Antioxidant capacity and phenolic profiles of lentils as affected by processing

Yeo, JuDong (2018) Antioxidant capacity and phenolic profiles of lentils as affected by processing. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Lentils are excellent sources of dietary fibre, carbohydrates, proteins, various vitamins, minerals, and bioactive compounds such as phenolic compounds. Epidemiological studies have reported their effects in lowering cholesterol and reducing the incidence of colon cancer, cardiovascular diseases, and type-2-diabetes. In the present study, effects of germination, hydrothermal (boiling) treatment, and dehulling on the antioxidant capacity of soluble- and insoluble-bound phenolics of lentils were examined. Upon germination, an increasing trend in the antioxidant capacity in the insoluble-bound phenolics (IBPs) and a declining trend in that of the soluble phenolics (except total phenolic contents) were observed during 4 days of germination. Based on the results, a new indicator, the ratio of insoluble-bound phenolics to soluble phenolics (SPs), was suggested as an effective means to monitor changes in the antioxidant activity of lentils during germination. The hydrothermal/boiling process also led to important findings. As expected, the hydrothermal process decreased the content of insoluble-bound phenolics in the lentil cultivars tested due to the release of bound phenolics from cell wall matrices. Interestingly, the decrease of bound phenolics was not proportionally reflected in the increase of soluble phenolics, possibly due to the loss of phenolics during the hydrothermal process via interaction with proteins and other seed components. Among lentil cultivars used, the hulls of 3494-6 showed the most effective antioxidant potential, while Maxim displayed the lowest in most measurements. Meanwhile, the dehulling process revealed the predominant distribution of phenolics in the hulls as compared to the dehulled grains, as observed for both soluble- and insoluble-bound phenolics of lentils in their antioxidant potential and inhibitory activities against oxidation of LDL cholesterol and DNA strand breakage. In the HPLC-ESI- MSᴺ analysis, different classes of soluble phenolics such as phenolic acids, flavonoids, and proanthocyanidins were found in the hulls of all four tested lentil cultivars examined. The insoluble-bound phenolics has often been ignored in many evaluations by different research groups and hence this work has expanded the depth of knowledge in the field of food phenolics.

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