Additives od aids? Evaluation of aroma compounds release from oenological tannins of different botanical origins.

Abstract

Oenological tannins are products extracted from various botanical sources, such as mimosa, acacia, oak gall, quebracho, chestnut and tara. The polyphenolic component is obtained through a solid-liquid extraction also using specific solvents, then removed by evaporation or freeze-drying. Tannins are employed in two phases of winemaking, during the pre-fermentative phase or during fining with different purposes such as modulate antioxidant activity, colour stabilization, bacteriostatic activity, protein stabilization and modulation of sensory properties. To date, the current regulatory framework is not very clear. In fact, the Codex Alimentarius classifies commercial tannins as “food additives” but also as “processing aids”. The main distinction is that “additives” have a technological function in the final food, whereas “processing aids” do not. In this sense, oenological tannins, despite the technological treatments, could contain aromatic compounds of the botanical species they belong to and release them to the wine. The aim of this study was the evaluation of the release of aroma compounds by oenological tannins of different botanical origins. Twenty-six tannins from two different producers were extracted for forty-eight hours with a hydroalcoholic solution (15% ethanol) on an orbital shaker (70 rpm). Free volatile compounds and glycosidic precursors have been analysed thanks to SPE- and SPME-GC-MS techniques. All volatile compounds were found to be in wide ranges. Terpenes for example ranged from 0.04 µg/L to 19.1 µg/L, with three samples above 15 µg/L. In one case, a sample was found to have a concentration of a cyclic terpene (1,8-cineole) above the odor threshold. Fair concentrations, although below the odor threshold were found for cis- and trans-linaloloxide. Benzenoids as expected showed the highest concentrations, over 1.6 mg/L but also in this case with great variations. In this case, vanillin showed high levels, above the odor threshold in several samples. Other compounds (norisoprenoids, fatty acids and alcohols) were present in traces. Most of the studied products showed low levels of aroma compounds, benzenoids apart, however in some samples, few compounds were present in high concentrations beyond the odor threshold, with the potential ability to modify the sensory profile of a wine.