Folate assay of foods by traditional and tri-enzyme treatments using cryoprotected Lactobacillus casei

Variables affecting the efficacy of the microbiological assay of folate in foods were examined. Spinach, fortified bread and two ready-to-eat breakfas t cereals were extracted with or without autoclaving and centrifugation. Au toclaving and centrifugation lowered the yield of total folate in all foods . The food sample, after digestion with protease and cr-amylase was deconju gated with chicken pancreas or human plasma (tri-enzyme treatment) or simpl y with conjugase alone (tradition single enzyme treatment). The tri-enzyme treatment was a significant improvement over the single enzyme treatment on ly in fortified bread. Deconjugation with chicken pancreas gave a significa ntly higher folate value than did human plasma in all foods except spinach. Folate assay by cryoprotected frozen Lactobacillus casei was compared with serially sub-cultured inocula. Using the cryoprotected frozen inoculum too k a shorter time, was less tedious, gave better reproducibility and was mor e economical than using the conventional serial culture. The effects of the size of test tubes on the growth of culture and the wavelength at which tu rbidity was measured to achieve maximum detection were also investigated. L .casei grew faster in small tubes than in larger ones. The absorbance peak at 540 nm was higher than that at 620 nm. (C) 2000 Elsevier Science Ltd. Al l rights reserved.