Folates in berries

Folate concentrations in berries and berry products were investigated, determining folate retention from raw material to the final product. Folate content was quantified using a modified and systematically evaluated radioprotein-binding assay (RPBA). The optimised RPBA was demonstrated to be a useful method for folate quantification in berries containing mainly 5-CH₃-H₄folate. Results after internal evaluation regarding selectivity, background radiation, unspecific binding, and accuracy are presented. To avoid unspecific binding purification of sample extracts by solid phase extraction prior to quantification was included for some berries. Microbiological assay (MA) and high performance liquid chromatography (HPLC) were used to compare obtained folate concentrations and to characterise individual folate forms in tested matrices. The predominating folate form in all tested berries was 5-CH₃-H₄folate. Therefore, the recently commercially available natural form (6S)-5-CH₃-H₄folate was chosen as calibrant. Berries rich in folate were rosehips (100-180 µg/100g fresh weight) and strawberries (70-90 µg/100g fresh weight). These two model berries were used to study factors affecting the folate content in berries. Significant effects on folate content were observed from cultivar, grade of ripeness and year of harvest. Folate retention in the two model berries was studied during storage, drying procedures and in commercial products. After storage of fresh strawberries in the refrigerator high folate retention was obtained, whereas storage in room temperature and at exposure to light resulted in folate losses. In rosehips folate retention during various drying procedures was improved by minimising the drying time using high temperature and cutting of berries into slices. Water content affected the stability of both folates and ascorbic acid during drying. Almost no folate losses occurred when strawberries were cooked as jam or stewed as strawberry desserts from frozen berries, with a folate retention of 79-103%. Commercial products from both berries contained 10-20 µg of folate per 100 g FW. Berries and semi-manufactures of berries are suitable ingredients in various food products to increase their nutritional value regarding folate intake. A newly developed human ileostomy model suitable for evaluating folate bioavailability from these products is presented. Increased intake of berries and berry products could well be an alternative to folate supplements and fortification