P.L.H. McSweeney

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

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.

Advanced dairy chemistry

Advanced dairy chemistry , Advanced dairy chemistry , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Advances in the study of proteolysis during cheese ripening

Cheese ripening involves a complex series of biochemical, and probably some chemical events, that leads to the characteristic taste, aroma and texture of each cheese variety. The most complex of these biochemical events, proteolysis, is caused by agents from a number of sources: residual coagulant (usually chymosin), indigenous milk enzymes, starter, adventitious non-starter microflora and, in many varieties, enzymes from secondary flora (e.g., from Penicillium sp. in mould-ripened cheeses or Propionibacterium sp. in Swiss cheese). Proteolysis in cheese has been the subject of active research in the last decade; there have been developments in the analytical techniques used to monitor proteolysis and patterns of proteolysis in many cheese varieties have now been investigated. This review focuses on certain aspects of proteolysis, including proteolytic agents in cheese and specificity of some ripening enzymes, comparison of proteolysis and contribution of proteolysis to cheese flavour.

Lipolysis and free fatty acid catabolism in cheese: a review of current knowledge

The progress of lipolysis and its effect on flavour development during cheese ripening is reviewed. The review begins by describing the structure and composition of milk fat and thereafter discusses current knowledge regarding the role of various lipolytic agents and their influence on lipolysis in various cheese varieties. While free fatty acids (FFA) liberated during lipolysis directly affect cheese flavour, they are also metabolized to other highly flavoured compounds, including methyl ketones and lactones. The pathways of FFA catabolism and the effect of these catabolic products on cheese flavour are discussed. Finally, the current methods for the quantification of FFA in cheese are reviewed and compared.

Contribution of the indigenous microflora to the maturation of cheddar cheese

Abstract Cheddar cheeses were made from raw milk, pasteurised milk (72°C, 15 s) or milk produced from skim milk which had been microfiltered using an Alfa-Laval MFS-1 MF unit and mixed with pasteurised cream (72°C, 30 s). Microfiltration (MF) reduced the total bacterial count (TBC) by > 99% and MF cheesemilk had a lower TBC than pasteurised milk; counts of non-starter lactic acid bacteria (NSLAB) were

Characterization of proteolysis during the ripening of semi-dry fermented sausages

The respective contribution of indigenous enzymes and enzymes from starter bacteria to proteolysis in fermented sausages were determined by comparing the proteolytic changes occurring in sausages resulting from the presence of a proteolytic strain of Staphylococcus carnosus, i.e. S. carnosus MC 1 to the proteolytic changes occurring in control sausages containing glucono-δ-lactone (GDL) and an antibiotic mixture. Proteolysis was quantified by assaying for non-protein nitrogen (NPN) and free amino acids. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and reversed phase high performance liquid chromatography (RP-HPLC) were used to qualitatively assess the proteolytic changes in the sarcoplasmic and myofibrillar proteins as ripening progressed. The concentration of NPN and free amino acids increased in both sausages initially, but subsequently decreased towards the end of ripening in sausages inoculated with the starter culture. SDS-PAGE showed a similar pattern of proteolysis of sarcoplasmic proteins in both sausages, while of the two sausage types; the S. carnosus MC 1 inoculated sausages exhibited the most intense degradation of myofibrillar proteins, especially myosin and actin. RP-HPLC profiles of 2% trichloroacetic acid (TCA)-soluble peptides for the two sausage types were similar, with the production of numerous hydrophilic peptides. N-Terminal amino acid sequence analysis and sequence homology with proteins of known primary structure showed that six of the TCA-soluble peptides were released from the sarcoplasmic (myoglobin and creatine kinase) and myofibrillar (troponin-I, troponin-T and myosin light chain-2) proteins. In addition, the initial degradation of sarcoplasmic proteins was due to the activity of indigenous proteinases, while both indigenous and bacterial enzymes contributed to the initial degradation of myofibrillar proteins. Furthermore, indigenous enzymes were responsible for the release of TCA-soluble peptides, which, were further hydrolysed by bacterial enzymes.

