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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, physicochemical, 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 (54.00µg), 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 βcarotene. 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 βcarotene (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 (14.20µg, 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 CONTENT
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
CHAPTER ONE
1.0 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. Unsuccessful previous attempts to produce carbonated roselle drink were made by some individuals in the carbonated drink industry. The main reasons for failure were the occurrence of fermentation, precipitation and fading of the red colour intensity of the bottled drink (Saeed and Ahmed,
1972).
Globally, many researchers have noted the food potentials of the different parts of sorrel plant (Mclean, 1973; Duke and Atchley, 1984; Nnam and Onyeke, 2003; Rich, 2004 and Yadong et al., 2005). The calyx could be processed to produce jam, marmalade, jelly, ices, ice cream, herbal tea, wine, juice, syrup, sauces, gelatin and butter. Sorrel calyx has some medicinal uses such as the treatment of bilious attacks, decreasing the viscosity of the blood, reducing blood pressure and as diuretic for stimulating intestinal peristalsis. It can also be used to treat cancer, cough, and scurvy (Yadong et al.,2005). The leaves could be useful in producing curries, as vegetable in soup, eaten raw in salads, as a purée in eating rice and fish. Sorrel leaves have some medicinal uses (Duke and Atchley, 1984). It has diuretic effects and could lower temperature during fever. It acts as an emollient and sedative for digestive and kidney functions. It sooths cough and decreases the rate of absorption of alcohol (Rich, 2004). Products from the seeds are food condiments, coffee, essential oil, foofoo, porridge, animal feed, oily soups, and sauces. The seed has medicinal uses as diuretic, laxative and tonic for addressing debility challenges of patients. It may appear that no standard recipe has been evolved for the development of the products as novel food from the under-exploited food crop.
1.2 Statement of the problem
The high cost of many commercial products has affected their consumption. Many low income families can not afford to use them. In Nigeria, there are many indigenous food crops that can be used as replacement of costly raw materials used in industries and also could be useful in the dietary modification and diversification programme but little or no information exists in literature about their production. Some of these plants may not have been identified and studied. Peliminary evaluation of sorrel calyx, seed and leaf shows that they have rich nutrient potentials and may become useful in commercial food production. The different parts of the plant have however, limited use.
A major set back in functionality of sorrel production is the recipe to use in the development of those products mention by many authors. Attempts have been made in the past to use sorrel plant in production of food but there was no recipe available. Wide spread utilization of product from sorrel plant does not grow in many part of the country. It only grows in the Northern part of Nigeria. Again the common product produced either Zoborodo drink does not stay longer before it gets spoil and the colour fad. Diversifying the utilization of this indigenous nutritious plant through the development of new products from the different parts of the plant would provide some new value-added products into the family menu. This will improve the nutrient intake and nutritional status of the populace.
1.3 Objectives of the study
The general objective of this study was to develop products from sorrel calyx, seed and leaf and evaluate the products for nutrients, phytochemical, antinutrients, food toxicant, physico-chemical, sensory and storage properties of the products and compare with existing products.
The specific objectives were to:
- develop recipes for the production of sorrel jelly and cordial juice;
- produce jelly and cordial juice from sorrel calyx; food condiment and oil from sorrel seed; and seasoning from sorrel leaf;
- determine the nutrients, phytochemicals, antinutrients and food toxicant composition of the products made from sorrel calyx, seed and leaf;
- determine the physico-chemical properties of sorrel seed oil;
- assess the acceptability of the products from sorrel calyx, seed and leaf;
- determine the effect of storage period on microbial, coliform and mould counts of the products; and
- compare the products produced with existing products.
1.4 Significance of the study
The results of the study will encourage food industries to exploit the different parts of sorrel plant raw materials for making some commercial products. This may make such products more readily available and within the reach of the poor masses. The results of the study can extend the food uses of sorrel calyx, seed and leaf as a positive step in the dietary diversification programme. The effects of comparism of the existing products and products made from sorrel plant on the chemical, sensory and storage properties will stimulate consumers to know what they are eating.
Sorrel plant can contribute to the economic improvement of Nigeria through the production, use and sale of different food products from its calyx, seed and leaf. The development of products from sorrel calyx, seed and leaf will stimulate nutritionists and food scientists to investigate other indigenous food plants for commercial purposes. The results will provide recipes that would assist Home Economics Extension workers to demonstrate the use of sorrel plant to formulate different products. It will also stimulate production of large quantities of the plant to generate income. The information from the study may be useful to food product developers and Nutritionists as a vechile to fight against micronutrients deficient to the numerous consumers of sorrel products. The products made from the calyces, seeds and leaves can provide good health when consumed in a right quantity. Sorrel plant can contribute to upgrade the nutritional quality of foods if more effort is geared towards their increased cultivation, processing and utilization. Adequate processing is necessary to improve the acceptability of the products and availability of the nutrients.
