Effects of grinding and storage for one month on retention of vitamin A in premixes and mineral supplements.

Tested standardized procedures for handling premixes and mineral supplements from time of sampling to time of analysis for vitamin A have not been developed, which could account for some unexplained inconsistent and low analytical results. Grinding premix samples and storing them in a freezer for one month had little effect on amount of vitamin A found, but there was a significant loss (about 10%) after storage for one month at room temperature. Results on replicated determinations of vitamin A in unground and ground mineral supplements and on effect of storage were somewhat more variable than for premixes, but only the loss (about 12%) during storage for one month at room temperature was significant.

Determination of vitamin K in foods: a review.

Vitamin K receives less dietary attention and fewer assays in foods than other fat-soluble vitamins. It is widely distributed in foods, usually at low concentrations. The human requirement is small. Intestinal bacteria synthesize vitamin K, which presumably helps provide the metabolic requirements for vitamin K. An RDA for vitamin K has not been published, but infants fed milk-substitute formulas risk vitamin K deficiency and it is recommended that those formulas contain supplemental vitamin K. Vitamin K in foods includes phylloquinone (K1) found in plants and several menaquinones (K2) found in animals and synthesized by microorganisms. Many vitamin K methods were developed primarily to identify forms present and determine their relative bioactivities. Until recently bioassays with chicks were the only practical methods to determine vitamin K content of foods. Various physicochemical methods have been developed to determine vitamins K in pure solutions, concentrates, and pharmaceuticals. Because of low concentrations of vitamin K in foods and the extensive purifications of extracts required, there has been only limited use of physicochemical methods, such as column chromatography, thin-layer chromatography, and high-performance liquid chromatography, with foods; the latter method perhaps offers the greatest possibilities for further development.

Determination of vitamin D in foods: a review.

Determining vitamin D content in foods is difficult because in natural foods of highest vitamin D activity, and even in vitamin D-fortified foods, only small quantities are present, and many other compounds are extracted along with vitamin D that cause difficulties in purifying the extract or in the spectrophotometry or colorimetry that follows. Several physicochemical methods--such as spectrophotometric, colorimetric, thin-layer chromatographic, adsorption, partition, gas-liquid, and high-performance column chromatographic--have been tried for assay foods for vitamin D, but none of them have been accepted for official or routine use; they are time consuming and expensive, or lack the required sensitivity, precision, or accuracy. Curative biological assays, based on degree of healing of a leg bone of rats previously made rachitic, is the generally accepted method to determine vitamin D content of foods. However, that method also requires too much time and is expensive. The recently developed high-performance liquid chromatographic method may offer the most for establishing a satisfactory physicochemical method for determining vitamin D in foods. Many of the difficulties and problems in assaying foods for vitamin D are discussed.

Determination of vitamin A in foods--a review.

Formerly, few foods were routinely analyzed for vitamin A, but recent emphasis on nutrient requirements, nutrient labeling, and use of dietary convenience foods has created need for determining vitamin A in a variety of foods. There are many vitamin A methods--some suitable for certain products only. For regulatory purposes, the FDA specifies the AOAC method where it is applicable. However, some food analysts and organizations continue with their own vitamin A methods. If possible, a single, widely applicable general method should be used for vitamin A in foods. Vitamin A may be determined by spectrophotometric, colorimetric, and fluorometric procedures. Sometimes chromatography is required as an important part of the method. Colorimetric procedures with SbCl3 are now most widely used to measure vitamin A (retinol) in foods. If vitamin A content is high enough and extracts sufficiently free of interfering substances, spectrophotometric or flurometric methods are satisfactory. Methods in various stages of development for determining vitamin A in foods are based on flurospectrophotometry, gas-liquid chromatography, high-performance liquid chromatography, and automation. To estimate total vitamin A nutritional value of certain foods may also require determination of vitamin A isomerization and contents of carotenes, cryptoxanthin, reinaldehyde, and apo-carotenal.