Faculty of Applied Sciences
Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/5
Browse
5 results
Search Results
Item Valorisation of bambara and cowpea haulms for bioethanol production(2020) Okuofu, Somiame Itseme; Pillai, Santhosh Kumar KuttanBambara and cowpea are important pulses grown in semi-arid South Africa due to their balanced nutrient profile and drought resilient capacity. The haulm is the lignocellulosic residue obtained after grain harvest and are rich in carbohydrates. However, these haulms are underutilised and under researched. The aim of the study, therefore, was to investigate the potential to valorise bambara haulms (BGH) and cowpea haulms (CH) to bioethanol which is the most promising biofuel with commercial prospects currently. The structural and chemical composition of BGH and CH was elucidated using techniques such as compositional analysis, XRD, FTIR, ICP-AES, and SEM. Results indicated a volatile matter and fixed carbon mass fraction of 77.70% and 13.15% (w/w) in BGH and 76.16% and 16.26% (w/w) in CH respectively. The polysaccharides make up the largest fraction (51%), followed by extractives (> 20%), while the lignin in BGH (12%) and CH (10%) was low. X-ray diffraction pattern showed a higher percentage of amorphous regions in BGH (78%) than CH (56%). CH was then subjected to dilute acid pretreatment (DAP) to enhance biosugar production for bioethanol fermentation. The effects of operational factors for DAP including temperature, time, and acid concentration on sugar yield and inhibitor formation was investigated and optimised using response surface methodology (RSM). The solid recovered after DAP was subjected to prehydrolysis with simultaneous saccharification and fermentation (PSSF). In addition, the pretreatment hydrolysate was detoxified and fermented to ethanol using cocultures of Saccharomyces cerevisiae BY4743 and Scheffersomyces stipitis wild type (PsY633). A total ethanol titre of 15.67 g/L was obtained corresponding to 75% conversion efficiency. On the other hand, BGH was subjected to deep eutectic solvent (DES) pretreatment. Five deep eutectic solvents were prepared and screened for their effectiveness in improving enzymatic sugar yield. This was achieved by pretreating BGH with each DES followed by a 48 h enzymatic saccharification. Choline chloride – lactic acid (ChCl-LA) treatment provided the most promising result and was further optimised by investigating the effect of different temperatures and time on cellulose loss and enzymatic sugar yield. ChCl-LA pretreatment at 100°C for 1 h was observed to be the best condition for maximum sugar recovery. The hydrolysate thus obtained was concentrated and fermented for 72 h with S. cerevisiae BY4743. A maximum ethanol yield of 11.57 g/L was obtained. From the results, it is evident that bambara and cowpea haulm are promising substrates for bioethanol production. Dilute acid hydrolysis was shown to be effective in the pretreatment of CH with over 85% of the theoretical sugar recoverable for conversion to bioethanol. In addition, deep eutectic solvents are effective media for breaking the recalcitrance in BGH to achieve high sugar yield for conversion to bioethanol. However, further studies are required to reduce cellulose loss during pretreatment to improve bioethanol yield.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 Characterisation and application of bambara protein-polysaccharide complex coacervates in encapsulation of bioactive compounds(2019) Busu, Nyasha M.; Amonsou, Eric OscarBambara groundnut (Vigna subterranea) is a leguminous crop that is indigenous to Africa. In South Africa, the legume is cultivated in KZN, Limpopo and Mpumalanga where it is considered a traditional food. Bambara groundnut is a good source of protein (15 – 28 %) and contains substantial amounts of starch. The legume thrives well in areas of low agricultural input. Despite its good protein content, bambara groundnut is mostly cultivated in rural areas for by subsistence farmers. In recent years, there has been increased interest in bambara groundnut protein as an alternative protein source. The purpose of this study is to investigate the complexation behavior of bambara protein with gum Arabic and test the application of the formed complexes in encapsulation and delivery of bioactive compounds. In the first part of this study, four protein fractions extracted at different pH including the salt-solubilisation method were complexed with gum Arabic. The protein content as well as physicochemical properties (SDS-PAGE, FTIR, Zeta potential, SEM) of the protein fractions and resulting bambara protein-gum Arabic (BPI-GA) complexes were then investigated. In subsequent parts of the study, bambara protein extracted by the salt-solubilisation method was complexed with gum Arabic. The influence of ionic strength and biopolymer mixing ratio on complex formation was investigated. Subsequently, the emulsification properties, foaming properties, encapsulation efficiency and release properties of the formed complexes were also investigated under simulated gastric and intestinal pH conditions. The salt-soluble fraction