Identification of technological/metabolic/environmental profiles associated with cheeses accumulating the neuroactive compound tryptamine

Tryptamine is a neuromodulator of the central nervous system. It is also a biogenic amine, formed by the microbial decarboxylation of L-tryptophan. Tryptamine accumulation in cheese has been scarcely examined. No studies are available regarding the factors that could influence its accumulation. Determining the tryptamine content and identifying the factors that influence its accumulation could help in the design of functional tryptamine-enriched cheeses without potentially toxic concentrations being reached. We report the tryptamine concentration of 300 cheese samples representing 201 varieties. 16% of the samples accumulated tryptamine, at between 3.20 mg kg-1 and 3012.14 mg kg-1 (mean of 29.21 mg kg-1). 4.7% of cheeses accumulated tryptamine at higher levels than those described as potentially toxic. Moreover, three technological/metabolic/environmental profiles associated with tryptamine-containing cheese were identified, as well as the hallmark varieties reflecting each. Such knowledge could be useful for the dairy industry to control the tryptamine content of their products.

Effect of Oryctolagus cuniculus (rabbit) rennet on the texture, rheology, and sensory properties of white cheese

Calf rennet has long been used in cheese-making. Because of calf rennet shortage and high cost, novel proteases were needed to meet industry's increasing enzyme demand. Recombinant chymosins and camel chymosin were started to be used in the industry. There is no study in the literature subjecting use of rabbit rennet in cheese production. Chemical, rheological, and sensorial characteristics of white cheese made with rabbit rennet were investigated in this study. Quality characteristics of rabbit rennet cheese (RC) were compared to cheeses produced with commercial calf (CC) and camel chymosins (CLC). RC and CLC exhibited higher hardness and dynamic moduli values throughout the storage as compared to CC. Although moisture levels of cheese samples were similar at day 60, CC had much lower hardness and dynamic moduli values than CLC and RC. While the appearance and structure were better for CLC, the highest odor and taste scores were obtained by RC during 60 days of storage. The results of this investigation proposed that rabbit rennet could be a suitable milk coagulant for white cheese production. Our results showed that rabbit rennet has comparable cheese-making performance with camel chymosin and could be a good alternative for calf chymosin.

Effect of proteolysis during Cheddar cheese aging on the detection of milk protein residues by ELISA

Cow milk is a common allergenic food, and cow milk-derived cheese retains an appreciable level of allergenicity. The specific and sensitive detection of milk protein residues in foods is needed to protect milk-allergic consumers from exposure to undeclared milk protein residues contained in foods made with milk or milk-derived ingredients or made on shared equipment or in shared facilities with milk or milk-derived ingredients. However, during cheese ripening, milk proteins are degraded by chymosin and milk-derived and bacterial proteases. Commercial allergen-detection methods are not validated for the detection of residues in fermented or hydrolyzed products. The objective of this research was to evaluate commercially available milk ELISA kits for their capability to detect milk protein residues in aged Cheddar cheese. Cheddar cheese was manufactured at a local dairy plant and was aged at 5°C for 24 mo, with samples removed at various time points throughout aging. Milk protein residues and protein profiles were measured using 4 commercial milk ELISA kits and sodium dodecyl sulfate-PAGE. The ELISA data revealed a 90% loss of milk protein residue signal between the youngest and oldest Cheddar cheese samples (0.5 and 24 mo, respectively). Sodium dodecyl sulfate-PAGE analysis showed protein degradation throughout aging, with the highest level of proteolysis observed at 24 mo. Results suggest that current commercial milk ELISA methods can detect milk protein residues in young Cheddar cheese, but the detection signal dramatically decreases during aging. The 4 evaluated ELISA kits were not capable of detecting trace levels of milk protein residues in aged cheese. Reliable detection of allergen residues in fermented food products is critical for upholding allergen-control programs, maintaining product safety, and protecting allergic consumers. Furthermore, this research suggests a novel use of ELISA kits to monitor protein degradation as an indication of cheese ripening.

Influence of the Ripening Time on the Viscoelastic Behaviour of Tetilla Cheese

Controlled shear stress tests were used to monitor the changes of viscoelastic properties in industrial samples of Tetilla cheese with the ripening time. The linear viscoelastic range was determined from both stress sweep and creep-and-recovery tests conducted at 20ºC. One-week-old samples were found to be more rigid and elastic, and to exhibit broader linear ranges, than older samples. Mechanical spectra recorded at the same temperature confirmed this trend since viscoelastic moduli G’ and G" decreased markedly during the first week of ripening, indicating a loss of structure during this period. Besides, physico-chemical information (pH, water content, protein content, nitrogen fractions, and s1 and β casein fractions) was obtained by analytical methods. Quite good correlation between rheological and chemical results was found. For each ripening time, an additional study of mechanical spectra as a function of temperature was performed. A marked increase of the power law exponents as temperature is raised is observed after the second week. Crosslink breakdown and the resulting structural weakening of the micellar network through casein hydrolysis during ripening can explain this result. The whole study provided similar results to those found for other type of cheeses and, also, allowed the classification of samples into two groups of markedly different behaviour, namely, one-week-old samples and older samples. In conclusion more than one week of ripening is needed to reach the adequate texture standardisation of Tetilla cheese.

