Prominent strains of kefir grains in the formation of volatile compound profile in milk medium; the role of Lactobacillus kefiranofaciens subsp. kefiranofaciens, Lentilactobacillus kefiri and Lentilactobacillus parakefiri

Development of probiotic yogurt products incorporated with Lactobacillus kefiranofaciens OSU-BSGOA1 in mono- and co-culture with Kluyveromyces marxianus

The bacterium Lactobacillus kefiranofaciens OSU-BDGOA1 and yeast Kluyveromyces marxianus bdgo-ym6 were previously isolated from kefir grains and have shown probiotic traits in mono- and coculture. This research evaluates the effect of introducing probiotic kefir microorganisms in monoculture and in coculture alongside yogurt starter cultures on the physicochemical and rheological properties, volatile flavor compounds, survival of the microorganisms during simulated digestion, and sensory attributes of the final fermented products. The incorporation of Lactobacillus kefiranofaciens OSU-BDGOA1 in monoculture showed promising outcomes, resulting in a final product showing more solid-like characteristics and potentially improving the texture of the product. There was also a significant increase in the concentration of desirable volatile flavor compounds in the yogurt with the monoculture, particularly 2,3-butanedione, displaying a positive correlation with buttery flavor in the sensory analysis. The inclusion of L. kefiranofaciens in monoculture also promoted better sensory attributes and was significantly better than the yogurt with the coculture with the yeast showing promising results for the incorporation of this probiotic bacterium into functional fermented dairy products.

Dynamic alterations of flavor, functional nutrients, and microbial community during fermentation of different animal milk kefirs

Kefir is a traditional dairy beverage, usually made from cow or goat milk fermented with kefir grains, and has many health benefits. To elucidate the fermentation patterns of animal milk kefirs during the fermentation process and find the optimal milk types, cow, camel, goat, and donkey milk were fermented with kefir grains for 0, 1, 3, 5, and 7 days. Volatile and non-volatile metabolites and microbial changes were dynamically monitored. The results showed that volatile flavor substances were massively elevated in four kefirs on days 1-3. Lipids and carbohydrates gradually decreased, while amino acids, small peptides, and tryptophan derivatives accumulated during fermentation in four kefirs. Besides, four kefirs had similar alterations in Lactobacillus and Acetobacter, while some distinctions existed in low-abundance bacteria. Association analysis of microorganisms and volatile and non-volatile metabolites also revealed the underlying fermentation mechanism. This study found that appropriately extending the fermentation time contributed to the accumulation of some functional nutrients. Furthermore, goat and donkey milk could be the better matrices for kefir fermentation.

Ginger beer derived from back-slopping: Volatile compounds, microbial communities on activation and fermentation, metabolites and sensory characteristics

Physicochemical parameters, microbial diversity using sequencing and amplicon, and metabolite concentrations from Ginger Bug and Ginger Beer were characterized. Furthermore, the sensory aspects of the beverage were determined. The longer ginger bug activation time (96 h) resulted in higher production of organic acids and alcohols, increased phenolic and volatile compounds concentration, greater microbial diversity, and increased lactic acid bacteria and yeasts. In the same way, the longer fermentation time (14 days) of ginger beer resulted in higher ethanol content, volatile compounds, and phenolic compounds, in addition to better sensory characteristics. Our results showed that ginger beer produced with ginger bug and fermented for 14 days showed better volatile and phenolic compound profiles, physicochemical parameters, microbial diversity, and sensory characteristics.

