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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Optimum pre-reducing agents used to convert Se(VI) to Se(IV) for speciation analysis of inorganic selenium in tomato were investigated by FI-HGAAS. It was found that optimal conditions of Se(IV) consisted of 2 M HCl as carrier and 0.3%(w/v) NaBH 4 in 0.2%(w/v) NaOH as reducing agent. Concerning the completely pre-reduction of Se(VI), various reducing agents were studied including KCl, KBr, KI, ascorbic acid and thiourea in association with dilute and concentrate HCl and effect of temperature. From results, two optimal pre-reducing agents:0.5%(w/v) KI/conc. HCl and 0.5%(w/v) thiourea/conc. HCl and heating for 30 min were chosen, giving a linearity between 5 and 25 ng/mL. LOD and LOQ were 0.5 and 2 ng/L, respectively. Both of pre-reducing agents were then applied to tomato digest based on dry basis of its sample, which comparatively resulted in 5.10 mg Se(IV)/kg and 29.12 mg Se(VI)/kg using 0.5%(w/v) KI/conc. HCl, and 3.84 mg Se(IV)/ kg and 22.29 mg Se(VI)/kg using 0.5%(w/v) thiourea/conc. HCl.