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Stability of folacin in swisschard during storage and cooking
The effects of storage temperature and cooking methods on folacin content in swisschard were studied. Free and total folic acid (FFA, TFA) were determined by microbiological assay using Lactobacillus casei (ATCC 7469). The preliminary studies showed that the leaf size affects the folacin content in swisschard and the vitamin is concentrated in leaf-blade whereas the midrib is a poor source of folacin. The vegetable obtained from local supermarkets showed that the folacin activity in swisschard is dependent on holding time at the retail store post-harvest. The vegetable stored in plastic bags retained highest activity of FFA and TFA as compared to swisschard stored under moist and open conditions at room temperature. The temperature dependent degradation of folacin in swisschard showed a first-order reaction kinetics and followed the Arrhenius equation. The activation energy was 29 Kcal/mol for FFA and 27 Kcal/mol for TFA. The swisschard stored in refrigerator retained nearly 100 percent folacin with moderate fluctuations over a period of 10 days. The vegetable was cooked by four methods: microwave, boiling, stir-frying and steaming. There was a significantly greater loss of FFA than TFA due to cooking. Steaming retained highest total folacin activity but there was no significant difference in vitamin retention by microwave cooking, stir-frying and steaming. The boiling of the vegetable caused significantly higher losses of the vitamin than the other three methods of cooking. The swisschard showed higher folacin activity compared to known good sources of the vitamin in both raw and cooked state. One hundred grams of cooked vegetable had 210 pg. of folacin per 100 g. which is half of the Recommended Dietary Allowance for an adult.