Abstract
Kefir beverage (KB) is a fermented milk initiated by kefir grains rich with starter probiotics. The KB produced in this study seemed to contain many chemical compounds elucidated by gas chromatography–mass spectrometry (GC-MS) and IR spectra. These compounds could be classified into different chemical groups such as alcohols, phenols, esters, fatty esters, unsaturated fatty esters, steroids, polyalkenes, heterocyclic compounds and aromatic aldehydes. Both KB and neutralized kefir beverage (NKB) inhibited some pathogenic bacteria including Escherichia coli ATCC11229 (E. coli), Listeria monocytogenes ATCC 4957 (L. monocytogenes), Bacillus cereus ATCC 14579 (B. cereus), Salmonella typhimurium ATCC 14028 (Sal. typhimurium) as well as some tested fungal strains such as Aspergillus flavus ATCC 16872 (A. flavus) and Aspergillus niger ATCC 20611 (A. niger), but the inhibitory activity of KB was more powerful than that obtained by NKB. It also appeared to contain four lactic acid bacteria species, one acetic acid bacterium and two yeast species. Finally, the KB inhibited distinctively both S. aureus and Sal. typhimurium bacteria in a brain heart infusion broth and in some Egyptian fruit juices, including those made with apples, guava, strawberries and tomatoes.
Highlights
Natural fermented foods are quite promising for the promotion of human health as they contain natural probiotics that improve many metabolic properties [1,2,3,4,5,6,7,8,9]
The present study aims to (i) investigate kefir’s antimicrobial activity in vitro and in foods, (ii) isolate and identify kefir’s microbiota and (iii) determine kefir’s bioactive compounds by means of available instrumental analysis such as IR spectroscopy and gas chromatography–mass spectrometry (GC-MS) analysis
kefir beverage (KB) was prepared at our experimental conditions at an initial pH value of about 6.5, incubation temperature of 30 ◦C and incubation time of 24 h
Summary
Natural fermented foods are quite promising for the promotion of human health as they contain natural probiotics that improve many metabolic properties [1,2,3,4,5,6,7,8,9]. Other metabolites of probiotics such as organic acids, ethanol, acetaldehydes, and bacteriocins inhibit microbial pathogens [10,11,12]. These probiotic metabolites and other natural agents such as modified proteins of either plant or animal origin as well as plant extracts are quite promising to be used as food additives as they control food spoilage processes and could even kill the resistant variants of bacteria [13,14,15,16,17,18,19]. Yeast and lactic acid bacteria coexisting symbiotically result in milk kefir fermentation [26]
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