NEW APPROACHES TO REMOVING ALKYL-METHOXYPYRAZINES FROM GRAPE JUICE AND WINE

Grape-based products, including wine, are amongst the world’s most important value-added horticultural commodities, both economically and culturally. 3-isobutyl- (IBMP) and 3-isopropyl- (IPMP) 2-methoxypyrazine are important grapeand insect-derived flavour compounds in some grape juices and wine, and are responsible for undesirable green characters associated with under-ripe grapes or infestation from Coccinellidae. Here we present data on two novel approaches to removing these compounds from juice and wine. Firstly, we describe a protein-based technology that binds and removes IPMP and IBMP in juice. The lipocalin Mouse Major Urinary Protein 1 (mMUP) was expressed in Pichia pastoris, secreted, and purified using anion exchange chromatography. mMUP, combined with a 10 KD cut-off PES membrane filtration system, resulted in a reduction of IPMP and IBMP in juice of > 98%. However, removal of methoxypyrazines from wine using this technique may be limited by ethanol-induced changes in the mMUP structure. Therefore, a 2nd approach is being developed that takes advantage of the sorptive properties of various polymeric materials. A range of food-grade polyethylene-, polypropylene- and silicon- based polymers were evaluated for their capacity to remove IPMP and IBMP from red wine. Candidate polymers were standardized to a common surface area and added to red wine for 2 hrs. Quantification of IPMP and IBMP using HS-SPME-MD-GC-MS showed reductions of up to 40% for some polymers, and minimal changes to the sensory characteristics of the wine. We conclude there is capacity to significantly mediate the impact of methoxypyrazines on juice and wine quality using these biotechnology tools.