AOAC963_12.pdf

27.5.05AOAC Official Method 963.12Acids (Alpha and Beta) in HopsSpectrophotometric MethodFirst Action 1963Final Action 1964A. Reagents(a) Methanol.Reagent grade. A in 1 cm cell 0.060 at 275 nmagainst H2O.(b) Alkaline methanol.Add 0.2 mL 6M NaOH to 100 mLmethanol, (a). Solution must be fresh.(c) Benzene.Reagentgrade.Ain1cmcell0.20.3g,startnewdetermination.Letflaskstanduntil supernate clears.Diluteappropriatealiquotofbenzeneextractwithalkalinemetha-nol, A(b), so that A falls within most accurate range of instrumentused. For hops containing ca 8% total alpha and beta acids, pipet5 mL benzene extract into 50 mL volumetric flask and dilute to vol-ume with alkaline methanol (Dilution I); then dilute 4.00 mL Dilu-tionIto50mLwithalkalinemethanol(DilutionII).Forhopsofhighalphaandbetaacidcontent,dilute4.00mLDilutionIto100mLforDilution II.DetermineAofDilutionIIat275,325,and355nm,firstsettingin-strumentto0Awithblankpreparedbydiluting5mLbenzene,A(c),with alkaline methanol in same sequence used for test portions.D. Calculations(a) % alpha acids = d (51.56A355+ 73.79A325 19.07A275)whered=dilutionfactor,andA355,A325,andA275=AofDilutionIIatrespectivewavelengths.Fordilutionsequence5to50mL,followedby second dilution of 4 to 50 mL,d = =5050 10020100045 1000025.(b) %betaacids=d(55.57A35547.59A325+ 5.10A275)whered and A355, A325, and A275have same values as in (a).Report both alpha and beta acids to 1 decimal place.References: ASBC: Hops 6A.JAOAC 46, 291(1963). 2000 AOAC INTERNATIONAL食品伙伴网http:/