Retention of chlorophylls in frozen French bean, green asparagus and pea prepared for consumption depending on pre-treatment before freezing and the temperature of frozen storage

The investigation involved French bean, green asparagus and pea. The evaluation concerned fresh material; material after blanching and cooking; and frozen vegetables prepared for consumption after 0, 4, 8 and 12 months of frozen storage. In the investigation the tradition method of freezing — blanching before freezing (TT product) and the modified technology — cooking before freezing (MT product) were used. The obtained MT product only requires defrosting and heating in a microwave oven. Frozen products were stored at −20 °C and −30 °C. Fresh bean contained 9.67 mg chlorophylls; green asparagus 6.76 mg and pea 9.21 mg in 100 g fresh matter. Blanching, cooking, frozen storage and the preparation of vegetables for consumption brought about varied decreases in the analysed pigments. Products prepared for consumption after 12 months of frozen storage retained the following amounts of total chlorophylls compared to that found in the raw material: French bean 63–81%; green asparagus 46–79% and pea 73–97%, depending on the investigated sample. The MT products contained 14–27% less chlorophyll than TT products; frozen products stored at −30 °C contained 6–29% more chlorophyll than those stored at −20 °C