title: Rapid measurement of 3-alkyl-2-methoxypyrazine content of winegrapes to predict levels in resultant wines.
abstract: We describe an optimized protocol for analysis of the herbaceous smelling 3-alkyl-2-methoxypyrazines (MPs) in whole berries that predicts MPs in resultant red wines. Berries are homogenized by bead-milling with a deuterated standard prior to headspace solid phase microextraction (HS-SPME) and quantification by two-dimensional gas chromatography time-of-flight-mass-spectrometry (GCxGC-TOF-MS). In the case of 3-isopropyl-2-methoxypyrazine (IPMP), GCxGC-TOF-MS successfully resolved interferences that coeluted with the analyte in the first dimension. HS-SPME parameters (pH, queue time, incubation time, extraction time, extraction temperature) were optimized by a statistical experimental design. Good method accuracy was observed (consistent ratio of unlabeled analyte to labeled standard) at 10 min extraction times when 80 degrees C extraction temperatures were employed, although increasing sensitivity was observed for longer extraction times (up to 140 min). Standard addition of 3-isobutyl-2-methoxypyrazine (IBMP) and IPMP into preveraison and harvest ripe berry matrices showed good linearity (r(2) >0.99 in all cases), with limits of detection ranging from 0.6 to 1.8 pg/g. The protocol was validated by comparing IBMP in 16 lots of Cabernet Franc berries (range = undetectable to 18.4 pg/g) to the resulting wines (range = undetectable to 14.5 pg/g). Berry and wine MP content were strongly correlated, (r(2) = 0.97, p < 0.0001). Following correction for CO(2) loss, the observed concentration of IBMP in wines was 67 +/- 13% of the IBMP concentration observed in berries.
authors.affiliation: Department of Food Science and Technology, Cornell University, Geneva, New York, USA.
authors.forename: Imelda
authors.initials: I
authors.lastname: Ryona
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Pan
authors.forename: Gavin L
authors.initials: GL
authors.lastname: Sacks
mesh_terms: D002849:Chromatography, Gas; D005638:Fruit / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D009812:Odorants / Q000032:analysis*; D011719:Pyrazines / Q000032:analysis*; D027843:Vitis / Q000737:chemistry*; D014920:Wine / Q000032:analysis*
chemical_list: D011719:Pyrazines; C024267:2-isopropyl-3-methoxypyrazine; C034376:2-isobutyl-3-methoxypyrazine