Development of Products from Sorrel (Hibiscus sabdariffa) and Evaluation of their Nutrients, Phytochemicals, Antinutrients, Toxicants, Physico-Chemical, Sensory and Storage Properties.
ABSTRACT
The objectives of the study were to develop products from sorrel calyces, leaves and seeds, evaluate the products for nutrients, phytochemicals, antinutrients, food toxicant, physico- chemical, microflora, sensory, storage properties and compare the products produced with existing products.
Dry red sorrel calyces, leaves and seeds were used for the study. Pilot study was carried out to standardize recipe used for the formulation of the products. The products developed were jelly, cordial juice, food condiment, food seasoning and oil.
Sorrel jelly and cordial juice were produced from sorrel calyx using standardized recipe and procedure by International jellies and preserved Association. Sorrel food condiments were produced from fermented sorrel seeds and sorrel oil was produced from sorrel seed.
Sorrel food seasoning was produced from sorrel leaf. The nutrients, phytochemicals, antinutrients, food toxicant and sensory properties of the products were determined using AOAC methods. The sorrel seed oil was evaluated for physico-chemical properties using standard procedures.
Similar products (grape jelly, black currant cordial juice, royco food condiment, rosemary seasoning and groundnut seed oil) by flavour, colour and texture used by consumers served as control for evaluation of the products developed.
The products were kept at room temperature 28±2ºC to determine the keeping qualities for sixteen (16) months. Sorrel jelly had significantly higher (p<0.05) crude protein, crude fat, ash, calcium (Ca), iron (Fe), phosphorus (P), sodium (Na), copper (Cu) and β-carotene.
Sorrel jelly contained crude protein (5.51%), Fe (15.43mg), P (30.57mg), Cu (54.00µ g), ascorbate (18.10mg) and β-carotene (22.50µg). Sorrel cordial juice had significantly higher (p<0.05) crude protein, ash, Ca, Fe, P, Zn, Cu, ascorbate and β- carotene.
The cordial juice from sorrel calyx had significant amount of crude protein (18.43%), carbohydrate (68.77%), Fe (50.66mg), P (48.40mg), Cu (56.66µg), and ascorbate (36.10mg). Sorrel seasoning had significantly higher (p<0.05) fat, ash, crude fibre, Ca, P, Na, Zn, Cu and β-carotene.
The seasoning from sorrel leaf had significant quantity of crude protein (11.82%), carbohydrate (67.12%), Ca (414.00mg), P (841.66mg), ascorbate (39.53mg) and β-carotene (38.20µg). Sorrel food condiment had higher (p<0.05) protein, fat, crude fibre, P, Zn, Cu, ascorbic acid and β-carotene.
The sorrel condiment was rich in crude protein (30.67%), carbohydrate (60.78%), Fe (16.70mg), P (787.34mg), ascorbate (40.27mg) and β- carotene (38.40µg). The oil had higher (p<0.05) relative density (0.916ºC), refractive index (1.475ºC), saponification value (189.00mgKOH/g), iodine value (103.00mg) and β-carotene (14.20µ g, respectively).
Sorrel products developed contained significant quantities of flavonoids. There were generally traces of cyanide and phytate except in the seasoning. Tannins were low (0.38-2.40mg) in all products except sorrel juice and royco food condiment.
The sorrel products were preferred to the standard products except sorrel oil. The products developed from sorrel calyces, leaves and seeds have promising food potentials and were highly acceptable.
All the products had no microbial count for the 16 months storage period except for sorrel jelly, which had microbial count from the first two months (70-4 cfu /ml) and sorrel juice which had microbial count from 13 months (20-240 cfu/ml).
