Abstract
Kefir grains represent a symbiotic association group of yeasts, lactic acid bacteria and acetic acid bacteria within an exopolysaccharide and protein matrix known as kefiran. The mechanism of growth of a biomass of kefir after successive fermentations and optimal conditions is not well understood yet. Biomass growth kinetics were determined to evaluate the effects of temperatures (10 °C to 40 °C) and different substrates, such as monosaccharides (fructose, galactose, glucose), disaccharides (lactose, saccharose) and polysaccharides (Agave angustifolia fructans) at 2%, in reconstituted nonfat milk powder at 10% (w/v) and inoculated with 2% of milk kefir grain (105 CFU/g), after determining the pH kinetics. The best conditions of temperature and substrates were 20 °C and fructans and galactose. An increase in cells, grain sizes and a change in the morphology of the granules with the best substrates were observed using environmental scanning electron microscopy, confocal laser scanning microscopy and Image Digital Analysis (IDA). Kefir grains with agave fructans as their carbon source showed the higher fractal dimension (2.380), related to a greater co-aggregation ability of LAB and yeasts, and increase the formation of exopolysaccharides and the size of the kefir grains, which opens new application possibilities for the use of branched fructans as a substrate for the fermentation of milk kefir grains for the enhancement of cellular biomasses and exopolysaccharide production, as well as IDA as a characterization tool.
Highlights
Throughout history, water kefir and milk kefir have been consumed, both of which are produced from gelatinous particles called kefir granules
The objective of this study was to perform growth kinetics during milk kefir fermentation to determine the best fermentation conditions using monosaccharides, disaccharides and polysaccharides at different temperatures to determine their influence on the microbial content and morphological changes of kefir granules under environmental scanning electron microscopy (ESEM), confocal laser scanning microscopy (CLSM) and Image Digital Analysis (IDA)
Acetic acid is derived from carbohydrate metabolism, but a proportion is originated during fermentation because of yeast metabolism, which has been derived from an incomplete tricarboxylic acid cycle
Summary
Throughout history, water kefir and milk kefir have been consumed, both of which are produced from gelatinous particles called kefir granules. Milk kefir is a fermented dairy product from the Caucasus, Tibet and Mongolia consumed for its biological activity and functional properties as an antimicrobial, antibacterial, anti-inflammatory, immunomodulating, antioxidant, antihypertensive and hypocholesterolemic, among others [2–6], which are associated with its microbiological and physicochemical composition, as well as its possible application in the food industry or materials, such as gelling, texturizing, rheology or packaging [2], which are associated with its microbiological and physicochemical composition It is produced by the action of lactic acid bacteria, acetic acid bacteria and yeasts, which are embedded in a rubbery matrix known as kefir grain, composed of insoluble proteins and polysaccharides, which live symbiotically [6–8]. During the fermentation of sugars, valuable products such as exopolysaccharides (kefiran), organic acids (acetic acid, lactic acid) and volatile substances (ethyl acetate, acetaldehyde) are generated, in addition to the production of alcohol that gives flavor and increases the aroma of the final product, helping to improve the organoleptic properties [2,11,12]
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