Globally, there is growing interest to integrate nutrient–dense foods such as insect flour into food products to achieve nutritional goals and address food insecurity. Though cereal–based porridge is widely consumed in many sub–Saharan African countries, there is a lack of information on its enrichment with edible cricket, Scapsipedus icipe. The objective of this study was to develop and determine the nutritional composition, anti–nutrient content, sensory acceptability, microbial safety and storage stability of porridge flour formulations enriched with edible cricket. Porridge was prepared from the flour formulations with a cricket content of 0%, 10%, 15% and 20% (w/w). A sensory evaluation pretest, indicating 10% cricket-finger millet-amaranth flour as the most desirable porridge, informed the basis of using 10% cricket, 60% finger millet, and 30% amaranth for the preparation of four porridge flour samples, using traditional processing methods: germination, fermentation and roasting. Untreated formulation and an existing finger millet-based commercial porridge flour served as control. Cricket enriched formulations had high protein (2– folds), crude fat (3.4–4–folds) and energy (1.1–1.2–folds) compared to the commercial flour. Processing by germination and fermentation resulted in high phytic acid degradation (67% and 33% respectively) and improved mineral bioavailability. The iron content of the formulated flours ranged from 8.6–19.5 mg/100 g with the germinated sample having the highest content (19.5 mg/100 g). Zinc content was in the range of 3.1–3.7 mg/100 g while the range obtained for calcium was from 234.9 mg–278.6 mg/100 g. The commercial flour recorded zinc and calcium contents of 1.86mg/100g and 312.7mg/100 g respectively. Cricket enriched formulations had significantly (p< 0.05) higher content of vitamin B12, vitamin B5, vitamin B6, nicotinamide and thiamine when compared to the commercial flour. A total of 44 fatty acids methyl esters (FAMEs) were detected in the porridge flour oil extract using Gas Chromatography coupled to Mass Spectrometry (GC–MS). Of the 24 saturated fatty acids (SFAs) detected, Methyl hexadecanoate (palmitic acid) contributed the highest proportion followed by Methyl octadecanoate (stearic acid) across the flour samples. In addition, Methyl 9E–octadecenoate (oleic acid) was the predominant monounsaturated fatty acid (MUFA) whereas Methyl 9Z, 12Z–octadecadienoate (linoleic acid, LA) contributed the highest proportion of the polyunsaturated fatty acids (PUFAs). Αlpha–linolenic acid (ALA) was detected in all the cricket-enriched samples while docosapentaenoic acid (DHA) was only present in the fermented sample. Fermentation process caused a significant (p < 0.05) increase in the levels of PUFAs (30%) and MUFAs (14%) and a decrease in the SFAs (3%) while roasting process caused a significant (p < 0.05) increase in both MUFAs and SFAs by 27 and 10%, respectively. Total flavonoids were reduced during germination (42%) and roasting (10%) but increased during fermentation (13%), while tannin content decreased during germination (29%). Panelist–based sensory evaluation revealed significant differences (p < 0.05) among the porridge samples. Results suggest cricket formulations at 10, 15 and 20% were all acceptable with significant variations. 10% cricket formulation had the highest scores for all attributes. On the effect of processing, roasted and fermented samples had the highest sensory scores compared to the germinated porridge sample with the least overall acceptability score. The total viable plate count for the formulations ranged from 2.4 to 4.1 log10 CFU/g, whereas mold and yeast count was in the range of 1.4 to 1.7 log10 CFU/g. Roasted flour formulation had low counts of bacteria, yeasts and mold and low moisture content. The flour formulations packaged in paper bags exhibited higher variations in terms of microbial loads and moisture content as compared to those packaged in aluminium bags. This observation shows that enrichment combined with proper processing may improve the nutritional quality of cereal–based foods and reduce the levels of anti-nutrients. High sensory rating and low microbial count confirm that cricket flour can be used as an effective functional ingredient to enrich porridge flour.
