Four kinds of solvent extracts from three Chinese barley varieties (Ken-3, KA4B, and Gan-3) were used to examine the effects of extraction solvent mixtures on antioxidant activity evaluation and their extraction capacity and selectivity for free phenolic compounds in barley through free radical scavenging activity, reducing power and metal chelating activity, and individual and total phenolic contents. Results showed that extraction solvent mixtures had significant impacts on antioxidant activity estimation, as well as different extraction capacity and selectivity for free phenolic compounds in barley. The highest DPPH* and ABTS*+ scavenging activities and reducing power were found in 80% acetone extracts, whereas the strongest *OH scavenging activity, O2*- scavenging activity, and metal chelating activity were found in 80% ethanol, 80% methanol, and water extracts, respectively. Additionally, 80% acetone showed the highest extraction capacity for (+)-catechin and ferulic, caffeic, vanillic, and p-coumaric acids, 80% methanol for (-)-epicatechin and syringic acid, and water for protocatechuic and gallic acids. Furthermore, correlations analysis revealed that TPC, reducing power, DPPH* and ABTS*+ scavenging activities were well positively correlated with each other (p < 0.01). Thus, for routine screening of barley varieties with higher antioxidant activity, 80% acetone was recommended to extract free phenolic compounds from barley. DPPH* scavenging activity and ABTS*+ scavenging activity or reducing power could be used to assess barley antioxidant activity.

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Anaerobic fermentation was relatively difficult to optimize due to lack of monitoring parameters. In this paper, a new method was reported using extracellular oxidoreduction potential (ORP) to monitor 1,3-propanediol (1,3-PD) biosynthesis process by Klebsiella pneumoniae. In batch fermentation, cell growth, 1,3-propanediol production and by-products distribution were studied at four different ORP levels: 10, -140, -190 and -240 mV. From the results, the ORP level of -190 mV was preferable, which resulted in fast cell growth and high 1,3-propanediol concentration. The NAD+/NADH ratio was determined at different ORP levels, and a critical NAD+/NADH ratio of 4 was defined to divide fermentation environments into two categories: relatively oxidative environment (NAD+/NADH>4) and relatively reductive environment (NAD+/NADH<4). The former was correlative with high 1,3-propanediol productivity and high specific growth rate. The mechanism of ORP regulation was discussed. It is suggested that ORP regulation of fermentation might be due to its influence on the ratio of NAD+/NADH, which determined metabolic flux. Furthermore, a batch fermentation of modulating ORP following a profile in different levels corresponding to different fermentation stage was tested. The 1,3-PD concentration was 22.3% higher than that of constant ORP fermentation at -190 mV. Therefore, ORP is a valuable parameter to monitor and control anaerobic fermentation production.

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