showed the highest protein content (82%) whilst the lowest protein content (76%) was recorded at pH 2. The FTIR analyses revealed an increase in β-sheet content with decrease in pH of extraction. Complexation of the protein fractions with GA resulted in the optimal pHs of interaction shifting towards acidic regions (pHopt: 4.8 to 2.9) as pH of protein extraction became more acidic. Upon complexation, protein fractions produced coacervate yields ranging between 41 - 68%, with the pH 2 fraction recording the lowest (41%) yield. Further, addition of gum arabic seemed to broaden the turbidity profiles. When assessed by SEM, the particles appeared as spherical and aggregated structures between 100-200 nm.Item Incidence of mycotoxigenic fungi during processing and storage of bambara groundnut (Vigna subterranea) composite flour(2019) Olagunju, Omotola Folake; Ijabadeniyi, Oluwatosin Ademola; Mchunu, Nokuthula PeaceFungal contamination of food commodities is a global food security challenge that impacts negatively on the health of consumers. Mycotoxins are produced as secondary metabolites by some pathogenic fungi and may contaminate agricultural products while on the field or during harvesting and storage. Processing operations and storage conditions of temperature and relative humidity have marked effect on the ability of fungal pathogens to grow and produce mycotoxins in agricultural food commodities. The consumption of mycotoxin- contaminated foods, even at low doses over a prolonged period of time, may have deleterious effects on health of consumers. Bambara groundnut (Vigna subterranea (L.) Verdc) is an African legume gaining wide acceptance in various food applications due to its favourable nutritional composition, especially the high protein content. In several parts of Africa, it is used as a supplement in cereal-based foods, especially in weaning food for infants and young children. Bambara groundnut grows near or under the soil, which serves as inoculum of pathogenic fungi. Very little information is presently available on fungal and mycotoxin contamination of Bambara groundnut from Southern Africa. Hence, its safety for consumption from a mycological standpoint requires further studies. To establish the profiling of fungal contaminants in food commodities consumed in Durban, South Africa, 110 samples of regularly consumed food samples which included rice (23), spices (38), maize and maize-derived products (32), and Bambara groundnut (17) were randomly collected over a period of five months from retail stores and open markets. The food samples were screened for fungal contamination using conventional and molecular methods. Fungal isolates were characterized following DNA extraction, polymerase chain reaction and sequencing. Using a modified QuEChERS method, the detection and quantification of mycotoxins in Bambara groundnut was performed via Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS), and isolation and detection of the causative pathogen was carried out. The effect of processing operations of milling, a combination of roasting and milling, and spontaneous fermentation on the survival of the natural fungal population of Bambara groundnut, and aflatoxin production under simulated tropical conditions of storage was further studied. Processed Bambara groundnut flour samples were stored at temperature of 30±1 °C and 85±2% relative humidity for 30 days, vi and samples withdrawn at 5-day intervals for analyses, i.e., fungal counts, aflatoxin accumulation and changes in water activity during storage. Following the detection of aflatoxins in Bambara groundnut flour and the isolation of aflatoxigenic Aspergillus flavus in the seed, the effect of milling, roasting and milling, or lactic acid bacteria fermentation on the survival, growth and aflatoxin production of A. flavus in Bambara groundnut flour was studied. Irradiated seeds of Bambara groundnut were artificially inoculated with a 3-strain cocktail of A. flavus (2 x 106 spores/mL) and processed by milling, roasting at 140 °C for 20 min and milling. Slurries of irradiated Bambara groundnut flour were also inoculated with A. flavus spores and 1 x 108 CFU/mL inoculum of Lactobacillus fermentum or Lactobacillus plantarum. All inoculated samples were incubated at 25 °C for 96 h, samples withdrawn every 24 h were analyzed for viable A. flavus counts, changes in water activity during incubation, and aflatoxin production using Enzyme- linked Immunosorbent Assay (ELISA). Bambara groundnut flour samples fermented with lactic acid bacteria were further analyzed for pH, total titratable acidity, and viable lactic acid bacteria counts over the incubation period. The degradation of aflatoxin (AF) B1 by both lactic acid bacteria was also studied. Slurries of irradiated Bambara groundnut flour were spiked with 5 µg/kg of aflatoxin B1 (AFB1) and the percentage reduction over the incubation period was determined using HPLC. The survival, growth and aflatoxin production of A. flavus in Bambara groundnut and maize- composite flours as affected by milling, roasting and milling or lactic acid bacteria fermentation during storage was also