Proteomic analysis of goat milk kefir: Profiling the fermentation-time dependent protein digestion and identification of potential peptides with biological activity

Recent progress in the preparation of bioactive peptides using simulated gastrointestinal digestion processes

Bioactive peptides (BAPs) represent a unique class of peptides known for their extensive physiological functions and their role in enhancing human health. In recent decades, owing to their notable biological attributes such as antioxidant, antihypertensive, antidiabetic, and anti-inflammatory activities, BAPs have received considerable attention. Simulated gastrointestinal digestion (SGD) is a technique designed to mimic physiological conditions by adjusting factors such as digestive enzymes and their concentrations, pH levels, digestion duration, and salt content. Initially established for analyzing the gastrointestinal processing of foods or their constituents, SGD has recently become a preferred method for generating BAPs. The BAPs produced via SGD often exhibit superior biological activity and stability compared with those of BAPs prepared via other methods. This review offers a comprehensive examination of the recent advancements in BAP production from foods via SGD, addressing the challenges of the method and outlining prospective directions for further investigation.

Comprehensive species- and processing-specific peptide profiling of pasteurized, extended shelf-life and ultra-high temperature milk from cow, goat, sheep, buffalo, and mare

The present study aimed to identify endogenous milk peptides for species differentiation independent of heat exposure. Thus, comprehensive milk peptide profiles from five species and three types of heat treatments were analyzed by micro-flow liquid chromatography ion mobility quadrupole time-of-flight mass spectrometry (microLC-IM-QTOF) with subsequent database search leading to ≥ 3000 identified peptides. In the milks, 1154 peptides were unique for cow, 712 for sheep, 466 for goat, 197 for buffalo, and 69 for mare. Most peptides were detected in extended-shelf life (ESL) milk (2010), followed by ultra-high temperature (UHT) processed (1474) and pasteurized milk (1459 peptides), with 693 peptides present in all milk types. A blind test set of 64 samples confirmed eight species-specific, but heat-independent marker peptides in milk from cow, seven from goat, six from sheep, nine from buffalo, and three from mare. The generated peptide profiles can also be used to identify species- and heat-specific markers.

Nutritional and potential health benefits of fermented food proteins

BACKGROUND

Protein fermentation continues to gain popularity as a result of several factors, including the cost-effectiveness of the process and the positive correlation of fermented protein consumption, with a reduced risk of developing diet-related diseases such as diabetes and cardiovascular disorders, as well as their enhanced nutritional and techno-functional properties. Nonetheless, the nutritional and health benefits of food protein fermentation such as enhanced nutrient bioavailability, reduced antinutritional factors (ANFs) and enriched bioactive peptides (BAPs) are often overlooked. The present study reviewed recent work on the influence of protein fermentation on nutrition and health. In total, 322 eligible studies were identified on the Scopus and Google Scholar databases out of which 69 studies were evaluated based on our inclusion criteria.

RESULTS

Fermented protein ingredients and products show reduced ANF content, enhanced digestibility and bioavailability, and increased antioxidant and other biological activities, such as probiotic, prebiotic, angiotensin-converting enzyme inhibitory and antihypertensive properties. In addition, co-products in protein fermentation such as BAPs possess and could contribute additional sensory and flavor properties, degrade toxins, and reduce allergens in foods.

CONCLUSION

Thus, fermentation is not only a method for food preservation, but also serves as a means for producing functional food products for consumer health promotion and nutrition enrichment. © 2023 Society of Chemical Industry.

Modulation of soy protein immunoreactivity by different matrix structures of lactic acid bacterium-induced soy protein gels: Epitope destruction during in vitro gastroduodenal digestion and absorption

Soy allergy is a common health problem. Food structure may change the gastroduodenal digestion and absorption of soy proteins, thus leading to the modulation of the immunoreactivity of soy proteins. In this study, lactic acid bacterium (LAB)-fermented soy protein isolates (FSPIs) were prepared at four concentrations (0.2 %-5.0 %, w/v) to present various matrix structures (nongel, NG; weak gel, WG; medium gel, MG; and firm gel, FG) and subjected to in vitro dynamic gastroduodenal digestion model. The results of sandwich enzyme-linked immunosorbent and human serum IgE binding capacity assays demonstrated that FSPI gels, especially the FSPI-MG/WG digestates obtained at the early and medium stages of duodenal digestion (D-5 and D-30), possessed greater potency in immunoreactivity reduction than FSPI-NG and reduced to 1.9 %-68.3 %. The transepithelial transport study revealed that the immunoreactivity of FSPI-MG/WG D-5 and D-30 digestates decreased through the stimulation of interferon-γ production and the induction of dominant Th1/Th2 differentiation. Peptidomics and bioinformatics analyses illustrated that compared with FSPI-NG, the FSPI-gel structure promoted the epitope degradation of the major allergens glycinin G2/G5, β-conglycinin α/β subunit, P34, lectin, trypsin inhibitor, and basic 7S globulin. Spatial structure analysis showed that FSPI-gel elicited an overall promotion in the degradation of allergen epitopes located in interior and exterior regions and was dominated by α-helix and β-sheet secondary structures, whereas FSPI-MG/WG promoted the degradation of epitopes located in the interior region of glycinin/β-conglycinin and exterior region of P34/basic 7S globulin. This study suggested that the FSPI-gel structure is a promising food matrix for decreasing the allergenic potential of allergenic epitopes during gastroduodenal digestion and provided basic information on the production of hypoallergenic soy products.

