Capacity Of Lactic Acid Bacteria Research Articles

Ability of Lactic Acid Bacteria to Produce Volatile Phenols

Thirty-five strains of lactic acid bacteria (20 species) were screened for the ability to produce volatile phenols from the corresponding phenolic acids, <i>p</i>-coumaric and ferulic, in culture medium. The concentration of vinylphenols and ethylphenols in the growth medium was analyzed by gas chromatography. Results showed that 13 strains (37%) were able to produce volatile phenols from <i>p</i>-coumaric acid, although only three (9%) produced 4-ethylphenol, the final product of the <i>p</i>-coumaric acid metabolic pathway. The reduction step of this pathway was only found in the <i>Lactobacillus</i> genus: <i>L. brevis</i>, <i>L. collinoides,</i> and <i>L. plantarum.</i> Seven of the eight pediococci strains studied were able to produce 4-vinylphenol but not 4-ethylphenol from <i>p</i>-coumaric acid. The two <i>Oenococcus oeni</i> strains and the strain of <i>Leuconostoc mesenteroides</i> studied did not produce either of the two <i>p</i>-coumaric acid derivatives. Strains that produced volatile phenols were used in subsequent studies at lower phenolic acid concentrations. Experiments with added 5 mg/L of <i>p</i>-coumaric acid showed that some strains can still produce relatively high (up to 800 μg/L) concentrations of 4-ethylphenol. The capacity of lactic acid bacteria to produce volatile phenols from ferulic acid was much lower than its capacity to produce volatile phenols from <i>p</i>-coumaric acid.

Angiotensin I‐converting‐enzyme‐inhibitory and antimicrobial bioactive peptides

Bioactivities of peptides encrypted in major milk proteins are latent until they are released and activated by enzymatic proteolysis. After a brief description of the properties of some bioactive peptides, an overview of the angiotensin I‐converting‐enzyme (ACE)‐inhibitory and antimicrobial peptides is given. Emphasis is on the capacity of lactic acid bacteria to generate ACE‐inhibitory peptides and on the exploitation of the potential role of antimicrobial peptides derived from milk proteins.

Methionine catabolism and production of volatile sulphur compounds by OEnococcus oeni.

During malolactic fermentation (MLF), the secondary metabolisms of lactic acid bacteria (LAB) contribute to the organoleptic modification of wine. To understand the contribution of MLF, we evaluated the capacity of various wine LAB to metabolize methionine. Using gas chromatography (GC) coupled either with mass spectrometry (MS) or a flame photometry detector in sulphur mode (FPD), we studied this metabolism in laboratory media and wine. In laboratory media, several LAB isolated from wine were able to metabolize methionine. They formed methanethiol, dimethyl disulphide, 3-(methylsulphanyl)propan-1-ol and 3-(methylsulphanyl)propionic acid. These are known to have powerful characteristic odours and play a role in the aromatic complexity of wine. In various red wines, after MLF only the 3-(methylsulphanyl)propionic acid concentration increased significantly, as verified with several commercial starter cultures. This compound, which is characterized by chocolate and roasted odours, could contribute to the aromatic complexity produced by MLF. This study shows that LAB isolated from wine, especially OEnococcus oeni strains, the major species in MLF, are able to metabolize methionine to form volatile sulphur compounds. This is the first study to demonstrate the capacity of wine LAB to metabolize methionine.

Manufacture of Spanish hard cheeses from CO 2-treated milk

The suitability of milk preserved by refrigeration and CO 2 addition for the manufacture of rennet-coagulated Spanish hard cheeses was evaluated. Two types of cheeses were produced from milk preserved by refrigeration and CO 2 addition (pH 6.2) and were compared with controls made from fresh milk. Degasified (50–52 °C and 300 mm Hg) and pasteurised milk was employed for the manufacture of 30-day-old cheeses using a commercial starter. A degasified (30–32 °C and 350–375 mm Hg) mixture of 90% cow's and 10% ewe's raw milk was used for the manufacture of starter-free 75 day-old cheeses. Milk preservation did not affect multiplication and acidification capacity of lactic acid bacteria in cheeses from pasteurised milk but promoted lower levels of lactococci at first days of ripening in cheeses from raw milk and rendered lower amounts of lactic, pyruvic and succinic acids. Preservation did not affect the evolution of volatile compounds. Cheeses from preserved milk showed reduced clotting time, slightly higher cheese yields and increased curd hardness and whey losses during cheesemaking. The taste panel accepted cheeses from preserved milk. These results support the interest of CO 2-addition in preservation of milk for the manufacture of Spanish hard cheeses.

Afuega’l Pitu Cheese Quality: Carbon Dioxide Addition to Refrigerated Milk in Acid-coagulated Cheesemaking

Abstract The suitability of milk preserved by refrigeration and CO 2 addition for the manufacture of Afuega’l Pitu, a Spanish acid-coagulated short-ripened cheese, was evaluated at pilot scale using an autochthonous cheese starter. Cheeses manufactured, after milk pasteurisation, from vacuum degasified refrigerated CO 2 -treated samples (pH 6.2) were compared with two different control cheeses made from pasteurised milk either fresh or refrigerated. The multiplication and acidification capacity of lactic acid bacteria as well as the production of volatile compounds during cheesemaking and ripening were not affected by the previous refrigeration and CO 2 -treatment of raw milk nor by the residual CO 2 still present in pasteurised milk after degasification and pasteurisation. Residual CO 2 retarded the proteolysis although no differences on proteolysis and sensory properties were detected at the optimum time of consumption (15 days) between cheeses made from CO 2 -treated milk and those made from untreated control milk. CO 2 -treatment effectively prevents the decrease in cheese yield caused by the microorganisms present in raw milk of poor microbial quality. These results support the interest of the CO 2 -addition in preservation of milk for cheesemaking, specially when it has a high initial microbial load; the method can be satisfactorily used in the manufacture of Afuega’l Pitu cheese and may be extended to the production of other acid-coagulated cheeses.

RESEARCHES CONCERNING THE BIOSYNTHESIS OF EXOPOLYSACCHARIDES IN THE FERMENTED DAIRY PRODUCTS WITH THE YOGURT CULTURE YF-L 811

The exopolysaccharides produced by the lactic acid bacteria confer the possibility to obtain fermented dairy products of good quality, with desirable rheological properties, and diverse benefits for health. The capacity of lactic acid bacteria to produce exopolysaccharides is influenced by culture media and the conditions of growth.&#x0D; The purpose of this work was to study the thermophile yogurt culture YF-L 811, which contains Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The study was based on the capacity of the culture to produce exopolysaccharides in different temperature conditions and with different ingredients added in culture media. The amount of exopolysaccharides was correlated to viscosity of the yogurt.