Microbial communities and main features of labneh Ambaris, a traditional Lebanese fermented goat milk product

Labneh Ambaris is a traditional Lebanese dairy product typically made using goat milk in special earthenware jars. Its production is characterized by the regular additions of milk and coarse salt, all while draining the whey throughout a process that lasts for a minimum of 2 mo. In this study, 20 samples of labneh Ambaris, all produced by spontaneous fermentation, were studied. They were collected at the end of fermentation from different regions in Lebanon. Physicochemical and sensory properties were studied and microbial diversity was analyzed using culture-dependent and independent techniques. The V3-V4 region of the 16S rRNA gene and the ITS2 region were sequenced by DNA metabarcoding analyses for the identification of bacteria and yeast communities, respectively. Out of 160 bacterial and 36 fungal taxa, 117 different bacterial species and 24 fungal species were identified among all labneh Ambaris samples studied. The remaining ones were multi-affiliated and could not be identified at the species level. Lactobacillus was the dominant bacterial genus, followed by Lentilactobacillus, Lactiplantibacillus, Lacticaseibacillus, and Lactococcus genera, whereas Geotrichum and Pichia were the dominant fungal genera. The 20 samples tested had varying levels of salt, protein, and fat contents, but they were all highly acidic (mostly having a pH < 4). According to the sensory scores generated by classical descriptive analysis, all samples were described as having basic similar characteristics such as goat smell and flavor, but they could be differentiated based on various intensities within the same descriptors like salty and acidic. This work could be considered as a base toward obtaining a quality label for labneh Ambaris.

Design and Volatile Compound Profiling of Starter Cultures for Yogurt Preparation

Stable symbiotic starter cultures were created using selected strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus with antimicrobial activity against pathogens and necessary antibiotic sensitivity, growth kinetic parameters, and metabolic profiles. The volatile compound profiles of the obtained starter cultures were determined and their specificity was proven depending on the ratio of monocultures in each combination. The influence of the freeze-drying process on the starter cultures in relation to the production of aromatic components was investigated and it was demonstrated that this process had a significant effect on the content of the aroma-forming substances in the fermented milk. However, the influence of the pre-cooling process and crude fat content from 1.5 to 3.0% did not notably affect the levels of volatile compounds synthesized by the selected starter cultures. Comprehensive data for all volatile aromatic metabolites in the fermented milk were also obtained. These designed symbiotic starter cultures can be used to produce traditional Bulgarian yogurt with increased functional and probiotic properties.

Physical and chemical properties, structural characterization and nutritional analysis of kefir yoghurt

Scanning electron microscopy (SEM), Confocal laser scanning microscopy (CLSM) and low field nuclear magnetic resonance (LF-NMR) were used to analyse the relationship between the chemical, texture, rheology, microstructure and water distribution of kefir (yeast, acetic acid bacteria and Lactobacillus plantarum) yoghurt fermented by mixed bacteria and L. plantarum L₁ fermented yoghurt. This work was conducted to prepare a real champagne yoghurt and explore the difference between it and ordinary yoghurt. The nutritional evaluation of the two treatment groups was carried out by amino acid analysis, and the volatile flavour substances of the two treatment groups were detected by solid phase microextraction (SPME)-gas chromatograph (GC)-mass spectrometry (MS). Results showed that the addition of acetic acid bacteria and yeast increased the water content of kefir, resulting in a decrease in its water-holding rate. Moreover, the increase in acidity weakened the connection between the protein networks, the flocculent protein structure was not more densely stacked than the L₁ group, and the internal bonds were unstable. The rheological results showed that the apparent viscosity decreased faster with the increase in shear force. The CLSM and LF-NMR showed that the hydration and degree of freedom of kefir yoghurt protein decreased, resulting in an increased protein network density. The SEM showed that the cross-linking between kefir casein clusters was considerably tight to form small chains, the pore distribution was uneven, and a weak cheese structure was formed. In addition, the volatile flavour substances in the kefir group increased the phenylethyl alcohol, isobutanol, and isoamyl alcohol compared with those in the L₁ group, with a slight refreshing taste brought by alcohol and special soft malt alcohol aroma and rose aroma not found in ordinary yoghurt, which was more in line with the characteristics and taste of traditional kefir champagne yoghurt. Graphical Abstract.

