Comprehensive analytical profiling of soluble and bound phenolics of beans from selected underutilised legumes

Tan, Poh Hwa (2018) Comprehensive analytical profiling of soluble and bound phenolics of beans from selected underutilised legumes. PhD thesis, University of Nottingham.

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Abstract

Beans are seeds of leguminous plants and are rich in macronutrients and micronutrients such as polyphenols predominantly phenolic acids and flavonoids that may have health benefits arising from their antioxidant and other properties. Beans, especially from underutilised legumes, may play an important role in future world food supply. However, there has been limited investigation into the nutritional composition of underutilised beans compared with commercial beans such as soya bean. Therefore, this study aimed to improve the extraction, identification and quantification methodologies for characterizing soluble free, conjugated and insoluble bound phenolics from underutilised beans using high performance liquid chromatography (HPLC) and liquid chromatography – mass spectrophotometry (LC-MS).

Six underutilised beans (adzuki bean, black eyed pea, bambara groundnut, lablab bean, mung bean, pigeon pea) were found to possess a comparable amount of antioxidant activity to commercial beans and this showed positive correlation with their phenolic compounds. Optimisation revealed that 80% methanol was most suitable for extracting soluble phenolics compared with 80% acetone and acetate buffer, although subsequent HPLC profiling showed strong similarities among all three solvents. Alkaline hydrolysis for 5 mins followed by SPE partitioning on soluble extracts and alkaline hydrolysis for 1 h followed by acetonitrile salting out liquid-liquid partitioning on residue were the optimum procedures for estimating the conjugated phenolics and releasing the bound phenolics. The methods showed better recovery, were more solvent friendly and had shorter drying times than ethylacetate liquid-liquid partitioning.

Using 20 phenolic standards, more phenolics were detected by LC-MS than HPLC. Black eyed pea had the most diverse soluble phenolics profile (n=13), followed by adzuki bean and bambara groundnut (n=11) whilst soya bean exhibited the most diverse bound phenolics profile (n=7), followed by pigeon pea and adzuki bean (n=5). Five phenolics were found at the highest concentration in bound extracts from adzuki bean (consist of gallic acid at least 5-fold higher than in soya bean), bambara groundnut (consist of protocatechuic acid at least 160-fold higher than in soya bean), lablab bean (consist of p-coumaric acid at least 3-fold higher than in soya bean), black eyed pea (consist of ferulic acid at least 0.5-fold higher than in soya bean), soya bean (sinapic acid) and others were found at highest concentrations in soluble extracts from different beans.

In conclusion, this study has achieved its objectives by developing the comprehensive profiling of phenolics for underutilised beans with optimised extraction methodologies and analysis techniques. The outcome was that underutilised beans are potential alternative resources to commercial beans since they possess higher concentrations of, and more diversified, phenolics than soya bean. This is the first report of optimised extraction methodologies and analysis techniques for the comprehensive analysis of phenolics in underutilised beans. It has generated phenolic profiles from the application of the optimised methodologies and produced useful reference databases for future studies and serves to create an awareness of the potential of underutilised beans as alternative food resources.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Tucker, Gregory
Barrett, Dave
Lim, Yin Sze
Keywords: underutilised legumes, micronutrients, phenolic, beans, leguminous plants
Subjects: S Agriculture > SB Plant culture
Faculties/Schools: UNMC Malaysia Campus > Faculty of Science > School of Biosciences
Item ID: 52216
Depositing User: TAN, POH HWA
Date Deposited: 18 Aug 2018 04:40
Last Modified: 07 May 2020 11:17
URI: http://eprints.nottingham.ac.uk/id/eprint/52216

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