Theses and dissertations (Applied Sciences)
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Item Quality and microbiological study of bambara groundnut fortified injera, a fermented flat bread(2020-04) Jula, Mellisa Nokulunga; Ijabadeniyi, Oluwatosin AdemolaCereal fermented products are popular in developing countries, especially in Asia and Africa, because of their unique taste and fulfilment. Throughout the years, they have played a vital part in bringing up infants as part of their weaning foods and contributing to the daily diet of many households. Food fortification and supplementation of cereal grains with inexpensive readily available legumes, which have higher protein content compared to cereals may lead to a potential decrease in protein-energy malnutrition. Underutilised and indigenous crops such as Bambara groundnut can be in incorporated into the fermentation of cereal fermented foods, such as injera. In this study, injera was prepared by substituting only 9% and 12% Bambara groundnut flour and comparing them with the traditionally fermented original control, which is injera made from only tef flour. The first part of the study was to identify and characterise the lactic acid bacteria (LAB) and yeast involved in the spontaneous fermentation of traditional tef-injera and the newly developed injera fortified with Bambara groundnut (which contains 12% Bambara groundnuts) at different fermentation intervals of 0, 24, 48, and 72 hour. A total of 70 LAB isolates and 30 yeast isolates were identified from both fermentations using rep-PCR fingerprinting followed by sequencing the 16S rRNA gene and the D1/D2 region of the 26S rRNA gene. Weissella confusa, Lc. lactis and Lb. curvatus predominated in both fermentations at different intervals of the fermentation. The second part of the study investigated the effectiveness of the isolated LAB starter cultures on the production of injera and injera fortified with Bambara groundnut after which their physicochemical properties were evaluated. There was a significant increase (p<0.05) in titratable acidity and a significant decrease in pH to below four within 24 hours; recorded for samples inoculated with LAB starter cultures when compared to samples fermented without inoculation. The third and fourth parts of the study investigated the proximate composition and storage stability of the injera samples. Injera fortified with 12% Bambara groundnut + LAB culture had a significantly high (p<0.05) protein of 23.21%, the lowest protein content being Tef injera at 7.35%. The protein digestibility of Tef injera increased with the addition of Bambara groundnut and LAB starter culture. The digestibility of protein increased from 40% for Tef injera to 80% for injera fortified with 12% Bambara flour + LAB culture. There was no significant increase (p >0.05) in the amino acid content after the addition of Bambara flour + LAB cultures; the amino acid concentrations were slightly lower than the standard concentration recommended by the Food and Agricultural Organisation/World Health Organisation for adults. Injera samples fortified with Bambara groundnut flour and inoculated with lactic acid starter cultures were stable with microbial counts ranging from 4.42 log cfu/g to 4.68 log cfu/g for TPC at 4 ̊C, yeast and mould, coliforms and aerobic spore formers were not detected in all the samples from day 0 to day three upon storage. Higher counts had been perceived at room temperature ranging from 4.60 log cfu/g to 7.53 log cfu/g for moulds and 4.90 log cfu/g to 9.26 cfu/g for TPC; coliforms were detected in one tef injera only ranging from 4.48 log cfu/g to 6.16 log cfu/g and no detection of aerobic spore formers in all samples. Refrigeration temperatures effectively maintained the microbiological quality of injera for three days. The nutritional quality, distinctively the protein content increased with the addition of Bambara groundnut flour and through the use of lactic acid bacteria as a starter culture This will potentially pave the way for the commercialisation of injera in the industry with the use of LAB starter culture to ensure a fast and continuous supply of fresh injera that is in high demand.Item Enzymatic modification of amadumbe flour for gluten-free applications(2018) Manhivi, Vimbainashe Edina; Kudanga, Tukayi; Amonsou, Eric OscarThe production of gluten-free bread from gluten-free flours remains a technological challenge. Different strategies have been employed to improve the dough rheological properties. Enzymatic modification of the proteins in dough may result in polymers that mimic gluten. In this study gluten-free amadumbe flour was modified using single and optimised multiple crosslinking enzyme systems for the improvement of rheological properties and bread quality. Specifically, compositional, rheological and thermal properties of amadumbe and cactus mucilages were investigated as potential hydrocolloids and as substrates for crosslinking enzymes in gluten-free bread production. The effects of laccase, tyrosinase and transglutaminase on amadumbe dough rheology were also investigated. Model reactions were used to demonstrate the different enzymatic reactions occurring in amadumbe dough treated with the crosslinking enzymes. The combination of enzymes was then optimised using response surface methodology (RSM), to produce dough with improved G’ and G”. Xanthan gum, amadumbe mucilage or cactus mucilage were then added to the dough with an optimum enzyme combination. The effect of these enzymes and hydrocolloids were studied on the bread properties. The mucilages had a similar composition of monosaccharides and amino acids, except for the absence of rhamnose in amadumbe mucilage. Cactus mucilage showed a pseudoplastic flow behaviour whilst amadumbe mucilage showed a Newtonian flow behaviour at up to 5% (w/v) concentrations. The mucilages contained phenolics and amino acids such as lysine, tyrosine and glutamine, which are potential enzyme substrates. Trametes versicolor laccase catalysed the crosslinking of phenolics and thiols producing a wide range of crosslinking products