44C-5 |
Detection of vacuum infusion of pectinmethylesterase in strawberry by activity staining |
P. BANJONGSINSIRI1, J. L. Ackerley, and L. Wicker. (1) Dept. of Food Science and Technology, University of Georgia, Athens, GA 30602-7610 Textural damage is one of the major problems in strawberries, occurring when harvesting, handling, and processing the fruit. Pectinmethylesterase (PME) is presumed to increase firmness by deesterification of pectin and chelation of calcium as crosslinks between carboxyl groups of adjacent chains. Vacuum techniques facilitate the incorporation of sugar, firming agents and PME in strawberries. However, no method exists to rapidly quantify PME infusion in intact fruit. The purpose of this study was to a develop method to quantify the effectiveness of PME infusion process in the strawberry tissues using an enzyme print technique. Fresh strawberries were halved, submerged in Valencia PME, which was diluted to 26 U/ml for each replication, and infused by vacuum of 84.65 kPa for 15 min at room temperature. PME activity in strawberry fruit was detected by modification of the hydroxylamine, ferric chloride staining procedure for PME isozymes. The pectin paper was prepared with blotting paper that was impregnated with 1% pectin buffered at pH 7.5. Fruits were blotted onto pectin paper 10 min at room temperature, paper was hot air dried, and stained for PME activity by hydroxylamine-ferric chloride. PME activity is seen as a yellow zone on a red-brown background of pectin paper. The vacuum process facilitated PME translocation within tissues. PME infusion was greatest in the bundle zone and minimal in the epidermis. Non infused and water infused control had no to slightly yellow zone. The PME print technique can be used as a rapid method to detect successful PME infusion. The localization of the enzyme in specific areas of the strawberry fruit will impact on any overall firmness of strawberries. Infusion of PME with the vacuum technique may be a valuable process aid to improve quality, particularly in strawberry pieces, purees or whole fruits.
Session 44C, Fruit & Vegetable Products: Chemistry
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