Our objective was to investigate the mode of interaction between selected food proteins and phenolic compounds. Bovine serum albumin (BSA), bovine beta-lactoglobulin, and soybean glycinin were used with the following phenolic compounds; 3,4,5-trihydroxybenzoic acid (gallic acid), 3,4-dihydroxy cinnamic acid (caffeic acid), p -hydroxycinnamic acid (courmaric acid), and 5,7-dihydroxy 4-methoxy isoflavone (biochanin A). The interaction was investigated using incubation temperatures of 35°, 45° and 55°C at pH 5, 7 and 9. Native and SDS-polyacrylamide gel electrophoresis (PAGE), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy were used to identify protein-phenol interactions. Certain phenolic compounds combined with BSA and prevented protein aggregation. In general, the thermal stability of the proteins increased as a result of interaction with phenolic compounds; the most pronounced effect was observed with beta-lactoglobulin in the presence of gallic acid at pH 7. The interaction of the phenols with the proteins resulted in changes in protein secondary structure. (Abstract shortened by UMI.)

No description available.

Thesis (PhD (Food Science))--University of Stellenbosch, 2006. / The aim of the study was to provide the South African wine industry with guidelines for the production of Pinotage wines with optimal total antioxidant capacity (TAC), while retaining sensory quality. The contribution of individual phenolic compounds to the wine TAC is important in this regard. The wine TAC was measured with the 2,2 -azino-di(3-ethylbenzo-thiazoline-sulphonic acid radical cation) (ABTS +) scavenging assay. The contributions of individual phenolic compounds to the wine TAC were calculated from their content in the wines and the Trolox equivalent antioxidant capacity (TEAC) of pure phenolic standards. The effects of climate region, vine structure, enological techniques (pre-fermentation maceration, juice/skin mixing, addition of commercial tannins, extended maceration) and maturation (oak barrels, alternative oak products, oxygenation) on the phenolic composition, TAC and sensory quality of Pinotage wines were also investigated. The TEAC values of quercetin-3-galactoside, isorhamnetin and peonidin-3-glucoside were reported for the first time. TEAC values observed for most compounds were much lower than those reported previously, although TEAC values for gallic acid, caftaric acid, caffeic acid and kaempferol were consistent with some previous reports. Caftaric acid and malvidin-3-glucoside were the largest contributors to the wine TAC. The contents of monomeric phenolic compounds and procyanidin B1, however, only explained a small amount (between 11 and 24%) of the wine TAC, with the remaining TAC attributed to oligomeric and polymeric phenolic compounds and other unknown compounds. Some synergy between different monomeric phenolic compounds was also demonstrated. All the viticultural and enological factors investigated affected the phenolic composition of Pinotage wines, while the wine TAC was only affected by some treatments. Changes in wine TAC could not always be explained by changes in phenolic composition as the contribution of oligomeric, polymeric and unknown compounds could not be assessed, but could play a large role. Differences in wine colour were also difficult to explain due to the large number of factors involved and the dark wine colour, which made objective measurements difficult. The concentration of vitisin A, an orange-red pyranoanthocyanin, was increased consistently as a result of prefermentation maceration treatments and affected the wine colour of oxygenated wines. Increased wine TAC was observed when cultivating Pinotage grapes on bush vines and in cooler climatic regions, compared to cultivation on trellised vines in warmer climatic regions. All the climatic regions and vine structure treatments, however, resulted in wines with good sensory quality. In terms of enological techniques, pumping-over, as opposed to punching-down and rotor treatments, is not recommended as a juice/skin mixing technique, due to reduced wine TAC, colour and sensory quality. Pre-fermentation maceration, addition of commercial tannin preparations, and oak maturation using traditional and alternative treatments, resulted in improved sensory quality, but with no change in wine TAC. However, optimisation of the tannin addition protocol may result in increased wine TAC if additions are made after fermentation or higher dosages are used. Oxygenation of Pinotage wine needs further investigation to optimise the protocol, as improvements to the wine colour and fullness were observed for some treatments, but loss of sensory quality and TAC were observed in most cases.

