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 (MWB). Samples were ice‐cooled, bagged, heat‐sealed and stored at −18C for 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 ∼49 mg/100 g; RAA content in fresh, BW‐blanched asparagus was ∼44 mg/100 g. Frozen, unblanched asparagus retained about 40% of original RAA content; BW‐blanched asparagus retained 61%, and MWB‐blanched asparagus retained 87%. After frozen storage all samples were darker than freshly blanched samples. Blanching increased and freezing decreased greenness of all samples. Blanching increased yellowness of fresh samples; after frozen storage, blanching treatment differences were lost. Unblanched samples had the highest appearance scores; unblanched and MW‐blanched samples had the highest color scores. Overall quality of the microwave blanched asparagus was as good as or superior to conventionally blanched asparagus.