Removal of Tannins and Improvement of in Vitro Protein Digestibility of Sorghum Seeds by Soaking in Alkali

Abstract

Soaking of sorghum seeds at 30°C in 0.05M sodium hydroxide and potassium hydroxide removed 75-85% of the tannins in 24 hr. Treatment at 100°C increased the rate of extraction and reduced the time required to leach 75-85% tannins from 24 hr to 20 min. Under similar conditions, 0.05M sodium carbonate removed 77% whereas soaking in distilled water removed only 30%. Dry matter loss due to the treatments with alkaline reagents ranged from 1.2-2.3%. Extraction of tannins in 0.05M alkaline solution at 100°C for 20 min improved in vitro protein digestibility of high tannin seeds 2~5 fold as compared to untreated seeds.

The Role of Dietary Phenolic Compounds in Protein Digestion and Processing Technologies to Improve Their Antinutritive Properties

“…In several studies, soaking of the legumes in distilled water was found to decrease polyphenol/tannin content and increase IVPD (Kataria and others ; Chau and Cheung ; Preet and Punia ; Rehman and Shah ; Abd El‐Hady and Habiba ; Shimelis and Rakshit ; Luo and Xie ; Pandey and Awasthi ). In contrast, for sorghum it was shown that only soaking in alkaline solution increases IVPD (Chavan and others ; Mukuru ; Vijayakumari and others ). In addition, soaking of black grams in sodium bicarbonate solution was found to be more efficient for tannin extraction and improvement of IVPD than soaking in boiling water, while soaking in sodium bicarbonate solution have shown to be even better (Rehman and Shah ).…”

Genetic Basis of Protein Digestibility in Grain Sorghum

“…In industrialized nations, sorghum is mainly cultivated as animal feed and more recently as a feedstock for biofuel production. Known chemical (or physical) mechanisms that render sorghum protein resistant to enzymatic digestion include covalent cross-linking between kafirin proteins (the main sorghum storage proteins) through disulfide bonding (S-S) (Duodu et al, 2003;Nunes et al, 2005;Belton et al, 2006), and interaction of protein with cellular chemical components such as polyphenol, phytic acid, lipids, starch, and nonstarch cell wall polysaccharides (Chavan et al, 1979;Makokha et al, 2002;Duodu et al, 2003;Nunes et al, 2004;Osman, 2004;Taylor et al, 2007;Wong et al, 2009). Decades of research to improve the trait has not yet produced high-protein-digestible sorghum cultivar with acceptable agronomic characteristics.…”

Tannins in Feedstuffs for Simple-Stomached Animals

“…Assayable tannin content of sorghum was shown to be reduced after soaking in water or alkaline solution (Price et al 1979). Soaking grains in aqueous sodium hydroxide and washing out alkali and extracted material improved the nutritional value, increased in vitro protein digestibility (Chavan et al 1979) and improved starch digestibility (Kock et al 1985). Soaking winged beans (Psophocarpus tetragonolobus L.) with distilled water, sodium hydroxide or potassium hydroxide for 24 h reduced tannin content by 5&90% (Sathe & Salunkhe, 1981).…”