## 3 Results and Discussion
### Antioxidant Activity (AOA) during Wort Fermentation and in Beer via DPPH and ABTS Assay  
The antioxidant activity via DPPH assay during fermentation among the five composite ports by each yeast strain are shown in Figure 5A,B. The AOA of the fermentation in each composite word was significantly different (\(p<0.05\)) and was more noticeable in the R80B20 and R100 treatments. The antioxidant activity of R80B20 and R100 in each fermentation treatment was similar (Figure 5). Likewise, the fermented words of B100, R40B60, and R60B80 shared similarity of antioxidant activity. The fermentation of words by \(\mathrm{POF}^{+}\) was associated with unstable antioxidant activity, as shown in Figure 5B, because of the \(\mathrm{POF}^{+}\) ability to metabolise phenolic acids, including ferulic acid to 4-vinylguaiacol and \(p\)-coumaric and sinapic acid to 4-vinylphenol and 4-vinylsyringol, respectively [5]. These phenolic derivatives possess less antioxidant. Each fermented word containing Riceberry rice malt between 40% (\(w/w\)) and 100% (\(w/w\)) had higher or equal antioxidant activity relative to B100. Although some antioxidants are associated with oxidation stability, others can serve as being pro-oxidant, thus influencing the total antioxidant stability of the fermented word or the end product of beer. Barley malt beer has been reported to have less oxidation stability compared to black rice malt beer [12]. The high antioxidant activity in R40B60, R60B40, R80B20, and R100 was attributed to the trace amount of monomeric anthocyanin present in the beer, the high vanillic acid content, and the potential of low pro-oxidant species possessed in rice malt relative to barley malt beer, as proposed by [PERSON] et al. [12]. In the course of bottled beer maturation with \(\mathrm{POF}^{-}\) for 4 weeks at 20 \({}^{\circ}\)C, the DPPH assay revealed a steady decline in antioxidant activity between 1-2 weeks, and it maintained stable antioxidant activity between 3 and 4 weeks. Hence, antioxidant activity via DPPH assay had ranges of 748.8-782.6 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 745.6-756.1 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 750.1-761.7 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 901.2-924.9 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, and 961.0-970.8 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L in B100, R40B80. R60B40, R80B20, and R100, respectively, in the beer produced with \(\mathrm{POF}^{-}\). In \(\mathrm{POF}^{+}\) beer, AOA was 756.8-785.7 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 778.3-795.2 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 820.6-835.0 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, 900.9-918.8 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, and 878.5-895.1 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L in B100, R40B80, R60B40, R80B20, and R100, respectively. Few data are available on the AOA of rice beer and composite beer with rice. However, [PERSON] et al. [11] reported AOA in rice beer via a DPPH assay with a range of 437-587 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L, which is below the values recorded in this study because of rice cultivar variation. Nevertheless, the range of AOA via DPPH was within the range of values recorded for some commercial Polish beer, such as wheat beer (\(>\)500 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L), lager (\(>\)1200 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L), bock beer (\(>\)2000 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L), and porter beer (\(>\)2200 \(\mathrm{\SIUnitSymbolMicro moL}\) TE/L) [29]. Figure 5: Changes in antioxidant activity via DPPH in fermented word (B100, R40B60, R60B40, R80B20, and R100) by the two yeast strains BRY 97 (_S. cerevisiae_), \(\mathrm{POF}^{-}\) (**A**); and Belle Saison (_S. cerevisiae_ _var. diastaticus_), \(\mathrm{POF}^{+}\) (**B**). The AOA of fermenting composite worts via ABTS assay is illustrated in Figure 6. The mean AOA via ABTS assay was significantly different among the treatment carried out for each yeast strain. The ABTS assay maintained a similar pattern, as reported for AOA via DPPH.