which included homo- and hetero-conjugates, as demonstrated by mass spectroscopy. Thiol and total phenolic contents of dough decreased by up to 28% and 93%, respectively, as laccase activity was increased (0-3 U/g flour), confirming crosslinking reactions. Laccase-catalysed modification of amadumbe dough increased dough viscoelasticity, as shown by the increase in G’ and G”. Tan δ decreased with increase in laccase activity indicating an increase in the elastic character of the dough. Tyrosinase oxidation resulted in a 7.7 – 39.4% decrease in dough free amine and a 16.8 – 46.3% decrease in the dough thiol content as activity was increased (0-80 U/g flour). Transglutaminase treatment decreased the dough free amino groups by 10 – 38.1% as activity was increased from 0 to 2 U/g flour. An increase in dough G’ and G”, showed that both transglutaminase and tyrosinase improved dough viscoelasticity. Evidence of transglutaminase and tyrosinase crosslinking was provided by relevant model reactions monitored by mass spectrometry. Reaction model data showed the formation of the glutamyl-lysine bond due to transglutaminase crosslinking, whilst tyrosinase crosslinking resulted in disulphide and dityrosine bond formation. The viscosity and elasticity of amadumbe dough containing soy protein were optimised using a central composite design and the enzyme combination resulting in maximum G’ and G”, and minimum Tan δ was selected and verified. The predicted optimal enzyme activities (LAC, 1.78 U/g flour), (TYR, 79 U/g flour) and TG, 1.97 U/g flour) resulted in amadumbe dough that had a higher G’ and G”, as well as bread with a higher specific volume and lower crumb hardness compared to the dough without enzymes or with a single enzyme system. Addition of cactus and or amadumbe mucilage to the dough containing the optimum enzyme combination further improved dough viscoelasticity, improved bread specific volume, and significantly (p < 0.05) reduced bake loss and crumb moisture loss. The better bread was produced from dough with an optimum enzyme combination and 2% cactus mucilage. Sensory evaluation revealed that enzymes and cactus mucilage improved bread texture, appearance and overall acceptability but did not significantly affect bread aroma and taste. Overall, the combined effect of multiple enzyme-catalysed modification of gluten-free amadumbe flour and amendment with hydrocolloid resulted in more acceptable bread quality than single enzyme systems or unmodified flour. Therefore the optimised combination of enzymes have potential for application in gluten-free bread production.Item Effect of pectin and emulsifiers on quality and stability of wheat composite bread(2018) Ajibade, Betty Olusola; Ijabadeniyi, Oluwatosin AdemolaFortification and supplementation of wheat flour with other flour sources containing essential amino acids such as lysine, for bread production could help overcome the problem of protein- energy malnutrition. Indigenous and largely underutilised crops such as millet and bambara groundnut could be incorporated into staple foods such as bread. In this study, the rheological behaviour and quality characteristics of dough and bread made from wheat-millet-bambara flour (WMB) containing mixtures of emulsifiers and apple pectin were investigated for their suitability in breadmaking. WMB was prepared by substituting wheat flour (WF) with 25% each of millet flour (MF) and bambara flour. Pectin was added (1.0-2.0 g/100 g flour) and emulsifiers namely sodium stearoyl lactylate (SSL) (0.25-0.4 g/100 g flour), polysorbate 80 (PS80) (0.5-0.8 g/100 g flour), and diacetyl tartaric acid ester of monoglycerides (DATEM) (0.1-0.25 g/100 g flour) were mixed and added in different proportions. A Mixolab was used to measure the rheological behaviour of dough. The resulting bread was analysed for physical characteristics, nutritional composition, and organoleptic properties. Bread samples were stored at room temperature (±25℃), refrigeration (4℃) and freezing (-18℃) for 7 days. The bread samples were then investigated for firmness, compression energy, colour, visual observation of mould growth (VO), total aerobic plate count (APC) and fungal counts (FC). From the Mixolab analysis of composite dough, a significant increase (p<0.05) in the dough development time and dough stability were observed. The loaf volume, specific volume and proximate composition of the composite bread increased significantly (p<0.05) relative to the control. The protein content (33%), protein digestibility (85%) and some essential amino acids (lysine: 54.6%; threonine: 36.4%) increased significantly (p<0.05) compared to wheat bread (control) WF. Sensory evaluation revealed above-average acceptability for composite bread. Also, the pectin-treated bread (PTB) was significantly different (p<0.05) in firmness (8.47 N) compared to wheat flour bread (WF) (10.33 N) at -18℃ after 7 days of storage. The WF had the lowest firmness (8.32 N) at room temperature (±25℃) storage lower than the PTB (9.25 N) and emulsifier-treated bread (ETB) (12.37 N) after 3 days storage at room temperature (±25℃). Bread firmness decreased significantly (p<0.05) with an increase in storage time for all samples. The APC for all bread samples ranged from 3.02 log cfu/g to 6.19 log cfu/g and fungal count (FC) ranged from 3.48 log cfu/g to 4.86 log cfu/g. The PTB had the highest APC (6.19 log cfu/g) among bread samples stored at room temperature (±25℃) while it also had the lowest APC (3.02 log cfu/g) at the same storage temperature (±25℃). It was found that all bread samples stored at -18℃ did not show no sign of mould growth. The use of bakery products’ acceptable limits of emulsifiers and pectin for this study significantly improved the dough rheology, physical characteristics, nutritional and sensory acceptability of WMB composite bread. The shelf life studies showed improved firmness, low microbial counts and a slower rate of degradation in cold storage conditions. This study revealed that there is potential for supplementation and fortification of wheat bread with flours from millet and bambara sources.