Investigation Of The Relationship Between T/C Ratio Of Iso-α-acid And Beer Flavor Stability

A method of cis/trans stereoisomers of iso-α-acid in beer and wort was established by HPLC using volatile mobile phase adding formic acid buffer. Zorbax Edipse XDB-C18 (4.6×250 mm, 5μm) was used for analysis after sample was obtained by solid phase extraction. The aim compounds were separated under an isocratic elution system of acetonitrile - formic acid buffer within 20 minutes. These peaks were identificatied acorrding to the combination of information obtained by LC/MS and the literature datas. The method was sensitive and accurate. The recoveries, relative standard deviation (RSD) and detection limits of iso-α-acids were 93.52%~97.40%, less than 5 % and 0.302 mg/L, respectively.The bitter substances will degrade in beer during storage, and the change of bitter substances in beer during storage was studied by determining cis/trans stereoisomers of iso-α-acid using HPLC. As a result, the trans form of iso-α-acid decreased faster, while the cis form decreased scarcely. The same brand with forced aging and natural aging except of the different brands of beers with forced aging were reviewed in this paper. The T/C ratio (total contents of trans-iso-α-acid / total contents of cis-iso-α-acid *100%)showed an evident linear relativity with staling time and stale flavor intensity, so it can reflect the extent of beer staling excluding the difference of manufacturing dates even brands, and it would become a new index to estimate beer staling better. The investigation of correlation T/C ratio with 5-HMF, TBA, DPPH, SI coefficient found the formation of 5-HMF is relate to the degrade of cis/trans stereoisomers of iso-α-acid probably. On base of above result and corresponding relationship of taste score and T/C ratio, The relation extent between T/C ratio and staling degree of beer was established, corresponding relationship as follow: With T/C﹥33.4, epresenting a fresh state; With T/C 26.1~33.4, representing a medium stale; with T/C﹤26.1, epresenting a severe state.The main factors effecting on T/C ratio were investigated from two angles of relative index in hop and the factors of wort boiling craft. Then relationship of hop index and T/C ratio was established. Equations model was proofed correct elementarily by pair t-test.