PRODUCTION OF YOGURT FROM SHEEPS MILK WHICH HAD BEEN CONCENTRATED BY REVERSE-OSMOSIS AND STORED FROZEN .1. PHYSICOCHEMICAL, MICROBIOLOGICALAND PHYSICAL STABILITY CHARACTERISTICS OF CONCENTRATES

Some physicochemical, microbiological and physical stability changes i n sheep's milk as a result of concentration by reverse osmosis (RO) an d long-term frozen storage were investigated. Skim milk was concentrat ed by RO to 24-26% total solids (TS), and mixed with cream to obtain r ecombined concentrates with 31.6-35.2% TS. A similar RO concentrate (3 2.1% TS) was prepared from whole milk. The concentrates were frozen an d stored at -20 degrees C for up to 6-8 months. No significant (P > 0. 05) difference in milk lipolysis (acid degree value) was observed betw een the control milk and the fresh or frozen RO milk concentrates. Fat oxidation (peroxide value) of milk was not affected by the RO process , and increased with storage time. The RO process resulted in signific ant (P less than or equal to 0.05) increases in the total bacterial an d coliform counts, which subsequently decreased during frozen storage. The physical stability of the thawed and reconstituted concentrates, especially those prepared from the whole milk, was excellent even afte r 6 months frozen storage. Copyright (C) 1996 Published by Elsevier Sc ience Ltd on behalf of the Canadian Institute of Food Science and Tech nology.