studied. Processed and irradiated Bambara groundnut flour, maize flour and maize-bambara composite flour (70:30) were inoculated with 2 x 107 spores/ml of A. flavus and stored for up to 10 weeks at a temperature of 25±2 °C and relative humidity of 75±2%. Samples were withdrawn weekly and analyzed for viable populations of A. flavus, concentrations of aflatoxins B1, B2, G1 and G2, changes in pH and water activity over the storage period. The colonization of Bambara groundnut by A. flavus and the effects of fungal infection on the seed coat, storage cells and tissue structures were also studied. Irradiated Bambara groundnut seeds were artificially inoculated with spore suspension of aflatoxigenic A. flavus (2 x 106 spores/mL) and stored at a temperature of 25±2 °C and relative humidity of 75±2% for 14 days. Samples were withdrawn at 24 h intervals for 4 days, then at 7 and 14 days and examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Various fungal genera were isolated from the food samples under study with Aspergillus (52.5%) and Penicillium (31.8%) as the dominant genera. All the 110 food samples were contaminated with more than one fungal species. A. flavus and other Aspergilli, Penicillium citrinum and Fusarium oxysporum were isolated from Bambara groundnut seeds. Aflatoxigenic A. flavus was isolated from Bambara groundnut seed, with a co-occurrence of Aflatoxin (AF) B1 (0.13–6.90 µg/kg), AFB2 (0.14–2.90 µg/kg), AFG1 (1.38–4.60 µg/kg), and AFG2 (0.15–1.00 µg/kg) in the flour. The fungal counts of the samples during storage significantly (p≤0.05) increased, irrespective of the processing method from 6.3 Log10 CFU/g in Bambara groundnut flour to 6.55 Log10 CFU/g in fermented Bambara groundnut flour. Aflatoxin concentration was affected markedly by the processing methods in Bambara groundnut flour (0.13 µg/kg) and fermented Bambara groundnut flour (0.43 µg/kg), aflatoxin was not detected in roasted Bambara groundnut flour. The survival and growth of A. flavus was also markedly affected by lactic acid bacteria fermentation and roasting during incubation. Within 24 h of fermentation with L. fermentum, significant (p≤0.05) changes were recorded in viable population of A. flavus (6.30‒5.59 Log10 CFU/mL), lactic acid bacteria count (8.54‒13.03 Log10 CFU/mL), pH (6.19‒4.12), total titratable acidity (0.77‒1.87%) and a reduction by 89.2% in aflatoxin B1 concentration. Similar significant changes were recorded in Bambara groundnut flour fermented with L. plantarum. Aspergillus flavus in the artificially contaminated seeds were completely eliminated by roasting. Aflatoxin production was not detected in Bambara groundnut flour samples over the incubation period. During storage for 10 weeks, the population of A. flavus significantly (p≤0.05) decreased in roasted Bambara groundnut flour from 7.18 to 2.00 Log10 CFU/g. Similar significant (p≤0.05) decrease in A. flavus viable counts was recorded in fermented Bambara groundnut flour from 6.72 to 2.67 Log10 CFU/g, however after 7 weeks of storage and beyond, A. flavus was not detected. Significant (p≤0.05) decrease in aflatoxin B1 (0.36‒0.26 µg/kg) and aflatoxin G1 (0.15‒0.07 µg/kg) accumulation was also recorded in roasted Bambara groundnut flour. While A. flavus viable population significantly (p≤0.05) decreased in maize-Bambara composite flour from 6.90 to 6.72 Log10 CFU/g, aflatoxin B1 accumulation significantly (p≤0.05) increased from 1.17 to 2.05 µg/kg. Microscopy studies showed that the seed coat of Bambara groundnut was rapidly colonized by A. flavus within 24 h of inoculation. The infection of internal tissues of the cotyledon was through the ruptured seed coat, resulting in a disruption of the cellular architecture. Cell wall collapse, development of cavities in parenchymatous cells and ruptured storage cells resulted from A. flavus infection of the seed. This study reports a high prevalence of fungal contamination in some food commodities consumed in Durban, South Africa. The isolation of live mycotoxin-producing fungi from the food commodities necessitates the need for regular routine checks to ensure the mycological safety of agricultural products offered for sale to consumers. The detection of aflatoxigenic A. flavus and aflatoxins in Bambara groundnut flour at levels above the maximum tolerable limits raises health concerns on its utilization in food applications, and in supplementary feeding for infants and young children. Although roasting was effective in degradation of aflatoxins in Bambara groundnut seeds, elimination of fungal contaminants was not achievable which resulted in continued production of aflatoxin during storage. Fermentation using L. fermentum or L. plantarum is effective in eliminating A. flavus and degrading AFB1 in Bambara groundnut flour. Compositing Bambara groundnut with maize increased aflatoxin production in the flour. It is therefore necessary to implement legislation for aflatoxins in Bambara groundnut, and develop effective management practices during planting, harvesting and storage that will mitigate A. flavus infection in Bambara groundnut.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.