ABSTRACT
Fruit yoghurt samples were produced from reconstituted full cream milk powder by fermentation using starter cultures of Lactobacillus bulgaricus and Streptococcus thermophilus (1:1 w/w) at 28 oC for 48 hours, and diced carrots and pineapple added at various proportions. The samples were analyzed for their proximate, physico-chemical, vitamin, mineral, microbial and sensory qualities. The results obtained revealed that the proximate composition ranged from 75.30 to 76.50%, 3.37 to 4.64%, 0.07 to 0.23%, 1.94 to 3.20%, 1.52 to 2.76%, 13.15 to 16.82% and 94.77 to 102.65 Kcal for moisture content, crude protein, crude fibre, fat, ash, carbohydrate and energy value respectively, whereas the physicochemical properties ranged from 4.41 to 4.66, 0.88 to 1.11%, 1.04 to 1.08, 6.08 to 7.94%, 3.76 to 6.37% and 20.26 to 24.91% for pH, total titratable acidity, specific gravity, total soluble solids (brix), lactose content and total solids respectively. The vitamins content of the yoghurt samples increases significantly (P<0.05) with an increment in diced carrot and pineapple, with values ranging from 31.14 to 69.84 μg/100g for vitamin A and 2.15 to 23.26 mg/100g for vitamin C. There was also increase in mineral content, with significant difference (P<0.05) being recorded among the samples except in calcium content. The value for minerals ranged from 116.31 to 128.17 mg/100g, 26.33 to 40.56 mg/100g, 52.03 to 69.31 mg/100g and 146.74 to 160.36 mg/100g for calcium, phosphorus, potassium and magnesium respectively. For microbial analysis, total viable count ranged from 10.00 x 106 to 36.00 x 106 cfu/g in the yoghurt samples and same value as total lactobacillus count. No fungal or coliform growth was observed in the samples. In terms of sensory attributes, appearance ranged from 7.30 to 7.70, mouth-feel 6.80 to 7.90, taste 6.40 to 7.60, aroma 6.80 to 7.40 and general acceptability from 6.70 to 7.80, when evaluated on a 9 - point hedonic scale. There was generally no significant difference (P>0.05) in sensory properties among the samples especially appearance, taste and aroma, indicating that the yoghurt samples with inclusion of diced carrot and pineapple could be equally acceptable to consumers. The result revealed that addition of carrot and pineapple to yoghurt could improve the quality of yoghurt produced.
TABLE OF CONTENTS
Title i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xii
Abstract xiii
CHAPTER 1: INTRODUCTION
1.1 Background of the study 1
1.2 Statement of problems 2
1.3 Justification 2
1.4 Objectives of the study 2
CHAPTER 2: LITERATURE REVIEW
2.1 Yoghurt 4
2.1.1 Description of yoghurt 5
2.1.2 History of yoghurt 5
2.1.3 Types of yoghurt 6
Based on the chemical composition of the product 6
Based on the physical nature of the product 7
Based on the flavour of the product 7
Yoghurt related products 7
2.1.4 Roles of Ingredients in yoghurt production 7
Milk 7
Water 8
Yoghurt’s starter culture 8
2.1.5 Nutritional value of yoghurt 9
2.1.6 Health benefits of yoghurt 10
2.2 Flavoured yoghurt 12
2.3 Fruits and vegetable in yoghurt production 13
2.4 Carrot 15
2.5 Pineapple 17
Queen pineapple 18
Kew pineapple 18
CHAPTER 3: MATERIALS AND METHODS
3.1 Source of materials 20
3.2 Sample preparation 20
3.2.1 Preparation of reconstituted milk 20
3.2.2 Preparation of diced carrot 20
3.2.3 Preparation of diced pineapple 23
3.2.4 Yoghurt production with inclusions of carrot and pineapple 23
3.3 Proximate analysis 23
3.3.1 Determination of moisture by gravimetric oven drying method 23
3.3.2 Determination of crude protein content by Kjeldahl method 29
3.3.3 Determination of fat content by the Soxhlet ether extraction reflux method 30
3.3.4 Determination of crude fibre 30
3.3.5 Determination of ash by muffle furnace ignition method 31
3.3.6 Determination of carbohydrate 31
3.3.7 Determination of caloric value 32
3.4 Physicochemical analysis 32
3.4.1 Determination of hydrogen ion concentration (pH) 32
3.4.2 Determination of total titratable acidity (TTA), (% lactic acid) 33
3.4.3 Determination of specific gravity 33
3.4.4 Determination of total soluble solids (brix) 33
3.4.5 Determination of lactose content 34
3.4.6 Determination of total solids 35
3.5 Vitamin analysis 35
3.5.1 Determination of vitamin A 35
3.5.2 Determination of vitamin C 36
3.6 Mineral analysis 36
3.6.1 Determination of calcium 36
3.6.2 Determination of phosphorus 37
3.6.3 Determination of potassium 37
3.5.4 Determination of magnesium 37
3.7 Microbial analysis 38
3.8 Sensory evaluation 39
3.9 Experimental design 40
3.10 Statistical analysis 40
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Proximate composition of yoghurt samples 43
4.2 Physicochemical properties of yoghurt samples 47
4.3 Vitamin content of yoghurt samples 50
4.4 Mineral content of yoghurt samples 52
4.5 Microbial characteristics of yoghurt samples 55
4.6 Sensory attributes of the yoghurt samples 57
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 60
5.2 Recommendation 60
REFERENCES 61
LIST OF TABLES
Table 3.1: Formulation of samples 27
Table 4.1: Proximate composition of yoghurt samples 44
