Folacin retention in vegetables cooked by microwave vs. conventional methods

This study investigates whether there is greater folacin retention in microwave cooked or in conventionally cooked vegetables. Three fresh vegetables: asparagus, broccoli and spinach were studied. Weighed (454 g) vegetable samples, with 57 ml distilled water added, were cooked by microwave oven or by stove-top cookery. Cooked vegetable weights and vegetable broth volumes were recorded. Free folic acid (FFA) and total folic acid (TFA) content of raw and cooked vegetables and drained vegetable broths were determined by a microbiological assay technique using Lactobacillus casei (ATCC 7469). Data were analyzed by computerized analysis of variance and Tukey’s HSD test for post hoc comparison of means. When spinach and broccoli were cooked there was a significant loss of both FFA and TFA due to either cooking method. Spinach retained significantly more FFA (P <. 01) when cooked by microwaves than when cooked conventionally. There was no significant difference in TFA content of spinach or in FFA and TFA content of broccoli due to cooking method. There was significant loss of FFA and TFA into the drained vegetable broth of both vegetables, but no significant difference in loss due to cooking method. Losses of FFA in the vegetable broth were 8.5% and l.l% for spinach, and 1.l% and 1.9% for broccoli for microwave and conventional methods respectively. Losses of TFA in the vegetable broth were 7.8% and 14.9% for spinach, and 6.8% and 4.6% for broccoli. Estimated losses due to destruction in cooking were: 13.9% and 23.2% FFA in spinach; 70.2% and 58% FFA in broccoli; 10.4% and 9.5% TFA in spinach; 19.8% and 22% TFA in broccoli, for microwave and conventional methods respectively. The F'FA content of asparagus was found to be erratic, probably due to the presence of conjugase in the natural vegetable, so the analysis for asparagus folacin content was discontinued. Based on this study, it can be stated that microwave cooking is as good as, but not superior to, conventional cooking with respect to folacin retention in vegetables.