Evaluation of kefir grain microbiota, grain viability, and bioactivity from fermenting dairy processing by-products

Abstract

Four dairy foods processing by-products (acid whey permeate [AWP], buttermilk [BM], sweet whey permeate [SWP], and sweet whey permeate with added milk fat globule ingredient [SWP+MFGM]) were fermented for 4 wk and compared with traditional kefir milks for production of novel kefir-like dairy products. Sweet whey permeates and SWP supplemented with 1.5% milk fat globule membrane (MFGM) proved to be the most viable by-products for kefir grain fermentation, exhibiting diverse abundance of traditional kefir microorganisms and positive indicators of bioactive properties. Grain viability was assessed with shotgun metagenomics, texture profile analysis, live cell counts, and scanning electron microscopy. Assessed bioactivities of the kefir-like products included antibacterial, antioxidant, potential anticancerogenic properties, and membrane barrier effects on human colorectal adenocarcinoma Caco-2 cells. All kefir grains were most abundant in Lactobacillus kefiranofaciens when analyzed with shotgun metagenomics. When analyzed with live cell counts on selective media, AWP kefir-like product had no countable Lactococcus spp., indicating suboptimal conditions for kefir grain microbiota survival and application for fermented dairy starter culture bacterium. Live cell counts were affirmed with kefir grain surface scanning electron microscopy images. The SWP treatment had the most adhesive kefir grain surface, and SWP+MFGM had the largest exopolysaccharide yield from grain extraction. All kefir and kefir-like products were able to achieve a 6-log reduction against Listeria innocua and Escherichia coli. Traditional milk kefirs had the highest antioxidant capacity for 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid; ABTS) assay. The AWP formulation had a significantly higher DPPH antioxidant activity compared with the other kefir and kefir-like products, and SWP had the lowest Trolox equivalence concentration in the ABTS assay. Sweet whey and supplemented milk fat sweet whey had upregulation of Cldn-1 and Ocln-1 gene expression, which correspond with a significant increase in transepithelial electrical resistance.