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Resveratrol is a phenolic compound that was present in the wine with ethanol addition will help in health promoting effects with consumption of wine. Types and the amount of phenolics were present in wines play a central role in control the oxidation in the human body. Phenolic compounds have an antioxidant property which can help in anti aging and some of the health problem. Wine quality is depending on some factor. There are certain factors that were affected the level of resveratrol in the wine such as the resveratrol evolution and its derivatives during fermentation, fungal pressure in the vineyard, vinification techniques, maceration time and fining agents, enzyme treatments, effect of cluster stems, types of species, yeast strain and effect of UV light (Kim Trollope, 2006).
2.5.1 The resveratrol evolution and its derivatives during fermentation
Resveratrol have higher level in the skin of grapes but minimum level of concentration in the flesh of grapes. Red wines are higher level of resveratrol than white wine. During red wines vinification, fermentation occurs on the skins while during white wines vinification, skins were removed during fermentation. From the starting of fermentation, the resveratrol gylcosides are very low. As the fermentation was progressed and ethanol was added, solubility of resveratrol and concentration thus increased (Vitrac et al., 2005).
2.5.2 Fungal pressure in the vineyard
When the fungal pressure in the vineyard is high, the resveratrol level in wine also increased. Fungal infection was shown to evoke the synthesis of resveratrol. After resveratrol was produced, it still need to be degraded by the exo-cellular enzyme which is laccase like the stilbene oxidase. Kim Trollope in 2006 was hypothesized that during the low pressure of botrytis, fewer grapes bunches was directly attacked by the pathogen and produced high levels of phytoalexins. Pathogen has not fully developed to the stage where production of phytoalexin degrading enzyme by the time that the grapes were harvested. Botrytis is a plant disease that blackens and weaken the flower buds which caused by the gray mold which was used in winemaking. When the Botrytis was low, resveratrol in wine will be higher. When Botrytis was low, there will be lesser grapes attacked directly by the pathogen. For those were not being affected can produce high levels of phytoalexins. So, there is higher level availability of resveratrol for the wines extraction. Resveratrol concentration is a balance between the plant production and fungal enzymes degradation. If Botrytis development was limited, resveratrol levels in wine will be as low as possible. The fungal pressure can affect the resveratrol concentration (Kim Trollope, 2006).
2.5.3 The vinification techniques
Vinification techniques play an important role in determined the levels of resveratrol in wine. Skills and experience can affect the vinification techniques that contribute to resveratrol level in wine. The grapes can be protected from the oxidation by sparging with the sulphur dioxide and ascorbic acid, it may result a higher level of resveratrol in wines. The grape undergo prefermentative oxygenation can decrease the levels of resveratrol. The level of resveratrol depending on the variety of grapes. Different variety of grapes have different resveratrol concentration. While during the cold soaking, the skins and the seeds were soaked in the cool environment which less than 20oC for one or two days in an alcoholic fermentation. This is to achieve an aqueous extraction without effects of ethanol on grape cells. While thermo-vinification involves heating for a short period of time after crushing the extraction from the skins. Then, it must cool and seeds are removed. Fermentation is incubated with yeast. During carbonic maceration, grapes are kept in a carbon dioxide environment. This is to allow respire and ferment until alcohol reaches 1% to 1.5% (v/v). After eight to ten days fermentation ceases as the glycolytic enzymes that conduct the fermentation lose activity. After that, bunches are then pressed and the run-off is inoculated and fermented without the skins. The result showed that wines that were produced by thermo-vinification has the highest resveratrol concentration which increase total resveratrol concentration by 266%, cold soaking was increased total resveratrol level by 27% while no resveratrol was detected in wines that undergo carbonic maceration (Clare et al., 2004).
2.5.4 The maceration time and fining agents
In 2004, Clare found that resveratrol concentration will decrease when maceration time was extended by ten days. Extending skin contact period by one week after fermentation reached dryness. Precipitation, adsorption and isomerisation to cis-resveratrol proposed to be the causes. Excessive maceration will cause extraction of astringent and bitter phenolic compounds that affect the quality of the wine. Fining agents that added to the wine to remove the compounds and bring effects on resveratrol levels. Polyvinylpolypyrrolidone (PVPP) decreased the concentration of resveratrol in wine by up to 90%. Charcoal and PVPP eliminate free resveratrol from wine (Clare et al., 2004).
