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Ebook In Vitro Starch Digestibility And Estimated Glycemic Index Of Sorghum Products

Submitted by wulan on Thu, 01/07/2010 - 08:07

Sorghum (Sorghum bicolor L. Moench) is an important source of dietary energy and a main food staple in semi-arid regions of Africa and Asia (Ezeogu et al. 2005). Due to its drought tolerance and adaptation attributes, this grain can be grown in those areas where agricultural and environmental conditions are unfavorable for the production of other crops. Sorghum is considered the world’s fifth most important cereal after wheat, rice, maize, and barley (Serna-Saldivar and Rooney 1995). Worldwide, over 35% of sorghum is grown directly for human consumption, while the rest is used primarily for animal feed, alcohol, and industrial products (Rooney and Awika 2004).

In the United States, sorghum utilization directly for human foods is very limited, but with potential to increase (e.g. white food-type sorghum flour has been introduced in gluten-free products such as breads and cookies). Moreover, some specialty sorghums high in tannins have recently shown high antioxidant activities comparable to those of high-antioxidant fruits like blueberries and plums (Awika et al. 2003); giving sorghum an opportunity in functional food markets.

Sorghum generally has the lowest starch digestibility compared to other cereals (Zhang and Hamaker 1998). The lower digestibility of cooked sorghum starch has been shown to affect the feeding value in livestock (Rowe et al. 1999), and to cause a higher loss of energy in humans (MacLean et al. 1981). Sorghum endosperm proteins play an important role in restricting the availability of starch (Rooney and Pflugfelder 1986).

Sorghum has extensive genetic variability between varieties, which is responsible for the considerable variation in the nutritional value of sorghum (Lamar 1973). According to Back Knudsen et al. (1988), low-polyphenol varieties are expected to be highly digestible. On the other hand, polyphenols present in several sorghum varieties (e.g. tannin sorghums) are known to alter digestion and absorption processes in simple-stomach animals (Waniska and Rooney 2000). However, Elkin et al. (1996) showed that tannins are only partially responsible for the variation in protein digestibility of sorghum grain cultivars. Therefore, other components also cause the differences in the availability of nutrients in sorghum. Among the factors that influence starch digestibility of cereals are the botanical source, food processing, gelatinization characteristics, particle size, amylose/amylopectin ratio and presence of lipid-amylose complexes (Frei et al. 2003).

CONTENTS

ABSTRACT
DEDICATION
ACKNOWLEDGMENTS
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
I INTRODUCTION
II LITERATURE REVIEW

    Sorghum
    Sorghum based food products
    Starch in sorghum
      Starch gelatinization
      Starch hydrolysis
      Factors affecting starch digestibility

    Starch digestibility and health

      Glycemic index
      Measuring glycemic index in vitro

III EFFECTS OF SORGHUM TYPE AND FRACTION ON STARCH AVAILABILITY OF EXTRUDATES

    Introduction
    Objective
    Materials and methods
      Sorghum grain characterization
      Grain preparation
      Particle size distibution
      Extrusion
      Moisture
      Expansion ratio
      Microscopy
      Starch fractions
      In vitro rate of starch digestion
      Statistical analysis

    Results and discussion

      Sorghum grain characterization
      Grain preparation and particle size distribution
      Extrusion
      Expansion ratio
      Microscopy
      Starch fractions
      In vitro rate of starch digestion

IV EFFECTS OF SORGHUM TYPE AND FRACTION ON STARCH AVAILABILITY OF PORRIDGES

    Introduction
    Objective
    Materials and methods
      Grain preparation
      Particle size distribution
      Porridge making
      Moisture
      Textural quality
      Microscopy
      Starch fractions
      In vitro rate of starch digestion
      Statistical analysis

    Results and discussion

      Grain preparation and particle size distribution
      Porridges
      Textural quality
      Microscopy
      Starch fractions
      In vitro rate of starch digestion

V EFFECT OF TANNIN SORGHUM BRAN ADDITION ON STARCH AVAILABILITY OF WHEAT BREAD

    Introduction
    Objective
    Materials and methods
      Sorghum grain preparation
      Tannin sorghum bran characterization
      Bread baking
      Moisture
      Starch fractions
      In vitro rate of starch digestion
      Statistical analysis

    Results and discussion

      Tannin sorghum bran characterization
      Breads
      Starch fractions
      In vitro rate of starch digestion

VI SUMMARY AND CONCLUSIONS

    Summary
      White sorghum products
      Tannin sorghum products
      Estimation of glycemic index

    Conclusions

LITERATURE CITED
APPENDIX A
VITA
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