paracasei into a standard yogurt starter culture can drastically improve its health promoting properties. However, besides being an advantage in itself, the incorporation of a new probiotic strain can significantly affect the overall composition of fermented milk. In this article, the effect of incorporation of the L. paracasei probiotic strains (KF1 and MA3) into several standard yogurt starter cultures (consisting of the following strains: Streptococcus thermophilus 16t and either Lactobacillus delbrueckii Lb100 or L. delbrueckii Lb200) was investigated. Such parameters as the degree of proteolysis, antioxidant activity, ACE-inhibitory activity, content of organic acids, profile of FAs and profile of volatile organic compounds were measured, and the influence of the starter culture composition on these parameters was described. It was demonstrated that, at least in the case of the studied strains, yogurt with L. paracasei had an advantage over the standard yogurt in terms of the content of acetoin, acetic acid, butyric acid and conjugated linoleic acid. Moreover, the incorporation of L. paracasei KF1 significantly improved the hypotensive properties of the resulting yogurt. Thus, the presented study provides insight into the bioactive molecules of probiotic yogurt and may be useful for both academia and industry in the development of new dairy-based functional products.

Properties and structural features of native and modified proteins of concentrates from white and brown rice

The physicochemical properties and structural features of proteins of concentrates (PC) from white and brown rice are described. Differences in a degree of proteolysis and the relationship between the functional and technological properties of proteins and their structure were established. Proteins from white rice had lower molecular weights (MW) than proteins from brown rice: 1.3–199.5 kDa versus 1.5–251.1 kDa. Most proteins were grouped in three low-molecular-weight fractions (МW 11.7–27.5 kDa) in PC from white rice and in one fraction with the high molecular weight (182–251.1 kDa) in PC from brown rice. In the process of hydrolysis, the MW of proteins (high-molecular-weight) of PC from white rice decreased from 199.5 to 120.2 kDa with generation of peptides with a molecular weight of &lt;1.3 kDa, while the MW remained unchanged upon hydrolysis of proteins of PC from brown rice. In the composition of PC from white rice, flavonoids interacted with protein fractions with molecular weights of 131, 10, and 4.0 kDa; while in PC from brown rice, they interacted with only one fraction with a molecular weight of 216 kDa. The quantity of flavonoids in PC from white rice was 2.3 times less than that in PC from brown rice. Elements of protein secondary structure were established for PC: α–helix, 310 — helix, β-structure, β-bends, and irregular shape. Proteolysis of proteins was accompanied by a decrease in the number of α-helices, increase in the proportion of β-structures and irregular regions, weakening of the hydrophobic properties of proteins and an increase in the number of S–S bonds; PC from brown rice was characterized by a higher content of –СН2 groups from the flavonoid family, as well as by a higher degree of unsaturation of groups of benzene nuclei, ketone and ester groups. A negative correlation was found between the foaming ability of PC and the upper boundaries of molecular weights (r = — 0.95), quantity of high-molecular weight proteins (r = — 0.80) and aggregation constants, and a positive correlation (r = + 0.8) with the number of S–S bonds. The high foaming ability is interrelated with proteins with a molecular weight of no more than 120 kDa. The results are intended to regulate the functional properties of protein products based on the characteristics of the physicochemical properties of native and modified proteins.