ABSTRACT
Tomato as an extremely nutritious vegetable crop is highly seasonal and perishable vegetables in nature, large quantities of this produce are wasted during peak harvesting periods and hence the need to develop suitable methods to convert the produce to shelf-stable products. Therefore this work was carried out to evaluate the chemical and sensory properties of stew produced from dried instant tomato prepared with three (3) drying methods. Tomato fruits were purchased from the market and subjected to drying processes using oven, sun and greenhouse drying methods. The samples were dried to constant weight and milled while fresh tomato was used as a control sample. Tomato stew was reconstituted from the dried samples and also from fresh tomato which served as control. The mineral nutrients (Ca, Mg, Na, K, P, Cu, Fe, Zn, and I), vitamins (vitamins A, C, B1, B2, B3 and B9) of both dried and stew samples as well as sensory quality of the stew samples were evaluated using standard procedures. Analysis of Variance (ANOVA) test was used to separate means that are significantly different at (p<0.05). The result shows increase in minerals contents of the dried samples when compared to the fresh tomato sample from (9.56mg, 10.61mg, 4.45mg, 218.98mg, 23.65mg,0.05mg, 0.39mg.0.15mg and 1.74μg/100g respectively for (Ca, Mg, Na, K, P, Cu, Fe, Zn and I) to the highest values of the dried samples (45.82mg, 42.50mg, 40.17mg,1072.90,143.45mg, 0.23mg,2.53mg, 1.27mg and 3.5μg/100) respectively for (Vitamin A, C, B1, B2, B3,) to the highest value of the dried sample. (3.85mg, 12.0mg, 0.03mg,0.024, 0.516mg, and 0.030mg/100g) with oven dried samples having the highest value of Vitamin A, C, and B9 while green house had the highest value for B1, B2 and B3. The prepared stew sample further decrease in the value of vitamin when compare to the uncooked dried sample. Sensory scores for the stew samples indicated that oven dried tomato stew sample compared more favorably with the fresh tomato stew in all the sensory attributes evaluated (taste, color, flavor, texture appearance and overall acceptability) with no significant difference (p<0.005) existing between the two dried samples. It was therefore concluded that dried tomato significantly increase in mineral content but decrease in vitamin content when compared to the fresh tomato sample with oven dried method retain the highest amount of nutrient contents in dried samples.
TABLE OF CONTENTS
TITLE PAGE i
CERTIFICATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
TABLE OF CONTENT v
LIST OF TABLES vii
LIST OF FIGURES viii
ABSTRACT ix
CHAPTER 1
INTRODUCTION 1
1.1 Statement of problem 3
1.2 Objectives of the study 3
1.2.1 General objective of the study 3
1.2.2 Specific objectives of the study 3
Significance of the study 4
CHAPTER 2
LITERATURE REVIEW
2.1 Tomato origin, description and distribution 5
2.2 Tomato production and cultivation 7
2.2.1 Growth requirement of tomato 9
2.3 Tomato seasonality and wastage in Nigeria 10
2.4 Morphology and quality of tomato fruit 11
2.5 Nutritional composition of tomatoes 13
2.5.1 Tomato bioactive components and modes of action 15
2.5.2 Food value of tomatoes 17
2.6 Health benefits of tomato 18
2.7 Processing and preservation of tomato 19
2.8 Dehydration methods for tomatoes preservation 21
2.8.1 Drying techniques and its effect on food preservation 22
CHAPTER 3
MATERIALS AND METHODS
3.1 Study design 25
3.2 Source of raw material collection 25
3.3 Sample preparation 25
3.3.1 Cleaning/preparation process of drying tomatoes into flour 25
3.3.2 Slicing of tomatoes 26
3.3.3 Drying of sliced tomatoes 26
3.3.3.1 Sun drying of sample 26
3.3.3.2 Oven drying of sample 27
3.3.3.3 Greenhouse drying of sample 27
3.3.4 Grinding of samples 27
3.3.5 Recipe for stew production 29
3.3.6 Stew preparation 30
3.4 CHEMICAL ANALYSIS 31
3.4.1 Determination of mineral content 33
3.4.1.1 Determination of sodium, potassium, magnesium, zinc, iron,
copper, calcium and phosphorus 33
3.4.1.2 Determination of iodine 33
3.4.2 Determination of vitamins 34
3.4.2.1 Determination of vitamin A 34
3.4.2.2 Determination of vitamin C 34
3.4.2.3 Determination of vitamins B1, B2, B3 and B9 35
3.5 Sensory evaluation 35
3.9 Statistical analysis 36
CHAPTER 4
RESULTS AND DISCUSSION 37
4.1 Chemical composition of samples 37
4.1.2 Mineral composition of dried tomato powder and stew samples 48
4.2 Sensory evaluation of tomato stew samples 55
CHAPTER 5
CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 58
5.2 Recommendations 59
References 60
LIST OF TABLES
Table 2.1: Proximate composition of tomato 14
Table 2.2: Mineral composition of tomato 14
Table 2.3: Vitamins composition of tomato 15
Table 3.1: Recipe for stew preparation 29
Table 3.2: Recipes used in meat seasoning 30
Table 4.1: Mineral composition of dried tomato powder samples 42
Table 4.2: Mineral composition of prepared tomato stew samples 46
Table 4.3: Vitamin composition of dried tomato powder samples 53
Table 4.4: Vitamin composition of prepared stew samples 54
Table 4.5: Sensory evaluation mean scores for tomato stew samples 57
LIST OF FIGURES
Figure 3.1 Tomato powder samples preparation process flow chart 25
Figure 3.2 Flow chart showing preparation process for reconstituted instant tomato stew for sensory evaluation. 28
CHAPTER 1
INTRODUCTION
