Folate content in frozen vegetarian ready meals and folate retention after different reheating methods

Folate content and retention were evaluated in 10 different precooked vegetarian ready meals before and after reheating. Folate was quantified using a validated high-performance liquid chromatography method. The only form of folate found was 5-methyltetrahydrofolate. Folate content in thawed ready meals varied from 23 to 81 mu g/portion (400g) on fresh weight basis. Products served with couscous and potatoes contained more folate than products served with rice. Folate retention during reheating was investigated in the microwave oven (900 W/5.5 min) in a saucepan on stove until the food reached 85 degrees C, and in oven (225 degrees C/40 min). The true vitamin retention varied for the three investigated portions as follows: on stove (63-93%), microwaving (55-89%) and in oven (50-92%). Our results indicate that folate content in the ready meals prior to reheating, contributed to 6-27% of the recommended intake (300 or 400 mu g folate per day). After reheating folate content was significantly (P < 0.05) reduced in some meals but were kept constant in others and folate content was reduced to 3-25% of the recommended value. No clear pattern in folate retention between different heating, methods was seen. However, the meals with ingredients suggesting high concentrations of antioxidants were less prone to loose folate when heated since the antioxidants probably protected the folates. (C) 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.