Vol. 77 No: 4

Title:
Variation during dormancy and the effect of freezing and postharvest incubation on the chemical composition of blackcurrant buds (Ribes nigrum L.)

Authors:
SANDRA M. GARLAND, ROBERT C. MENARY and CAROLINE J. CLAYE

pp: 489-497

Abstract:
The yield and chemical composition of extracts of buds collected from blackcurrant stems (Ribes nigrum L.) throughout dormancy were investigated. Selections from 'White Bud`, which produce higher levels of the odorous thiol, 4-methoxy-2-methyl-2-thiol-butane, were compared with the standard 'White Bud'. The dry bud weight of all variants decreased by 16% throughout dormancy until immediately before bud burst. The amount of volatiles extracted also decreased. The most discriminating feature distinguishing the new clones from 'White Bud were higher levels of 4-methoxy-2-methyl-2-thiol-butane, myrcene, bicyclogermacrene, caryophyllene oxide and hardwickic acid. β-Caryophyllene and the combination of β-phe1landrene and limonene were higher in ´White Bud`. The effects of post-harvest storage conditions on the volatile components of solvent extracts of blackcurrant buds were investigated. Fifty four per cent of the 4-methoxy-2-methyl-2-thiol butane and 18% of other volatile components were lost within 24 h of freezing. Longer term freezing resulted in a steady overall loss of volatile components. The effects of storage of fresh and previously frozen, hand-cut and machine-harvested buds at 10°C were investigated. Incubation of hand-cut buds in air and nitrogen for 48 h resulted in a 2.6 and a 1.4 fold increase of thiol content respectively. Levels declined thereafter. Thiols were also produced in buds which had been frozen prior to incubation with a 1.2 fold increase recorded in both hand-cut and machine-harvested buds following storage for 72 hours in air. The other terpene-based volatiles in hand-cut fresh buds increased slightly in all incubations, compared with a small decline in fresh machine-harvested buds. The volatile content of hand-cut buds which had been frozen prior to incubation remained relatively constant. In contrast, machine-harvested buds (previously frozen) showed a 1.9 fold increase in volatiles when incubated for up to 72 h. However, a decrease in volatiles was evident over a similar incubation period if machine-harvested buds were rolled for freezing.

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