Comparative Studies on the Effects of Different Modifications on the Cold Water Solubility of Starch from Selected Underutilized Legumes
Comparative Studies on the Effects of Different Modifications on the Cold Water Solubility of Starch from Selected Underutilized Legumes.
ABSTRACT
The industrial utilization of native starch is limited by its imperfect nature, hence the need for modifications.
The continued use of conventional crops such as cassava, maize, rice and potato as sources of starch for industrial uses adds to the demand pressure on these crops.
On the other hand, the isolation of starch from underutilized legumes will not only reduce this pressure, but will also add value to boost the economic potential of these legumes.
This work was aimed at comparing the effects of different modifications on the cold water solubility and functional properties of starch isolated from Vigna subterranea, Sphenostylis stenocarpa, Cajanus cajan, and Mucuna pruriens var pruriens.
The recovered starch yield ranged between 70 99 %. Most of the modifications enhanced the desirable properties of the starches.
The cold water solubility of the modified starches were in the range of 35 81 %, with acid-alcohol, alcohol- alkaline and acid hydrolysis modifications giving the best solubility, while heat moisture treatment and carboxymethylation modifications gave the least solubility.
Most of the modified starches had high swelling power, with the exception of the acid treated starches. The pH of the modified starches were around neutrality (pH 7) excluding acid-treated which was neutralised with a 1 M NaOH solution.
The water absorbing capacity of the starches increased with increasing solubility for most modified starches excluding the acid-treated starches.
There were reductions in the amylose content of most of the modified starches with the exception of the acid hydrolysed, pyrodextrinized and osmotic pressure treated starches.
The gelatinisation temperature of the modified starches reduced with increasing solubility. The gelatinisation temperature analyses of the starches ranged between 68 and 72 0C for the native starches and 34 and 60 0C for the modified starches.
The moisture contents of the modified starches were relatively low. The clarity of the starches varied, with the oxidized and acid-alcohol treated starches giving the highest clarity.
The modified starch yield ranged between 70 % and 99 %. Based on visual assessments, the samples were relatively clean and white with a minor contribution of colour from the seed coat of the grains.
There were some variations in the transmittance properties of the pastes of the native and modified starches.
These properties of modified starches suggest that starches from underutilized legumes could be used in the production of cold water soluble starch thereby increasing its value addition.
TABLE OF CONTENTS
Title Page ……………….i
Certification …………..ii
Dedication …………….iii
Acknowledgement ….iv
Abstract …………………v
Table of contents ……vi
List of tables ………….x
List of figures ………..xi
List of plates …………xiii
List of abbreviation..xiv
CHAPTER ONE: INTRODUCTION
1.1 Legumes ……………………………………………2
1.2 Underutilized legumes ……………………….2
1.1.1.1 Cajanus cajan ……………………………….4
1.1.1.2 Mucuna pruriens var pruriens ……….4
1.1.1.3 Sphenostylis stenocarpa ………………..5
1.1.1.4 Vigna subterranea ………………………..6
1.2 Starch ………………………………………………7
1.2.1 Sources of starch …………………………….7
1.2.2 Structure and properties of starches ..7
1.2.3 Components of starch ……………………9
1.2.3.1 Major components of isolated starch 9
1.2.3.1.1 Amylose …………………………………….9
1.2.3.1.2 Amylopectin ……………………………..9
1.2.3.1.3 Minor components of isolated starch 10
1.2.4 Starch biosynthesis ……………………………..11
1.2.5 Biodegradation of starch ……………………..12
1.2.6 Starch extraction from grains and seeds ..13
1.2.7 Functional properties of starch in legumes13
1.2.7.1 Solubility and swelling power of starch in legumes 13
1.2.7.2 Gelatinisation of starch in legumes …………………….14
1.2.7.3 Retrogradation of starch in legumes …………………..15
1.2.7.4 Pasting properties of starch in legumes ……………….15
1.2.7.5 Paste clarity of starch in legumes ………………………..16
1.2.7.6 Amylose content of starch in legumes ………………….16
1.3 Modification of starch ……………………………………………..17
1.3.1 Physical modification of starch ………………………………17
1.3.1.1 Annealing of starch …………………………………………….18
1.3.1.2 Heat moisture treatment of starch ……………………….18
1.3.1.3 Non-thermal physical modification of starch …………19
1.3.1.4 Pre-gelatinisation of starch ………………………………….19
1.3.1.5 Osmotic pressure treatment of starch ……………………20
1.3.2 Enzymatic modification of starch ……………………………21
1.3.3 Biotechnology modification of starch …………………….. 21
1.3.4 Chemical modification of starch ……………………………..22
1.3.4.1 Esterification of starch ………………………………………..23
1.3.4.2 Acetylation of starch …………………………………………..23