TABLE OF CONTENTS
PLAGIARISM DECLARATION FORM iii
LIST OF TABLES ix
LIST OF FIGURES x
ACRONYMS AND ABBREVIATIONS xi
CHAPTER ONE: INTRODUCTION
1.1. Background to the study 1
1.2. Statement of the problem 4
1.3. Justification of the study 4
1.4. Objectives 5
1.4.1. Overall objective 5
1.4.2. Specific objectives 5
1.5. Hypotheses 6
CHAPTER TWO: LITERATURE REVIEW
2.1. Entomophagy culture 7
2.2. Nutritional aspect of edible insects 8
2.2.1. Protein composition 8
2.2.2. Fat content 9
2.2.3. Fiber contents 10
2.2.4. Micronutrient content 10
2.3. Consumer acceptance of edible insects 10
2.4. Methods of processing edible insects 11
2.5 Production and consumption of finger millet and amaranth grains 12
2.5 Nutrient and anti-nutrient content of millet and amaranth grains 13
2.5. Processing methods and their effect on the nutritional value of millet and amaranth grains 15
2.6. Microbial safety of composite flours and storage stability 16
2.7. Sensory acceptability of composite flour products 17
CHAPTER THREE: MATERIALS AND METHODS
3.1. Collection of raw materials 19
3.2. Preparation of raw materials 19
3.2.1. Preparation of crickets 19
3.2.2. Processing of finger millet and amaranth grains 19
3.3. Composite flours formulation 20
3.4 Experimental design 21
3.5. Assessing the chemical composition 22
3.5.1. Analysis of proximate composition 22
3.5.2. Determination of mineral composition 22
3.5.3. Fatty acids determination 23
3.5.4. Determination of water–soluble vitamins 25
3.5.5. Determination of fat-soluble vitamins 26
3.5.6. Assessment of phytic acid, tannins, and flavonoids 27
3.5.7. Determination of mineral bioavailability 27
3.6. Microbiological analysis 28
3.7. Porridge preparation and sensory evaluation 29
3.8. Shelf–life determination 30
3.9. Data analysis 30
CHAPTER FOUR: RESULTS
4.5. Proximate composition 31
4.6. Fatty acids 33
4.7. Vitamin content 41
4.8. Mineral content 42
4.9. Phytic acid, tannins, and flavonoids 44
4.10. Phytic acid/mineral molar ratios 45
4.11. Flavor optimization 46
4.12. Effect of different processing methods on sensory acceptability 49
4.13. Microbial quality of porridge flour samples 52
4.14. Influence of packaging material on microbial load and stability of flours 53
CHAPTER FIVE: DISCUSSION
5.1. Proximate composition 56
5.2. Mineral composition 58
5.3. Fatty acid composition 58
5.4. Vitamin content 60
5.5. Phytic acid, tannins and flavonoids 61
5.6. Phytate/mineral molar ratio 64
5.7. Sensory evaluation 64
5.8. Microbial quality and storage stability 66
CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS
6.1 : Conclusions 68
6.2 : Recommendations 69
Appendix 1: Type of grains and cricket used in this study 96
Appendix 2: Sensory evaluation questionnaire 96
LIST OF TABLES
Table 2.1: Overall nutritional composition of crickets (Acheta domesticus), finger millet and amaranth grain 9
Table 3.1: Formulations for CF1, CF2, CF3 and CF4 composite flours (%) 21
Table 4.1: Proximate and energy values of porridge flour on dry weight basis (dwb) 32
Table 4.2: Compositions of fatty acids (µg/g of oil) of porridge flour samples analyzed using Gas Chromatography coupled to Mass Spectrometry (GC-MS) 34
Table 4.2: Cont’ 35
Table 4.2: Cont’ 36
Table 4.2: Cont’ 37
Table 4.3: Vitamin content (mg/100 g) in porridge flour products 42
Table 4.4: Mineral content of the porridge flour formulations on dry weight basis (dwb) 44
Table 4.5: Mineral bioavailability as influenced by processing methods 46
Table 4.6: Sensory scores for different attributes of flour enriched with cricket powder 48
Table 4.7: Effect of processing on sensory scores for different attributes of finger millet– amaranth flour enriched with cricket powder 50
Table 4.8: Total viable, yeast and mold count (CFU/g) in different flours enriched with cricket..................................53
LIST OF FIGURES
Figure 2.1: Edible cricket (Scapsipedus icipe) and its preparations for human consumption 7
Figure 4.1: Porridge flour samples 31
Figure 4.2: Fatty acid groups in porridge flour samples as influenced by processing 38
Figure 4.3: Total fatty acid composition in different porridge flour samples 39
Figure 4.4: Principal component analysis (PCA) biplots showing the variation of fatty acid methyl esters (FAMEs) among the different porridge flour samples 40
Figure 4.5: Phytochemical content in porridge flour samples 45
Figure 4.6: PCA plot for formulation similarities 47
Figure 4.7: PCA plot for organoleptic scores for different product formulations 49
Figure 4.8: Porridges from the formulated flours 50
Figure 4.9: PCA plot for sensory scores for different treatment formulations 51
Figure 4.10: Principal component analysis (PCA) of six sensory attributes perceived significantly different among flour formulations 52
Figure 4.11: Influence of packaging and storage duration (from 0 to 6 months) on the microbial count, moisture concentration, and free fatty acids in flour formulations 55
