Comparison of Biochemical Changes in Kefirs Produced from Organic and Conventional Milk at Different Inoculation Rates of Kefir Grains

The purpose of this study was to assess effects of milk variety (organic and conventional) and the inoculation rate (0.2 g 100 g-1 and 0.5 g 100 g-1) as kefir grains on organic acids, volatile organic compounds (VOCs) and free amino acids (FAAs) as well as basic chemical composition of kefi r. Total organic acids (10.2 g kg-1), total FAA (0.007 g 100 g-) and VOCs such as fatty acids (0.123 g kg-1) and benzene-containing components (0.066 g kg-1) were higher in conventional milk kefir than those (9.54 g kg-1, 0.006 g kg-1, 0.095 g kg-1and 0.042 g kg-1, respectively) in organic milk kefir. Increase in inoculation rate of kefi r grains was directly proportional to increases in succinic and lactic acids, VOCs acetaldehyde, ethanol, ethyl acetate, benzene derivatives, free fatty acids C4, C6 and total FAAs especially proline, tyrosine, cysteine and valine amino acids. As a result, the most biochemical changes in kefir samples showed considerably differences depending on the both inoculation rate of grains and milk origin, and panelists liked kefir made from organic milk with 0.2% inoculation rate as grains due to probably the low lactic acid (6.43 g kg-1), toluene (0.004 g kg-1), butanoic acid (0.010 g kg-1), total FAA (0.006 g kg-1) and the high carbohydrate (54.84 g kg-1) concentrations.