Heat resistance of Escherichia coli O157:H7 in apple juice.

Journal of food protection (1996-03-01)
D F Splittstoesser, M R McLellan, J J Churey
ABSTRACT

The objective was to determine the effect of cider composition on the heat resistance of Escherichia coli O157:H7. The average D52 value in a model Empire apple juice was 18 min with a z value of 4.8 degrees C. Increasing the Brix from 11.8 to 16.5 degrees had no effect on thermal resistance, while increasing L-malic acid from 0.2 to 0.8%, or reducing the pH from 4.4 to 3.6 sensitized the cells to heat. The greatest effect on heat resistance was afforded by the preservatives benzoic and sorbic acids: D50 values in ciders containing 1,000 mg/l were 5.2 min in the presence of sorbic acid and only 0.64 min in the presence of benzoic acid. Commercial apple juice concentrates yielded lower numbers of survivors than single-strength juices even though their higher sugar concentrations of about 46 degrees Brix increased heat resistance.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
L-(−)-Malic acid, ≥95% (titration)
Sigma-Aldrich
L-(−)-Malic acid, ReagentPlus®, ≥99%
Sigma-Aldrich
L-(−)-Malic acid, 97%, optical purity ee: 99% (GLC)
Sigma-Aldrich
L-(−)-Malic acid, suitable for cell culture, BioReagent, suitable for insect cell culture
Sigma-Aldrich
L-(−)-Malic acid, BioXtra, ≥95%
Supelco
L-(−)-Malic acid, certified reference material, TraceCERT®