A robust nanoLC high-resolution mass spectrometry methodology for the comprehensive profiling of lactic acid bacteria in milk kefir

Consumer attention to functional foods containing probiotics is growing because of their positive effects on human health. Kefir is a fermented milk beverage produced by bacteria and yeasts. Given the emerging kefir market, there is an increasing demand for new methodologies to certify product claims such as colony-forming units/g and bacterial taxa. MALDI-TOF MS proved to be useful for the detection/identification of bacteria in clinical diagnostics and agri-food applications. Recently, LC-MS/MS approaches have also been applied to the identification of proteins and proteotypic peptides of lactic acid bacteria in fermented food matrices. Here, we developed an innovative nanoLC-ESI-MS/MS-based methodology for profiling lactic acid bacteria in commercial and artisanal milk kefir products as well as in kefir grains at the genus, species and subspecies level. The proposed workflow enables the authentication of kefir label claims declaring the presence of probiotic starters. An overview of the composition of lactic acid bacteria was also obtained for unlabelled kefir highlighting, for the first time, the great potential of LC-MS/MS as a sensitive tool to assess the authenticity of fermented foods.

Identification of Potential Bioactive Peptides in Sheep Milk Kefir through Peptidomic Analysis at Different Fermentation Times

Sheep farming is an important socioeconomic activity in most Mediterranean countries, particularly Spain, where it contributes added value to rural areas. Sheep milk is used in Spain mainly for making cheese, but it can be used also for making other dairy products, such as the lactic-alcoholic fermentation product known as kefir. Dairy products have health benefits because, among other reasons, they contain molecules with biological activity. In this work, we performed a proteomics strategy to identify the peptidome, i.e., the set of peptides contained in sheep milk kefir fermented for four different periods of time, aiming to understand changes in the pattern of digestion of milk proteins, as well as to identify potential bioactive peptides. In total, we identified 1942 peptides coming from 11 different proteins, and found that the unique peptides differed qualitatively among samples and their numbers increased along the fermentation time. These changes were supported by the increase in ethanol, lactic acid, and D-galactose concentrations, as well as proteolytic activity, as the fermentation progressed. By searching in databases, we found that 78 of the identified peptides, all belonging to caseins, had potential biological activity. Of these, 62 were not previously found in any milk kefir from other animal species. This is the first peptidomic study of sheep milk kefir comprising time-course comparison.

The Evaluation of Activity of Selected Lactic Acid Bacteria for Bioconversion of Milk and Whey from Goat Milk to Release Biomolecules with Antibacterial Activity

The aim of the study was to assess the antibacterial features of functional macromolecules released during the fermentation of goat milk and whey from goat milk by selected lactic acid bacteria strains that are components of kefir grain microflora. Two milk sources were used: goat milk and whey from goat milk. The lactic acid bacteria (LAB) and indicator microorganisms used were Lactobacillus plantarum PCM 1386, Lactobacillus fermentum PCM 491, Lactobacillus rhamnosus PCM 2677, Lactobacillus acidophilus PCM 2499, Escherichia coli PCM 2793, Salmonella enteritidis PCM 2548, Micrococcus luteus PCM 525, and Proteus mirabilis PCM 1361. The metabolic activity of LAB was described by the Gompertz model, and the parameters proposed for this experiment were the maximum rate of change of electrical impedance and potential biodegradability. Antibacterial activity was examined using the culture method in a liquid medium, determination of the reduction in indicator microorganisms, and optical density changes. Results show that the selective LAB produced certain active biomolecules with antibacterial activity from whey, a by-product that is sometimes troublesome for goat milk processors to manage. Lactobacillus acidophilus is a microorganism that is characterized by the highest metabolic activity in goat milk and whey from goat milk. It has the possibility to produce macromolecules with antibacterial activity.

Bioactive Antimicrobial Peptides from Food Proteins: Perspectives and Challenges for Controlling Foodborne Pathogens

Bioactive peptides (BAPs) derived from food proteins have been extensively studied for their health benefits, majorly exploring their potential use as nutraceuticals and functional food components. These peptides possess a range of beneficial properties, including antihypertensive, antioxidant, immunomodulatory, and antibacterial activities, and are naturally present within dietary protein sequences. To release food-grade antimicrobial peptides (AMPs), enzymatic protein hydrolysis or microbial fermentation, such as with lactic acid bacteria (LAB), can be employed. The activity of AMPs is influenced by various structural characteristics, including the amino acid composition, three-dimensional conformation, liquid charge, putative domains, and resulting hydrophobicity. This review discusses the synthesis of BAPs and AMPs, their potential for controlling foodborne pathogens, their mechanisms of action, and the challenges and prospects faced by the food industry. BAPs can regulate gut microbiota by promoting the growth of beneficial bacteria or by directly inhibiting pathogenic microorganisms. LAB-promoted hydrolysis of dietary proteins occurs naturally in both the matrix and the gastrointestinal tract. However, several obstacles must be overcome before BAPs can replace antimicrobials in food production. These include the high manufacturing costs of current technologies, limited in vivo and matrix data, and the difficulties associated with standardization and commercial-scale production.

