18D-22 |
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C.-H. LIAO, Food Safety Intervention Technologies Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598 Microbial spoilage accounts for a large proportion of the loss of baby carrots stored at low temperature. One type of spoilage is characterized by its mushy appearance and total disintegration of plant tissues. The microorganisms and the tissue-macerating enzymes involving in this type of spoilage have not yet been investigated. The objectives of this study were to isolate and characterize the pectolytic psychrotrophs associated with spoilage of baby carrots and to analyze the pectin-degrading enzymes produced by pectolytic psychrotrophs in cultures and the corresponding pectinases present in macerated tissue fluids. Macerated tissue fluids were plated onto a pectate-containing agar medium and incubated at 4º C for isolation of pectolytic flora. Bacterial isolates obtained were characterized based on morphological and biochemical properties. Activities of polygalacturonase (PG) and pectate lyase (PL) were determined based on the release of reducing or 4,5-unsaturated oligogalacturonates end products by PG or PL, respectively. Pectolytic pseudomonads, comprising three fluorescent groups similar to P. fluorescens biotypes II, III, and V and a non-fluorescent group similar to P. fragi, accounted for over 20% of total psychrotrophs examined. These pseudomonads produced PL or PG even when grown at refrigeration temperature. Activities of PL or PG were detected in macerated tissue fluids (pH£4). Three strains of lactic acid bacteria tentatively identified as members of Leuconostoc also produced PG at 4ºC. Mesophilic Erwinia and Flavobacterium capable of inducing spoilage only at elevated temperatures (³10ºC) were detected. Spoilage of refrigerated baby carrots may be caused by diverse groups of pectolytic Pseudomonas and Leuconstoc. Production of PL and/or PG by these organisms is detectable both in cultures and in macerated tissues and is assumed to be required for induction of tissue-maceration. Suppressing the growth of pectolytic psychrotrophs possibly represents a critical control point for reducing the spoilage of baby carrots.
Session 18D, Food Microbiology: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |