| Beers were formed by malt, hops and water as the main raw material, they are brewed into low alcohol wine containing carbon dioxide by yeast. Beer becomes the one of third drink consumption of the world. During the fermentation process, beer generates many volatile and non-volatile through a series of reactions. Although they have very law content, but the impact on the flavor of beer cannot be ignored. In certain range of contents, because these substances can generate a unique flavor of beer, it will affect the taste of beer if the content is too high or too low, thus will affect the overall flavor quality of the beer. Free fatty acid is one of these compounds. Free fatty acid exists in the form of C6-C12mainly in beer, octoic acid, caproic acid, capric acid, twelve calcium carbonate are formed by the decomposition of long chain fatty acid, beer form nasty putrid smell sometimes, these putrid smell is caused mainly by the free fatty acid. In addition, the effect of some long chain fatty acids on the flavor of the beer is also very important, Because of the function of enzyme and the reaction of free radical, hydroperoxide was fonned by fatty acid oxidation. After the further cracking or polymerization producing, hydrogen peroxide forms lower fatty aldehydes, acids and other compounds so that beer form aging odor. In this paper, we establish gas chromatographic method of fatty acid in beers, we studied on the relationship between free fatty acids and beer aging by forced aging at60℃for36days, By adding antioxidants during the mashing process so as to inhibit the form of free fatty acids of the aging precursor in beer. It plays an important role in understanding the mechanism of beer aging, prolonging the shelf of beer and impoving beer flavor.Free fatty acid in beer was analyzed by GC-MS method that it was extra ted by dichloromethane-methanol solution and it was esterified by concentrated sulfuric acid that can be better dectected. This experiment studied the effects of the different initial temperature(35℃,50℃and80℃)and different heating rates(3℃/min,5℃/min,10℃/min)on the determination of fatty acid. Finally, the best conditions of gas chromatography is determined:chromatographic column:FFAP; detector:FID;carrier:high putity nitrogen, flow is2mL/min; the temperature of the vaporization chamber is250℃; the temperature of detevtor is260℃; the program of column temperature:50℃ramain2min, temperature was rised to100℃at the speed of5℃/min and keeped1min, then it rosed to220℃at the speed of5℃/min and keeped10min; aplitless was used as sampling method,correlation coefficient of the standard curve of each fatty acids were determined by external standard method, the correlation coefficients of octanoic acid, myristic acid, palmitic acid, linoleic acid, stearic acid were0.9938,0.9853,0.9908,0.9907,0.9918respectively. Recovery rate was high and reproducibility is good that can meet the testing requirements.Beer was aged at60℃for36days, the correlation of between fatty acids, TBA value, polyphenol content and aging days were analyzed. Study found that each fatty acid have different changes during the beer aging. Octanoic acid content increased, but not significantly stearic acid and palmitic acid present irregular change, the content of myristic acid and linoleic acid is significantly reduced,it presents significant negative correlation with beer aging index of TBA and the aging days. The correlation between the fatty acid content in four beers and TBA value was analyzed, it is found that TBA value present significantly negatively correlation with myristic acid and linoleic. The results above indicate that myristic acid and linoleic acid in beer may be related with the beer aging.Different contents of potassium metabisulfite, tea poly phenol, tannin, sodium erythorbate was added during wort mashing process and analyzed single factor experiment. The experimental results show that the effect of ascorbic acid on free fatty acid was not significant, so futher experiment only optimized other three additive quantities. the influence significance of three additives on the response were analyzed by the response surface:potassium metabisulfite>tea polyphenol> tannin. It is know by design7.0software when the contents of potassium metabisulfite, tea polyphnol, tannin were100mg/L,60mg/L,60mg/L respectively, TBA values was the lowest for0.103mg/L. The optimum adding amount of antoxidants are added during mashing, the finished beer is aged36days at60℃, the change of content of myristate acid, linoleic acid and TBA were studied. The experimental results show that the addition of antioxidants can effectively improve the flavor stability of beer during the mashing process. So beer aging will be inhibited effectively, the shelf of beer will be extended. |
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