Thesis (M. Sc.Voedselwet.)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Phenolic compounds in wine, due to their antioxidant activity, are reportedly responsible for the health-promoting properties of wines. The effect of cultivar and in-bottle ageing on the antioxidant activity of South African wines in different types of antioxidant assays was, therefore, investigated. The antioxidant activity of commercial South African red (Cabernet Sauvignon, Ruby Cabernet, Pinotage, Shiraz, Merlot) and white (Sauvignon blanc, Chenin blanc, Chardonnay, Colombard) cultivar wines was compared using the 2,2’-azino-di-(3-ethylbenzothialozine-sulphonic acid) radical cation (ABTS·+) scavenging, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·) scavenging and microsomal lipid peroxidation (MLP) assays. The red wines was more effective than the white wines on an “as-is” and an equal total phenol content. The total antioxidant activity (TAAABTS and TAADPPH) of Ruby Cabernet was the lowest of the red wines, but the antioxidant potency (APABTS and APDPPH) of red wine phenolic fractions did not differ (P ³ 0.05). Ruby Cabernet and Pinotage were the least effective inhibitors of MLP, while Merlot was the most effective of the red wines. Pinotage phenolic fractions had lower (P < 0.05) APMLP than that of other red wines. Of the white wines, Chardonnay and Chenin blanc had the highest and lowest effectivity respectively according to all antioxidant parameters. Ascorbic acid present in some wines increased and decreased their TAA and % MLP inhibition respectively. TAA and % MLP inhibition correlated well (r ³ 0.7, P < 0.001) with total phenol content of red and white wines, as well as with flavanol content of red wines and tartaric acid ester content of white wines. The % MLP inhibition also correlated well with flavanol content of white wines. No correlation (P > 0.01) was obtained between TAA or % MLP inhibition and monomeric anthocyanin content of red wines. In the deoxyribose assay, red wines were more pro-oxidant and exhibited lower hydroxyl radical scavenging and metal chelating abilities than white wines. The effect of in-bottle ageing on antioxidant activity of wines was determined using the ABTS·+ and DPPH· scavenging assays. The TAA and total phenol content of experimental red (Pinotage and Cabernet Sauvignon)and white (Chardonnay and Chenin blanc) cultivar wines, decreased (P < 0.05) during 12 months of storage at 0, 15 and 30 ºC. The TAAABTS of Cabernet Sauvignon and Chardonnay, stored at 30 ºC were lower (P < 0.05) than at 0 ºC. The APABTS and APDPPH of most wines also decreased during storage. The monomeric anthocyanin content of red wines decreased (P < 0.05) rapidly at 15 and 30 ºC. The flavanol content of wines (except Chenin blanc) increased during the first 9 months, decreasing again after 12 months, while minor changes in the flavonol and tartaric acid ester content of both red and white wines were observed. The TAAABTS exhibited a good correlation (r ³ 0.7, P < 0.001) with total phenol content of red and white wines, as well as with flavonol and tartaric acid ester content of red and white wines and flavanol content of white wines. The monomeric anthocyanin content of red wines correlated (r = 0.50, P < 0.001) weakly with TAAABTS. The decrease in the TAAABTS of wines could thus be mainly attributed to a decrease in their total phenol content. / AFRIKAANSE OPSOMMING: Die antioksidant aktiwiteit van fenoliese komponente in wyn is waarskynlik