Effects of blanching, freezing and storage on folacin contents of spinach

Extract: The [free' and total'] folacin activities (FFA and TFA) in fresh spinach held at 3 temperatures, and in blanched spinach stored frozen were determined by Lactobacillus casei assay. Holding at room temperature for 10 hours, in a refrigerator for 7 days, and in a freezer for 10 weeks resulted in only 7%, 26%, and 27% loss of TFA, respectively. However, FFA increased markedly, up to 185%, under these conditions due to endogenous conjugase activity which was active even at -22 degrees C. Microwave blanching and quick freezing caused only 14-16% loss of TFA and yet effectively inactivated conjugase. Water blanching resulted in twice as much folate loss as microwave blanching. Both FFA and TFA remained stable when blanched spinach was stored frozen for up to 20 weeks in tightly sealed pouches with little or no air present. On the other hand, a continuous loss of TFA, up to 27%, occurred in the unevacuatively pouched fresh spinach during 10 weeks of frozen storage. These results suggest that the [total] folates in spinach are relatively stable under proper post-harvest holding conditions and that blanched and then frozen spinach may retain more than 80% of the folacin in the fresh spinach when the air is excluded from the packaging. (author)