ESTERASES OF LACTIC ACID BACTERIA

MEDINA, R.B., ABEIJÓN MUKDSI, M.C., GÓNZALEZ, S.N

Tucumán

Conferencia; III SIMPOSIO INTERNACIONAL DE BACTERIAS LÁCTICAS; 2009

Esterases are carboxyl ester hydrolases that catalyse the cleavage and formation of ester bonds. These enzymes play a major role in agricultural, food and pharmaceutical industries. In our laboratory we evaluate esterase contribution to flavour compound generation in dairy products and their health-promoting effects related to antioxidant compounds release (hydroxycinnamic acids). Regarding esterase involvement in flavour development, these enzymes mainly hydrolyse carboxyl ester linkages of water-soluble substrates, as short-chain fatty acid esters and only triglycerides composed of short-chain fatty acids. However, four types of ester-forming reactions can be catalysed by esterases under certain conditions: esterification, alcoholysis, acidolysis and transesterification. Lactic acid bacteria isolated from argentinean goat´s and ewe’s milk cheese presented very complex esterase systems, with multiple esterases able to hydrolyse triglycerides releasing short-chain fatty acids from 2 to 6 carbon atoms in miniature cheese models, thus contributing to the characteristic flavour of these cheeses. These bacteria also showed ability to synthesise esters by alcoholysis and esterification mechanisms when cell-free extracts were incubated in phosphate buffer containing ethanol plus triglyceride (alcoholysis) and ethanol plus free fatty acid (esterification). Strains evaluated were able to synthesise ethyl esters from 2 to 10 carbon atoms, mainly ethylbutanoate and ethylhexanoate. A great variability among strains was observed.  Higher ester levels were detected when cell- free extracts were incubated in presence of  free fatty acids and ethanol as substrates, indicating the prevalence of esterification mechanism in these strains. In miniature cheese models synthesis of ethylacetate, ethylbutanoate and ethylhexanoate was observed. Moreover, the health-promoting effects of esterases (cinnamoyl esterases) derive from their ability to hydrolyse hydroxycinnamate esters, present in cereal bran, releasing hydroxycinnamic acids (ferulic, sinapic, caffeic, p-coumaric acids) with antioxidant properties. This esterase activity is necessary to cleave ester bonds and release the free acids into the gut lumen, which then become available for absorption or further metabolism. In our laboratory we selected strains with feruloyl esterase activity and evaluated the effect of oral administration of these strains to mice. When Lactobacillus fermentum CRL 1446 was administrated for 7 days (107 cfu/ml/day), intestinal feruloyl esterase activity increased, mainly in large intestine content. For this dose the oxidative status of treated animals improved, since a 30-40% decrease of plasmatic lipoperoxide levels was observed.Esterases playa major role in flavour and antioxidant compounds generation and therefore can be use for development of novel functional foods.