verantwoordelik vir die gesondheidsvoordele daarvan. Die studie het dus gepoog om effek van kultivar en veroudering na bottelering op die antioksidant aktiwiteit van Suid-Afrikaanse wyne te ondersoek. Die antioksidant aktiwiteit van kommersiële Suid-Afrikaanse rooi (Cabernet Sauvignon, Ruby Cabernet, Pinotage, Shiraz, Merlot) en wit (Sauvignon blanc, Chenin blanc, Chardonnay, Colombard) kultivarwyne is vergelyk deur middel van die 2,2’-azino-di-(3-etielbensotialosien-sulfoon suur)-radikaal katioon (ABTS·+) vernietigingstoets, 2,2-difeniel-1-pikrielhidrasielradikaal (DPPH·) vernietigingstoets en mikrosomale lipiedperoksidasietoets (MLP). Die antioksidant aktiwiteit en die antioksidant kragtigheid (AK) van die rooiwyne was beter as dié van witwyne in al drie antioksidant toetse. Die totale antioksidant aktiwiteit (TAAABTS en TAADPPH) van Ruby Cabernet was die laagste van die rooiwyne, terwyl die AKABTS en AKDPPH van rooiwyn fenoliese fraksies nie van mekaar verskil (P ³ 0.05) het nie. Van die rooiwyne, het Ruby Cabernet en Pinotage die laagste en Merlot die hoogste effektiwiteit in die MLP toets getoon. Die AKMLP van Pinotage se fenoliese fraksies was die laagste van die rooiwyne. Die witwyne, Chardonnay en Chenin blanc, het onderskeidelik die beste en swakste antioksidant aktiwiteit en AK van die witwyne getoon in al drie antioksidant toetse. Askorbiensuur wat in sommige witwyne voorgekom het, het die TAA van hierdie wyne verhoog, maar hul % MLP inhibisie verlaag. Die TAA en % MLP inhibisie het goed gekorreleer (r ³ 0.7, P < 0.001) met die totale fenolinhoud van rooi- en witwyne, asook die flavanolinhoud van rooiwyne en die wynsteensuur-esterinhoud van witwyne. Die % MLP inhibisie het ook goed gekorreleer met die flavanolinhoud van witwyne. Geen korrelasie (P > 0.1) is waargeneem tussen antioksidant aktiwiteit van rooiwyne en hul monomeriese antosianien-inhoud. Rooiwyn was meer pro-oksidatief in die deoksieribose toets as witwyne, maar was die swakste hidroksieradikaalvernietigers en metaalcheleerders.Die effek van veroudering na bottelering op die antioksidant aktiwiteit van wyne soos bepaal met die ABTS·+ en DPPH· vernietigingstoetse, is ondersoek. Die TAA en die totale fenolinhoud van eksperimentele rooi- (Pinotage en Cabernet Sauvignon) en witwyne (Chardonnay en Chenin blanc) het afgeneem (P < 0.05) tydens opberging na bottelering by 0, 15 en 30 ºC oor 12 maande. Opberging by 30 ºC het ‘n groter vermindering (P < 0.05) in die TAAABTS waarde vir Cabernet Sauvignon en Chardonnay veroorsaak as by 0 ºC. Die meeste wyne se APABTS en APDPPH waardes het ook verminder (P < 0.05) na 12 maande. Drastiese vermindering (P < 0.05) in die monomeriese antosianieninhoud van rooiwyne is opgemerk tydens opberging by 15 en 30 ºC. Tydens die eerste 9 maande se opberging het die flavanolinhoud van wyne toegeneem (P < 0.05) en daarna afgeneem (P < 0.05) tot by 12 maande, terwyl flavonol- en wynsteensuuresterinhoud van beide rooi- en witwyne min verandering ondergaan het. Die totale fenolinhoud van rooi- en witwyne, asook die flavonol en wynsteensuur-esterinhoud van rooi-en witwyne en die flavanolinhoud van witwyne, het goed gekorreleer (r ³ 0.7, P < 0.001) met die TAAABTS. In teenstelling met die resultate vir kommersiële kultivarwyne, was die TAAABTS van rooiwyne swak gekorreleer (r = 0.5, P < 0.001) met hul monomeriese antosianieninhoud. Die afname in TAAABTS van wyne tydens veroudering kon dus meestal toegeskryf word aan die afname in hul totale fenolinhoud.