Effect of frozen storage on some characteristics of kefir samples made from cow's and goat's milk

This study was aimed to determine the changes in kefir samples (CK and GK) made from cow's and goat's milk during frozen storage. The CK and GK samples were first stored at +4 degrees C for 14 and 21 days. Thereafter, all the samples were frozen at -35 degrees C for 24 h and kept at -18 degrees C for 45 days. There was no significant change in the fat, protein, acidity and pH values in both samples during the storage. The values of viscosity, WI and C* were higher in the CK samples while the syneresis value was higher in the GK samples throughout the frozen storage. The microorganisms (Lactococcus spp., Lactobacillus spp., Leuconostoc spp., total mesophilic aerobic bacteria and yeasts) found in kefir made from goat's milk were more affected from the frozen storage. In both samples, the changes in organic acids and volatile flavor components were not significant during frozen storage, except acetic, citric and oxalic acids and acetaldehyde in GK sample. In addition, CK samples were preferred sensorially more by the panellists during frozen storage.