Percent water absorption: A simple method for estimation of sorghum grain hardness

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INTRODUCTION

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop in the world after wheat, rice, maize and barley in terms of production (FAO 2011). It is primarily used as a food crop in Asia and Africa. In Africa south of the Sahara, it is the second major crop produced after maize. It remains an important crop in Southern Africa and other semi-arid regions of the world because of its agronomical advantages. It is drought-tolerant, it can withstand water-logging and unlike maize, it requires minimum agricultural inputs for its cultivation (Belton and Taylor 2004). Furthermore, it is mostly cultivated and consumed by the small-scale farmers in the semi-arid regions of the world and thus contributes to food and nutritional security because it is an important supplier of carbohydrates and proteins to the diets (Dendy 1995; Rohrbach and Obilana 2003).

LITERATURE REVIEW

This review discusses what is known in the literature about sorghum, its physico-chemical properties, how these impact end-use quality and methods for determining end-use quality. The literature on enzymes responsible for darkening of processed plant-based foods, primarily polyphenol oxidase and their mechanisms of action is discussed. A review of sorghum processing methods and technologies is also presented.

Sorghum kernel structure

The sorghum kernel is described as a naked caryopsis (Rooney and Miller 1982) which varies widely in size and shape among sorghum varieties. The sorghum kernel is spherical in shape measuring 4 mm long, 2 mm wide and 2.5 mm thick. The kernel weight ranges from 25 to 35 mg, test weight ranges from 55 to 61 kg/hL and density ranges from 1.28 to 1.36 g/cm3 (Rooney and Miller 1982; Serna-Saldivar and Rooney 1995).

Tangential abrasive dehulling device (TADD)

The TADD has a resinoid disk mounted horizontally beneath eight to twelve sample cups. Grain is placed in the cups and the disk is set to rotate using a motor (Oomah, Reichert and Youngs 1981). The grain pericarp is rubbed off by the disk and the fines that are generated are swept out of the machine into the fines collection bag by means of an air flow produced by a fan. The harder the grain, the slower the material is abraded off. Kernel hardness is calculated in terms of the time taken to remove a certain weight percentage of the grain, or percentage of the grain removed over a fixed time (Taylor and Duodu 2009).

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DECLARATION
DEDICATION
ACKNOWLEDGEMENTS
ABSTRACT
1. INTRODUCTION
1.1 STATEMENT OF THE PROBLEM
1.2 LITERATURE REVIEW
1.2.1 Sorghum kernel structure
1.2.2 Sorghum grain colour
1.2.3 Chemical composition of sorghum
1.2.4 Sorghum phenolic compounds
1.2.5 Polyphenol oxidase (PPO)
1.2.7 Concluding remarks
1.2.8 Hypotheses and Objectives
2.RESEARCH
2.1 Percent water absorption: A simple method for estimation of sorghum grain hardness
2.1.1 Abstract
2.1.2 Introduction
2.1.3 Materials and methods
2.1.4 Results and discussion
2.1.5 Conclusions
2.2 Relationship between polyphenol oxidase activity and sorghum porridge colour
2.2.1 Abstract
2.2.2 Introduction
2.2.3 Materials and methods
2.2.4 Results and discussion
2.2.5 Conclusions
2.3 Sorghum grain colour assessment using Tristimulus colorimetry and UV-visible
spectrophotometry of sodium hydroxide extracts
2.3.1 Abstract
2.3.2 Introduction
2.3.3 Materials and Methods
2.3.4 Results and discussion
2.3.5 Conclusions
2.4 Characterisation of phenolic compounds and pigments in sodium hydroxide extracts from
kernels of different sorghum types using UPLC/PDA/MS
2.4.1 Abstract
2.4.2 Introduction
2.4.3 Materials and Methods
2.4.5 Conclusions
3. GENERAL DISCUSSION
3.1 Methodologies: A critical review
3.2 Research findings
3.2.1 Physical characteristics
3.2.2 Chemical characteristics
3.3 Developing a system for integrating end-use quality evaluation in the value chain of sorghum
production and utilization
3.3.1 Activities and information flow amongst stakeholders
4. CONCLUSIONS AND RECOMMENDATIONS
5. REFERENCES