Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

Paul W. Wilson

Abstract

White flesh sweetpotatoes (Ipomoea batatas (L.) Lam) are a major food crop in developing countries. This study was to evaluate the protein and carotenoid content and quality of various white fleshed African sweetpotatoes and Apios americana tubers for use as a weaning food. The sweetpotato and Apios are not normally considered sources of carotenoids and proteins, but the wide use of sweetpotatoes as a source of carbohydrate and the renewed interest in Apios warrant the study of carotenoids and proteins in these crops. Total carotenoids ranged from 0$\mu{\rm g}$/100g to 260$\mu$g/100g (fresh weight basis) for sweetpotatoes. Apios total carotenoids ranged from 10 to 40$\mu$g/100 (fresh weight basis). Processing reduced total carotenoids in sweetpotatoes, from 20 to 250$\mu$g/100g. The Hunter color values varied both in the raw and processed samples. $\beta$-Carotene, $\alpha$-carotene and canthaxanthin were identified by isocratic reverse phase HPLC. The values for $\beta$-carotene ranged from zero to 146$\mu$g/100g(fresh weight basis) in the sweetpotatoes, and between 2 and 17$\mu$g/100g in the puree. Carotenoids were confirmed by mass spectroscopy. Apios and two other cultivars did not show any carotenoids. The sweetpotatoes protein content ranged from 4.26 to 8.23 percent fresh weight after pureeing and freeze drying. These were formulated into a rat diet by increasing protein content with pigeon peas (Cajanus cajan) and other dietary supplements, in 60:40 ratio (root crop: pigeon peas). The pigeon peas raised the protein content to 10% for protein efficiency ratio (PER) studies. PER for diets was found to range from 1.57 to 1.92 compared to a PER of 2.5 for casein, indicating significant differences (p $<$ 0.05) in protein quality among the different diets. The data, indicates that one sweetpotato cultivar (T1702) would be suitable for formulating weaning food, due to a higher protein content and higher protein quality, shown by amino acid profile and PER. Processing into puree lowered the amino acid contents from raw roots but in varying degrees. There was a significant difference between the amino acids in the sweetpotato cultivars (p $<$ 0.05) and between sweetpotatoes and Apios. In vitro studies showed low digestibility, probably due to trypsin inhibitors. The computed-PER values for all test materials were very low too, suggesting that this is not a very good method of measuring protein quality in root crop based diets. This study shows that some white flesh sweetpotatoes with complimentation may be used as a source of protein for weaning food but not as a source of $\beta$-carotene. Apios, despite its high level of protein, is not a very good weaning food because the amino acids do not seem to be available to facilitate growth in the rats studied. Further studies need to be done to determine how 1-2 year old children perform on such a weaning food.

Pages

132

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