CORRELATION BETWEEN CITRIC ACID,THYMUS VULGARISEXTRACT AND NaCl, AND HEAT SENSITIVITY AND CASEINASE PRODUCTION BYAEROMONAS CAVIAEANDA. SOBRIA

Abstract

The effects of citric acid, Thymus vulgaris extract and NaCl on the heat sensitivity of Aeromonas spp. were examined in three different situations in this study. First, the effects of pretreatment with nutrient broth plus 0.03% citric acid, nutrient broth plus 0.3% T. vulgaris extract, nutrient broth plus 2.5% NaCl or nutrient broth plus 3% NaCl on the survival and caseinase production by heated A. caviae 166 and A. sobria 74 were investigated. Pretreatment of Aeromonas spp. with these preservatives for 1 or 6 days significantly increased their resistance to subsequent heating at 54C. However, pretreatment of Aeromonas strains with nutrient broth plus 2.5% NaCl or nutrient broth plus 3% NaCl before heating at 54C significantly (P < 0.05) decreased the production of caseinase by the heated cells. Second, the effect of post‐treatment with preservatives after heating of Aeromonas strains was examined. Post‐treatment of Aeromonas strains with the tested preservatives for 7 days after heating at 54C for 20 min prevented a complete recovery of cells and decreased the caseinase production compared with Aeromonas cells that were incubated in nutrient broth alone for 7 days after heating at 54C. Third, the effect of the type of the heating menstruum on the heat sensitivity of Aeromonas strains was investigated in this study. Heating in NaCl (0.85%) containing citric acid (0.03%) was the most effective treatment in killing Aeromonas spp. Heating in NaCl (0.85%) containing T. vulgaris extract (0.3%) or in NaCl (3.85%) slightly increased the resistance of cells to heat. PRACTICAL APPLICATIONS The results obtained in this study can be applied in the food industry, where combination of mild heat treatment and addition of low doses of chemical preservatives to food is nowadays frequently used. This study determined the heat sensitivity and caseinase production by A. caviae and A. sobria at three different conditions that may be encountered during processing of food industrially or at home. Firstly, the effect of pretreatment with some preservatives on the heat sensitivity and caseinase production by the tested Aeromonas. spp. was studied. Secondly, the effect of post‐treatment with preservatives on growth and caseinase production by the heated (54C) Aeromonas cells was investigated. Thirdly, effect of presence of preservatives in the heating menstruum on the heat sensitivity of Aeromonas spp. was studied.