Cheese: Physical, Biochemical, and Nutritional Aspects

Publisher Summary This chapter discusses the physical, biochemical, and nutritional aspects of cheese. Cheese is the most diverse, most scientifically interesting, and most challenging group of dairy products. While most dairy products, if properly manufactured and stored, are biologically, biochemically, and chemically very stable, cheeses are biologically and biochemically dynamic and, consequently, inherently unstable. Cheese manufacture and ripening involves a complex series of consecutive and concomitant microbiological, biochemical, and chemical events, which, if synchronized and balanced, lead to products with highly desirable flavors, but when unbalanced, result in off-flavors. Considering that a basically similar raw material (milks from a very limited number of species) is subjected to a generally common manufacturing protocol, it is fascinating that such a diverse range of products can be produced.

Manufacture of Cheddar cheese with and without adjunct lactobacilli under controlled microbiological conditions

Abstract Cheddar cheeses were manufactured under controlled microbiological conditions to study the influence of selected strains of mesophilic lactobacilli on proteolysis and flavour development. In each of two trials, a control cheese (containing only a Lactococcus starter) and four experimental cheeses (containing the Lactococcus starter and adjunct lactobacilli) were manufactured. The Lactobacillus inocula were Lb. casei ssp. casei (4 strains), Lb. casei ssp. pseudoplantarum (4 strains), Lb. curvatus (4 strains) or Lb. plantarum (2 strains). In the experimental cheeses, counts of lactobacilli ranged from 10 4 to 10 5 cfu g −1 at milling and increased to ~5 × 10 7 cfu g −1 after 4 weeks. Control cheeses remained free of lactobacilli for up to 97 days and thereafter the counts did not exceed ~5 × 10 5 cfu g −1 . Addition of lactobacilli positively influenced flavour acceptability of the cheese after ripening for 6 months at 7 °C. Cheeses manufactured with Lb. plantarum or Lb. casei ssp. pseudoplantarum adjuncts received the best grades. PAGE and RP-HPLC indicated only relatively minor differences in proteolysis between the control and experimental cheeses; however, the experimental cheeses showed higher levels of free amino acids, as well as differences in profiles of individual free amino acids, when compared to the controls. The addition of low numbers of selected strains of Lactobacillus spp. to cheesemilk, while having only a relatively minor influence on proteolysis, positively influenced the quality of Cheddar cheese.

Metabolism of Residual Lactose and of Lactate and Citrate

This chapter discusses metabolism of residual lactose and of lactate and citrate. During the manufacture of cheese curd, lactose is converted to lactic acid (mainly the L-isomer) by the starter bacteria. In the case of Cheddar-type cheeses, most of the lactic acid is produced in the vat before salting and moulding whereas for most other varieties, acidification occurs mainly after the curds have been placed in moulds. For many common varieties, the pH of the curd reaches ∼5.0–5.3 within ∼12 h from the start of cheesemaking. Further, lactate is an important substrate for a series of reactions in cheese during ripening: in most cheeses, L-lactate is racemized to D-lactate by the non-starter lactic acid bacteria flora; lactate is catabolized in Swiss-type cheese by Propionibacteriurn freudenreichii subsp, shermanii, which is important for the development of characteristic eyes and flavor; lactate is catabolized to CO 2 and H 2 O by Penicillium camemberti in surface mould-ripened cheeses, such as Camembert and Brie, which is important for texture development; in the presence of O 2 . The relatively low concentration of citrate in milk belies the importance of its metabolism in many cheeses made using a mesophilic culture. Approximately 94% of the citrate in milk is soluble and most of it is lost in the whey; however, the concentration of citrate in the aqueous phase of cheese is ∼3 times that in whey, presumably reflecting the concentration of colloidal citrate; Cheddar cheese contains 0.2–0.5% citrate.

Biogenesis of Flavour Compounds in Cheese

“There is a cheese for every taste preference and a taste preference for every cheese” (Olson, 1990). Starting from milk, a substrate, which although not entirely flavourless, is rather bland, a cheesemaker can make any of the ca. 500 varieties of cheese listed in IDF (1982), each variety having a unique, characteristic flavour and aroma. The flavour of cheese is among its principal attributes and has been the subject of scientific investigation since the begining of this century. Initally, it was believed that cheese flavour might be due to a single compound but the “Component Balance Theory” (Mulder, 1952; Kosikowski and Mocquot, 1958) proposed that cheese flavour is due to the correct balance and concentration of a wide range of sapid and aromatic compounds. During the intervening 40 years, there has been extensive research on the flavour of several cheese varieties, but despite this effort, only limited information is available on the chemistry of the flavour of most varieties and the flavour of none is characterized sufficiently to permit its reproduction by mixtures of pure compounds.