Proteomic approach-based comparison of metabolic pathways and functional activities of whey proteins derived from Guishan and Saanen goat milk

Guishan goats, a unique goat breed in Yunnan Province, have a long history and representation, but their whey protein and function remain unclear. In this study, we carried out a quantitative analysis of the Guishan and Saanen goat whey proteome using a label-free proteomic approach. A total of 500 proteins were quantified from the 2 kinds of goat whey proteins, including 463 common proteins, 37 uniquely expressed whey proteins (UEWP), and 12 differentially expressed whey proteins (DEWP). Bioinformatics analysis indicated that UEWP and DEWP were mainly involved in cellular and immune system processes, membrane, and binding. In addition, UEWP and DEWP in Guishan goats participated primarily in metabolism and immune-related pathways, whereas Saanen goat whey proteins were associated mostly with environmental information processing-related pathways. Guishan goat whey promoted the growth of RAW264.7 macrophages more than Saanen goat whey, and significantly reduced the production of nitric oxide in lipopolysaccharide-stimulated RAW264.7 cells. This study provides a reference for further understanding these 2 goat whey proteins and finding functional active substances from them.

Assessment of In Vitro Digestive Behavior of Lactic-Acid-Bacteria Fermented Soy Proteins: A Study Comparing Colloidal Solutions and Curds

This study investigated the effect of lactic-acid-bacteria fermentation on the microstructure and gastrointestinal digestibility of soy proteins using a digestomics approach. Fermented soy protein isolates (FSPIs) under varied fermentation-terminal pH demonstrated a colloidal solution (FSPI-7.0/6.0) or yogurt-like curd (FSPI-5.0/4.0) state. Cryo-electron microscopy figures demonstrated the loosely stacked layer of FSPI-7.0/6.0 samples, whereas a denser gel network was observed for FSPI-5.0/4.0 samples. Molecular interactions shifted from dominant ionic bonds to hydrophobic forces and disulfide bonds. The gastric/intestinal digestion demonstrated that the curd samples afforded a significantly low particle size and high-soluble protein and peptide contents in the medium and late digestive phases. A peptidomics study showed that the FSPI-6.0 digestate at early intestinal digestion had a high peptidome abundance, whereas FSPI curd digestates (FSPI-5.0/4.0) elicited a postponed but more extensive promotion during medium and late digestion. Glycinin G2/G4 and β-conglycinin α/α' subunits were the major subunits promoted by FSPI-curds. The spatial structures of glycinin G2 and β-conglycinin α subunits demonstrated variations located in seven regions. Glycinin G2 region 6 (A349-K356) and β-conglycinin α subunit region 7 (E556-E575), which were located at the interior of the 3D structure, were the key regions contributing to discrepancies at the late stage.

Catalase post-translational modifications as key targets in the control of erythrocyte redox homeostasis in children with obesity and insulin resistance

Insulin resistance (IR) is the most common metabolic disturbance in children with obesity. Children with obesity and insulin resistance (ObIR+) display a detriment in erythroid antioxidant defenses, caused by an impaired catalase activity and the increase in oxidative and pro-inflammatory markers. Therefore, erythrocytes from ObRI+ are more vulnerable to any oxidative stress elicitor. Since catalase is one of the erythrocytes' first antioxidant defenses, we intended to delve into the mechanisms underlying catalase's impaired activity. Given the lack of cellular organelles in erythrocytes, which prevents protein synthesis, we aimed study catalase post-translational modifications (PTMs) as targets of pro-inflammatory and pro-oxidant status of these cells in children with obesity and IR. Catalase levels of O-glycosylation, tyrosine nitration and S-glutathionylation were analyzed by Western blotting (WB) using immunoprecipitated catalase (IP-CAT) from erythrocyte lysates. Furthermore, Catalase was also identified by LC-MS/MS after isolation and enrichment of erythrocyte nitrosated proteins with a biotin switch approach. The results obtained suggest that catalase inhibition seen in children with obesity is partly due to the increase in the S-nitrosation of the enzyme. Indeed, exogenous administration of nitric oxide (NO) to cultured erythrocytes resulted in a decrease in catalase activity in all groups. Signals of other PTMs (O-glycosylation, Tyr-nitration and S-glutathionylation) were also detected in the erythrocyte catalase in every groups, although levels of catalase O-glycosylation and S-glutathionylation decreased in ObIR+. No evidence of differences in Tyr-nitration of catalase levels were found among groups. The study again highlights the role of erythrocytes as sensors of the inflammatory and pro-oxidant response to which these cells are subjected in children with obesity and insulin resistance.

Novel insight into the transformation of peptides and potential benefits in brown fermented goat milk by mesoporous magnetic dispersive solid phase extraction-based peptidomics

Brown fermented goat milk as an excellent source of bioactive peptides has only been partially elucidated. Meticulously synthesized MOF@MG as magnetic sorbent for enriching endogenous peptides owned higher reproducibility and uniform distribution of peptides PI compared with ultrafiltration. Combined with UHPLC-Q-Orbitrap, fermentation for 12 h in brown goat milk with the highest overall acceptable degree through sensory evaluation was utilized to explore the transformation of peptides and health benefits, with trypsin or plasmin hydrolyzing proteins and aminopeptidase or carboxypeptidase hydrolyzing peptides to small peptides or amino acids. A total of 1317 peptides were identified by database matching (1259) and de novo sequencing (58), among 18 peptides could originate from gene-independent enzymatic formation and top 25 characteristic peptides were quantified with concentration ranging from 0.12 to 6.40 mg L^-1. Bioinformatic analysis results indicated that brown fermented goat milk possesses higher health benefits because of more than 50 peptides with potential bioactivity.

