Inactivation of Listeria monocytogenes during drying and storage of peach slices treated with acidic or sodium metabisulfite solutions

This study evaluated whether treating inoculated peach slices with metabisulfite or acidic solutions enhanced inactivation of Listeria monocytogenes during dehydration and storage. Inoculated (five strain mixture of L. monocytogenes, 7.9 log cfu/g) peach slices were treated, dried for 6 h at 60degreesC and stored aerobically at 25degreesC for 14 d. Predrying treatments of inoculated peach slices included: (1) no treatment (control); or 10 min immersion in: (2) sterile water, (3) 4.18% sodium metabisulfite, (4) 3.40% ascorbic acid, or (5) 0.21% citric acid solutions. Samples were plated on tryptic soy agar with 0.1% pyruvate (TSAP) and PALCAM agar for enumeration of surviving bacteria. Immersion in sterile water reduced bacterial populations on peach slices by 0.7 log cfu/g (TSAP and PALCAM). Immersion in the sodium metabisulfite solution reduced populations by 1.5-2.0 log cfu/g, while acidic pretreatments reduced populations by 0.5-0.8 log cfu/g. After 6 h of dehydration, populations on control or water immersed slices were reduced by 3.2-3.4 log cfu/g, whereas populations on slices treated with sodium metabisulfite or acidic solutions were reduced by 4.3-5.1 log cfu/g (TSAP) and 5.3-6.2 log cfu/g (PALCAM), respectively. Bacteria were detectable by direct plating at 14 d of storage, except on acid treated slices. Immersion in acidic or metabisulfite solutions, before dehydration, should enhance inactivation of L. monocytogenes contamination on peach slices during dehydration and storage. (C) 2004 Elsevier Ltd. All rights reserved.