Breakdown and biosynthesis of esters by lactic acid bacteria isolated from fruits and flowers of Northern Argentina

RUIZ RODRIGUEZ, L.; HEBERT, E.M.; DE VUYST, L.; MOZZI, F.; MOHAMED, F.; MEDINA, R.

San Miguel de Tucuman

Simposio; SIBAL 2016. V International Symposium on Lactic Acid Bacteria. Benefitting from Lactic Acid Bacteria. Progress in Health and Food.; 2016

Lactic acid bacteria (LAB) are a diverse group of microorganisms used as starter cultures in several food fermentations due to their interesting features. Often, the use of autochthonous LAB rather than allochthonous strains is increasingly preferred as starters. Also, the selection of cultures with enzymatic activities and technological properties adapted to a fermentable substrate is necessary for improved fermentation processes. Notably, flavor is one of themost important characteristics involved in the acceptance of products by consumers. Esterases are enzymes with a key role during flavor development in fermented foods. These enzymes are either able to hydrolyze or synthesize esters. While the equilibrium between both processes depends on several parameters, the different reaction products give specific and differential organoleptic traits to fermented foods. We aimed to evaluate both the esterase activity and fruity ester-synthesizing activity of LAB strains from fruits and flowers of Northern Argentina, as an interesting feature of potential starter cultures for fruit juice fermentation. The esterase-specific activity (ESA) of cell-free extracts (CFE) from 96 different LAB strains was determined spectrophotometrically (OD560) using a-naphthyl (a-NA) derivatives (C2, C3, C4, C8, C10 and C12 carbon atoms) as substrates (30 °C, 60 min). Fifty-one strains belonging to 5 genera (Lactococcus, Weissella, Leuconostoc, Lactobacillus, and Enterococcus) showed ESA with at least 2 a-NA derivatives; all of them being active against a-NA-C3 and none against a-NA-C12. ESA on a-NA-C2, C3, C4 and C8 was distributed among the LAB strains studied, whereas only Leuc. mesenteroides FMy1-2 and Lb. rhamnosus H3F-210 hydrolyzed a-NA-C10. Subsequently, 10 strains (2 Lc. Lactis, 2 W. minor, 2 Leuc. mesenteroides, 1 Leuc. pseudomsenteroides, 1 Lb. brevis and 1 Lb. rhamnosus) exhibiting the highest ESA values (3.6-32.4 U/mg protein) were selected to determine ester-biosynthesizing activity using CFE, free fatty acids (butanoic acid or hexanoic acid) plus ethanol. After 24 h of incubation at 30 °C, esters were extracted and determined by GC. Variable ester-synthesizing activities dependent on the strains and substrates were found. Thus, strains of Leuc. mesenteroides were able to produce Et-isoC5, EtC6, and EtC10 from different substrates in variable amounts (2.03-4.80 ppm), displaying diverse ester-synthesizing activity values (1.32-6.68 U/mg). The results showed that hydrolysis and synthesis of esters were strongly strain-dependent. Further investigations are necessary to evaluate the implication of the different compounds produced in the sensorial properties of fermented foods.