2.5.5 The treatments of using enzyme
Pectolytic enzyme was used in the winemaking. They break down the skin cell walls of the grapes to increase juice yield and also facilitate the color of phenolic compounds extraction and stability. The preparation of commercial enzyme often contain some impurities in which the extraneous Î²-glucosides were formed. The resveratrol levels will be affected by the conversion of resveratrol glucosides to aglycones and enzyme facilitated the extraction from the skins. The dosage of the enzyme was also affected the level of resveratrol. The fermentation process must treat with the pectolytic enzymes. The resveratrol level was increased after pectolytic enzyme treatment. Wine treated with enzyme contained resveratrol levels 33% higher than control wine. There is an effect of enzyme on resveratrol level in wine (Sacchi et al., 2005).
2.5.6 Effect of cluster stems
Baveresco has done research on the effect of cluster stems on resveratrol concentration of wines in 2000. Resveratrol was extracted from the cluster stems in a hydro-alcoholic solution and with methanol to mimic wine. The study was to look for cis- resveratrol and trans- resveratrol. But in this study the cis resveratrol was not detected. Three different amounts of stems and four times of extraction were then evaluated. The highest amount of stems that is 0.9 g/100ml was yielded the greatest amount of resveratrol for both the hydro-alcoholic solution with 1.4mg/L and methanol with 0.2 mg/L. During the 4 days period, the methanol extraction was 0.2 mg/L and for the hydro-alcoholic solution was 1.2mg/L. There was a resveratrol concentration decreased during 4 to 8 days. The degradation of oxidative or transformation to an unknown compound was responsible for the decrease of resveratrol level. The stem addition components were used as a method in increasing the resveratrol level in wine eventhough they able to recognise that other undesirable compounds can be extracted from the stems during fermentation step (Baveresco et al., 2000).
2.5.7 The types of species
Mark R. LeBlanc in 2006 was investigated the trans and cis resveratrol concentration from 18 different wines that included eight commercial wines of V. vinifera species, five commercial wines of muscadine species, two commercial wines of V. labrusca, a muscadine port and two V. vinifera ports were studied. All of the muscadine species wines sampled had higher cis and trans resveratrol concentrations compared with other types of wines sampled. The muscadine species wines had around 9.2 and 31.9 mg/L of cis resveratrol and 4.9 and 13.4 mg/L of trans resveratrol. The V. vinifera species wines were between 0.8 to 3.3 mg/L cis resveratrol and around 1.1 and 4.5 mg/L of trans resveratrol. The two commercial V. labrusca wines had between 1.5 and 4.0 mg/L cis resveratrol and between 1.1 and 2.7 mg/L trans resveratrol. The muscadine port wine had 3.3 mg/L cis resveratrol and 3.6 mg/L trans resveratrol and while for the V. vinifera port wines had between 0.3 and 0.1mg/L cis resveratrol and had no trans resveratrol detected. The wine made from muscadine grapes had higher cis and trans resveratrol concentration compared to wines that made from V. labrusca or vinifera grapes. For all muscadine wines the cis resveratrol was higher concentration than trans resveratrol (Mark R. LeBlanc, 2006).
2.5.8 Yeast strain
When resveratrol was tested in a laboratory liquid culture, Kim Trollope in 2006 found that the yeast can cause resveratrol decreased in concentration. Kim Trollope studied the effect of the yeast strain on the evolution of resveratrol and its glucosides in the wine. Kim Trollope found out that the yeast strain used to conduct for the fermentation process. As the fermentation was precede, the levels of cis- and trans-piceid decreased. A high level of alcohol was produced the strain of Saccharomyces cerevisiae that caused a 32% decreased in the level of resveratrol. For a low level of alcohol was produced the strain of Metschnikowia pulcherrima that caused a reduction of 20% decreased in level of resveratrol. The decreased was caused by the uptake and the metabolism or the adsorption to the yeast cell wall. The yeast strain was used to conduct the fermentation, the level of resveratrol decreased as the fermentation proceeds. There was a decreased level in glucoside. There was a reduction in free forms of resveratrol compared than glucoside. Some strains can cause a decrease in both resveratrol forms and some also affecting on level of trans-resveratrol. A positive correlation between the total resveratrol concentration and the total phenolics in wine and both were considered yeast strain dependent (Kim Trollope, 2006).
2.5.9 Effect of UV light
Mark R. LeBlanc in 2006 has studied that the UV light can influence the production of resveratrol in the tissues of grapevine. There are some changes in the phytoalexin concentration of the grape leaf tissue after exposure to UV light. Mark R. LeBlanc studied four Vitis species which were three American species such as Vitis rupestris, Vitis cineria and Vitis labrusca, and also three cultivars of Vitis vinifera. All three American species showed a higher resveratrol synthesis capacity compared with V. vinifera. The V. rupestris and V. cineria had higher resveratrol synthesis capacity than V. labrusca. All American species took longer time to reach peak resveratrol concentration (30 to 45 hours) compared to V. vinifera (18 to 25 hours) (Mark R. LeBlanc, 2006).