1.3.4.3 Succinylation of starch ………………………………………..23
1.3.4.4 Phosphorylation of starch ……………………………………24
1.3.4.5 Etherification of starch ………………………………………..25
1.3.4.6 Propylation of starch …………………………………………..25
1.3.4.7 Cationization of starch …………………………………………25
1.3.4.8 Crosslinking of starch ………………………………………….26
1.3.4.9 Oxidation of starch ………………………………………………27
1.3.4.10 Acid hydrolysis of starch ……………………………………..28
1.3.4.11 Carboxymethylation of starch ……………………………….28
1.3.4.12 Pyrodextrinization of starch …………………………………29
1.3.4.13 Acid alcohol modification of starch ……………………….29
1.4 Applications of starch …………………………………………………30
1.5 Problem statement and justification …………………………….31
1.5.1 Aims and objectives …………………………………………………31
CHAPTER TWO: MATERIALS AND METHODS
2.1 Materials …………………………………………………….32
2.1.1 Reagents ………………………………………………….32
2.1.2 Collection of legumes ………………………………..32
2.2 Methods …………………………………………………….33
2.2.1 Legume preparation and starch isolation ……33
2.2.2 Starch yield percent …………………………………33
2.2.3 Cold water solubility ………………………………..33
2.2.4 Modification of starch ………………………………34
2.2.4.1 Physical modification …………………………….34
2.2.4.1.1 Annealing …………………………………………..34
2.2.4.1.2 Heat moisture treatment …………………….34
2.2.4.1.3 Osmotic pressure treatment ………………..34
2.2.4.2 Chemical modifications …………………………34
2.2.4.2.1 Acetylation ………………………………………..34
2.2.4.2.2 Acid alcohol modification …………………..35
2.2.4.2.2.1 Acid alcohol 50% modification …………35
2.2.4.2.2.2 Acid alcohol 70 % modification ………..35
2.2.4.2.3 Acid hydrolysis ………………………………….35
2.2.4.2.4 Alcohol alkaline modification ……………..36
2.2.4.2.5 Alcohol alkaline modification- 20 % …….36
2.2.4.2.6 Alcohol alkaline modification- 50 % ……..36
2.2.4.2.7 Carboxymethylation ……………………………36
2.2.4.2.8 Crosslinking ……………………………………….37
2.2.4.2.9 Oxidation …………………………………………..37
2.2.4.2.10 Phosphorylation ……………………………….37
2.2.4.2.11 Pyrodextrinization …………………………….38
2.2.4.2.12 Succinylation …………………………………….38
2.2.5 Determination of the functional properties of starch 38
2.2.5.1 Swelling power ………………………………………………….38
2.2.5.2 pH ……………………………………………………………………38
2.2.5.3 Water absorption capacity …………………………………..39
2.2.5.4 Amylose content determination …………………………..39
2.2.5.5 Gelatinization temperature ………………………………….39
2.2.5.6 Moisture content ………………………………………………..40
2.2.5.7 Paste clarity ………………………………………………………..40
CHAPTER THREE: RESULTS
3.1 Images of different isolated starches ……………………………………………………41
3.2 Results for percentage starch yield ……………………………………………………..48
3.3 Effects of modifications on the cold water solubility of starch ……………….55
3.4 Effects of modifications on the swelling power …………………………………….58
3.5 Effects of modifications on the pH ………………………………………………………61
3.6 Effects of modifications on the water absorption capacity ……………………..64
3.7 Effects of modifications on the amylose and amylopectin content ………….67
3.8 Effects of modifications on the gelatinisation temperature ……………………72
3.9 Effects of modifications on the moisture content ………………………………….75
3.10 Effects of modifications on the paste clarity ……………………………………….78
3.11 Morphology of starch granules ………………………………………………………….83
CHAPTER FOUR: DISCUSSION AND CONCLUSION
4.1 Discussion …………………………………88
4.2 Conclusion……………………………….. 96
4.3 Suggestions for further studies ……96
References ……………………………………..97
Appendices ……………………………………118
INTRODUCTION
Starch is an abundant organic polysaccharide molecule in nature with two main components– amylose and amylopectin.
The industrial utilisation of native starch is limited because of its imperfect nature therefore the importance of modifications for both industrial and food applications (Kavlani et al., 2012).
Legumes are fruits or seeds of prime importance in human and animal nutrition and contain moderate amounts of carbohydrate and protein.
The legumes in the study (Cajanus cajan, Mucuna pruriens var pruriens, Sphenostylis stenocarpa, and Vigna subterranea) is usually cultivated by the rural community.
Such subsistence cultivation makes this legume, which show promise despite its shortcomings, underutilized and neglected.
In order to increase legume production and utilisation, one of the approaches is to exploit its major components, starch through value- added product design and development strategy (Shimelis et al., 2006).
Harnessing the potentials of underutilized legumes as invaluable sources of starch could be a way out (Adebowale et al., 2002; Adebowale and Lawal 2003; Shimelis et al., 2006).
Producing starch and starch derivatives from conventional plants like cassava, maize, rice and potato places too much demand on them, particularly as they have to meet the needs of both domestic and industrial uses; thus, the need to include legumes more so, underutilized ones (Lawal, 2004).
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