Table 4.2: Physicochemical properties of yoghurt samples 48
Table 4.3: Vitamin content of yoghurt samples
Table 4.4: Mineral content of yoghurt samples 53
Table 4.5: Microbial characteristics of yoghurt samples evaluated at 10-6 56
LIST OF FIGURES
Figure 3.1: Flow chart for preparation of reconstituted whole milk from whole milk powder with modifications as described by Sanful (2009) and Ihemeje et al. (2015) 21
Figure 3.2: Flow chart for preparation of diced carrot with modifications to the method described by Stewart (2014) and May (2020) 22
Figure 3.3: Flow chart for preparation of diced pineapple as described by KitchenNostalgia (2012) 24
Figure 3.4: Flow chart for preparation of plain yoghurt and fruit yoghurt using modification to methods described by Ihemeje et al. (2015), and Salih and Abdalla (2017) 28
LIST OF PLATES
Plate 1: Pictures of raw materials 25
a = Whole milk
b = Starter culture
c = Carrot
d = Pineapple
Plate 2: Pictures during production 26
a = Milk powder
b = Reconstituted milk
c = Pasteurized milk
d = Activation of starter culture
e = Blanched diced carrot
f = Blanched diced pineapple
Plate 3: Pictures of yoghurt samples 41
a = Yoghurt (after incubation)
b = Yoghurt (homogenized)
c = Yoghurt with added carrot and pineapple at different
proportions (Samples E, D, C, B, A)
d = Fruit yoghurt samples (Samples E, D, C, B and A)
Plate 4: Some pictures during analysis 42
a = Drying (Moisture content)
b = Ashing (Ash content)
c = Titration (TTA)
d = Poured agar plates (Microbial count)
e = Sensory evaluation of fruit yoghurt samples
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Yoghurt is one of the most consumed fermented milk products in the world (Willey et al., 2008). It is a coagulated milk product that results from the fermentation of lactose in milk by Lactobacillus bulgaricus and Streptococcus thermophilus (Njoya et al., 2016). Yoghurt is rich in protein, vitamins and minerals, and contains more fat than the milk source. Yoghurt have been prepared from milk obtained from cows, goat, sheep, camels and other animals even the leopard (Gangwar et al., 2016). It is now sold with different flavours such as fruits, vegetables, spices and herbs which are added to milk before fermentation or served with fruits (like strawberry) (Ihemeje et al., 2015; Roy et al., 2015; Amal et al., 2016).
Yoghurt has been proved to be suitable to make almost complete food by incorporating inexpensive nutrient sources. Fruits (like strawberry, apple, watermelon, papaya, mango, banana, grape and pineapple) and vegetables (like carrots and cucumber) are rich sources of vitamins, minerals fibre and antioxidants which can be used in making value-added yoghurt (Roy et al., 2015).
Carrot (Daucus carota) is a root vegetable, horn-like in shape, usually orange in colour with other varieties like purple, red, white and yellow. The taproot is the most commonly eaten part of the carrot (Ihemeje et al., 2015). Carrot is source of dietary fibre and of the trace mineral molybdenum rarely found in many vegetables. It is also a good source of manganese, magnesium and potassium. Carotenoids, polyphenols and vitamins present in carrot act as antioxidants, anti-carcinogens and immune enhancers (Carlos and Dias, 2014).
Pineapple (Ananas comosus) is a tropical plant in the Biomeliaceae family. It is the second most important tropical fruit in terms of world production (Altendorf, 2017). Raw pineapple is loaded with vitamins, enzymes and minerals including vitamin C, calcium, phosphorus, manganese and potassium which are important to health. It is also rich in fibre and calories, and low in fat and cholesterol (Debnath et al., 2012; Kasa and G/Yohanis, 2017).
1.2 STATEMENT OF PROBLEMS
Yoghurt is widely consumed by all, but it is best for those with lactose intolerance as their bodies cannot breakdown lactose which is milk sugar. In food production, sensory appeal is necessary as it is one of the essential strategies associated with the market success of fermented products like yoghurt. This sensory characteristic of yoghurt has been linked to its popularity as a food component (Routray and Mishra, 2011; Ihemeje et al., 2015).
1.3 JUSTIFICATION
Sensory appeal is very essential strategy associated with market success of fermented products like yoghurt (Routray and Mishra, 2011). There is need to introduce fruits (like pineapple) and vegetables (like carrots) to produce yoghurt with spicy taste, characteristic aroma and colour. This will also improve the nutritional composition of yoghurt produced (Ihemeje et al., 2015; Amal et al., 2016; Njoya et al., 2016; Mbaeyi-Nwaoha et al., 2017).
1.4 OBJECTIVES OF THE STUDY
The main objective of this study is “Quality assessment of yoghurt produced with inclusions of carrot and pineapple”.
The specific objectives are:
i. to produce yoghurt with inclusions of carrot and pineapple.
ii. to determine the physicochemical, vitamins and minerals composition of the yoghurt.
iii. to determine the microbial quality and the sensory characteristics of the yoghurt.
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