The effect of maturity and crop load on the browning and concentration of phenolic compounds of Thompson Seedless and Regal Seedless

[摘要] ENGLISH ABSTRACT: Thompson Seedless and Regal Seedless are two white seedless table grapecultivars widely produced in South Africa. Both cultivars are susceptible to berrybrowning, especially Regal Seedless. Browning leads to annual financial losses fortable grape growers. Although a correlation between harvest maturity and theoccurrence of browning seems to exist, it is still unclear whether maturity levels arethe actual contributing factor. The aim of the study was to establish if harvestmaturity and crop load could influence the occurrence of browning of both cultivars.The impact of harvest maturity and crop load on phenolic compound concentration inthe berry skin of both cultivars was also investigated. Total external browning ofRegal Seedless and Thompson Seedless occurred in much higher percentages thaninternal browning. Regal Seedless showed a tendency to decreased total externalbrowning with harvest maturity. The main reason for this is that net-like browning,which is the greatest contributor to total external browning, decreased with harvestmaturity, in all three seasons. External browning of Thompson Seedless increasedwith harvest maturity in both seasons. Contact browning was the greatest contributorto total external browning of Thompson Seedless. Crop load did not significantlyinfluence berry browning of Regal Seedless or Thompson Seedless grapes. Theflavan-3-ol concentration (catechin, epicatechin, procyanidin B1 and procyanidin B2)in Regal Seedless generally increased with harvest maturity, whereas in ThompsonSeedless the general tendency was a decrease in the flavan-3-ol concentration withharvest maturity. The development of phenolic compound concentration withmaturity could not be correlated with the occurrence of berry browning. Crop load didnot affect flavan-3-ol concentration. When the flavan-3-ol concentration of RegalSeedless and Thompson Seedless were compared at different harvest maturities theconcentrations of flavan-3-ols were clearly much higher in the skin of Regal Seedless than in the skin of Thompson Seedless (for both the 2008 & 2009seasons). Comparison of the browning incidence with harvest maturity for these twocultivars (see above) clearly reveals that external browning of Regal Seedlessoccurred in much higher percentages than on Thompson Seedless. Regal Seedlesshad much higher levels of external browning than Thompson Seedless. Theconcentration of flavan-3-ols in the skin of white seedless cultivars may be anindication of the cultivar's susceptibility to external browning.

[发布机构] Stellenbosch University