Microbial and quality changes during storage of raw oyster treated with high hydrostatic pressure.

摘要

Effects of high hydrostatic pressure (HHP; 350 MPa for 15 min at 10 or 22 degrees C) on the quality of raw oysters during storage (14 days at 10 degrees C) were investigated. Total viable cell count (TVCC) in untreated oysters increased greatly during storage (1.6 x 102 vs. 5.6 x 109 cfu/ml at day 0 and 4, respectively). In HHP treated oysters, the TVCC increased slowly from approx. 101 cfu/ml at day 0 to approx 103 cfu/ml after 7 days of storage. In untreated oysters, lactic acid bacterial counts (LABC) increased greatly during storage (3.3 x 103 to 7.2 x 109 cfu/ml at days 0 and 4, respectively). In HHP treated oysters, LABC were not detected until day 5 of storage and reached only about 102 cfu/ml after 8 days of storage. In untreated oysters, pH value decreased gradually from 6.19 at day 0 to 5.83 after 4 days of storage. In HHP treated oysters, pH value was 6.07, 6.03 and 5.82 after 4, 8 and 14 days of storage, respectively. In untreated oysters, volatile basic nitrogen (VBN; an index of freshness) was 16.8% at day 0 but increased rapidly from day 1 to a value of 30.1 mg% after 4 days of storage. In HHP treated oysters, VBN remained fairly constant during storage (20 and 23 mg% after 4 and 8 days of storage, respectively). Hunter L*, a* and b* values increased during days 1-2 of storage but then remained fairly constant with increasing storage time. Demerit scores were compared between untreated and HHP-treated oysters. Demerit scores increased as follows: untreated raw oysters at day 0 of storage < HHP-treated oysters (4 and 8 days storage) < untreated oysters (4 days of storage).