Graduate Thesis Or Dissertation
 

Vitamin B₆ enrichment of wheat flour : stability and bioavailability

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9z903423t

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  • This investigation consisted of two parts: A. stability, B. bioavailability of vitamin B₆ in wheat. Three variables; whole wheat flour (WHW), white flour (W) and W enriched with vitamin B₆ (WB₆) were tested. Stability of vitamin B₆ during bread making and storage of bread and flour was determined. Bread was prepared from the three types of flour under commercial and home conditions. Two methods, straight dough and sponge dough for bread making were compared under home conditions. Vitamin B₆ content of dough before fermentation, after proofing and of bread was determined by a microbiological method. The WB₆ dough prepared using the sponge dough method showed a significant increase in the vitamin B₆ content during fermentation (P < 0.05). A significant baking loss of 10-15% was observed in the WHW and W breads prepared under commercial conditions (P < 0.05), and of 5-12% in WHW, WB₆ (P < 0.01) and W (P < 0.05) breads made using the sponge dough method. Storage stability of vitamin B₆ was determined in the comb mercially prepared WB₆ bread and all purpose flour enriched with vitamin B₆. There was no significant change in vitamin B₆ levels in the bread stored under frozen and refrigerated conditions for seven and four weeks, respectively. However, a significant drop of 10% was observed in the vitamin B₆ content of the bread after three days of storage at room temperature (P < 0.01). Vitamin B₆ content of the WB₆ flour did not change when stored over a period of 26 weeks at room temperature. Bioavailability of vitamin B₆ was studied in nine men, age 21-33 years. Each week one of the three types of bread, WHW (570 g), WB₆ (600 g) and W (600 g) was fed daily to each subject using a 3X3 Latin square design. The WHW, WB₆ and W bread supplied 1.20, 1.18 and 0.35 mg of vitamin B₆, respectively, while 0.38 mg was supplied by the constant diet. The daily vitamin B₆ intake was set at 1.5 mg, of which approximately 3/4 was supplied from WHW or WB₆ bread. During the period when W bread was consumed, the subjects also received an oral dose of 0.81 mg of vitamin B₆ in order to maintain a constant daily intake throughout the study. The predominant form of vitamin B₆ in the diets was found to be pyridoxine. Twenty-four hour urines, daily fecal collections and fasting blood samples three days per week were analyzed for vitamin B₆ and its metabolites, using microbiological, chromatographic and fluorometric techniques. The fecal vitamin B₆ level was significantly higher when WHW bread was fed as compared to when WB₆ or W bread was fed (P < 0.01). There was no significant difference in the urinary excretion of total and free vitamin B₆ in relation to the type of bread. The predominant form of vitamin B₆ in urine was found to be pyridoxal. The urinary 4-pyridoxic acid content was significantly lower when the diet was based on WHW bread as compared to WB₆ or W bread (P < 0.01). The percentage of the daily intake of vitamin B₆ accounted for by the excretory products analyzed in this study was 91.6 when WHW bread was fed. The corresponding percentages when WB₆ and W breads were fed were 81.5 and 79.8, respectively. The plasma vitamin B₆ and pyridoxal phosphate levels were slightly lower when WHW bread was consumed as compared to WB₆ or W bread. These data suggest that vitamin B₆ was not as available from WHW bread as from WB₆ and W bread. The availability of vitamin B₆ from WB₆ and W bread as determined in the present study was similar. For the populations who are dependent on refined wheat products, enrichment of flour with vitamin B₆ will be of advantage. However, enrichment of refined wheat products cannot replace completely the benefits of consuming whole wheat products.
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