Page 13 - MALOLACTIC FERMENTATION – IMPORTANCE OF WINE LACTIC ACID BACTERIA IN WINEMAKING

THE CHEMISTRY OF MALOLACTIC FERMENTATION
PETER COSTELLO, PH.D.
The term “malolactic fermentation” (MLF) describes the enzymatic conversion of L-malic acid to L-lactic acid and CO2 by lactic acid bacteria (LAB) cells after they have grown (Wibowo et al. 1985). This biological deacidification reaction is well recognized as one of the main meta- bolic capabilities of LAB in wine, and its conduct is of major commercial importance to the winemaking process. In addition to the deacidification reaction that characterizes MLF, it is becoming increasingly recognized that a diverse range of other metabolic activities are associ- ated with the growth and development of LAB in wine, which can have a significant influence on wine quality. In this section, the primary metabolic characteristics of LAB are outlined, with particular emphasis given to MLF, as well as to some of the other metabolic reactions of LAB that can affect wine properties.
GENERAL METABOLIC PROPERTIES OF LACTIC ACID BACTERIA
LAB constitute a ubiquitous group of bacteria that occur in a range of environments, including many foods and beverages. Importantly, these bacteria are primarily noted for their ability to produce lactic acid from a fermentable carbohydrate source. Lacking heme-linked cyto- chromes and catalase, LAB obtain energy from carbohydrates by fermentative metabolism (Kandler 1983).
LAB can be broadly classified as either homofermentative or heterofermentative according to the types of end products produced from the fermentation of glucose. Homofermentative LAB, including the Pediococci and some of the Lactobacilli, utilize the Embden-Meyerhof-Par- nas (EMP) glycolytic pathway to convert the hexose sugar – glucose – mainly to lactic acid. In this pathway, two moles of lactic acid and two moles of adenosine triphosphate (ATP) are produced for each mole of glucose fermented. On the other hand, the heterofermentative Lactobacilli and the Leuconostocs lack some key enzymes of the EMP pathway and ferment
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