Application and validation of autochthonous Lactobacillus plantarum starter cultures for controlled malolactic fermentation and its influence on the aromatic profile of cherry wines
Introduction
Wine is a product of a series of complex biochemical reactions taking place at different stages of the wine-making process (Barrajón et al., 2011), mainly consisting of alcoholic fermentation (AF) and malolactic fermentation (MLF), driven by wine microorganisms including yeasts and lactic acid bacteria (LAB). During AF, yeast strains, especially Saccharomyces cerevisiae, play a significant role, which dominate the conversion of carbohydrates into ethanol and carbon dioxide and are accompanied by the formation and modulation of many wine metabolites. MLF is a secondary fermentation that usually takes place during AF or at the end of AF, being conducted mainly by LAB genera, such as Lactobacillus, Leuconostoc, Oenococcus and Pediococcus (Ugliano and Moio, 2005, du Toit et al., 2011). The main function of this fermentative stage is to decarboxylate malic acid and convert it into lactic acid, and simultaneously involves changes to the chemical and physical composition of wines (Boido et al., 2009, Nehme et al., 2010). There is a number of reports showing changes in the volatile aroma profile of wines after MLF, summarised by Sumby, Grbin, and Jiranek (Sumby et al., 2010).
Currently, Oenococcus oeni is the main species used in MLF as LAB starters, but researches have demonstrated that some Lactobacillus plantarum species can also grow in wines and display the ability to survive the harsh conditions of wine (high ethanol concentrations, low pH and temperatures and sulphur dioxide) (G-Alegria et al., 2004, Lerm et al., 2011, Lee et al., 2012, Bravo-Ferrada et al., 2013), and simultaneously, possess many other favourable characteristics (du Toit et al., 2011, Lerm et al., 2011). For instance, the introduction of some Lb. plantarum strains to the fermenting musts could significantly modify the wine aroma profile due to a more diverse enzymatic profile Lb. plantarum strains possess than that of O. oeni (Lerm et al., 2011). Also, Lb. plantarum isolates can synthesize antimicrobial peptides which might help prevent the production of undesired compounds, by the way of inhibiting the indigenous LAB microflora (Du Toit and Pretorius, 2000, Knoll et al., 2008). However, the performance of those Lb. plantarum strains over MLF, and their effect on the wine quality, still needs intensive investigation. And more evidence from fruit wine-making practice, other than grape wine, should be supplied, in order to explore the great potential of such genus and for the wider application in the wine industry.
Cherry wine is one of the most popular fruit wines consumed worldwide (Xiao et al., 2015a, Xiao et al., 2015b). This product is well-known for its distinct flavor and health function due to the enrichment of many different antioxidant components (Sun et al., 2012, Xiao et al., 2015a, Xiao et al., 2015b). Nowadays, the consumption of cherry wine has become very popular in China, especially East China, and it is out of question that the special characteristic and distinct flavor of this product will receive more scrutiny in the future. Regarding use and effect of Lb. plantarum strains on the characteristics of cherry wines, there have been limited literature available (Sun et al., 2013). In order to address this issue, we aim to use an indigenous strain of Lb. plantarum SGJ-24 which was previously isolated from the cherry orchard, in association with selected commercial S. cerevisiae strains. Also, with the aim of making comparisons of the difference between Lb. plantarum and O. oeni, a commercial O. oeni strain of 31 MBR was used in a parallel experiment. During fermentation, the implantation rate of inoculated LAB was determined, and after MLF resultant wines were analyzed and compared for analytical, aromatic and sensory profiles.
Section snippets
Cherries and microorganisms
Cherry fruits of “Rainer” and “May Duck” picked at commercial maturity during the 2013 harvest season were used in this work. A commercial S. cerevisiae strain of Lalvin GRE (Lallemand Inc., Montreal, Canada), one commercial O. oeni strain of 31MBR, and one autochthonous Lb. plantarum strain (SGJ-24) were used for the fermentations.
Strain isolation and culture conditions
Lactic acid bacteria were isolated from cherry wines of spontaneous MLF during the 2013 vintage. A total of 200 kg of cherries, from 16 different cherry orchards in
Screening of MLF starters
The following selection criteria were used to reduce the number of screened strains: fast growth, fast acidification and high tolerance (single restrictor of pH, SO2, ethanol; and combined factors). During the assay of malolactic performance using a synthetic medium (SW), most of the tested strains were found to be able to consume l-malic acid completely after 20–45 days, and 16 strains showing faster growth and faster acidification (within 20 days) were selected and submitted to the second
Conclusions
Wine composition and desired outcome of the wine are important criteria for the correct choice of LAB strain for MLF, as it influences the final chemical composition and sensory profile of wine. The present study used an autochthonous Lb. plantarum strain of SGJ-24 to conduct MLF in Rainer and May Duck cherry wines, in comparison with a commercial O. oeni strain of 31 MBR. Results obtained from MLF process demonstrated that Lb. plantarum SGJ-24 showed a shorter LP period and a greater
Acknowledgement
This work was financially supported by the National Youth Science Foundation of China (No. 31301565 and No. 31501577), the Project of Shandong Province Higher Educational Science and Technology Program (J13LE10), Natural Science Foundation of Shandong Province (ZR2012CQ009) and Science and Technology Development Planning of Yantai (2012125).
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