Inactivation of Salmonella during drying and storage of carrot slices prepared using commonly recommended methods.

Abstract

This study evaluated the influence of drying treatments and aerobic storage (25 degrees C, 30 d) on inactivation of a five-strain mixture of Salmonella (7.8 log colony-forming units [CFU]/g) on carrot slices. Treatments included (1) control, (2) steam blanching (88 degrees C, 3 min), (3) water blanching (88 degrees C, 3 min), (4) immersion in 3.23% NaCl (25 +/- 3 degrees C, 5 min), and (5) oven heating (80 degrees C, 15 min) after drying. Treatments were selected from recommendations made by Cooperative Extension Services for ability to maintain characteristics of dried vegetables and possible antimicrobial effects. Carrot slices were inoculated with the Salmonella mixture, left for 15 min to allow for attachment, then treated (steam blanched, water blanched, or 3.23% NaCl immersion) and dehydrated (60 degrees C, 6 h), or left untreated, dehydrated (60 degrees C, 6 h), and heated (80 degrees C, 15 min). Samples were analyzed by spread-plating on tryptic soy agar with 0.1% pyruvate (TSAP) and xylose lysine deoxycholate (XLD) agar for bacterial enumeration. Initial populations (6.96 to 7.18 log CFU/g) were reduced by 3.2 to 3.3 log CFU/g immediately after steam or water blanching, and by 0.6 log CFU/g following immersion in 3.23% NaCl. After 6 h dehydration, reductions were 1.3 to 2.0 (control), 4.0 to 4.7 (steam blanched), 3.5 to 4.3 (water blanched), and 1.9 to 2.6 (3.23% NaCl) log CFU/g. Reductions on samples heated after drying were 1.7 to 2.4 log CFU/g. All samples had populations > 1.7 log CFU/g after 6 h drying and 30 d storage at 25 degrees C and, therefore, may pose a food safety risk. Modified treatments are needed to further enhance inactivation of Salmonella on dehydrated carrots.