Differences in Protein Profiles of Kefir Grains from Different Origins When Subcultured in Goat Milk

Proteins not only serve as a nitrogen source for microorganisms but are the main skeleton of kefir grains. After subculturing in goat milk for 4 months, proteins and peptides in three kefir grains from China, Germany, and the United States were analyzed. Except for the S-layer protein from special Lactobacillus sp., α_s1-casein, α_s2-casein, and β-casein from goat milk were found in kefir grains. These proteins could form aggregates through a covalent interaction with polysaccharides to maintain the morphological stability of the grains. Furthermore, they were highly related to the microbiota in kefir grains. Additionally, a number of hydrophilic/hydrophobic peptides that were hydrolyzed by extracellular proteases were found from kefir grains. A correlation may exist between peptides and Lactobacillus sp. in kefir grains. Bioactive peptides, including DKIHPF, LGPVRGPFP, and QEPVLGPVRGPFP, were found from these kefir grains. The results indicated that goat milk as a substrate affects the protein and peptide composition of kefir grains.

Comprehensive identification of SWI/SNF complex subunits underpins deep eukaryotic ancestry and reveals new plant components

Over millions of years, eukaryotes evolved from unicellular to multicellular organisms with increasingly complex genomes and sophisticated gene expression networks. Consequently, chromatin regulators evolved to support this increased complexity. The ATP-dependent chromatin remodelers of the SWI/SNF family are multiprotein complexes that modulate nucleosome positioning and appear under different configurations, which perform distinct functions. While the composition, architecture, and activity of these subclasses are well understood in a limited number of fungal and animal model organisms, the lack of comprehensive information in other eukaryotic organisms precludes the identification of a reliable evolutionary model of SWI/SNF complexes. Here, we performed a systematic analysis using 36 species from animal, fungal, and plant lineages to assess the conservation of known SWI/SNF subunits across eukaryotes. We identified evolutionary relationships that allowed us to propose the composition of a hypothetical ancestral SWI/SNF complex in the last eukaryotic common ancestor. This last common ancestor appears to have undergone several rounds of lineage-specific subunit gains and losses, shaping the current conformation of the known subclasses in animals and fungi. In addition, our results unravel a plant SWI/SNF complex, reminiscent of the animal BAF subclass, which incorporates a set of plant-specific subunits of still unknown function.

Underlying evidence for the health benefits of fermented foods in humans

Fermented foods (FFs) have been a part of our diets for millennia and comprise highly diverse products obtained from plants and animals all over the world. Historically, fermentation has been used to preserve food and render certain raw materials edible. As our food systems evolve towards more sustainability, the health benefits of FFs have been increasingly touted. Fermentation generates new/transformed bioactive compounds that may occur in association with probiotic bacteria. The result can be specific, advantageous functional properties. Yet, when considering the body of human studies on the topic, whether observational or experimental, it is rare to come across findings supporting the above assertion. Certainly, results are lacking to confirm the widespread idea that FFs have general health benefits. There are some exceptions, such as in the case of lactose degradation via fermentation in individuals who are lactose intolerant; the impact of select fermented dairy products on insulin sensitivity; or the benefits of alcohol consumption. However, in other situations, the results fail to categorically indicate whether FFs have neutral, beneficial, or detrimental effects on human health. This review tackles this apparent incongruity by showing why it is complex to test the health effects of FFs and what can be done to improve knowledge in this field.

Fate of Bioactive Compounds during Lactic Acid Fermentation of Fruits and Vegetables

Consumption of lactic acid fermented fruits and vegetables has been correlated with a series of health benefits. Some of them have been attributed to the probiotic potential of lactic acid microbiota, while others to its metabolic potential and the production of bioactive compounds. The factors that affect the latter have been in the epicenter of intensive research over the last decade. The production of bioactive peptides, vitamins (especially of the B-complex), gamma-aminobutyric acid, as well as phenolic and organosulfur compounds during lactic acid fermentation of fruits and vegetables has attracted specific attention. On the other hand, the production of biogenic amines has also been intensively studied due to the adverse health effects caused by their consumption. The data that are currently available indicate that the production of these compounds is a strain-dependent characteristic that may also be affected by the raw materials used as well as the fermentation conditions. The aim of the present review paper is to collect all data referring to the production of the aforementioned compounds and to present and discuss them in a concise and comprehensive way.

Use of kefir peptide (Kef-1) as an emerging approach for the treatment of oxidative stress and inflammation in 2K1C mice

The benefits of kefir consumption are partially due to the rich composition of bioactive molecules released from its fermentation. Angiotensin-converting enzyme (ACE) inhibitors are bioactive molecules with potential use in the treatment or prevention of hypertension, heart failure, and myocardial infarction. Here, the in vivo actions of the Kef-1 peptide, an ACE inhibitor derived from kefir, were evaluated in an angiotensin II-dependent hypertension model. The Kef-1 peptide showed a potential anti-hypertensive effect. Additionally, Kef-1 exhibited systemic antioxidant and anti-inflammatory activities. In smooth muscle cells (SMCs), the Kef-1 peptide decreased ROS production through the reduced participation of NADPH oxidase and mitochondria. The aorta of 2K1C mice treated with Kef-1 showed lesser wall-thickening and partial restoration of the endothelial structure. In conclusion, these novel findings highlight the in vivo biological potential of this peptide demonstrating that Kef-1 may be a relevant nutraceutical treatment for cardiovascular diseases.

