Faba bean : a New Zealand study on an underutilized plant-based protein source : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Palmerston North, New Zealand
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2024
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Massey University
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Abstract
Faba bean (Vicia faba) is a high protein legume crop that is highly underutilized in most parts of the world, including New Zealand. The objective of this research was to investigate the varieties of faba beans that are native to New Zealand based on their physical and micro structural features and how they affect cooking properties of the beans. A readily available commercial variety was used for extraction of protein concentrates and an optimum extraction method was researched in this study. The physical and micro-structural characteristics of the four faba bean native varieties (Early Long Pod, Evergreen, Coles Dwarf and Janet) and their relationship with cooking time were studied. The Janet variety has the highest sphericity, equivalent diameter, thousand kernel weight, seed volume and surface area. The Evergreen variety was the most distinguishable in colour as it presented green hues in comparison to the others which had comparable brown tones. The beans were subjected to boiling and the time taken for appropriate tenderness of the bean was investigated. The Janet variety took the longest cooking time of around an hour and 15 minutes and the least for Evergreen variety. Similarly, beans which had been subjected to prior overnight soaking showed significant decrease in cooking time to around 35 minutes. These results were in accordance with microstructure results which showed that raw beans of the Janet variety had the thickest cotyledon cell wall and the highest degree of surface irregularities suggesting slower water absorption in the seed. Scanning electron microscope showed the presence of large spherical starch globules in a protein granule matrix enclosed in a cell wall. The ground bean flours showed high levels of protein (24-27%) and starch content (35-39%). Rapid Visco Analyzer presented results for pasting temperature, which was roughly 76-77°C for all varieties, was essential to comprehend the behaviour of starch gelatinization and shed gave light on the minimum temperature required to cook the flour and the functional characteristics of starch in a range of applications. The high protein concentration of the faba beans presented the opportunity for extraction of protein concentrates. A commercial variety of faba beans was used to extract protein concentrates using aqueous extraction techniques, mainly acidic, alkaline and neutral conditions. The alkaline method produced the highest yield and the purest concentrate among the three methods. Acidic conditions caused significant change in the physical colour of the concentrate after extraction, leading to a bright and fine powder compared to the coarser and darker concentrates extracted by water and alkaline methods. and other functional properties of the concentrate. The concentrates when subjected to protein denaturation using a Differential Scanning Calorimeter, showed that water extracted concentrates had the highest denaturation temperature which represented the denaturation of legumin and the low temperature in acid extraction method represented the denaturation of vicilin. During strain-dependent rheological experiments, the high yield strain values for water extraction method helped explain the flexible and elastic protein network of this concentrate. Also, protein concentrates were studied using SDS-PAGE to characterize the type of proteins present in the concentrates. Alkaline extraction showed higher amounts of both high and low molecular weight components of convicilin, α-legumin and β-legumin; acid extraction showed higher amount of low molecular weight bands corresponding to α-legumin, β-legumin and a small number of lectins (thin band) with low intensity bands; water extraction showed thick and intense high and low molecular weight bands corresponding to all the native protein constituents including convicilin and α- and β-legumin. Individual protein bands could be seen clearly on the gel by reducing the disulphide linkages to reveal distinct molecular weight bands using β-mercaptoethanol as a reducing agent.
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Figure (i) and Table (iii) are reproduced with their respective publisher's permission.