Testing of folate conjugase from chicken pancreas vs commercial enzyme and studying the effect of cooking on folate retention in Thai foods

Crude enzyme from chicken pancreas as a source of folate conjugase was prepared in a lyophilised form Homogeneity stability and activities were checked against a commercial enzyme Subsequently the prepared crude enzyme was used to investigate the process of folate extraction in various food matrices and study the effect of cooking on folate retention in several Thai foods The lyophilised enzyme was homogeneous and contained 4 mu g endogenous folate per g of prepared lyophilised crude enzyme The stability of the lyophilised enzyme and the diluted enzyme kept at 4 C was at least 12 months and 3 days respectively The activity of the prepared lyophilised folate conjugase used at the level of 20 mg/g sample was evaluated by a microbiological assay of total folate in brown rice egg whole milk powder soybeans and asparagus It showed comparable results to that of the commercial enzyme Single enzyme treatment (folate conjugase alone) was sufficient for the determination of folate content in brown rice soybeans and asparagus However for egg and whole milk powder it was necessary to apply tri enzyme treatment as this showed a significantly higher level (at P < 0 05) of total folate than that obtained using only single or di enzyme (protease + folate conjugase) treatments Among the representative foods studied the levels of total folate ranked in order of concentration were soybeans > egg > asparagus > brown rice > steamed mackerel (common form sold) (305 117 95 41 and 24 mu g/100 g wet weight basis respectively) After cooking the true retention of total folate in the cooked foods ranged from 60% in brown rice (cooked in an electric rice cooker) up to 82% in boiled asparagus On a wet weight basis the total folate content in boiled soybeans boiled asparagus boiled egg, fried mackerel and cooked brown rice was 100 84 72 22 and 12 mu g/100 g respectively One boiled egg (50 g) contributes 36 mu g folate which is equal to 18% of the Thai Recommended Daily Intake (RDI) and thus It can be considered as a good source of folate based on one serving size A serving of boiled soybeans (70 g) or boiled asparagus (80 g) is an excellent source of folate each contributing about 35% of the Thai RDI (C) 2010 Elsevier Inc All rights reserved