Angiotensin-I-Converting Enzyme Inhibitory Peptides in Goat Milk Fermented by Lactic Acid Bacteria Isolated from Fermented Food and Breast Milk

In this study, angiotensin-I-converting enzyme inhibitory (ACEI) activity was evaluated in fermented goat milk fermented by lactic acid bacteria (LAB) from fermented foods and breast milk. Furthermore, the potential for ACEI peptides was identified in fermented goat milk with the highest ACEI activity. The proteolytic specificity of LAB was also evaluated. The 2% isolate was inoculated into reconstituted goat milk (11%, w/v), then incubated at 37°C until pH 4.6 was reached. The supernatant produced by centrifugation was analyzed for ACEI activity and total peptide. Viable cell counts of LAB and titratable acidity were also evaluated after fermentation. Peptide identification was carried out using nano liquid chromatography mass spectrometry (LC-MS/MS), and potential as an ACEI peptide was carried out based on a literature review. The result revealed that ACEI activity was produced in all samples (20.44%-60.33%). Fermented goat milk of Lc. lactis ssp. lactis BD17 produced the highest ACEI activity (60.33%; IC50 0.297±0.10 mg/mL) after 48 h incubation, viable cell counts >8 Log CFU/mL, and peptide content of 4.037±0.27/mL. A total of 261 peptides were released, predominantly derived from casein (93%). The proteolytic specificity of Lc. lactis ssp. lactis BD17 through cleavage on the amino acid tyrosine, leucine, glutamic acid, and proline. A total of 21 peptides were identified as ACEI peptides. This study showed that one of the isolates from fermented food, namely Lc. lactis ssp. lactis BD17, has the potential as a starter culture for the production of fermented goat milk which has functional properties as a source of antihypertensive peptides.

Effect of enzymatic hydrolyzed protein from pig bones on some biological and functional properties

Pig bone residue is considered a potential source of hydrolysates from its protein with added value uses in the food industry. This work deals with the enzyme hydrolysis of pig bone protein. The conditions for extracting the protein hydrolysate were optimized and the equation obtained allowed samples with different degrees of hydrolysis (DH) to be extracted to study how the biological properties of in-vitro hydrolized protein affected digestibility, determination of the inhibitory activity of the angiotensin-converting enzyme and the antioxidant activity and its functional properties. It was found that the emulsifying capacity and emulsion stability increased at intermediate DH values, after which these properties decreased with the increase in DH. The in-vitro digestibility and angiotensin-converting enzyme (ACE) of the hydrolysates are also clearly affected by the DH. The amino acid composition of the hydrolized protein is also determined.

Foodomic-Based Approach for the Control and Quality Improvement of Dairy Products

The food quality assurance before selling is a needed requirement intended for protecting consumer interests. In the same way, it is also indispensable to promote continuous improvement of sensory and nutritional properties. In this regard, food research has recently contributed with studies focused on the use of 'foodomics'. This review focuses on the use of this technology, represented by transcriptomics, proteomics, and metabolomics, for the control and quality improvement of dairy products. The complex matrix of these foods requires sophisticated technology able to extract large amounts of information with which to influence their aptitude for consumption. Thus, throughout the article, different applications of the aforementioned technologies are described and discussed in essential matters related to food quality, such as the detection of fraud and/or adulterations, microbiological safety, and the assessment and improvement of transformation industrial processes (e.g., fermentation and ripening). The magnitude of the reported results may open the door to an in-depth transformation of the most conventional analytical processes, with the introduction of new techniques that allow a greater understanding of the biochemical phenomena occurred in this type of food.

The Emerging Scenario of the Gut-Brain Axis: The Therapeutic Actions of the New Actor Kefir against Neurodegenerative Diseases

The fact that millions of people worldwide suffer from Alzheimer’s disease (AD) or Parkinson’s disease (PD), the two most prevalent neurodegenerative diseases (NDs), has been a permanent challenge to science. New tools were developed over the past two decades and were immediately incorporated into routines in many laboratories, but the most valuable scientific contribution was the “waking up” of the gut microbiota. Disturbances in the gut microbiota, such as an imbalance in the beneficial/pathogenic effects and a decrease in diversity, can result in the passage of undesired chemicals and cells to the systemic circulation. Recently, the potential effect of probiotics on restoring/preserving the microbiota was also evaluated regarding important metabolite and vitamin production, pathogen exclusion, immune system maturation, and intestinal mucosal barrier integrity. Therefore, the focus of the present review is to discuss the available data and conclude what has been accomplished over the past two decades. This perspective fosters program development of the next steps that are necessary to obtain confirmation through clinical trials on the magnitude of the effects of kefir in large samples.

KFP-1, a Novel Calcium-Binding Peptide Isolated from Kefir, Promotes Calcium Influx Through TRPV6 Channels

INTRODUCTION

Kefir is an acidic and alcoholic fermented milk product with multiple health-promoting benefits. A previous study demonstrated that kefir enhanced calcium absorption in intestinal Caco-2 cells. In this study, kefir-fermented peptide-1 (KFP-1) is isolated from the kefir peptide fraction, and its function as a calcium-binding peptide is characterized.

METHODS AND RESULTS

KFP-1 was identified as a 17-residue peptide with a sequence identical to that of κ-casein (residues 138-154) in milk protein. KFP-1 is demonstrated to promote calcium influx in Caco-2 and IEC-6 small intestinal cells in a concentration-dependent manner. TRPV6, but not L-type voltage-gated calcium channels, is associated with the calcium influx induced by KFP-1. An in vitro calcium binding assay indicates that the full-length KFP-1 peptide has a higher calcium-binding capacity than the two truncated KFP-1 peptides, KFP-1∆C5 and KFP-1C5. Alexa Fluor 594 labeling shows that KFP-1 is taken up by Caco-2 cells and interacts with calcium ions and TRPV6 protein. Moreover, KFP-1 is found moderately resistant to pepsin and pancreatin digestions and enhanced calcium uptake by intestinal enterocytes in vivo.

