AN IN VITRO METHOD TO ESTIMATE BIOAVAILABLE VITAMIN B-6 IN FOODS AND ITS APPLICATION TO EVALUATE UNIT OPERATIONS IN FOOD PROCESSING (BEEF, BEANS, FLOUR, MILK, NFDM)

ATHULA EKANAYAKE, Purdue University

Abstract

A two stage enzymatic digestion method, which released bioavailable B-6 vitamers from processed, fortified model foods is described. The procedure involved a digestion at pH 2.0 with pepsin for 3 hours, followed by a 12 hour digestion with pancreatin at pH 8.0. After an HCl-methanol precipitation, the released vitamers were quantified by reverse phase high performance liquid chromatography. The vitamers showed good correlation to the results from a rat growth study done in parallel. Recoveries were 100% for both pyridoxine and pyridoxamine and 70% for pyridoxal. Verification of the applicability of the in vitro method was sought by estimating the bioavailable vitamin B-6 content of ground beef round, lima beans, whole wheat flour and non-fat dry milk. The values obtained were compared to those reported in the literature, where the bioavailability was determined by a rat bioassay. The ratio of the bioavailable to the total vitamin B-6 content compared favorably for ground beef round, whole wheat flour and non-fat dry milk. For lima beans, however, the ratios were not comparable. This may be attributed to the differing distribution of the vitamin B-6 between the five vitamer forms in the two lima bean samples used for the assay. Pyridoxine was the largest contributor to the vitamin B-6 of the lima bean samples as reported in the literature. In the present study, pyridoxal and pyridoxal-5'-phosphate contributed most. Unit operations for a rehydrated canned lima bean process were evaluated in terms of the effect on bioavailability of vitamin B-6 using the in vitro technique. Blanching resulted in the leaching of about 20% of the pyridoxine into the blanch water. Neither of the other vitamers nor their bioavailability was significantly affected by blanching. In the enzymatic digests of the heat processed samples, pyridoxal and pyridoxal-5'-phosphate were not found. This was interpreted as a loss in bioavailability, because the acid hydrolysates of both the blanched and heat processed samples showed a similar pyridoxal content. The differing accounts in the literature could be interpreted more meaningfully, to confirm that although vitamin B-6 was not chemically destroyed in heat processing, its bioavailability was reduced by almost 50%.

Degree

Ph.D.

Subject Area

Food science

COinS