BREAK-DOWN AND SYNTHESIS OF ESTERS BY LACTIC ACID BACTERIA ISOLATED FROM FRUITS AND FLOWERS OF NORTHERN ARGENTINA

L. DE VUYST; F. MOZZI; F. MOHAMED; R. MEDINA; L.G. RUIZ RODRÍGUEZ; E.M. HÉBERT

San Miguel de Tucumán

Simposio; SIBAL 2016 - V International Symposium on LACTIC ACID BACTERIA; 2016

CERELA-CONICET

Lactic acidbacteria (LAB) are frequentlyused in food fermentations due to their interesting features. The use of autochthonous LAB rather thanallochthonous strains is preferred as starterscultures. In addition, the selection of cultures with enzymaticactivities and technological properties adapted to a fermentable substrate isnecessary for improved fermentation processes. Flavor is one of the most important characteristics involved inthe acceptance of products by consumers. Esterases are enzymes with a key role during flavor development infermented foods. These enzymes are either able to hydrolyze or synthesizeesters. While the equilibrium betweenboth processes depends on several parameters, the different reaction-productsgive specific and differential organoleptic traits to fermented foods. We aimed to evaluate both the esterase andfruity ethyl ester-synthesizing activities of LAB strains isolated from fruitsand flowers from Northern Argentina as interesting feature of starter culturesfor fruit juice fermentation. Ninety-six LAB strains from differentfruit/flower samples were studied. Cell-free extracts (CFE) were obtained bycentrifugation from 10 mL of cultures grown in MRSfru at 30 °C for 16 h. Thepellets were washed 3 times with 50-mM phosphate buffer (pH 7), mixed withglass beads (150-212 µm) and buffer in a 1:4:1 (mg cells:µl buffer:mg beads)ratio, and disrupted using a Mini Bed Beater-8 (Biospec Products) for 10 min atmaximum speed. Cell debris and glass beads were removed and supernatants wereused as CFE. Protein content was determined by Bradford using BSA as standard.The esterase activity  of each CFE wasdetermined spectrophotometrically (OD560 nm) using α-naphthyl (α-NA)derivatives (C2, C3, C4, C8, C10 and C12 carbon atoms) as substrates andmeasuring  the α-NP released afterincubation for 1 h at 30 °C. U: amount of α-naphthol released by 1 mL of CFE/min. Esterase specific activity (ESA): Units per milligram of protein (U/mg). Thestudied strains were capable of hydrolyzing and synthesize esters, being theformer activity the most widespread property among the strains. Hydrolysis andsynthesis of esters were strongly strain-dependent.The LAB strains evaluated inthis work are able to synthesize SCFA ethyl esters, which can be a desirable flavorproperty in fermented fruit-derived foods.