[Effect of the quality and quantity of dietary proteins on vitamin A depletion rate, and biological availability of vitamin A precursors].

The effect of quantity and quality of protein from cereal and legume sources on the rate of vitamin A depletion was evaluated through changes in retinol serum levels and liver stores in male and female Wistar strain rats. A total of 64 animals were distributed into four groups and fed ad libitum with diets adequate in all nutrients, except vitamin A. The protein in the diets was derived from 91% common maize (Diet A); 91% Opaque-2 maize (Diet B), 64% common maize plus 27% precooked common black bean flour (Diet C), and 64% Opaque-2 maize with 27% bean flour (Diet D). The total depletion period lasted 60 days and four rats per group were sacrificed at 15, 30 and 60 days. A total of 4 animals were sacrificed at 0 day to count with a basal serum and hepatic retinol concentration value. The 16 depleted remaining rats were used for the carotene bioavailability study with dehydrated carrots. During the first 15 days the greater rate of depletion was observed in animals fed the highest protein quality diet made from Opaque-2 maize and beans (Diet D), which also caused the greatest weight increase. The least depletion rate and lowest weight gain was obtained with the common corn diet (Diet A). Diets B and C caused intermediate depletion rates, with Diet B (Opaque-2 maize) being more effective than Diet C in spite of its lower protein content. At the end of 60 days all groups presented depletion levels not statistically different. Thus, these results confirm that protein quantity and quality from basic staple foods influence mobilization of retinol liver reserves. The 16 remaining depleted rats were then divided into four groups and fed a standard 14% casein diet to which 25, 50 and 75% of the retinol requirements was added to obtain a reference standard biological response. The fourth group was fed with an amount of dehydrated and ground carrot containing 67.1 mg % of total carotenoids. After seven days, serum and hepatic retinol were obtained, from which a regression equation of liver retinol to diet retinol was calculated (microgram % liver retinol per 100 g of rat) = 2.47 + 0.063 (microgram retinol/g diet) (r = 0.585). From this equation the bioavailability of carrot carotenoids was established with a value of 21.8% comparable to the FAO/WHO value previously reported.