Accelerated ripening of Cheddar cheese with the aminopeptidase of Brevibacterium linens and a commercial neutral proteinase

Development of an immunological method for studying the incorporation of ripening enzymes in cheese curd

Polyclonal antibodies raised against partly purified aminopeptidase were specific to cell-free extracts ofLactobacillus caseisubsp.pseudoplantarumUL 137, and did not cross react with any other proteins in Cheddar cheese, at least during the first week of maturation. A sandwich enzyme-linked immunosorbent assay (ELISA) was developed in order to quantify cell-free extracts in the cheese curd, and was also used to determine the efficiency of encapsulation of cell-free extracts in liposomes. This method was very sensitive and exhibited a detection limit of ∼10 μg total protein/g cheese and ∼1 μg total protein/ml liposome suspension. The efficiency of encapsulation of cell-free extracts into liposomes was ∼55–60%. The retention of liposome-encapsulated cell-free extracts was ∼14 times that of non-encapsulated extracts.

Biotechnological methods to accelerate cheddar cheese ripening

Cheese is one of the dairy products that can result from the enzymatic coagulation of milk. The basic steps of the transformation of milk into cheese are coagulation, draining, and ripening. Ripening is the complex process required for the development of a cheese's flavor, texture and aroma. Proteolysis, lipolysis and glycolysis are the three main biochemical reactions that are responsible for the basic changes during the maturation period. As ripening is a relatively expensive process for the cheese industry, reducing maturation time without destroying the quality of the ripened cheese has economic and technological benefits. Elevated ripening temperatures, addition of enzymes, addition of cheese slurry, attenuated starters, adjunct cultures, genetically engineered starters and recombinant enzymes and microencapsulation of ripening enzymes are traditional and modern methods used to accelerate cheese ripening. In this context, an up to date review of Cheddar cheese ripening is presented.

Aspects of enzymology and biochemical properties of Brevibacterium linens relevant to cheese ripening: a review

Brevibacterium linens is a major surface microorganism that is present in the smear of surface-ripened cheeses. The enzymology and biochemical characteristics of B. linens influence the ripening and final characteristics of smear surface-ripened cheeses. Proteolytic, peptidolytic, esterolytic, and lipolytic activities, which are of particular importance in the ripening process, are discussed in detail. This review also describes the production of volatile compounds, especially sulfur-containing ones, by B. linens, which are thought to be important in respect to the flavor of smear surface-ripened cheeses. The unique orange-colored carotenoids and the factors effecting their production by B. linens are also presented. The catabolism of aromatic amino acids, bacteriocin production, plasmids, and miscellaneous biochemical and physiological properties (peptidoglycan type, antibiotic resistance, insecticide degradation, and biotechnological applications) of B. linens are discussed. The problem associated with the current taxonomical classification of B. linens strains caused by strain variation is evaluated. Finally, the application of B. linens cell extracts or its proteolytic enzymes as cheese ripening accelerants for semi-hard or hard cheese varieties is considered.

Conversion of methionine to thiols by lactococci, lactobacilli, and brevibacteria

Methanethiol has been strongly associated with desirable Cheddar cheese flavor and can be formed from the degradation of methionine (Met) via a number of microbial enzymes. Methionine gamma-lyase is thought to play a major role in the catabolism of Met and generation of methanethiol in several species of bacteria. Other enzymes that have been reported to be capable of producing methanethiol from Met in lactic acid bacteria include cystathionine beta-lyase and cystathionine gamma-lyase. The objective of this study was to determine the production, stability, and activities of the enzymes involved in methanethiol generation in bacteria associated with cheese making. Lactococci and lactobacilli were observed to contain high levels of enzymes that acted primarily on cystathionine. Enzyme activity was dependent on the concentration of sulfur amino acids in the growth medium. Met aminotransferase activity was detected in all of the lactic acid bacteria tested and alpha-ketoglutarate was used as the amino group acceptor. In Lactococcus lactis subsp. cremoris S2, Met aminotransferase was repressed with increasing concentrations of Met in the growth medium. While no Met aminotransferase activity was detected in Brevibacterium linens BL2, it possessed high levels of L-methionine gamma-lyase that was induced by addition of Met to the growth medium. Met demethiolation activity at pH 5.2 with 4% NaCl was not detected in cell extracts but was detected in whole cells. These data suggest that Met degradation in Cheddar cheese will depend on the organism used in production, the amount of enzyme released during aging, and the amount of Met in the matrix.

Identification of yeasts and coryneform bacteria from the surface microflora of brick cheeses

Coryneform bacteria and yeasts of 21 brick cheeses from six German dairies, produced by using undefined ripening cultures, were identified. Arthrobacter nicotianae, Brevibacterium linens, Corynebacterium ammoniagenes, Corynebacterium variabilis and Rhodococcus fascians were found in significant numbers. Out of 148 coryneform isolates 36 could not be identified at the species level. With the exception of a large rennet cheese, the coryneform microflora of rennet and acid cured cheeses were similar, but the cheeses had clearly different yeast populations. Debaryomyces hansenii and Galactomyces geotrichum prevailed in rennet cheeses while Kluyveromyces marxianus and Pichia membranaefaciens were the main species found in acid cured cheese. The dominance of Yarrowia lipolytica probably indicates an improper yeast population, resulting in poor cheese quality. Some of the species identified are potential candidates for designing a defined ripening culture for rennet red smear cheese.

Isolation and characterization of Linocin M18, a bacteriocin produced by Brevibacterium linens

Brevibacterium linens M18, isolated from red smear cheese, produces a substance that inhibits the growth of Listeria spp. and several coryneform and other gram-positive bacteria. No gram-negative bacteria were inhibited. The substance is heat labile, sensitive to proteolytic enzymes, and stable between pH 3 and 12. High levels of this bacteriocin, named Linocin M18, were obtained in the stationary growth phase. Linocin M18 was purified by ultrafiltration, ultracentrifugation, and gel filtration chromatography. In its native form, it is a proteinaceous aggregate with a high molecular weight. Fractions with Linocin M18 activity contained particles of 20 to 30 nm in diameter. The bacteriocin consists of a single protein subunit with a molecular mass of 31 kDa and an isoelectric point of 4.5 N-terminal sequence analysis yielded Met-Asn-Asn-Leu-Tyr-Arg-Glu-Leu-Ala-Pro-Ile-Pro-Gly-Pro-Ala-Ala-Ala-Glu- Ile. Significant homology with published sequences was lacking.