Co-inoculation of a pectinolytic <i>Aureobasidium pullulans</i> strain and <i>Saccharomyces cerevisiae</i> for low-temperature red fermentation: A strategy to enhance the colour and sensory properties of Malbec wines

Low-temperature fermentation is employed to improve aroma production and retention in red wines but at the expense of polyphenol and pigment extraction. In this study, the strategy of co-inoculating the pectinolytic strain Aureobasidium pullulans GM-R-22 with a commercial Saccharomyces cerevisiae for the low-temperature fermentation (LTF, 17.5 °C) of Malbec red grapes was evaluated at pilot scale, and compared with a traditional fermentation (TF, 25 °C), to compensate for the lower extraction of colour and polyphenols at low maceration temperature. The effects of this strategy on the chromatic, phenolic, technological, antioxidant and sensory properties of Malbec wines were assessed during fermentation and up to 12 months of bottle storage. A. pullulans (Ap) grew and remained viable during 4 days of LTF, without affecting the fermentation and growth kinetics of S. cerevisiae (Sc), and significantly higher levels of pectinase activity (about 4.5-fold) were detected in LTF (Ap + Sc) compared to LTF (Sc) and TF (Sc) vinifications. At the end of the fermentation, LTF (Ap + Sc) wine showed higher colour intensity (CI), total anthocyanins (TA), total polyphenolic index (TPI) and a* with a lower L*, b* and filtration time (25 %) than LTF (Sc) wine. After 12 months of bottle storage, CI, TPI, TA and monomeric, copigmented and polymeric anthocyanins were significantly higher in LTF (Ap + Sc) than in LTF (Sc) and statistically equal to TF (Sc), although the CIELAB parameters and the antioxidant activity showed no statistical differences compared to control wines. Sensory analysis showed that the LTF (Ap + Sc) wine had greater colour intensity and violet hue than the LTF (Sc) wine, reaching the colour attribute scores of the TF (Sc) wine, and was particularly characterised by a spicy aroma, unlike the wines fermented in the absence of A. pullulans. This is the first study to demonstrate the performance of A. pullulans in pilot-scale fermentation and the efficiency of its pectinases in improving the extraction and stability of red wine colour fermented at low temperatures, approaching or achieving the levels of chromatic and phenolic parameters of the traditionally fermented Malbec wine.