A multi-functional survey of the properties of Lacticaseibacillus paracasei subsp. tolerans NOC-122, Levilactobacillus parabrevis NOC-111 and Latilactobacillus curvatus NOC-110

This study aimed to reveal the physicochemical and organoleptic effects of three functional lactic acid bacteria (LAB) isolates in a milk medium: Lacticaseibacillus paracasei subsp. tolerans NOC-122, Levilactobacillus parabrevis NOC-111 and Latilactobacillus curvatus NOC-110. A total of 200 indigenous LAB strains isolated from artisanal tulum cheeses were screened for potential proteolytic and lipolytic activity, citrate-lyase-synthesizing and exopolysaccharide-producing ability. Furthermore, a total of six fermented products were produced using these strains as a single culture or as a co-culture. The physicochemical and microbiological properties, angiotensin-converting-enzyme (ACE) inhibitor activity, and the amino acid and volatile aroma compound profiles were determined. According to the results, NOC-110 and NOC-122 were effective in increasing ACE-inhibitory activity. On the other hand, NOC-122 was responsible for a fresh cheesy, slightly oily flavour when used as a single culture. NOC-111 gave a fresh, fruity and slightly herbal flavour; NOC-110 gave a flavour similar to that of NOC-122 when they were used as a single culture. Also, co-cultures of the strains were investigated. The results of the study provide a guide to the usability of these isolates as single or co-cultures in the production of dairy-based food. These findings can be of value for many future studies and innovative food products.

Volatile Composition and Sensory Profile of Lactose-Free Kefir, and Its Acceptability by Elderly Consumers

Lactose-free products are crucial in the diet of lactose-intolerant elderly consumers, one of them being kefir due to its unique chemical composition and diversity of valuable microflora. The study aimed at determining the volatile compound profile and the corresponding sensory attributes of lactose-free kefir (LFK) as compared with the traditional one (TK). The perception of main sensory attributes and hedonic acceptability of LFK by elderly were also studied. The LFK contained two times more ketones, especially 3-hydroxy-2-butanone and 2,3-butanedione, that probably contributed to the high intensity of creamy aroma. A substantial share of acetic acid in LFK was not associated with high intensity of sour aroma, probably being masked by the creamy aroma, perceived as dominating. LFK was sensed as sweeter and more milky than the traditional one. The intense sweet taste of LFK was due to higher amounts of glucose and galactose than in TK, and was perceived as “just about right” by 63% of elderly subjects in the just-about-right (JAR) scale. The lower acidity of LFK than that of TK, assayed both instrumentally and by sensory assessment, was highly appreciated by 73% of elderly subjects as “just about right” in JAR scale. These two taste attributes dominated in liking the lactose-free kefir by elderly subjects.

Traditional Grain-Based vs. Commercial Milk Kefirs, How Different Are They?

Traditional kefir, which is claimed for health-promoting properties, is made from natural grain-based kefir, while commercial kefirs are made of defined mixtures of microorganisms. Here, approaches are described how to discriminate commercial and traditional kefirs. These two groups of kefirs were characterized by in-depth analysis on the taxonomic and functional level. Cultivation-independent targeted qPCR as well as next-generation sequencing (NGS) proved a completely different microbial composition in traditional and commercial kefirs. While in the traditional kefirs, Lactobacillus kefiranofaciens was the dominant bacterial species, commercial kefirs were dominated by Lactococcus lactis. Volatile organic compounds (VOCs) analysis using headspace-gas chromatography-ion mobility spectrometry also revealed drastic differences between commercial and traditional kefirs; the former built a separate cluster together with yogurt samples. Lactose and galactose concentrations in commercial kefirs were considerably higher than in traditional kefirs, which is important regarding their health properties for people who have specific intolerances. In summary, the analyzed commercial kefirs do not resemble the microbial community and metabolite characteristics of traditional grain-based kefir. Thus, they may deliver different functional effects to the consumers, which remain to be examined in future studies.