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Hardness Changes and Endosperm Modification During Sorghum Malting in Grains of Varying Hardness and Malt Quality

¹Institute for Food, Nutrition and Well-being and Department of Food Science, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa. ²Agricultural Research Council–Grain Crops Institute, Private Bag X1251, Potchefstroom 2520, South Africa. ³Discipline of Dietetics and Human Nutrition, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3209, South Africa. ⁴Cereal Quality Laboratory, Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, U.S.A. ⁵Extraordinary professor, Department of Food Science, University of Pretoria, South Africa. ⁶Corresponding author. Phone: +27 124204296. E-mail: john.taylor@up.ac.za

This study examined the interaction between sorghum grain hardness and sorghum malt quality in terms of diastatic power and free amino nitrogen with endosperm modification during malting. The changes in kernel hardness during malting of four commercial sorghum cultivars of differing quality in terms of endosperm texture and potential malt quality were measured using tests for hardness and density, and endosperm modification was followed by scanning electron microscopy. The general pattern of modification during sorghum malting was confirmed to start at the endosperm–scutellum interface and then continue into the floury endosperm toward the kernel distal end. Significantly, a cultivar of intermediate hardness and low malting quality remained harder and modified more slowly than a harder cultivar of high malting quality. It appeared that intrinsic grain hardness and malt amylase and protease activity both affected malt hardness and endosperm modification, but amylase and protease activity had a greater effect because of their degradation of endosperm starch and protein. Of the hardness and density tests studied, the tangential abrasive dehulling device (TADD) gave the best measure of hardness throughout malting; maximum range was 24–100% kernel removed over five days of malting. Also, the data agreed with the observed malt modification rates. Thus, the TADD may have application as a simple and rapid test for estimating sorghum malt quality.