20-2 |
Optimizing firmness improvement of vegetables and fruits by activating endogenous pectin methylesterase |
M. C. BOURNE, Food Science & Technology, Cornell Univ., New York State Agricultural Experiment Station, 630 W. North St., Geneva, NY 14456-1371 Early research on the effect of endogenous PME on firming of processed snap beans using chemical indices of enzyme activity (generation of methanol and H+) showed that the optimum blanch temperature is 170-175F. Our studies on the kinetics of thermal softening of vegetable tissue showed there are two types of firmness in vegetable tissue: type 1 degrades rapidly when heated, while type 2 is resistant to thermal degradation. Using this two-substrate theory, and measuring the effect of PME activity by a physical test (back-extrusion force) instead of by chemical tests showed that the optimum blanch temperature for increasing firmness is 140-150F. This long time-low temperature (LTLT) blanch gives significant increases in firmness of canned, frozen, or dehydrated vegetables and some fruits. Vegetables given the LTLT blanch respond more strongly to the addition of calcium and/or H+ than vegetables blanched at 170-212F. The combined effect of LTLT blanch plus Ca plus H+ yields canned vegetables whose firmness approaches that of the raw product.
Session 20, Enzymes in fruit and vegetable processing
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