Characterization and association of bacterial communities and nonvolatile components in spontaneously fermented cow milk at different geographical distances

Comparative analyses of the bacterial communities present in the spontaneously fermented milk products of Northeast India and West Africa

Introduction

Spontaneous fermentation of raw cow milk without backslopping is in practice worldwide as part of the traditional food culture, including "Doi" preparation in earthen pots in Northeast India, "Kindouri" of Niger and "Fanire" of Benin prepared in calabash vessels in West Africa. Very few reports are available about the differences in bacterial communities that evolved during the spontaneous mesophilic fermentation of cow milk in diverse geographical regions.

Methods

In this study, we used high throughput amplicon sequencing of bacterial 16S rRNA gene to investigate 44 samples of naturally fermented homemade milk products and compared the bacterial community structure of these foods, which are widely consumed in Northeast India and Western Africa.

Results and discussion

The spontaneous milk fermentation shared the lactic acid bacteria, mainly belonging to Lactobacillaceae (Lactobacillus) and Streptococcaceae (Lactococcus) in these two geographically isolated regions. Indian samples showed a high bacterial diversity with the predominance of Acetobacteraceae (Gluconobacter and Acetobacter) and Leuconostoc, whereas Staphylococcaceae (Macrococcus) was abundant in the West African samples. However, the Wagashi cheese of Benin, prepared by curdling the milk with proteolytic leaf extract of Calotrophis procera followed by natural fermentation, contained Streptococcaceae (Streptococcus spp.) as the dominant bacteria. Our analysis also detected several potential pathogens, like Streptococcus infantarius an emerging infectious foodborne pathogen in Wagashi samples, an uncultured bacterium of Enterobacteriaceae in Kindouri and Fanire samples, and Clostridium spp. in the Doi samples of Northeast India. These findings will allow us to develop strategies to address the safety issues related to spontaneous milk fermentation and implement technological interventions for controlled milk fermentation by designing starter culture consortiums for the sustainable production of uniform quality products with desirable functional and organoleptic properties.

Influence of Fermentation Container Type on Chemical and Microbiological Parameters of Spontaneously Fermented Cow and Goat Milk

Fermented goat milk is an artisanal beverage with excellent nutritional properties. There are limited data on its physicochemical properties, fatty acids, phenolic acids, and on any insight on microbiota. The aim of this research was to conduct a pilot study to compare these parameters in raw cow and goat milk before and after spontaneous fermentation in a clay pot and glass container at 37 °C for 24 h. Both types of milk and fermentation containers significantly affected the pH, acidity, proximate composition, viscosity, and whiteness index of fermented milks. A total of 17 fatty acids were identified in fermented milks, where palmitic, stearic, and myristic were the main saturated acids, and oleic and linoleic acids were the main unsaturated ones. These profiles were primarily influenced by the type of raw milk used. Three to five phenolic acids were identified in fermented milks, where quinic acid was the major phenolic compound, and salviolinic acid was identified only in raw goat milk. Preliminary metataxonomic sequencing analysis showed that the genera Escherichia spp. and Streptococcus spp. were part of the microbiota of both fermented milks, with the first genus being the most abundant in fermented goat milk, and Streptococcus in cow's milk. Moreover, Escherichia abundance was negatively correlated with the abundance of many genera, including Lactobacillus. Overall, the results of this pilot study showed significant variations between the physicochemical properties, the fatty and phenolic acids, and the microbial communities of goat and cow fermented milk, showing the opportunity to further investigate the tested parameters in fermented goat milk to promote its production.

Traditional Fermented Dairy Products in Southern Mediterranean Countries: From Tradition to Innovation

Fermented dairy products have been essential elements in the diet of Southern Mediterranean countries for centuries. This review aims to provide an overview of the traditional fermented products in Southern Mediterranean countries, with a focus on fermented dairy products, and to discuss innovative strategies to make improved versions of these traditional products. A large variety of fermented dairy products were reviewed, showing high diversity, depending on the used raw materials, starter cultures, and preparation procedures. Traditionally, dairy products were fermented using spontaneous fermentation, back-slopping, and/or the addition of rennet. Compared with commercial products, traditional products are characterized by peculiar organoleptic features owing to the indigenous microflora. The main limitation of traditional products is preservation as most products were consumed fresh. In addition to drying, brine or oil was used to extend the product shelf life but resulted in high salt/fat products. Several studies suggested alternative ingredients/processing to make revised products with new flavors, improved nutritional quality, and a longer shelf life. There is still plenty of room for more research to obtain a better understanding of the indigenous microflora and on quality improvement and standardization to reach a wider market.

Dairy streptococcal cell wall and exopolysaccharide genome diversity

The large-scale and high-intensity application of Streptococcus thermophilus species in milk fermentation processes is associated with a persistent threat of (bacterio)phage infection. Phage infection of starter cultures may cause inconsistent, slow or even failed fermentations with consequent diminished product quality and/or output. The phage life cycle commences with the recognition of, and binding to, a specific host-encoded and surface-exposed receptor, which in the case of S. thermophilus can be the rhamnose-glucose polysaccharide (RGP; specified by the rgp gene cluster) or exopolysaccharide (EPS; specified by the eps gene cluster). The genomic diversity of 23 S . thermophilus strains isolated from unpasteurized dairy products was evaluated, including a detailed analysis of the rgp and eps loci. In the present study, five novel eps genotypes were identified while variations of currently recognized rgp gene cluster types were also observed. Furthermore, the diversity of rgp genotypes amongst retrieved isolates positively correlated with phage diversity based on phageome analysis of eight representative dairy products. Our findings therefore substantially expand our knowledge on S. thermophilus’ strain and phage diversity in (artisanal) dairy products and highlight the merit of phageome analysis of artisanal and traditional fermented foods as a sensitive marker of dominant microbiota involved in the fermentation.

Different growth behaviors and metabolomic profiles in yogurts induced by multistrain probiotics of Lactobacillus casei Zhang and Bifidobacterium lactis V9 under different fermentation temperatures

The growth behaviors and metabolomic profiles in yogurts induced by multistrain probiotics of Lactobacillus casei Zhang (LCZ) and Bifidobacterium lactis V9 (V9) at the fermentation termination and 10 d of storage at 4°C under different fermentation temperatures (37°C and 42°C) were compared using metabolomics based on liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. The growths of LCZ and V9 were affected by fermentation temperatures; the viable cell density of LCZ was higher at 37°C than that at 42°C; however, V9 was higher at 42°C. Multistrain probiotics had higher contribution to the changes in volatile and nonvolatile metabolomic profiles at 42°C than those at 37°C. At fermentation termination, there were 2 common enriched pathways increased by multistrain probiotics at 37°C and 42°C, which were biosynthesis of peptides and amino- and nucleotide-sugar metabolism. At 10 d of storage, 4 common increased enriched pathways were alanine, aspartate and glutamate metabolism; tyrosine metabolism; valine, leucine, and isoleucine degradation; and valine, leucine, and isoleucine biosynthesis. This work provided a detailed insight into different effects of different multistrain probiotics of LCZ and V9 fermentation temperatures on the growth behaviors and volatile and nonvolatile metabolomic profiles of yogurts.