CONCLUSION

These data suggest that KFP-1, a novel calcium-binding peptide, binds extracellular calcium ions and enters Caco-2 and IEC-6 cells, and promotes calcium uptake through TRPV6 calcium channels. The present study is of great importance for developing kefir-derived metal ion-binding peptides as functional nutraceutical additives.

Proteomic analysis of differentially expressed whey proteins in Saanen goat milk from different provinces in China using a data-independent acquisition technique

Whey proteins of Saanen goat milk samples from 3 provinces in China (Guangdong, GD; Inner Mongolia, IM; Shaanxi, SX) were characterized and compared using data-independent acquisition quantitative proteomics technique. A total of 550 proteins were quantified in all 3 samples. There were 44, 44, and 33 differentially expressed proteins (DEP) for GD versus IM, GD versus SX, and IM versus SX, respectively. Gene ontology annotation analysis showed that the largest number of DEP for the 3 comparisons were as follows: for biological processes: response to progesterone, glyceraldehyde-3-phosphate metabolic process, and negative regulation of megakaryocyte differentiation; for molecular functions: antioxidant activity, binding, and peroxiredoxin activity; and for cellular components: the same category of extracellular regions for the 3 comparisons, respectively. Pathways for the DEP of 3 comparisons were (1) disease; (2) synthesis and metabolism; and (3) synthesis, degradation, and metabolism. Protein-protein interaction network analysis showed that DEP for GD versus SX had the most interactions.

Bioactive peptide release and the absorption tracking of casein in the gastrointestinal digestion of rats

Bovine casein is considered as an important source of many bioactive peptides (BAPs), which can also be produced via in vitro simulated gastrointestinal hydrolysis. To perform their physiological functions, some active peptides need to pass through the intestinal epithelial barrier and keep their structural integrity after oral administration. Owing to the complexity of in vivo digestion and absorption, there have been few studies in this area. In this study, casein was labeled with FITC to trace its digestion and absorption in Sprague Dawley (SD) rats. Gastric juice, intestinal fluid, blood, and intestinal tissue samples were collected at different time-points for preservation and analysis after intragastric administration. The results showed that CN-FITC exhibited good labeling stability in the gastrointestinal digestive juice both in vivo and in vitro, suggesting its potential to be used for the detection and tracking of casein hydrolysate. After the intra-gastric administration of FITC, the diffusion rates of fluorescent substances in serum were much higher than in the CN-FITC group. The maximum peptide content in the CN-FITC group during intestinal digestion was achieved 2 h after administration, and electrophoretic analysis of the hydrolysate composition suggested that the molecular weights of the peptides were mainly concentrated in the range of 3.4-10 kDa. The hydrolyzed peptides from CN-FITC could be absorbed into the blood just 1 h after administration. Frozen sections of rat duodenal tissue were observed under a confocal laser scanning microscope, and they showed that the CN-FITC digested products were absorbed from villi to mucosa in the rat intestines, and the casein-hydrolyzed polypeptides were accumulated significantly in tissue samples 2 h after administration. The peptides were mainly absorbed in the duodenum on the basis of absorption experiments using an everted gut sac. After intestinal digestion for 2 h, peptides with weights less than 5 kDa were enriched and identified using LC-MS-MS, and they were found to be mainly derived from β-casein, containing potential angiotensin-I-converting enzyme inhibitory, antioxidant, dipeptidyl peptidase IV inhibitory, and morphine-like peptides. The peptides from casein hydrolysate were tracked entering the blood through the intestinal epithelial barrier in the form of complete fragments, and they might exert potential physiological activity in vivo.

Storage Stability of Antioxidant in Milk Products Fermented with Selected Kefir Grain Microflora

The aim of the study was to assess the antioxidant potential of goat’s milk and whey from goat’s milk fermented with selected bacteria strains from kefir grain (L. plantarum, L. fermentum, L. rhamnosus and L. acidophilus) with regard to fermented cow’s milk with the same bacteria strains. The assessment of antioxidant potential was made by ABTS, DPPH, TPC and FRAP methods. The work also assessed metabolic activity of tested lactic acid bacteria using measurement of electrical impedance changes in the growing medium. The highest values describing the antioxidant potential were found for fermented milk by L. acidophilus. It was also found that the time of cooling storage causes significantly increasing the antioxidant potential of most analyzed samples. Metabolic activity of tested lactic acid bacteria was the highest for cow’s milk. The course of curves for goat’s milk and whey from goat’s milk was similar, which confirms the differences between cow and goat milk.

Antiviral activity of fermented foods and their probiotics bacteria towards respiratory and alimentary tracts viruses

The recent COVID-19, a viral outbreak calls for a high demand for non-conventional antiviral agents that can reduce the risk of infections and promote fast recovery. Fermented foods and their probiotics bacteria have recently received increasing interest due to the reported potential of high antiviral activity. Several probiotics strains demonstrated broad range of antiviral activities and different mechanisms of action. This article will review the diversity, health benefits, interaction with immune system and antiviral activity of fermented foods and their probiotics bacteria. In addition, the mechanisms of action will be reviewed to determine the broad range potential antiviral activity against the respiratory and alimentary tracts viruses. The probiotics bacteria and bioactive compounds in fermented foods demonstrated antiviral activities against respiratory and alimentary tracts viruses. The mechanism of action was reported to be due to the stimulation of the immune system function via enhancing natural killers cell toxicity, enhance the production of pro-inflammatory cytokines, and increasing the cytotoxic of T lymphocytes (CD3⁺, CD16⁺, CD56⁺). However, further studies are highly recommended to determine the potential antiviral activity for traditional fermented foods.

