The microbial profile of cheese is a primary determinant of cheese quality. Microorganisms can contribute to aroma and taste defects, form biogenic amines, cause gas and secondary fermentation defects, and can contribute to cheese pinking and mineral deposition issues. These defects may be as a result of seasonality and the variability in the composition of the milk supplied, variations in cheese processing parameters, as well as the nature and number of the non-starter microorganisms which come from the milk or other environmental sources. Such defects can be responsible for production and product recall costs and thus represent a significant economic burden for the dairy industry worldwide. Traditional non-molecular approaches are often considered biased and have inherently slow turnaround times. Molecular techniques can provide early and rapid detection of defects that result from the presence of specific spoilage microbes and, ultimately, assist in enhancing cheese quality and reducing costs. Here we review the DNA-based methods that are available to detect/quantify spoilage bacteria, and relevant metabolic pathways in cheeses and, in the process, highlight how these strategies can be employed to improve cheese quality and reduce the associated economic burden on cheese processors.

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Nucleic acid-based approaches to investigate microbial-related cheese quality defects

The principal pathways for the formation of flavour compounds in cheese (glycolysis, lipolysis and proteolysis) are reviewed. Depending on variety, microflora and ripening conditions, lac- tate may be metabolized by a number of pathways to various compounds which contribute to cheese flavour or off-flavours. Citrate metabolism by citrate-positive lactococci or Leuconostoc spp. is important in certain varieties (e.g., Dutch cheeses). Lipolysis results directly in the formation of flavour compounds by liberating free fatty acids (FFA). FFA may also be metabolized to alkan-2-ones and fatty acid lactones. Proteolysis of the caseins to a range of small- and intermediate-sized peptides and free amino acids (FAA) probably only contributes to the background flavour of most cheese varieties, but FAA are important precursors for a range of poorly-understood catabolic reactions which produce volatile compounds essential for flavour.

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Biochemical pathways for the production of flavour compounds in cheeses during ripening: A review

Flavour development in dairy fermentations, most notably cheeses, results from a series of (bio)chemical processes in which the starter cultures provide the enzymes. Particularly the enzymatic degradation of proteins (caseins) leads to the formation of key-flavour components, which contribute to the sensory perception of dairy products. More specifically, caseins are degraded into peptides and amino acids and the latter are major precursors for volatile aroma compounds. In particular, the conversion of methionine, the aromatic and the branched-chain amino acids are crucial. A lot of research has focused on the degradation of caseins into peptides and free amino acids, and more recently, enzymes involved in the conversion of amino acids were identified. Most data are generated on Lactococcus lactis, which is the predominant organism in starter cultures used for cheese-making, but also Lactobacillus, Streptococcus, Propionibacterium and species used for surface ripening of cheeses are characterised in their flavour-forming capacity. In this paper, various enzymes and pathways involved in flavour formation will be highlighted and the impact of these findings for the development of industrial starter cultures will be discussed.

Flavour formation by lactic acid bacteria and biochemical flavour profiling of cheese products

Advances in the study of proteolysis during cheese ripening.

Review: Compounds Involved in the Flavor of Surface Mold-Ripened Cheeses: Origins and Properties

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Bitter flavour in dairy products. II. A review of bitter peptides from caseins: their formation, isolation and identification, structure masking and inhibition L Lemieux, Re Simard

/pdf/bitter-flavour-in-dairy-products-ii-a-review-of-bitter-4by82proo9.pdf

Bitter flavour in dairy products. II. A review of bitter peptides from caseins: their formation, isolation and identification structure masking and inhibition

Following a definition of bitte mess and a mention of the Iink between the bitterness of peptides and their content of hydrophobie amino acid residues, a detailed description is given of the numerous factors Iikely to influence the development of bitter off-flavour defect in dairy products with emphasis on cheese. Factors such as milk quality, pH, psychrotrophic bacteria, fat and minerai content, the cheese manufacturing process including the cooking temperature, salt concentration and manner of draining the curd, the acidity or the pH of cheese, and sanitary processing and hygienic packaging conditions are less important than bacterial proliferation in the cheese vat and the type and amount of starter and rennet used. The major roles played by these last three factors are better understood since the development of the aseptic vat technique. Finally, possible ways are mentioned of keeping the concentration of bitter peptides below the threshold level for bitter taste detection.

https://hal.archives-ouvertes.fr/hal-00929271/document

Bitter flavour in dairy products. I. A review of the factors likely to influence its development, mainly in cheese manufacture

/pdf/astringency-a-textural-defect-in-dairy-products-489oiy17g9.pdf

L. Lemieux

Papers

Bitter flavour in dairy products. II. A review of bitter peptides from caseins: their formation, isolation and identification structure masking and inhibition

Bitter flavour in dairy products. I. A review of the factors likely to influence its development, mainly in cheese manufacture

Astringency, a textural defect in dairy products