Micronisation of cowpeas : the effects on sensory quality, phenolic compounds and bioactive properties
Year: 2013
Type: dissertation
Abstract: Cowpeas (Vigna unguiculata L. Walp) are legumes recognised as a good source of proteins in \ndeveloping countries. Cowpeas are mostly utilised as cooked whole seeds. This is often \nachieved only after boiling for up to 2 hours, resulting in high energy consumption and a long \ntime for food preparation. Micronisation of pre-conditioned cowpeas (± 41 % moisture at 153 \n°C) reduces their cooking time. During micronisation, cowpea seeds are exposed to \nelectromagnetic radiation with a wavelength range of 1.8 to 3.4μm. For biological materials, \nthe penetration of infrared rays into the food material causes intermolecular vibration, this \nresult in a rapid increase in temperature and water vapour pressure within the seed. \nMicronisation changes physico-chemical properties of cowpea seeds that may affect sensory \nproperties of cooked cowpeas. Micronisation may also affect cowpea bioactive components \nsuch as phenolic compounds and hence their antioxidant properties and bioactive properties. \nThis study aimed at (1) determining the effects of micronisation of pre-conditioned cowpeas \non sensory properties of cooked cowpeas and (2) determining the effects of mironisation of \npre-conditioned cowpeas on the phenolic compounds, radical scavenging properties and their \nprotective effects against oxidative damage of biomolecules (i.e. low density lipoproteins \n(LDL), deoxyribonucleic acid (DNA) and red blood cells (RBC). \n© University of Pretoria \nvi \nMicronisation significantly reduced cowpea cooking time by 28 to 49 %, depending on \ncowpea type. There were significant (P<0.05) increases in roasted aroma and flavour, mushy \ntexture and splitting in all micronised samples. Bechuana white, a light brown cowpea type, \nwas more mushy and split than others. There were significant decreases in firmness, \nmealiness and coarseness after micronisation for all cowpea types. Micronised cowpeas were \ndarker (lower L* values) than unmicronised cooked cowpeas. Darkening was more evident in \nlight coloured than dark coloured cowpea types. Although micronisation reduces cowpea \ncooking time, it also affects sensory properties of cowpeas. This might have an influence on \nconsumer acceptance of micronised cowpeas. \nTwenty seven phenolic compounds were identified in the cowpea types studied: 6 phenolic \nacids, 14 flavonols and 7 flavan-3-ols. Protocatechuic acid, p-coumaric acid, 4- \nhydroxybenzoic acid and ferulic acid were the major phenolic acids in cowpeas. Catechin, \ncatechin-3-O-glucoside, myricetin, rutin, quercetin and its mono and diglycosides were \npresent in all cowpea types analysed. Dr Saunders (701.7−849.2 μg/g) (red in colour) and \nGlenda (571.9−708.1 μg/g) (dark brown in colour) contained the highest total phenolic \ncontents, followed by Bechuana white (361.5−602.3 μg/g) (light brown in colour) and \nBlackeye (152.0−224.5 μg/g) (cream in colour). More of the flavonols were identified in red \nand dark brown compared to light brown and cream cowpea types. The red cowpea type \ncontained all the dimers and oligomeric flavan-3-ol species identified in this study. \nIn all cowpea types, extracts from unmicronised (uncooked) cowpeas inhibited copperinduced \nLDL oxidation in a dose dependent manner. Extracts from all samples analysed \nexhibited protective effects against AAPH (2, 2'-azobis (2-amidinopropane) hydrochloride) \ninduced RBC haemolysis and DNA damage. Extracts from more pigmented cowpeas, i.e. Dr \nSaunders, Glenda and Bechuana white, had significantly (P<0.05) higher levels of total \nphenolics, total flavonoids and radical scavenging properties than Blackeye (less pigmented). \nExtracts from more pigmented cowpeas also offered higher protection against AAPH-induced \nDNA and copper-induced LDL oxidation damage than extracts from less pigmented cowpeas. \nThese results indicate protection of biomolecules e.g. DNA, LDL and RBC) from oxidative \ndamage and have a potential to reduce oxidative stress implicated in the development of \nchronic diseases. This is because cowpea phenolic compounds possess the ability to reduce \noxidative damage associated with development of these diseases. \n© University of Pretoria \nvii \nPigmented cowpea types may be recommended for health applications as they show more \npotential as source of antioxidants compared to the less pigmented cowpeas. \nExtracts from micronised (uncooked and cooked) samples of Dr Saunders and Glenda \ncowpeas had significantly higher concentrations of ferulic acid and p-coumaric acid \ncompared with unmicronised samples. Para-coumaric acid concentrations were higher in all \nmicronised samples of Blackeye cowpeas than in unmicronised samples. The micronisation \nprocess could release cell wall bound ferulic acid and p-coumaric, increasing their \nconcentrations in micronised samples. On the contrary, extracts from all micronised samples \nof Bechuana white and Glenda cowpeas had lower concentrations of catechin than \nunmicronised samples. Results indicated that total extractable phenolics were lower in \nmicronised samples of cowpea types than unmicronised samples. Futhermore, extracts from \nmicronised samples of all cowpea types showed less protective effect against LDL oxidation \nthan extracts from unmicronised samples. \nHowever, for most cowpea types there was no significant difference in total flavonoid \ncontents (TFC) and Trolox equivalent antioxidant capacity (TEAC) values of cooked samples \nof both micronised and unmicronised. Micronisation did not affect the protective effects of \ncowpeas against AAPH-induced RBC haemolysis and oxidative DNA damage. \nMicronisation, followed by cooking, may have generated heat-induced antioxidants such as \nMaillard reaction products contributing to radical scavenging properties in micronised \n(cooked) cowpea samples. Though micronised samples had lower concentrations of some \nphenolic compounds and total extractable phenolics than unmicronised samples, micronised \ncowpea samples still exhibited radical scavenging properties and offered protective effects \nagainst oxidative damage of LDL, DNA and RBC and therefore may offer potential health \nbenefits to consumers.
Author: Eugénie Kayitesi
Language: English
Subfield: Biochemistry (medical)
Field: Medicine
Domain: Health Sciences
SDG: Zero hunger
Open Access status: green
Funder: University of Pretoria
OpenAlex ID: W2786935266