Deactivating the bacteria and yeast in kefir using heat treatment, irradiation and high pressure

Kefir was treated by autoclaving, irradiation, ohmic heating and high-press ure treatment. Untreated kefir had 8.58 log cfu g(-1) lactococci, 8.60 log cfu g(-1) lactobacilli and 5.09 log cfu g(-1) total yeasts. Heat treatments (autoclaving, at 110 degreesC for 3 min and ohmic heating-internal tempera ture 72 degreesC) deactivated the bacteria and yeast in kefir. Deactivated kefir had micro-flora counts of 0.59 log cfu g(-1) or less. Changes in the structure of the kefir protein and lipids were seen in transmission electro n micrographs. Irradiation of kefir at 5 kGy, and high-pressure treatment 4 00 MPa 5 or 30 min deactivated the bacteria and yeast in kefir and left the structure of the protein and lipid of the product unchanged. Crown Copyrig ht (C) 2001 Published by Elsevier Science Ltd. All rights reserved.