An evaluation of the effect of catalase and 3,3-thiodipropionic acid on the recovery of freeze-injured coliform bacteria

Abstract

Coliform bacteria isolated from ground beef were frozen in 0.1 M phosphate buffer at −18°C for 72 h. Before and after freezing, colony counts were made in tryptic soy agar (TSA) (Difco) and in TSA supplemented with 680 units of catalase ml − and 1% 3,3-thiodipropionic acid (TDPA), respectively. The two H 2O 2 scavengers exerted no enhancing effect on cell recovery in the non-selective medium. Catalase and TDPA were also added to the TSA bottom layer in the selective dual-plating repair detection procedure described by Ray and Speck [(1978) Appl. Environ. Microbiol. 35, 883–885] using violet red bile agar (VRBA) as the selective medium. After freezing, approximately 70% of surviving cells could be recovered using TSA and TSA supplemented with catalase or TDPA (TSAC, TSAT). A total of 19 samples of various frozen food products (ice cream, pastries, ground meat and vegetables) were examined for coliform bacteria by the repair detection procedure with unsupplemented TSA and TSA with catalase or TDPA. Coliforms were detected in 15 samples. The logarithmic mean colony count with the TSA/VRBA procedure was 1350 g −1. With TSAC/VRBA and TSAT/VRBA the counts were 1590 and 1400 g −, respectively. These counts did not differ significantly from those obtained with unsupplemented TSA/VRBA ( P>0.05).