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Novel mild fractionation of faba bean (Vicia faba L.) and physicochemical and functional characterization of protein as a food ingredient
- Author / Creator
- Jeganathan, Brasathe
Alternative planet-friendly protein sources are increasingly acknowledged as a sustainable solution to supplement the global animal-derived protein demand. Among the pulses, faba bean (Vicia faba L.) has such potential. The isolation of faba bean protein can minimise the anti-nutritional, flatulence-causing, and beany flavour compounds. Optimization of faba bean fractionation warrants the understanding of the distribution patterns of macro-components within the bean. Dry fractionation methods are a sustainable alternative to energy-intensive alkali extraction but can lead to relatively moderate protein enrichment. Depending on the extraction method, protein functionality may vary; however, such information is limited for faba bean proteins. Therefore, a systematic investigation was performed to characterise the faba beans, evaluate different fractionation techniques, and assess the physicochemical and functional properties of the protein fractions.
In the first study, the abaxial (cotyledon-seed coat) and adaxial (cotyledon-cotyledon) topographies of pulses were confirmed to have varietal differences associated with their micromorphological characteristics and the complex cuticle layer on their adaxial surface, which would impact their ease of milling/pearling. In the second study, compositional analyses of sequentially pearled fractions of high-tannin (HT, Athena) and low-tannin (LT, Snowbird) faba bean cultivars demonstrated a decreasing trend of protein, ash and total dietary fibre contents from outer to inner layers, which was offset by starch. The 55-57% single-step pearling flour had a higher protein content (LT: 39.1% and HT: 37.4%) compared to whole beans (LT: 30.5% and HT: 29.6%). Aqueous fractionation of the single-step pearling flour resulted in protein and starch isolates and dietary fibre concentrates. The protein and dietary fibre contents of LT and HT faba beans were positively correlated with the increasing particle size, which was offset by starch (study three). Subjecting the dehulled bean flours to Air-Currents-Assisted Particle Separation (ACAPS) resulted in both protein- and dietary fibre-rich coarse fractions. Aqueous extraction and micellization of the ACAPS-treated coarse fractions (250-500 μm) resulted in protein isolates (LT:.97.7 % and HT: 94.3%).
The impact of different mild wet fractionation conditions was established in the fourth study in terms of yield, purity and recovery of faba bean protein concentrates/isolates (PCs/PIs). Although salt-soluble globulins (74-75%) were the primary proteins in faba beans, PIs resulting from dialysis (D) or micellization (M) following water extraction at 35°C (W35) at a solvent/feed ratio of 2 had higher protein contents (LT: >93% and HT: 96%) than PCs from NaCl(aq) solution (1% (w/v)) extraction at 23ºC (S23) followed by D (LT: 79.1% and HT: 81.6%) or alkali extraction followed by acid precipitation (AA) (LT: 87.1% and HT: 86.3%). High levels of naturally occurring minerals in faba beans contributed to the extractability of high-quality PIs by W35, including albumins. W35-PIs were low in raffinose family oligosaccharides, tannins and trypsin inhibitory activity.
The size distribution of the PI particles obtained by W35 and S23 was similar in water suspensions (study five). The pre-dominantly amorphous nature of PCs/PIs was confirmed by XRD. Based on XRD and FTIR analyses, β-sheet structures were the most abundant secondary structures and W35 extraction had minimal impact. W35-D-PIs had superior solubility, colour parameters and foam stability compared to the AA-PCs (study six). Emulsion stability and foaming and emulsifying capacities of W35-PIs were comparable to those of AA-PCs. S23-D-PCs had relatively limited functional properties, probably due to the interference of salt deposits. AA-PCs had superior hydration capacities and low surface hydrophobicity, but starch and dietary fibre could have also contributed. The gelation of faba bean protein was temperature-dependent and influenced by the degree of protein denaturation (Appendix C). W35-D-PIs had the highest stress and strain at fracture at their minimum gelling concentration and formed the strongest gels. Faba bean protein with konjac glucomannan and canola oil formed more stable networks comparable to that of whole eggs. Thus, the potential of W35-D-PIs for use in vegan liquid egg analogue formulations was demonstrated.
In summary, the findings established that the inclusion of pearling or ACAPS as upstream processing steps prior to wet fractionation of faba beans uses less water than conventional methods and has the potential to create new markets for the underutilised high tannin faba bean cvs. and generate novel “clean label” food ingredients. Overall, the W35-PIs demonstrated superior physicochemical and functional properties compared to S23-PCs and are chemical-free sustainable alternatives to AA-PCs for food applications.
- Graduation date
- Fall 2023
- Type of Item
- Doctor of Philosophy
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