Monitoring of the vitamin C content of frozen green beans and Padrón peppers by HPLC

HPLC (using a C18 column, water at pH 2·2 as mobile phase, and UV detection) was used to monitor the vitamin C content of deep-frozen (-22°C) green beans and Padrón peppers over 12 months. Unblanched beans and peppers lost ⩾97% of their vitamin C within 1 month of freezing, whether or not they were contained in bags sealed under vacuum. Blanching reduced the beans' vitamin C content by 28%, but limited further decreases to between 3 (vacuum sealed) and 10% (no vacuum) in 12 months. These results confirm the utility of blanching in the preservation of vegetables by deep-freezing.