Due to its wide use in nutritional therapy, a capsicum oleoresin extraction from hot chilli pepper was optimized using ultrasound assisted extraction. Under optimal conditions, a 0.1g sample in 10mL of a 20% water in methanol solution was extracted at 50°C for 20min to remove phytochemicals consisting of oleoresin, phenolics, carotenoids, flavonoids, capsaicinoids (pungency level), reducing sugars. Antioxidant and antidiabetic activities of the crude extracts from 14 chilli pepper varieties were examined. The antioxidant and antidiabetic activities of some phenolic compounds were also tested individually. The results showed that these chilli pepper samples are a rich source of phytochemicals with antioxidant and antidiabetic activities. High antioxidant activity of the extracts was evaluated using the 2,2-diphenyl-1-picrylhydrazyl, N,N-dimethyl-p-phenylenediamine dihydrochloride, 2,2'-azino-bis(3-ethylbenzothiazolin-6-sulfonic acid) and ferric ion reducing antioxidant power assays. The crude extracts had a lower level of sugars induced by the inhibitory effect of α-amylase activity. Thus, their enzymatic inhibitory effect might have resulted from a synergism among the phytochemicals concerned. Therefore, a diet with this type of food may have beneficial health effects.
Use of dimethyl sulfoxide (DMSO) as a suitable extraction solvent under the optimum conditions of microwave assisted extraction (MAE) prior to total phenolics determination and antioxidant activity assay was conducted. The MAE method was done with 0.05 g sample in 10 mL DMSO at 500 W within 5 min. The effects of DMSO on various antioxidant activities using DPPH(·+), DMPD(·+), ABTS(·+) and FRAP, and Folin-Ciocalteu reagent were investigated. From the results, it is clearly demonstrated that the DMSO itself shows no effect on any of those antioxidant assays including total phenolics content. The DMSO extracts of 14 local chilli varieties gave their antioxidant activities in the following ranges: DPPH, 3.07-20.0; DMPD, 1.52-6.61; ABTS, 20.4-56.0; FRAP, 8.98-42.1 mg GA/g DW. Their total phenolics contents were found in the range of 53.7-200 mg GA/g DW. This study demonstrates that DMSO was found as the most suitable extraction solvent for antioxidants and phenolics from chilli. In addition, analysis of the data obtained among four antioxidant activity assays with respect to total phenolics shows a highly significant and positive regression coefficient (r > 0.92), indicating the total phenolics are primarily responsible for their antioxidant activity of the chilli extract.
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