18C-16

Y. CHOI¹, J. Lee¹, and R. R. Eitenmiller². (1) Department of Food Science and Technology, Chungbuk National University, 48 Gaeshin-dong Heungduk-gu, Cheongju, Chungbuk, 361-763, South Korea, (2) Dept. of Food Science and Technology, Univ. of Georgia, Food Science Bldg., Athens, GA 30602-7610

Microbiological assay is accepted as the best and most versatile method for the determination of folate in foods. A trienzyme extraction using Pronase¢ē, α-amylase and conjugase (γ-glutamyl hydrolase) is commonly used to extract folate from foods to measure total folate.

To optimize folate extraction by the trienzyme procedure prior to microbiological assay of red kidney beans (Phaseolus vulgaris) using response surface methodology (RSM).

Ground samples were homogenized with 0.1M potassium phosphate buffer (pH 7.8) containing 1 % ascorbic acid (w/v). These homogenates were heated 15 min at 100C to inactivate native enzymes and break down folate binding protein and subjected to trienzyme extraction. RSM was used to optimize Pronase¢ē, α-amylase and conjugase digestion. Then, total folate content in each sample was determined by microbiological assay using Lactobacillus casei (ssp. rhamnosus) ATCC 7469 by a 96-well microplate technique.

Extraction parameters were optimized for the microbiological assay of folate in red kidney beans using RSM. After response surface regression (RSREG), the second-order polynomial equation was fitted to the experimental data. The analysis of variance showed that the model appeared to be adequate (R²=0.8941) with no significant lack of fit (P > 0.1). From statistical analysis, α-amylase and Pronase¢ē digestions were found to be significant factors (P < 0.05). On the other hand, conjugase digestion was not significant (P > 0.1). It is thought that the times of conjugase digestion (4, 12, 20 hr) were too long in this study. This indicates the conjugase digestion could be shortened (less than 4 hr). Ridge analysis showed that the optimal extraction conditions were 1.3 hr for Pronase¢ē, 2.1 hr for α-amylase, and 14.3 hr for conjugase to obtain maximal folate assay values.

This study provides an optimized extraction procedure for the assay of total folate in red kidney beans.

Session 18C, Food Chemistry: Food composition, analysis and volatiles
2:00 PM - 5:30 PM, Sunday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana