The role of tomato juice serum in malolactic fermentation in wine

Abstract

Malolactic fermentation (MLF) is a common process in winemaking to reduce wine acidity, maintain microbial stability and modify wine aroma. However, successful MLF is often hampered by their sluggish or stuck activity of malolactic bacteria (MLB) which may be caused by nutrient deficiency, especially when MLB are inoculated after alcoholic fermentation (Alexandre et al., 2004; Lerm et al., 2010). Identification and characterization of essential nutrients and growth factors for MLB allows for production of highly efficient nutrient supplements for MLF. While the growth-inducing effect of tomato juice, the so-called ‘tomato juice factor’ (glycosylated pantothenic acid) on lactic acid bacteria in the culture medium without ethanol has been described a long time ago (Imamoto et al. 1972; Eto and Nakagawa 1975; Okada et al, 2000), still, the effect in high alcohol wine matrix remains to be elucidated. Aim: The aim of the current work was to study the possible role of TJF in inducing the malolactic conversion in wine. Materials and Methods: The synthetic grape must was fermented with EC-1118 wine yeast (Lalvin®, Lallemand Inc.) to the final ethanol concentration of 10-11%, pH 3.5 and glucose/fructose concentration of less than 3 g/L. The model wine was transferred into 100 ml fermenters and the whole freeze-dried tomato juice serum (TJS) or its molecular fractions obtained with size exclusion chromatography (SEC) were added. The wines were then inoculated with a commercial Oenococcus oeni strain VP41 (Lalvin®, Lallemand Inc.). The MLF was followed for 22 days and the conversion of malic acid to lactic acid was measured with HPLC. Glycosylated pantothenic acid was determined with indirect enzymatic method after hydrolysis of β-Glucosidase and liberated pantothenic acid was quantified by LC-MS. Results and Discussion: Our experiments showed that the addition of lyophilized TJS to model wine enabled to complete malolactic conversion in 18 days, while in control fermentation only 10 % of malic acid was consumed in the same time. The TJS was then fractionated using SEC and the effect of the collected fractions on MLF performance was tested using the same experimental setup. We observed the significant variation of MLF activity between different SEC fractions. The treatment of TJS with β-glucosidase revealed that from all pantothenic acid ~58% is glycosylated. These results suggest that TJS is a vital supplement, containing essential nutrients like glycosylated pantothenic acid for MLB, which results in quicker and more reliable MLF in wine.