Changes in the S-alk(en)yl cysteine sulfoxides and their biosynthetic intermediates during onion storage

Changes in the S-alk(en)yl cysteine sulfoxides and their biosynthetic intermediates during onion storage

1999

A:PS

Seven onion cultivars representing different storage durations, photoperiodic requirements and flavour intensities were greenhouse grown and th bulbs stored for 3 or 6 months at 5ñ3øC and 0.8-1.1 kPa vapour pressure deficit Bulbs were evaluated using HPLC for changes in S-alk(en)yl cysteine sulfoxide (ACSO) flavour precursors and gamma-glutamyl peptide (gamma-GP) biosynthetic intermediates before storage and monthly thereafter. Before and during storage, cultivars differed in total ACSO, (+)S-methyl-L-cysteine sulfoxide (MCSO), trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide (PRENCSO), (+)propyl-L-cysteine sulfoxide (PCSO), S-2 carboxypropyl glutathione (2-CARB) and gamma-L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide (gammaGPECSO) concentrations. During storage MCSO generally decreased while PRENCSO increased in concentration for most cultivars. The linear increase in PRENCSO concentration during storage was accompanied by a linear decrease in gammaGPECS concentration. While not measured in this study, these trends indicate gamma-glutamyl transpeptidase activity throughout bulb storage. gamma-Glutamyl transpeptidase was previously reported to be active only in the later stages of bulb storage or during bulb sprouting. Changes in ACSO and gamma-GP compounds during storage did not follow previously reported changes during storage for enzymatically formed pyruvic acid (EPY) for these cultivars. To better understand what causes flavour changes in onions during storage, future investigations should include analysis of the enzymes involved in flavour development and ACSO hydrolysis products.

v.124(2):177-183, AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, JOURNAL

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