Functional metaproteomic analysis of alcohol vinegar microbiota during an acetification process: A quantitative proteomic approach

Vinegar is elaborated using a semi-continuous submerged culture of a complex microbiota of acetic acid bacteria. The genus Komagataeibacter provides much of the proteins of the metaproteome, being K. europaeus the main species working in this environment. In this work, the protein profile of the vinegar microbiota, obtained by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in samples from different cycle times of an acetification process using an alcohol medium, has been used to describe the functional metaproteome throughout the process. The analysis was focused on Komagataeibacter species which supplied about 90% of the metaproteome and particularly K. europaeus which accounts for more than 70%. According to these results, the natural behaviour of a microbial community in vinegar has been predicted at a quantitative proteomic level. The results revealed that most of the identified proteins involved in the metabolism of amino acids, biosynthesis of proteins, and energy production related-metabolic pathways increased their expression throughout the cycle loading phase and afterwards experimented a decrease coming into play other proteins acting against acetic acid stress. These findings may facilitate a better understanding of the microbiota's role and contributing to obtain a quality product.

Heat-Treatments Affect Protease Activities and Peptide Profiles of Ruminants' Milk

Proteases present in milk are heat-sensitive, and their activities increase or decrease depending on the intensity of the thermal treatment applied. The thermal effects on the protease activity are well-known for bovine milk but poorly understood for ovine and caprine milk. This study aimed to determine the non-specific and specific protease activities in casein and whey fractions isolated from raw bovine, ovine, and caprine milk collected in early lactation, and to determine the effects of low-temperature, long-time (63°C for 30 min) and high-temperature, short-time (85°C for 5 min) treatments on protease activities within each milk fraction. The non-specific protease activities in raw and heat-treated milk samples were determined using the substrate azocasein. Plasmin (the main protease in milk) and plasminogen-derived activities were determined using the chromogenic substrate S-2251 (D-Val-Leu-Lys-pNA dihydrochloride). Peptides were characterized using high-resolution liquid chromatography coupled with tandem mass spectrometry. The activity of all native proteases, shown as non-specific proteases, was similar between raw bovine and caprine milk samples, but lower (P < 0.05) than raw ovine milk in the whey fraction. There was no difference (P > 0.05) between the non-specific protease activity of the casein fraction of raw bovine and caprine milk samples; both had higher activity than ovine milk. After 63°C/30 min, the non-specific protease activity decreased (44%; P > 0.05) for the bovine casein fraction only. In contrast, the protease activity of the milk heated at 85°C/5 min changed depending on the species and fraction. For instance, the activity decreased by 49% for ovine whey fraction, but it increased by 68% for ovine casein fraction. Plasmin and plasminogen were in general inactivated (P > 0.05) when all milk fractions were heated at 85°C/5 min. Most of the peptides present in heat-treated milk were derived from β-casein and αS1-casein, and they matched the hydrolysis profile of cathepsin D and plasmin. Identified peptides in ruminant milk samples had purported immunomodulatory and inhibitory functions. These findings indicate that the non-specific protease activity in whey and casein fractions differed between ruminant milk species, and specific thermal treatments could be used to retain better protease activity for all ruminant milk species.

A comprehensive review on bioactive peptides derived from milk and milk products of minor dairy species

Abstract

Milk from different species has been exploited for the isolation of various functional ingredients for decades. Irrespective of the source, milk is considered as a complete food, as it provides essential nutrients required by the human body. Proteins and their fractions are valuable sources of bioactive peptides that might exert a health beneficial role in the human body such as immune-modulation, antioxidant activity, ACE-inhibitory activity, anti-neoplastic, anti-microbial, etc. In milk, bioactive peptides may either be present in their natural form or released from their parental proteins due to enzymatic action. The increasing interest in bioactive peptides among researchers has lately augmented the exploration of minor dairy species such as sheep, goat, camel, mithun, mare, and donkey. Alternative to cow, milk from minor dairy species have also been proven to be healthier from infancy to older age owing to their higher digestibility and other nutritive components. Therefore, realizing the significance of milk from such species and incentivized interest towards the derivatization of bioactive peptides, the present review highlights the significant research achievements on bioactive peptides from milk and milk products of minor dairy species.

Graphical abstract

Kefir Peptides Prevent Estrogen Deficiency-Induced Bone Loss and Modulate the Structure of the Gut Microbiota in Ovariectomized Mice

Osteoporosis is a major skeletal disease associated with estrogen deficiency in postmenopausal women. Kefir-fermented peptides (KPs) are bioactive peptides with health-promoting benefits that are produced from the degradation of dairy milk proteins by the probiotic microflora in kefir grains. This study aimed to evaluate the effects of KPs on osteoporosis prevention and the modulation of the composition of the gut microbiota in ovariectomized (OVX) mice. OVX mice receiving an 8-week oral gavage of 100 mg of KPs and 100 mg of KPs + 10 mg Ca exhibited lower trabecular separation (Tb. Sp), and higher bone mineral density (BMD), trabecular number (Tb. N) and bone volume (BV/TV), than OVX groups receiving Ca alone and untreated mice, and these effects were also reflected in bones with better mechanical properties of strength and fracture toughness. The gut microbiota of the cecal contents was examined by 16S rDNA amplicon sequencing. α-Diversity analysis indicated that the gut microbiota of OVX mice was enriched more than that of sham mice, but the diversity was not changed significantly. Treatment with KPs caused increased microbiota richness and diversity in OVX mice compared with those in sham mice. The microbiota composition changed markedly in OVX mice compared with that in sham mice. Following the oral administration of KPs for 8 weeks, the abundances of Alloprevotella, Anaerostipes, Parasutterella, Romboutsia, Ruminococcus_1 and Streptococcus genera were restored to levels close to those in the sham group. However, the correlation of these bacterial populations with bone metabolism needs further investigation. Taken together, KPs prevent menopausal osteoporosis and mildly modulate the structure of the gut microbiota in OVX mice.