ACRONYMS AND ABBREVIATIONS
ALA Alpha-linolenic acid
AOAC Association of Official Analytical Chemists
CF Composite flour
CFU Colony-forming units
DHA Docosapentaenoic acid
EPA Eicosapentaenoic Acid
FAO Food and Agriculture Organization of the United Nations
FAME Fatty acids methyl ester
FM Finger millet
GC-MS Gas Chromatography-Mass Spectrometry
Icipe International Centre of Insect Physiology and Ecology
KDHS Kenya Demographic and Health Survey
PDA Potato dextrose agar
PEM Protein-energy malnutrition
PUFA Polyunsaturated fatty acid
RDA Recommended Dietary Allowance
SDG Sustainable Development Goals
SFA Saturated fatty acid
SSA Sub–Saharan Africa
UNICEF United Nations Children’s Fund
UPLC Ultra-performance liquid chromatography
WHO World Health Organization
CHAPTER ONE: INTRODUCTION
1.1. Background to the study
Malnutrition is a serious health concern in children under the age of five in sub–Saharan African (SSA) countries (Akombi et al., 2017; WHO/UNICEF, 2019). Notably, the most common forms of malnutrition reported in these countries are protein–energy malnutrition (PEM) and deficiencies of important micronutrients including iron, zinc, and vitamin A (Stevens et al., 2013; WHO, 2020). Kenya tops the list of 20 countries that account for 80% of the world’s malnourished children (Bryce et al., 2006) where stunting, wasting, and underweight in children below five years have been estimated at 26, 4, and 11%, respectively (KDHS, 2014). Malnutrition in infancy and early childhood affects physical growth and cognitive behavior leading to delays in mental and motor development, as well as increased morbidity and mortality (Akombi et al., 2017). Low socio– economic status is considered the key underlying cause where the children lack food or survive on diets of low nutritional quality, coupled with improper feeding practices, inadequate care and high rates of infections (Akombi et al., 2017; Anigo et al., 2010). Besides, commercially fortified weaning foods or animal proteins remain unaffordable to most households due to high costs (Muhimbula et al., 2011). Therefore, improving the quality of complementary foods through food- to-food fortification with edible insects is essential in the realization of Sustainable Development Goal (SDG) 2 of Zero hunger which aims at sustainable and improved food and nutritional security and agricultural sustainability (United Nations, 2018).
Porridge is an important traditional beverage in many African countries (Onyango et al., 2004). This porridge is mainly prepared from sorghum, finger millet, cassava and maize flour and serves as an important complementary food for children as well as a refreshing drink for adults (Onyango & Wanjala, 2018; Wanjala et al., 2016). Despite these staples being rich in carbohydrates, their energy and nutrient densities are extremely low (Dewey, 2013). These cereals may also be less nutritious owing to the presence of anti–nutritional factors which form insoluble complexes with protein and key minerals primarily zinc, iron, calcium, and magnesium, thereby leading to poor uptake of these nutrient components (Zhang et al., 2020).
The African continent is blessed with a rich diversity of food crops, most of which have received little or no attention in terms of research and development of policy frameworks that could promote their effective commercial and industrial utilization. Grain amaranth (Amaranthus spp.) and finger millets are some of such neglected and underutilized species that could be used to produce porridge products to serve as important traditional beverages and complementary food for adults and children, respectively, in Africa (Mmari et al., 2017; Onyango et al., 2000). Finger millet grain contains high amounts of proteins and minerals compared to other staple cereals (Saleh et al., 2013; Singh & Raghuvanshi, 2012). On the other hand, amaranth grain is a pseudo–cereal richer in quality protein, lipids and micronutrients (Njoki et al., 2015). Amaranth (Amaranthus spp.) is an indigenous African leafy vegetable grown in at least fifty tropical countries and consumed by several million people (Békés et al., 2017; Ochieng et al., 2019) for many nutritional reasons. Farmers in sub-Saharan Africa cultivate amaranth either for its leaves or for its grain (Ochieng et al., 2019). The leaves are rich in vitamin C and pro-vitamin A as well as in iron, zinc, and calcium (Yang et al.,2009). The grains are also rich in quality protein, lysine, and calcium and are consumed directly or used to fortify maize flour (Njoki et al., 2015; Macharia et al.,2011). However, these grains contain high content of anti–nutrients mostly in the form of phytic acid (Pastor & Ačanski, 2018; Shibairo et al., 2014). These anti-nutrients can be reduced to improve the nutritional quality through traditional food processing methods including soaking, germination, fermentation, roasting, and milling (Saleh et al., 2013).