Nutrition education programmes should be mounted in communities to disseminate information on the production of sorrel products to mothers, young girls and food industries for diversification of the products and their uses.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
List of Tables xii
List of Figures xiv
List of Plates xv
List of Appendices xvi
ABSTRACT xvii
1.0 CHAPTER ONE – INTRODUCTION 1
1.1 Background to the study 1
1.2 Statement of the problem 2
1.3 Objectives of the study 3
1.4 Significance of the study 4
2.0 CHAPTER TWO – REVIEW OF RELATED LITERATURE 5
2.1 Sorrel plant and its origin (Habiscus sabdariffa) 5
2.2 Description of sorrel plant 6
2.3 Uses of sorrel plant (calyx, seed,leaf) 9
2.4 Nutrient composition of the different parts of sorrel plant (calyx, seed and Leaf) 14
2.5 Phytochemicals 18
2.6 Antioxidants 30
2.7 Antinutritional and food toxicant factors (phytate, tannins, cyanide, trypsin inhibitor) 31
2.8 Antinutrients and food toxicant composition of the different parts of sorrel plant (calyx, seed and leaf ) 35
2.9 Processing techniques (heat treatment, milling,soaking, dehulling, fermentation) 36
2.10 Nutritional composition of fermented food 42
2.11 pH and titratable acidity 44
2.12 Products formulated in the study from sorrel calyx, leaf and seed 47
2.12.1 Jelly 47
2.12.2 Juice 49
2.12.3 Food condiment 52
2.12.4 Seasonings 54
2.12.5 Oil (seed oil) 57
2.13 Sensory properties of products developed 58
2.14 Microbiological studies 62
3.0 CHAPTER THREE – MATERIALS AND METHODS 64
3.1 Materials (calyces, seeds, leaves) 64
3.2 Development of products (calyces, seeds, leaves) 64
3.3 Chemical analysis 83
3.4 Phytochemical analysis 94
3.5 Estimation of antinutrients and food toxicant 97
3.6 pH and titratable acidity 98
3.7 Physico-chemical properties 99
3.8 Sensory evaluation 99
3.9 Storage studies 100
4.0 CHAPTER FOUR – RESULTS 102
4.1 Effect of fermentation 102
4.2 Chemical composition of sorrel jelly and grape jelly 104
4.3 Phytochemical composition of sorrel jelly and grape jelly 105
4.4 Antinutrient and food toxicant of sorrel jelly and grape jelly 105
4.5 Titratable acidity and pH of sorrel and grape jellies 106
4.6 Chemical composition of sorrel cordial juice and black currant cordial juice 106
4.7 Phytochemical compositions of sorrel cordial juice and black currant cordial juice 107
4.8 Antinutrient and food toxicant of sorrel cordial juice and black currant cordial juice 108
4.9 Titratable acidity of sorrel cordial juice and black currant cordial juices 108
4.10 Chemical composition of sorrel food and royco food condiments 108
4.11 Phytochemical compositions of sorrel food and royco food condiments 110
4.12 Antinutrient and food toxicant composition of sorrel food and royco food condiments 110
4.13 Chemical composition of sorrel and rosemary seasonings 111
4.14 Phytochemical compositions of sorrel and rosemary seasonings 112
4.15 Antinutrient and food toxicant compositions of sorrel and rosemary seasoning 112
4.16 Physico-chemical properties of sorrel seed oil and groundnut seed oil 112
4.17 Sensory properties of the products 113
4.18 Storage period of the products 116
5.0 CHAPTER FIVE – DISCUSSION, CONCLUSION AND RECOMMENDATIONS 118
5.1 Effect of fermentation periods on proximate, minerals and vitamin composition of sorrel seed condiment 118
5.2 Chemical composition of sorrel jelly, sorrel cordial juice, sorrel food condiment and sorrel food seasoning 122
5.2.1 Sorrel jelly 122
5.2.2 Sorrel cordial juice 125
5.2.3 Sorrel food condiment 129
5.2.4 Sorrel food seasoning 132
5.3 Physico-chemical properties of sorrel seed oil 134
5.4 Sensory evaluation of products; sorrel jelly, cordial juice food condiment and food seasoning 136
5.5 Microbiological studies 137
Conclusion 139
Recommendations 140
REFERENCES 141
APPENDICES 159
INTRODUCTION
1.1 Background to the Study
Plant foods are the most important dietary source for satisfying the nutritional needs of the majority of people in developing countries due to their availability, low cost and acceptability. The enormous potential of some plant foods still however remain untapped.
In Nigeria, some commercial foods are becoming very expensive and out of the reach of many families, particularly poor families. There is need to explore the use of some locally available, cheap and nutritious food crops in the production of derivable commercial products.
This would diversify the diet and help alleviate the malnutrition problems experienced by many people in different parts of the country (WHO, 2008a).
Sorrel plant (Hibiscus sabdariffa) is an acid tasting herb of the Malvaceas family (McLean, 1973; James, 2003; Yadong, Chin, Malekian & Berh, 2005).
The plant is an annual crop widely grown in the northern part of Nigeria, with promising nutritional potential (Onyeke, 2001). It is one of the under-exploited food crops of Nigeria. Sorrel plant bears edible calyces, seeds and leaves.
The different parts of the plant appear to have potentials exploitation by the food processing industry (McLean, 1973; James, 2003). Limited research has however been carried out on the development of products from the calyx, seed and leaf of the sorrel plant.
Already, there is a popular drink produced from sorrel calyx which is used for entertainment during ceremonies. This drink has been concentrated to produce bottled carbonated juice (Karkadeh juice) and reported by McLean (1973) in Sudan.
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