MICROWAVE BLANCHING EFFECTS ON COLOR, CHEMICAL AND SENSORY CHARACTERISTICS OF FROZEN ASPARAGUS

Asparagus was blanched for 4 min using: conventional boiling water (BW ), steam (ST), microwave (MW), or microwave heated in boilable bags (M WB). Samples were ice-cooled, bagged, heat-sealed and stored at -18C f or 4 weeks. Peroxidase activity was reduced from 98-114 units in fresh , unblanched to 1-7 units in blanched asparagus. Reduced ascorbic acid (RAA) content in fresh, unblanched asparagus was similar to 49 mg/100 g; RAA content in fresh, BW-blanched asparagus was similar to 44 mg/1 00 g. Frozen, unblanched asparagus retained about 40% of original RAA content; BW-blanched asparagus retained 61%, and MWB-blanched asparagu s retained 87%. After frozen storage all samples were darker than fres hly blanched samples. Blanching increased and freezing decreased green ness of all samples. Blanching increased yellowness of fresh samples; after frozen storage, blanching treatment differences were lost. Unbla nched samples had the highest appearance scores; unblanched and MW-bla nched samples had the highest color scores. Overall quality of the mic rowave blanched asparagus was as good as or superior to conventionally blanched asparagus.