The Effect of Micronization Operational Conditions on the Physicochemical Properties of Navy Beans (Phaseolus vulgaris L.)

Microwave and micronization treatments affect dehulling characteristics and bioactive contents of dry beans (Phaseolus vulgaris L.)

BACKGROUND

Heat pretreatment is considered the first step in grain milling. This study therefore evaluated microwave and micronization heat treatments in improving the dehulling characteristics, phenolic composition and antioxidant and α-amylase activities of bean cultivars from three market classes.

RESULTS

Heat treatments improved dehulling characteristics (hull yield, rate coefficient and reduced abrasive hardness index) depending on bean cultivar, whereas treatment effects increased with dehulling time. Micronization increased minor phenolic components (tartaric esters, flavonols and anthocyanins) of all beans but had variable effects on total phenolic content depending on market class. Microwave treatment increased α-amylase inhibitor concentration, activity and potency, which were strongly correlated (r²  = 0.71, P < 0.0001) with the flavonol content of beans. Heat treatment had variable effects on the phenolic composition of bean hulls obtained by abrasive dehulling without significantly altering the antioxidant activity of black and pinto bean hulls. Principal component analysis on 22 constituents analyzed in this study demonstrated the differences in dehulling characteristics and phenolic components of beans and hulls as major factors in segregating the beneficial heat treatment effects.

CONCLUSION

Heat treatment may be useful in developing novel dietary fibers from beans with variable composition and bioactivity with a considerable range of applications as functional food ingredients.

Effect of micronisation of pre-conditioned cowpeas on cooking time and sensory properties of cooked cowpeas

BACKGROUND

Cowpea is mostly utilised as cooked whole seeds. This is often achieved only after boiling for up to 2 h, resulting in high energy consumption and a long time for food preparation. Micronisation of pre-conditioned cowpeas reduces their cooking time. Micronisation changes the physicochemical properties of cowpea seeds, which may affect the sensory properties of cooked cowpeas. Consumer acceptance and utilisation of micronised cowpeas depend on their sensory properties. Micronised and unmicronised samples of Blackeye, Bechuana white, Glenda and Dr Saunders cowpeas were subjected to cooking time, descriptive sensory and colour analyses.

RESULTS

Micronisation significantly reduced cowpea cooking time by 28-49%. There were significant (P < 0.05) increases in roasted aroma and flavour, mushy texture and splitting in all micronised samples. Bechuana white was more mushy and split than others. There were significant decreases in firmness, mealiness and coarseness after micronisation for all cowpea types. Micronised cowpeas were darker (lower L* values) than unmicronised cooked cowpeas. Darkening was more evident in light-coloured than dark-coloured cowpeas.

CONCLUSION

Micronisation reduces cowpea cooking time but also affects sensory properties of cowpeas such as introducing roasted flavours that may not be familiar to consumers. This might have an influence on consumer acceptance of micronised cowpeas.