All recent health recommendations include admonitions to reduce calories, maintain desirable weight, reduce fat, increase complex carbohydrates, and ensure an adequate intake of nutrients. Such recommendations require that we know not only nutrient composition of foods, but also potential losses and decreased bioavailability due to postharvest treatment and chemical interactions. This article discusses in some detail the reactions of concern that cause such changes and their potential alleviation with several key nutrients. The nutrients discussed were chosen as a result of the conclusions of the Joint Nutrition Monitoring Report of the Department of Health and Human Services and the U.S. Department of Agriculture. Obviously other choices could have been made, but the authors felt that the nutrients chosen--ascorbic acid, thiamin, vitamin A, carotenoids, calcium, and iron--were representative of a key profile of nutrients whose reactivity makes them vulnerable to losses in bioavailability, as well as being noted in the Joint Nutrition Monitoring Report.

A method for determining the amount of B-carotene stereoisomers using spectrophotometric analysis was developed. Water-soluble Bcarotene was dissolved in pH 6.0 buffer and heated. The stereoisomers formed were separated by column chromatography and quantified using spectrophotometric analysis. The %Dn/Di i value (absorbance of the &-peak divided by the absorbance at the maximum wavelength) determined for the B-carotene solutions was found to be linearly correlated to the isomer composition (r = 0.971).

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