Differentiation of lactic acid bacteria strains by postelectrophoretic detection of esterases.

Lactic acid bacteria (LAB) comprise a diverse group of Gram-positive, non-spore-forming microorganisms. These bacteria are widely used in food technology. The species identification of LAB depends mainly on physiological and biochemical criteria. The esterolytic systems of LAB remain poorly characterized. Esterases (EC 3.1.1.3) represent a diverse group of hydrolases catalyzing the cleavage and formation of esters bonds Screening of esterases is usually performed either by employing chromophoric substances (e.g., alpha- or beta-naphthyl esters of short-chain fatty acids). The post-electrophoretic detection of esterases is a sensitive technique applied in bacterial systems, that mainly provides information on the similarity of strains within the same species or subspecies according to their esterase patterns. This technique is principally used to determine the number and substrate specificity of esterases and lipases, revealing the complexity of lipase and esterase systems. The present chapter describes the technique of polyacrylamide gel electrophoresis (PAGE; in the absence of sodium dodecyl sulfate [SDS]), in non-denaturing conditions, to find intracellular fractions for strain typing of LAB.

Determination of esterolytic and lipolytic activities of lactic acid bacteria.

Lactic acid bacteria (LAB) are considered weakly lipolytic compared with many other groups of bacteria (e.g., Pseudomonas, Bacillus, and Achromobacter). The esterolytic and lipolytic systems of dairy LAB remain poorly characterized. Esterases from lactic acid bacteria, yeasts, and Pseudomonas organisms may be involved in the development of fruity flavors in foods, and pregastric lipase and esterases are essential for the development of typical flavor in Italian cheese. Microbial lipases and esterases may improve quality or accelerate the maturation of cheeses, cured bacon, and fermented sausages. Lipases are defined as glycerol ester hydrolases (EC 3.1.1.3) that hydrolyze tri-, di-, and monoglycerides present at an oil-water interface. Esterases (EC 3.1.1.6) hydrolyze esters in solution and may also hydrolyze tri- and especially di- and monoglycerides containing short-chain fatty acids. Some probiotic strains of LAB can hydrolyze the triglycerides, releasing most short and medium chain, and essential fatty acids, which are valuable to today's health-conscious consumer. Medium chain fatty acids (C6-C14), in particular, have become accepted treatment for patients with malabsorption symptoms, a variety of metabolic disorders, cholesterol problems, and infant malnutrition. These probiotic bacteria could alleviate lipase deficiency in the digestive tract during digestion (steatorrhea). In this chapter, we describe different methods routinely used in our laboratory to determine the esterolytic and lipolytic activity of LAB. These techniques include the use of alpha- and beta-naphthyl derivatives of fatty acids (chromogenic method), the p-nitrophenyl (pNP) derivative of fatty acids (chromogenic method), and triglycerides (agar-well assay technique and titrimetric test) as substrates.