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 breakfast cereals were extracted with or without autoclaving and centrifugation. Autoclaving and centrifugation lowered the yield of total folate in all foods. The food sample, after digestion with protease and cr-amylase was deconjugated with chicken pancreas or human plasma (tri-enzyme treatment) or simply with conjugase alone (tradition single enzyme treatment). The tri-enzyme treatment was a significant improvement over the single enzyme treatment only in fortified bread. Deconjugation with chicken pancreas gave a significantly 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 took a shorter time, was less tedious, gave better reproducibility and was more 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 turbidity 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. All rights reserved.