Biochemical characterisation of the esterase activities of wine lactic acid bacteria

Esters are an important group of volatile compounds that can contribute to wine flavour. Wine lactic acid bacteria (LAB) have been shown to produce esterases capable of hydrolysing ester substrates. This study aims to characterise the esterase activities of nine LAB strains under important wine conditions, namely, acidic conditions, low temperature (to 10 degrees C) and in the presence of ethanol (2-18% v/v). Esterase substrate specificity was also examined using seven different ester substrates. The bacteria were generally found to have a broad pH activity range, with the majority of strains showing maximum activity close to pH 6.0. Exceptions included an Oenococcus oeni strain that retained most activity even down to a pH of 4.0. Most strains exhibited highest activity across the range 30-40 degrees C. Increasing ethanol concentration stimulated activity in some of the strains. In particular, O. oeni showed an increase in activity up to a maximum ethanol concentration of around 16%. Generally, strains were found to have greater activity towards short-chained esters (C2-C8) compared to long-chained esters (C10-C18). Even though the optimal physicochemical conditions for enzyme activity differed from those found in wine, these findings are of potential importance to oenology because significant activities remained under wine-like conditions.

Protease, peptidase and esterase activities by lactobacilli and yeast isolates from Feta cheese brine

AIMS

The study of peptidase, esterase and caseinolytic activity of Lactobacillus paracasei subsp. paracasei, Debaryomyces hansenii and Sacchromyces cerevisiae isolates from Feta cheese brine.

METHODS AND RESULTS

Cell-free extracts from four strains of Lact. paracasei subsp. paracasei, four strains of D. hansenii and three strains of S. cerevisiae, isolated from Feta cheese brine were tested for their proteolytic and esterase enzyme activities. Lactobacillus paracasei subsp. paracasei strains had intracellular aminopeptidase, dipeptidyl aminopeptidase, dipeptidase, endopeptidase and carboxypeptidase activities. Esterases were detected in three of four strains of lactobacilli and their activities were smaller with higher molecular weight fatty acids. The strains of yeasts did not exhibit endopeptidase as well as dipeptidase activities except on Pro-Leu. Their intracellular proteolytic activity was higher than that of lactobacilli. Esterases from yeasts preferentially degraded short chain fatty acids. Lactobacilli degraded preferentially beta-casein. Caseinolytic activity of yeasts was higher than that of lactobacilli.

CONCLUSIONS

The results suggest that Lact. paracasei subsp. paracasei and yeasts may contribute to the development of flavour in Feta cheese.

SIGNIFICANCE AND IMPACT OF THE STUDY

Selected strains could be used as adjunct starters to make high quality Feta cheese.

Peptidolytic, esterolytic and amino acid catabolic activities of selected bacterial strains from the surface of smear cheese

Enzymes produced by bacteria present on the surface of smear cheeses play essential roles in flavour development during cheese ripening. In this study, strains including brevibacteria, corynebacteria, staphylococci and brachybacteria, from the surface of two smear cheese (Tilsit and Gubeen) were screened for a range of enzyme activities including aminopeptidase (substrates: Leu-pNA and His-pNA), dipeptidase (Met-Ala, Ala-Met, Pro-Ala, His-Leu and Pro-Leu), tripeptidase (Phe-Gly-Gly, Gly-Gly-Gly and Leu-Ala- Pro), esterase (beta-naphthyl butyrate, beta-naphthyl caprate and beta-naphthyl palmitate). L-methionine aminotransferase and cystathionine lyase activities. There were marked differences in the activities observed between different bacteria studied. Brachybacteria showed low activity on all substrates assayed. There was no consistency in activities within groups of related bacteria. For example, Staphylococcus equorum 14 showed higher activity than S. equorum 6 on all the substrates tested. Among the corynebacteria, Coryebacterium ammoniagenes CA8 had greatest aminopeptidase, esterase and cystathionine lyase activity while C. casei B showed more di- and tri-peptidase activity. It was noted that individual bacteria displayed similar activities on all three esterase substrates, i.e., the chain length of the fatty acid did not appear to affect activity. L-Methionine aminotransferase activity was observed in only one strain (S. equorm 14) whereas all strains had cystathionine lyase activity.

Adjunct cultures: recent developments and potential significance to the cheese industry

Several previous reviews have described different ways to enhance the flavor and texture of cheese, including use of live cells and nonviable attenuated cells as adjunct cultures. However, comparisons between viable and nonviable cultures were never discussed in these reviews. In addition, recent publications on adjunct cultures have not been covered in previous reviews. This article will survey the more recent work on adjunct cultures--with particular attention to whether the adjuncts contained viable or nonviable cells--and propose areas where additional research is needed.

Hydrolysis of esters by staphylococci

The objective of this work was to characterize the hydrolysis of esters by staphylococci in order to understand if they could contribute to the release of free fatty acids in sausage. Cell-free extracts and extracellular concentrates of staphylococci were examined for esterase activities against p-nitrophenyl esters and for lipolytic activities against triolein. Staphylococci showed intracellular and extracellular esterase activities with different esterase electrophoretic patterns. Cell-free extracts of S. xylosus, S. warneri and S. saprophyticus preferentially hydrolysed p-nitrophenyl butyrate whereas their extracellular concentrates were mainly active against p-nitrophenyl butyrate, p-nitrophenyl caproate and p-nitrophenyl caprylate. In addition their extracellular concentrates hydrolysed triolein. The two strains of S. carnosus differed as they did not show pronounced p-nitrophenyl substrate specificity and did not hydrolyse triolein. Staphylococci hydrolysed esters at a high rate between 15 and 25 degrees C; acidic conditions inhibited the hydrolysis. The hydrolysis was also reduced when the water activity was decreased by addition of polyethylene glycol or glycerol.