Grape compounds interactions

Overview of Yeast Interactions with Grape Compounds. 315... 

Over recent decades, research into the role of yeast in the development of wine flavour has revealed complex interactions between this microbe and grape compounds many of these interactions contribute to the appearance, aroma, flavour and texture of wine. When wood is used in fermentation, some wood-derived flavour compounds can also be modified by yeasts. Together, all these compounds that are present in must, and produced and modified during fermentation, and by other processes, contribute to the distinctive varietal character of wine. 

Table 8D.2 Summary of yeast metabolic interactions with grape compounds...

However, in the same grape must, interactions also depend on the strains. LAB growth can be much easier in the wines which are made when certain yeast strains are dominant (Fomachon 1968). Yeasts differences can be attributed to many factors such as the production of varying levels of SO and fatty acids as well as specific proteinaceous molecules and mannoproteins. The last two compounds should act as inhibitors (Comitini et al. 2005) or activators, respectively (Diez et al. 2010). 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Yanes and coworkers [43] demonstrated an application of IL for aqueous CE for fhe separation of phenolic compounds (flavonoids) found in grape seed exfracfs. By using [C Qlm] (n = 2,4) ILs as additives for the running electrolyte, a simple and reproducible electrophoretic method for the separation of polyphenols was developed. If was speculated that the separation mechanism was based on an association between the imidazolium cations and the polyphenols. The role of fhe alkyl substituents on the imidazolium cations was investigated and discussed [43]. The anion has little effect on the separation while a related study demonstrated that interaction between phenolic compounds and the IL cations in water occurred through n-n interactions. 

Protein haze in white wine thus differs in several aspects from protein haze in beer. It is well established that beer protein haze is due to interactions between proteins, derived from the barley storage protein hordein and rich in proline, and hop polyphenolic compounds (Bamforth 1999 Miedl et al. 2005 Siebert 1999 Siebert and Lynn 2003). White wine proteins are not derived from storage proteins of grape seed nor are they as rich in proline as hordein. In addition, wine protein haze formation cannot be eliminated by removing polyphenolic compounds by PVPP (Pocock et al. 2006) while in beer this has been applied as a commercial strategy (Leiper et al. 2005 Madigan et al. 2000). 

Flavanol oligomers and polymers are also called condensed tannins or proan-thocyanidins. The term tannin refers to their capacity to interact or react with proteins and precipitate them out. When heated under acidic conditions, these molecules release red anthocyanidin pigments, hence the term proanthocyanidins. The term leucoanthocyanidin, also referring to this particular property, is sometimes encountered in the literature. However, this should be restricted to another group of compounds, flavan 3,4-diols, which are intermediates in the biosynthetic pathway leading to flavanols and anthocyanins (Stafford and Lester 1984 Nakajima et al. 2001 Abrahams et al. 2003) but have never been isolated from grapes, presumably due to their instability. 

Profiling and content of such compounds in grape products depends on the grape variety and how it interacts with berry ripeness and climatic and agronomic factors (Marais et al., 1992). 

In contrast, if all proteins have to be extracted, e.g. for the study of the grape biology, it is necessary to adopt a multi-step method in order to minimize protein losses occurring with rupture of the cells and proteins interaction with phenolic compounds. 

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