45G-20 |
Storage effect on esterase activity in fresh-cut cantaloupe melon |
O. LAMIKANRA and M. A. Watson. Food Processing & Sensory Quality Research Unit, USDA-ARS-Southern Regional Research Center, 1100 Robert E. Lee Blvd., PO Box 19687, New Orleans, LA 70179-0687 Esters, particularly those with acetate as the acyl portion, constitute one of the most important classes of compounds that impact the aroma of fruits. In cut fruits and vegetables, increased interaction of enzymes with their substrates occurs as a result of the loss of internal compartmentation that keeps them separate. Wound stress, such as that induced as a consequence of tissue disruption in cut fruits and vegetables may cause cleavage of acyl groups in esters as part of the plant tissue defense response. Recent studies indicate that refrigerated storage of cut cantaloupe melon caused significant decreases in concentration of esters over a period of 24 h. The objective of this study was to determine the effect of storage time and temperature on esterase enzymes in fresh-cut cantaloupe melon and how this might affect loss of ester compounds in the fruit. Esterase activity in cut cantaloupe melon stored at 4 and 15 oC was monitored spectrophometrically by measuring the production of p-nitrophenol from p-nitrophenyl acetate substrate. Enzymatic activity, after 24 h in storage, was reduced by 40% and 10% in fruit stored at 4 oC and 15 oC, respectively. Esterase in cantaloupe melon was determined by isoelectric focusing to be carboxylesterase with 2 isozymes (pI=6.1 and pI=9.5) and low thermal stability. The inhibitive effects of Zn2+, Cu2+, and Ni2+ (40, 62 and 85% respectively) and the non-inhibitory action of eserine, EDTA, and phenylacetic acid on enzymatic activity indicate that esterase enzyme in cantaloupe melon is regulated by metalloproteases, presumably metallo-exoproteases. The loss of enzymatic activity during storage of the cut fruit observed in this study and the previously reported loss of esters that occurred under identical storage conditions suggest a non-rate limiting enzymatic initiation of the ester degradation process right after the fruit is cut.
Session 45G, Fruit & Vegetable Products: Vegetables (Fresh)
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