Bioactive peptides from food fermentation: A comprehensive review of their sources, bioactivities, applications, and future development

Bioactive peptides (BPs) are specific protein fragments that exert various beneficial effects on human bodies and ultimately influence health, depending on their structural properties and amino acid composition and sequences. By offering promising solutions to solve diverse health issues, the production, characterization, and applications of food-derived BPs have drawn great interest in the current literature and are of particular interest to the food and pharmaceutical industries. The microbial fermentation of protein from various sources is indubitably a novel way to produce BPs with numerous beneficial health effects. Apart from its lower cost as compared to enzymes, the BPs produced from microbial fermentation can be purified without further hydrolysis. Despite these features, current literature shows dearth of information on the BPs produced from food via microbial fermentation. Hence, there is a strong necessity to explore the BPs obtained from food fermentation for the development of commercial nutraceuticals and functional foods. As such, this review focuses on the production of BPs from different food sources, including the extensively studied milk and milk products, with emphasis on microbial fermentation. The structure-activity (antihypertensive, antioxidant, antimicrobial, opiate-like, anti-inflammatory, anticancer/antiproliferative, antithrombotic, hypolipidemic, hypocholesterolemic, and mineral binding) relationship, potential applications, future development, and challenges of BPs obtained from food fermentation are also discussed.

Effects of kefir grains from different origins on proteolysis and volatile profile of goat milk kefir

Microbial diversity in kefir grains is responsible for the production of goat milk kefir with unique peptides composition and volatile profile. High-throughput sequencing technique was used to analyze bacterial and fungal diversity of three different kefir grains which were originated from China, Europe Germany and United States. Peptides and volatile profile in goat milk kefir were determined by proteomic platform and Gas Chromatography-Ion Mobility Spectrometry, respectively. Clustering analysis indicated that the different content of Lactobacillus genera in different kefir grains was highly associated with the proteolytic ability in goat milk kefir. Contents of volatile compounds in goat milk kefir were also correlated to the bacteria and fungi in kefir grains (especially for Lactobacillus spp. and Saccharomyces spp.). The innovation of this study was to find a new way in exploration of the correlation of microbiota in kefir grains with the proteolytic ability and volatile profile of goat milk kefir.

Antimicrobial activity of goat’s milk fermented by single strain of kefir grain microflora

The aim of the study was to assess the antibacterial properties of bioactive compounds released during the fermentation of goat’s milk by selected bacterial strains that are part of the kefir grain microflora. The material used in the experiments was kefir grain microflora (Lactobacillus kefiranofaciens subsp. kefirgranum DSM 10550, Lactobacillus kefiri PCM 2501, Lactobacillus parakefiri DSM 10551, Lactobacillus brevis PCM 488, Lactobacillus delbrueckii subsp. lactis PCM 2611), goat’s and cow’s milk and whey from these kinds of milk. The antimicrobial activity was tested against E. coli, Salmonella, Micrococcus luteus and Proteus mirabilis. Based on the experiments, it was found that during the fermentation of whey and goat's milk, bioactive substances were released, which inhibit the growth of indicator microorganisms by up to 8 logarithmic cycles.

Influence of the production technology on kefir characteristics: Evaluation of microbiological aspects and profiling of phosphopeptides by LC-ESI-QTOF-MS/MS

The influence of production technology, namely, temperature, pH and 2-step fermentation (back-slopping approach), on the microbiological characteristics and on the phosphopeptide profile of kefir obtained with kefir grains was investigated. The growth of yeasts, lactic acid bacteria (LAB) and acetic acetic bacteria (AAB) in both grains and kefir was affected by the incubation temperature and by the use of back-slopping. In particular, at 25 °C the microbiota of kefir grains was mainly composed by LAB and yeasts, while at 18 °C yeasts represented the dominant group in kefir. Back-slopping at 25 °C determined a significant increase of AAB. A comprehensive characterization of potentially bioactive peptides, including caseino-phosphopeptides (CPPs), was performed, for the first time, in kefir obtained with kefir grains, using preliminary enrichment on hydroxyapatite followed by dephosphorylation and analysis by Liquid Chromatography-ElectroSpray Ionization-Quadrupole-Time of Flight-tandem mass spectrometry (LC-ESI-QTOF-MS/MS). As a result, seventy-three phosphopeptides, mostly arising from caseins (79% β-casein, 8% α_s1-casein and 9% α_s2-casein) and all including from three to five serine residues in their sequences, were identified. Seventy-one of them showed the typical motif "SerP-SerP-SerP-Glu-Glu", which is crucial for the ability of caseins to bind to minerals. Several peptides were observed, for the first time, from the 1-40 region of β-casein. As for the effect of production technology, phosphopeptide profiles of kefirs obtained at 25 °C and 18 °C were very similar, whereas kefir produced under acidic conditions showed a predominance of smaller peptides, suggesting a higher level of proteolysis. Conversely, kefir obtained through back-slopping at 25 °C contained longer peptides, thus indicating a lower proteolytic activity and a poor reproducibility in the kefir phosphopeptide profile occurring when grains are reused.