Study On Superoxide Dismutase During The Brewing

As a kind of antioxidase, superoxide dismutase (SOD) could scavenge active oxygen free radicals and reduce oxidative damage by them. Reports that whether SOD existing in raw materials for beer had effects on process of brewing and flavor stability of beer and how to influence them during the brewing were few. Changes of SOD activitiy during malting, mashing and fermentation and effects on the whole brewing process were studied in this paper.The Plackett-Burman multifactorial design was employed to find the important parameters affecting SOD activities in malts during malting, namely steeping time, germination temperature and kilning temperature. Box-Behnken experimental design was further used to optimize the levels of above three factors. By response surface methodology and canonical analysis, the optimal malting factors for higher SOD activities in malts were: steeping time 42.2 h, germination temperature 16.9℃and kilning temperature 82.9℃. Verification tests showed that the experimental data could be reliably predicted by the polynomial model.In order to investigate relationships between SOD activities in malts and reducing power of wort, SOD activities in twenty-nine samples of malts and reducing power of corresponding congress wort were analyzed. Successively, malt Ganpi-3 used as material, seven curves for isothermal mashing were employed to investigate effects of mashing temperature on SOD activity and reducing power of wort. The results showed that evident differences of SOD activities existed in malts samples (from 1205.6 U/g to 2126.0 U/g). And remarkable relativities between SOD activity and reducing power of congress wort were found to be at a positive significant level, of which R=0.898, P<0.01. SOD was gradually destroyed with increasing mashing temperature and 53.22 % of SOD activity survived after temperature was kept 60 min at 55℃. When mashing temperature reached 65℃, the activity of SOD sharply declined and the retention of 25.45 % was still found after 30 min. A great deal of SOD was mostly inactivated when mashing temperature reached 70℃and 80℃, only showing the retention of very low activity. As mashing temperature increased, the reducing power of wort was enhanced, which amounted to 3.75 mmol Vc/L within 100 min at 80℃. By response surface methodology and canonical analysis, the optimal mashing parameters for higher reducing power of wort were that temperature of protein rest was 46.9℃, initial pH of mashing was 5.0, ratio of grist to water was 1:5.5 and initial coarseness was 5.4.In order to investigate cooperative effects of SOD and CAT on antioxidant ability of wort, Ganpi-3 and Stirling malts used as material, exogenous SOD and CAT were added into filtrated wort. The optimal additions of SOD and CAT, namely 30 U/g and 16 U/g respectively, were obtained by evaluation of inhibiting rate of carbonyl compounds after extending at 50℃for 30 min. Successively, SOD and CAT were simultaneously added at mashing-in period with amount of 30U/g and 16 U/g, respectively. Compared with the blank, the corresponding two worts of Ganpi-3 and Stirling had the following predominant characteristics: TBZ values and trans-2-nonenal potential declined by 16.2 %, 17.2 %, 26.7 % and 26.3 % and reducing power and DPPH radical scavenging activity increased by 8.9 %, 10.7 %, 9.0 % and 7.6 %, respectively.In order to investigate effects of SOD and CAT on brewing process, physical and chemical index and flavor stability of beer, exogenous SOD and CAT were added solely and together into cold wort before fermentation. It was indicated that, compared with the blank, antioxidant activities of beer solely including CAT, beer solely including SOD and beer together including SOD and CAT were higher than the contrast, and contents of trans-2-nonenal decreased by 6.7 %,12.2 % and 14.4 %. After forced aging, total polyphenol content and antioxidant activities of beer both decreased to some extent, and decreased degree of these three varieties of beer was lower than the blank, but beer solely including SOD and beer together including SOD and CAT behaved remarkably. The above results showed that exogenous SOD and cooperative effects of SOD and CAT not only could restrain descent of phenolic compounds in beer, but also could improve flavor stability of beer.