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

Kamfer, De Witt (2014-12)

Thesis (MScAgric)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Thompson Seedless and Regal Seedless are two white seedless table grape cultivars widely produced in South Africa. Both cultivars are susceptible to berry browning, especially Regal Seedless. Browning leads to annual financial losses for table grape growers. Although a correlation between harvest maturity and the occurrence of browning seems to exist, it is still unclear whether maturity levels are the actual contributing factor. The aim of the study was to establish if harvest maturity and crop load could influence the occurrence of browning of both cultivars. The impact of harvest maturity and crop load on phenolic compound concentration in the berry skin of both cultivars was also investigated. Total external browning of Regal Seedless and Thompson Seedless occurred in much higher percentages than internal browning. Regal Seedless showed a tendency to decreased total external browning with harvest maturity. The main reason for this is that net-like browning, which is the greatest contributor to total external browning, decreased with harvest maturity, in all three seasons. External browning of Thompson Seedless increased with harvest maturity in both seasons. Contact browning was the greatest contributor to total external browning of Thompson Seedless. Crop load did not significantly influence berry browning of Regal Seedless or Thompson Seedless grapes. The flavan-3-ol concentration (catechin, epicatechin, procyanidin B1 and procyanidin B2) in Regal Seedless generally increased with harvest maturity, whereas in Thompson Seedless the general tendency was a decrease in the flavan-3-ol concentration with harvest maturity. The development of phenolic compound concentration with maturity could not be correlated with the occurrence of berry browning. Crop load did not affect flavan-3-ol concentration. When the flavan-3-ol concentration of Regal Seedless and Thompson Seedless were compared at different harvest maturities the concentrations 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 & 2009 seasons). Comparison of the browning incidence with harvest maturity for these two cultivars (see above) clearly reveals that external browning of Regal Seedless occurred in much higher percentages than on Thompson Seedless. Regal Seedless had much higher levels of external browning than Thompson Seedless. The concentration of flavan-3-ols in the skin of white seedless cultivars may be an indication of the cultivar’s susceptibility to external browning.

AFRIKAANSE OPSOMMING: Thompson Seedless en Regal Seedless is twee wit pitlose tafeldruif kultivars wat ekstensief in Suid-Afrika verbou word. Verbruining kan ‘n probleem wees by beide kultivars, spesifiek Regal Seedless. Die faktore wat aanleiding gee tot verbruining is nog nie duidelik bepaal nie. Alhoewel dit lyk of daar ‘n korrelasie tussen rypheidsgraad van die oes en verbruining kan wees is dit steeds onduidelik of oesrypheidsvlakke die werklike oorsaak van verbruining is. Die doel van die studie was om vas te stel of die rypheidsgraad van die oes en oeslading verbruining van beide kultivars kan beïnvloed. Die effek van oes rypheidsgraad en oeslading op konsentrasie van fenoliese verbindings in die korrelskil van beide kultivars is ook ondersoek. Totale eksterne verbruining van Regal Seedless en Thompson Seedless het in baie hoër persentasies voorgekom as interne verbruining. Daar was ‘n tendens by Regal Seedless dat totale eksterne verbruining verminder het soos die oes ryper geraak het as gevolg van netagtige verbruining, wat die grootste bydrae tot totale eksterne verbruining veroorsaak het. Netagtige verbruining se voorkoms het verminder oor al drie seisoene. Eksterne verbruining van Thompson Seedless het toegeneem met oes rypheid in beide seisoene. Kontak verbruining het grootste byrdae gelewer tot totale eksterne verbruining van Thompson Seedless. Oeslading het nie ‘n betekenisvolle invloed op verbruining van Regal Seedless en Thompson Seedless gehad nie. Die flavan-3-ol (katesjien, epikatesjien, prosianidien B1 en prosianidien B2) konsentrasie van Regal Seedless het met oes rypheid toegeneem. By Thompson Seedless was daar ‘n afname in die flavan-3-ol konsentrasie met oes rypheid. Daar was geen korrrelasie tussen die konsentrasie van fenoliese verbinding en die voorkoms van verbruining vir beide kultivars. Oeslading het nie ‘n betekenisvolle effek op die konsentrasie van fenoliese verbindings gehad nie. Vergelyking van die flavan-3-ol konsentrasie van Regal Seedless en Thompson Seedless by verskillende rypheidsgrade wys dat die konsentrasie baie hoër in die korrel skil van Regal Seedless as in die van Thompson Seedless (vir beide 2008 & 2009 seisoene). Die vergelyking van die voorkoms van verbruining met oesrypheid van beide kultivars wys duidelik dat eksterne verbruining van Regal Seedless in baie hoër persentasies voorkom as in Thompson Seedless. Flavan-3-ol konsentrasie in die skil van wit pitlose kultivars kan ‘n aanduiding wees van die kultivar se moontlike risiko vir die voorkoms van eksterne verbruining.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95886
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