Occurrence, origin and fate of pyroglutamyl-γ3-casein in cheese

High-speed cold centrifugation of milk modifies the microbiota, the ripening process and the sensory characteristics of raw-milk hard cheeses

The microbial population of raw milk plays a crucial role in the development of distinctive traits of raw-milk cheeses particularly appreciated by consumers. It was previously demonstrated that the microbial population of raw milk is modified by a high-speed centrifugation (also called bactofugation) conducted at 39 °C. The aim of the present study was to evaluate the effects of this process, performed once or twice, on the microbial, compositional, biochemical, and sensory characteristics of the derived hard cheeses. Experimental and control cheesemaking were conducted in parallel at a cheese factory during a 13-month period. Cheeses were analysed after 9, 15 and 20 months of ripening for microbial count, composition, proteolysis extent, volatile compounds, and sensory profile. Results evidenced that experimental cheeses were characterized by lower numbers of viable lactobacilli respect to control. Experimental cheeses also showed differences in the progress of primary and secondary proteolysis which, in turn, caused different patterns of free amino acids at all ripening times. Experimental cheeses had significantly lower content of esters and were differentiated from control for some traits by assessors. In conclusion, use of high-speed centrifugation of milk shall be discouraged if characteristic traits of raw-milk cheeses, particularly PDO cheeses, want to be retained.

Effects of microbial coagulants from Rhyzomucor miehei on composition, sensory and textural characteristics of long-ripened hard cheeses

The increasing use of rennet substitutes entails evaluating their performances on different types of cheese. The production of hard cheese using either microbial coagulants from Rhyzomucor miehei (MC) or calf rennet (CR) from different manufacturers was investigated in parallel cheese makings at three industrial dairies. Cheeses were analysed after 9, 12, 16 and 18 months of ripening. Minor differences in cheese composition were found between treatments, principally related to fat content. Cheeses produced with one out of the three MC showed slower primary proteolysis on both αs1- and αs0-casein, compared to the corresponding CR cheeses, indicating a different activity of this coagulant. The same cheeses also had significantly different sensory profiles at 9 months of ripening. Treatments did not differ in free amino acid composition nor in rheological parameters, regardless of ripening period. The long ripening of hard cheeses thus smooths possible differences attributable to MC.

Evaluating the Authenticity of the Raw-Milk Cheese Fontina (PDO) with Respect to Similar Cheeses

The implementation of quality assurance schemes for the assessment of PDO food authenticity is an issue involving manufacturers, traders, retailers and consumers. In this respect, reliable analytical methods are needed to integrate paper-trailing information. The feasibility of distinguishing the Italian Fontina PDO cheese from the generic Fontal cheese was preliminarily evaluated on a set of commercial samples by measuring selected parameters (pH, alkaline phosphatase activity, content of copper, volatiles, extent of proteolysis) related to the different manufacturing processes. The relative profile of free amino acids proved to be a promising tool. A new set of 41 samples of Fontina PDO cheese was collected at representative dairies within the recognized production area and analyzed for free amino acids. A chemometric model of Fontina PDO cheese was built based on the mean content and standard deviation of 15 free amino acids. On this basis, all of the PDO samples were correctly identified, whereas all of the Fontal cheeses were recognized as different cheeses.

Proteolytic Activity and Production of γ-Aminobutyric Acid by Streptococcus thermophilus Cultivated in Microfiltered Pasteurized Milk

A set of 191 strains of Streptococcus thermophilus were preliminarily screened for the presence of the genes codifying for cell envelope-associated proteinase (prtS) and for glutamate decarboxylase (gadB) responsible for γ-aminobutyric acid (GABA) production. The growth and proteolytic activity of the gadB-positive strains (9 presenting the prtS gene and 11 lacking it) were studied in microfiltered pasteurized milk. Degradation of both caseins (capillary electrophoresis) and soluble nitrogen fractions (HPLC) and changes in the profile of free amino acids (FAAs; ion-exchange chromatography) were evaluated at inoculation and after 6 and 24 h of incubation at 41 °C. None of the strains was capable of hydrolyzing caseins and β-lactoglobulin, and only two hydrolyzed part of α-lactalbumin, these proteins being present in their native states in pasteurized milk. Contrarily, most strains were able to hydrolyze peptones and peptides. For initial growth, most strains relied on the FAAs present in milk, whereas, after 6 h, prtS⁺ strains released variable amounts of FAA. One prtS⁺ strain expressed a PrtS^- phenotype, and two prtS^- strains showed a rather intense proteolytic activity. Only five strains (all prtS⁺) produced GABA, in variable quantities (up to 100 mg/L) and at different rates, depending on the acidification strength. Addition of glutamate did not induce production of GABA in nonproducing strains that, however, unexpectedly were shown to adopt the degradation of arginine into citrulline and ornithine as an alternative acid resistance system and likely as a source of ATP.