Globally, there has been a lot of effort in promoting edible insects as a potential solution to food and nutritional insecurity. Current research has established that edible insects contain adequate amounts of protein, unsaturated fatty acids, and essential micronutrients (Cheseto et al., 2020; Kinyuru et al., 2013; Rumpold & Schluter, 2013). Crickets, in particular, are an economically viable source of essential amino acids, fatty acids, vitamins and minerals chiefly zinc and iron (Magara et al., 2021). Besides, crickets are easy and relatively cheap to rear for commercial and subsistence use owing to their high feed conversion efficiency and reproductive potential (Oonincx et al., 2015).
Enriching cereal–based foods with edible insects may improve the nutritional value of staple foods (Ayieko et al., 2010; Kinyuru et al., 2015; Osimani et al., 2018). Enrichment combined with proper processing techniques can provide nutrient–dense food suitable for complementary feeding. However, for a stable intake and legislative purposes, insect–based foods must meet other essential standards such as food safety and sensory acceptability. Acceptance of edible insects as human food remains an obstacle in promoting entomophagy, and this is majorly associated with disgust sensitivity or food neophobia (Megido et al., 2016). Choice of insect–based products as part of the consumers’ regular diet can be related to a number of factors not limited to visual appearance, taste and good quality while overlooking the general environmental sustainability and/or protein quality (House, 2016). The current study, therefore, evaluates the differences among formulations of finger–millet–amaranth porridge flour enriched with cricket and the effect of processing methods on nutritional properties, anti–nutritional factors, sensory acceptability and storage stability.
1.2. Statement of the problem
High levels of Protein Energy Malnutrition (PEM) and hidden hunger are major challenges amongst children below five years in developing countries such as Kenya. In these countries, high starch and less nutrient–dense food such as cereals and tubers are customarily used for complementary feeding. These staples are an excellent source of nutritional energy but are considered low in various essential amino acids and micronutrients necessary for healthy growth (Dewey, 2013; Onweluzo & Nnamuchi, 2009; Tizazu et al., 2010), they also contain high anti– nutrient content which inhibit the bioavailability of essential minerals and lower protein digestibility. Feeding young children on these cereals and tubers exposes them to malnutrition. Furthermore, improper feeding practices, coupled with inadequate care and high rates of infections are other underlying factors associated with child malnutrition (Akombi et al., 2017; Anigo et al., 2010). On the aspect of food safety, contaminated complementary foods are associated with diarrhea and malnutrition among infants and young children, hence the need to ensure that complementary foods do not pose a risk of gastrointestinal diseases (Rahman et al., 2016). Therefore, the enrichment of cereal–based porridge flour using edible insects combined with proper processing techniques would result in a nutrient–dense food product suitable for weaning. Additionally, there is inadequate information on the utilization of edible insects such as crickets in complementary foods.
1.3. Justification of the study
Edible insects are widely acknowledged to contain adequate amounts of protein, unsaturated fatty acids, and essential micronutrients, thereby meeting the nutritional requirements for young children. Crickets are economically viable sources of essential amino acids and minerals like zinc, calcium, and iron. Suggestively, fortification of traditional staple food like finger millet–based porridge flour is a more effective way of alleviating malnutrition among infants and young children. Furthermore, suitable traditional processing methods such as fermentation, roasting and germination would reduce the anti–nutrient content hence improving nutrient bioavailability. The adoption of well–formulated finger millet–amaranth–cricket food would be impetus in curbing malnutrition among vulnerable groups, particularly young children under the age of five.
The study would also improve feeding practices, diversification of eating habits and promote the culture of consuming edible insects. In addition, the rearing and marketing of edible crickets could also provide an alternative means of income to many families hence improving their livelihoods.
1.4.1. Overall objective
The overall objective of this study was to develop and evaluate finger millet–amaranth-based porridge flour enriched with edible cricket.
1.4.2. Specific objectives
i. To determine the nutrient and anti–nutrient composition of composite flours formulated from finger millet, amaranth, and cricket flours.
ii. To determine the sensory acceptability of the porridges made from finger millet, amaranth and cricket composite flours.
iii. To determine the microbial safety of the composite flours made from finger millet, amaranth and cricket.
iv. To establish the shelf stability of the formulated composite flours made from finger millet, amaranth and cricket.
i. Composite flours formulated from finger millet, amaranth and cricket do not have the same nutrition value as commonly consumed porridge flour.
ii. Enrichment of finger millet-amaranth flour with cricket powder has no effect on the sensory acceptability of its porridge.
iii. The microbial load of the composite flour formulated from finger millet, amaranth and cricket is not within the recommended limit.
iv. The composite flour formulated from finger millet, amaranth and cricket is not shelf stable under conventional storage conditions.
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