This study was undertaken to determine whether pretreating inoculated Gala apple slices with
metabisulfite or acidic solutions enhanced the inactivation of Salmonella during
dehydration and storage. Apple slices inoculated with a five-strain mixture of Salmonella (7.6 log CFU/g) were pretreated, dried for 6 h at 60 degrees C, and stored aerobically at 25 degrees C for 28 days. Predrying treatments included (i) no treatment, (ii) 10 min of immersion in sterile water, (iii) 10 min of immersion in a 4.18%
sodium metabisulfite solution, (iv) 10 min of immersion in a 3.40%
ascorbic acid solution, and (v) 10 min of immersion in a 0.21%
citric acid solution. Samples were plated on tryptic soy
agar with 0.1%
pyruvate (
TSAP),
brilliant green sulfa (BGS)
agar, and
xylose lysine tergitol 4 (XLT4)
agar for the enumeration of bacteria. Populations were not significantly (P > 0.05) reduced by immersion in water but were reduced by 0.7 to 1.1 log CFU/g by immersion in acidic solutions. Immersion in the
sodium metabisulfite solution reduced populations by 0.4, 1.3, and 5.4 log CFU/g on
TSAP, BGS
agar, and XLT4
agar, respectively. After 6 h of
dehydration at 60 degrees C, populations on untreated and water-treated slices were reduced by 2.7 to 2.8, 2.7 to 2.9, and 4.0 to 4.2 log CFU/g as determined with
TSAP, BGS
agar, and XLT4
agar, respectively. In contrast, populations on slices treated with
sodium metabisulfite,
ascorbic acid, and
citric acid were reduced after 6 h of
dehydration by 4.3, 5.2, and 3.8 log CFU/g, respectively, as determined with
TSAP; by 4.7, 5.5, and 3.9 log CFU/g, respectively, as determined with BGS
agar; and by 5.5, 5.7, and 5.6 log CFU/g, respectively, as determined with XLT4
agar. Bacteria were still detectable by direct plating after 28 days except on slices treated with
ascorbic acid. Immersion in
metabisulfite or acidic solutions prior to
dehydration should enhance the inactivation of Salmonella during the
dehydration and storage of Gala apple slices.