Digestibility of sorghum proteins

Published information indicates that rice, maize, and wheat proteins are much more digestible in children than sorghum proteins are (66-81% compared with 46%). However, this digestibility difference cannot be demonstrated with the weanling rat, which gave digestibility values of 80% for cooked and 85% for uncooked sorghum gruels. Therefore, a search was made for a laboratory system sensitive to the digestibility differences between sorghum and other cereals. We found that porcine pepsin in vitro shows these digestibility differences. Using pepsin, we have found that uncooked sorghum proteins have a high digestibility (78-100%), which drops to a range of 45-55% after cooking. Two fermented sheet-baked sorghum products (kisra and abrey) from Sudan gave pepsin digestibility values of 65-86%. In contrast, unfermented cooked gruels made in our laboratory from the same flours used for the kisra and abrey gave pepsin values of only 44-56%. Therefore, fermentation improves pepsin digestibility of sorghum. The digestibility values of other sorghum-based foods prepared in the semiarid tropics need surveying. Those with high pepsin digestibility values hopefully should be more digestible (in children) than are the cooked sorghum gruels studied to date by human nutritionists.