Pepsin digestibility of proteins in sorghum and other major cereals

Abstract

We have shown previously that sorghum is highly digestible in the rat. However, other workers have shown that sorghum is much less digestible than wheat, maize, and rice in young children. Because the rat does not show these digestibility differences, we developed an empirical pepsin digestion method, furst reported in 1981, which simulates the digestion values found in children. In this report the method has been improved and used to analyze wheat, maize, rice, millet, and sorghum and certain processed samples of millet and sorghum. The pepsin digestion values parallel those found in children for wheat, maize, rice, and sorghum. In addition, a processed sorghum product that gave a high digestion value in children also gave a high value with the in vitro pepsin method.Sorghum [Sorghum bicolor (L.) Moench] is an important source of calories and protein for a large segment of the human population in the semiarid tropics.In a previous publication (1), the apparent digestibility of the proteins in four (cooked) sorghum gruels varied from 76.5% to 83.0% (average, 80.4%) in young rats. The same four sorghum flours, when cooked and fed to children of age 6-27 months, gave an average apparent digestibility value of only 46%, compared with values of 81%, 73%, and 66% for wheat, maize, and rice, respectively (2). Because the rat gave values for cooked sorghum that were the same as those MacLean et al. (2) found for cooked wheat in the child, we developed an empirical in vitro pepsin method (1) that more closely simulates MacLean's values in children. In this report we present improvements in our original method and data on the pepsin digestibility of the major cereals. We also include data on processed sorghum and millet products [sorghum and millet nasha (fermented baby foods) and extruded decorticated sorghum].MATERIALS AND METHODS found on the grain in Sudan), was added, and the mixture was incubated at 30'C for 12 hr. The slurry was fed to a laboratory drum dryer or was freeze-dried, and the dry residue was used for digestibility studies.Pepsin. The pepsin used was porcine pepsin 1:10,000 (Sigma). It had an activity of 1,200-2,000 units/mg of protein (A28) (3).Modified Pepsin Method (Residue Method). Ground cereal samples (200 mg) prepared with a Udy grinder and 0.4-mm screen were suspended in 35 ml of a solution of pepsin (1.5 mg/ml) in 0.1 M phosphate buffer (pH 2.0); the mixture was incubated with gentle shaking at 370C for 2 hr. Incubation for 3 hr raises all values about 10% above the 2-hr values; incubation for 1 hr lowers all values about 10% below the 2-hr values. Therefore, time of incubation is critical in the assay. After incubation the suspension was centrifuged (12,000 x g for 15 min at 40C), and the residue was suspended in 10 ml of 0.1 M phosphate buffer (pH 2.0) and centrifuged as before. The low-pepsin moist residue was freed from the walls of the centrifuge tube with a spatula and dumped in the center of Whatman filter paper no. 3 on a 43-mm Buchner funnel. Suction (aspirator) was applied, an...

Nutritional Composition of Spirulina Platensis Powder and Its Acceptability in Food Products.

“…In vitro protein digestibility was carried out by using the modified method of Mertz et al (1983). Total lysine was estimated as per the method described by Mertz et al (1975).…”

“…It has many therapeutic properties such as hypocholesterolemic, immunological, antiviral and antiglutagenic effects (McCarty, 2007). It is an excellent source of good quality protein (60-70%) with all essential amino acids in perfect balance and also provide high concentration of minerals and B-complex vitamins specially vitamin B 12 which is usually found in animal tissues (Devinamerin et al, 2007;Vijayarani et al, 2012). Spirulina supplements are available in powder, flakes, capsule and tablet forms.…”

Influence of micronization (infrared treatment) on the protein and functional quality of a ready-to-eat sorghum-cowpea African porridge for young child-feeding

“…The multi-enzyme and pepsin in vitro methods were used as they are simple, rapid and reproducible and have given comparable results to in vivo methods in rat models (Boisen & Eggum, 1991) and in young children (Mertz, Hassen, Cairns-Whittern, Kirleis, Tu, & Axtell, 1984). There was generally good agreement in terms of ranking of the treatments between the multi-enzyme and pepsin IVPD methods (Table 2).…”

Increasing the utilisation of sorghum, millets and pseudocereals: Developments in the science of their phenolic phytochemicals, biofortification and protein functionality

“…However, an intervention trial with infants recovering from Protein-Energy Malnutrition revealed that diets based on both high lysine and normal sorghum gave similarly very poor nitrogen absorption and retention (MacLean et al, 1981), even compared with data from other cereals. In vitro work carried in parallel with this trial indicated that the poor quality of sorghum protein was not just due to its low lysine content but also to the low digestibility of the sorghum protein in foods (Axtell et al, 1981;Mertz et al, 1984).…”