Tomato (Lycopersicum esculentum) belongs to the family “Solanaceae” and is a worldwide important agricultural commodity including the tropical countries like Nigeria (USDA, 2007). Tomatoes and tomato-based foods are considered healthy foods for several reasons because they are low in fat and calories, cholesterol-free and a good source of fibre and protein (Hsu, 2003). Owing to its rich source of vitamins and minerals, tomato is playing an important role in human diet (Lorenz, 2000). Also, tomatoes are good sources of basic nutrients and different bioactive ingredients like carotenoids, lycopene and other flavonoids, phenolic acids and ascorbic acid (Vitamin C) (Veillet et al., 2009). Tomato is however, one of the very perishable fruit; being a climacteric and perishable vegetable, tomatoes have a very short life span, usually 2-3 weeks. Depending on the humidity and temperature it ripens very fast, ultimately resulting in poor quality as the fruit become soft and unacceptable (Opiyo and Ying, 2005). The quality of tomato is determined by colour, appearance, flavour and firmness.
Tomato is utilized in greater amounts as fresh (salad), processed products (Beverages, Concentrates, sauces and canned assortments) and dehydrated products (component for pizza, different vegetable and spicy dishes) Akanbi et al., (2006). Extensive medical researchers reported that lycopene helps the human body fight against different types of cancers (prostate, breast), atherosclerosis and reduce blood cholesterol levels (Dumas et al., 2003; George et al., 2004). Tomatoes are also rich in minerals and minerals constitute about 8% of the dry matter content of tomatoes. Potassium and phosphate are the two major minerals among them (Kerkhofs et al., 2005; Xianquan et al., 2005).
Drying as a form of food processing however ensures the availability of perishable products all year round (Habou et al., 2003). Drying agricultural produce by sun drying is widely used in most of the developing countries of the tropical region. However, solar drying is an elaboration of sun drying and was the most hygienic method of drying (Bala and Woods, 2000). The aim of drying is to stop or limit the development of biochemical reaction and microorganisms in products by removing the free water from fresh products and decrease the microorganism rate until they cannot grow to extend shelf life of food materials. Drying of food materials also helps to decrease product volume significantly, increase of product diversity, increase of food process applications and improve the product quality (Maskan, 2001). However drying can accelerate some reactions that can adversely affect the product quality (Demiray and Tulek, 2008). This work is therefore designed to evaluate the chemical and sensory properties of stew produced from dried instant tomato prepared with three drying methods (sun drying, oven drying and greenhouse drying methods).
1.1 STATEMENT OF PROBLEM
Tomato fruit which is an extremely nutritious vegetable crop is highly seasonal. Being one of the highly perishable vegetables in nature, large quantities of the produce are wasted during peak harvesting periods of the crop. Due to high fluctuation in price and availability of tomatoes in the market between the seasons and some off-seasons, consumers demand has increased for processed products that keep more of their sensory properties and their nutritional value and (Verlent et al., 2006). In order to retain the nutritional benefits provided by the crop and make it available during off-season, it is rationale to process it to different shelf-stable products such as instant tomato powder. However, there is limited information on the nutritional and organoleptic implication of the drying process which needs to be ascertained, hence, the need for this study.
1.2 OBJECTIVES OF THE STUDY
1.2.1 General Objective of the Study
The general objective of this study is to evaluate the chemical and sensory properties of stew produced from dried instant tomato prepared with three drying methods (sun drying, oven drying and greenhouse drying methods).
1.2.2 Specific Objectives of the Study
The specific objectives of this study are to;
- produce instant tomato powder suitable for stew reconstitution
- evaluate the minerals (calcium, magnesium, sodium, potassium, phosphorus, copper, iron, zinc, and iodine) and vitamin (vitamin A, C, B1, B2, B3 and B9) composition of instant tomato powder
- determine the effect of drying methods on the minerals, vitamins and sensory attributes of reconstituted tomato stew.
1.3 SIGNIFICANCE OF THE STUDY
This work will be relevant to the general public by proffering the most suitable drying method for instant tomato powder for cooking purposes. It will also enable food scientists to select most suitable drying technique for tomato preservation.
In addition, this work will be useful for the tomato processing industries in selecting and applying the best drying method that is suitable in conserving the nutrients of tomato products thereby availing consumers, nutritious tomato product that is available all year round.
Finally, the work will also help Dietitians and Nutrition professionals to access and apply verified research information in selecting the best drying method that conserve the nutrients and quality integrity of dehydrated tomato products.
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