Elicitors used as a tool to increase stilbenes in grapes and wines

Chitosan is a polysaccharide produced from the deacetylation of chitin extracted from crustaceous and fungi. In winemaking chitosan is mainly used in the clarification of grape juice and wine, stabilization of white wines, removal of metals and to prevent wine spoilage by undesired microorganisms. The addition of chitosan to model wine systems was able to retard browning, reduce levels of metallic ions (Fe and Cu) and to protect varietal thiols due to its antiradical activity1. The present experiment was planned in order to evaluate the use of chitosan as a secondary antioxidant at three different stages of Sauvignon blanc fermentation and winemaking. Sauvignon blanc juices from three different locations were obtained at a commercial winery in Marlborough, New Zealand. One lots of grapes was collected from a receival bin and pressed into juice with a water-bag press, and a further juice sample was collected from a commercial pressing operation. Chitosan (1 g/L, low molecular weight, 75 – 85% deacetylated) was added to the juice after pressing, after cold settling, after fermentation, or at all these stages. Controls without any chitosan additions were also prepared.

3-Isobutyl-2-methoxypyrazine (IBMP) is one of the key molecules in wine aroma with a bell pepper aroma and a very low threshold in wine, 1-6 ng/L for white wine and 10-16 ng/L in red wine1. The differences in these thresholds are likely due to IBMP-non volatile matrix interactions. It has indeed been shown that polyphenols may influence the volatility of flavor compounds2. In the present study, we focus on IBMP-polyphenols interactions in relation to volatility and sensory perception in model wine solution. Methods: 1. GC-MS Static Headspace Analysis: Samples were analyzed by Static headspace analysis with an Agilent 7890A gas chromatograph coupled to HP 5975C mass spectrometry detector (Agilent Technologies, Santa Clara, CA, USA).

Vineyard exposure to smoke can lead to grapes and wine which exhibit objectionable smoky and ashy aromas and flavours, more commonly known as ‘smoke taint’ [1, 2]. In the last decade, significant bushfires have occurred around the world, including near wine regions in Australia, Canada, South Africa and the USA, as a consequence of the warmer, drier conditions associated with climate change. Considerable research has subsequently been undertaken to determine the chemical, sensory and physiological consequences of grapevine exposure to smoke. The sensory attributes associated with smoke-tainted wine have been linked to the presence of several smoke-derived volatile phenols, such as guaiacols, syringols and cresols [2].

In the winemaking process, several compounds that remain in the grape skins and seeds after the fermentation stage are bioactive-compounds (substances with potential beneficial effects on health) that can be extracted in order to recovery valuable substances with a high commercial value for the cosmetic, food (nutraceuticals) and pharmaceutical industries. The skins contain significant amounts of bioactive substances such as tannins (16-27%) and other polyphenolic compounds (2-6.5%) in particular, catechins, anthocyanins, proanthocyanins, quercetin , ellagic acid and resveratrol.

Since 2012, EU Commission approved compulsory labeling of wines treated with allergenic additives or processing aids “if their presence can be detected in the final product” (EU Commission Implementing Regulation No. 579/2012 of 29 June 2012). The list of potential allergens to be indicated on wine labels comprises sulphur dioxide and milk- and egg- derived fining agents, including hen egg lysozyme, which is usually added in wines as preservative. In some non-EU countries, the list includes gluten, tree nuts and fish gelatins. With the exception of lysozyme, all these fining proteins were long thought to be totally removed by subsequent winemaking processings (e.g. bentonite addition).