Principal component analysis of proteolytic profiles as markers of authenticity of PDO cheeses

The casein fraction of 13 Portuguese PDO cheeses were analysed using Urea-PAGE and reverse phase-high performance liquid chromatography (RP-HPLC) and then subjected to chemometric evaluation. The chemometric techniques of cluster analysis (CA) and principal component analysis (PCA) were used for the classification studies. Peptide mapping using Urea-PAGE followed by CA revealed two major clusters according to the similarity of the proteolytic profile of the cheeses. PCA results were in accordance with the grouping performed using CA. CA of RP-HPLC results of the matured cheeses revealed the presence of one major cluster comprising samples manufactured with only ovine milk or milk admixtures. When the results of CA technique were compared with the two PCA approaches performed, it was found that the grouping of the samples was similar. Both approaches, revealed the potential of proteolytic profiles (which is an essential aspect of cheese maturation) as markers of authenticity of PDO cheeses in terms of ripening time and milk admixtures not mentioned on the label.

Formation of early and advanced Maillard reaction products correlates to the ripening of cheese

The present study deals with the characterization of the ripening of cheese. A traditional German acid curd cheese was ripened under defined conditions at elevated temperature, and protein and amino acid modifications were investigated. Degree of proteolysis and analysis of early [Amadori compound furosine (6)] and advanced [N(ε)-carboxymethyllysine (4), N(ε)-carboxyethyllysine (5)] Maillard reaction products confirmed the maturation to proceed from the rind to the core of the cheese. Whereas 6 was decreased, 4 and 5 increased over time. Deeper insight into the Maillard reaction during the ripening of cheese was achieved by the determination of selected α-dicarbonyl compounds. Especially methylglyoxal (2) showed a characteristic behavior during storage of the acid curd cheese. Decrease of this reactive structure was directly correlated to the formation of 5. To extend the results of experimental ripening to commercial cheeses, different aged Gouda types were investigated. Maturation times of the samples ranged from 6 to 8 weeks (young) to more than 1 year (aged). Again, increase of 5 and decrease of 2 were able to describe the ripening of this rennet coagulated cheese. Therefore, both chemical parameters are potent markers to characterize the degree of maturation, independent of coagulation.

Proteolysis of Cabrales cheese and other European blue vein cheese varieties

The extent and level of proteolysis were evaluated in Cabrales and five other European blue vein cheese varieties, Bleu de Bresse, Danablu, Edelpilzkäse, Gorgonzola and Roquefort, by analysing their different N-containing constituents and determining the degree of casein hydrolysis. The electrophoretic patterns of the caseins in the cheeses confirmed their strong proteolysis, components featuring the lowest electrophoretic mobility offering the greatest resistance to subsequent hydrolysis. Component αs1 — I was detected in all varieties studied with the exception of Roquefort cheese.

Application of Exopolysaccharide-Producing Cultures in Reduced-Fat Cheddar Cheese: Composition and Proteolysis

Proteolysis during ripening of reduced fat Cheddar cheeses made with different exopolysaccharide (EPS)-producing and nonproducing cultures was studied. A ropy strain of Lactococcus lactis ssp. cremoris (JFR1) and capsule-forming nonropy and moderately ropy strains of Streptococcus thermophilus were used in making reduced-fat Cheddar cheese. Commercial Cheddar starter was used in making full-fat cheese. Results showed that the actual yield of cheese made with JFR1 was higher than that of all other reduced-fat cheeses. Cheese made with JFR1 contained higher moisture, moisture in the nonfat substance, and residual coagulant activity than all other reduced-fat cheeses. Proteolysis, as determined by PAGE and the level of water-soluble nitrogen, was also higher in cheese made with JFR1 than in all other cheeses. The HPLC analysis showed a significant increase in hydrophobic peptides (causing bitterness) during storage of cheese made with JFR1. Cheese made with the capsule-forming nonropy adjunct of S. thermophilus, which contained lower moisture and moisture in the nonfat substance levels and lower chymosin activity than did cheese made with JFR1, accumulated less hydrophobic peptides. In conclusion, some EPS-producing cultures produced reduced-fat Cheddar cheese with moisture in the nonfat substance similar to that in its full-fat counterpart without the need for modifying the standard cheese-making protocol. Such cultures might accumulate hydrophobic (bitter) peptides if they do not contain the system able to hydrolyze them. For making high quality reduced-fat Cheddar cheese, EPS-producing cultures should be used in conjunction with debittering strains.

Determination of cow's milk and ripening time in nonbovine cheese by capillary electrophoresis of the ethanol-water protein fraction

A novel method is reported for analyzing adulteration of goat and ewe cheeses with cow's milk: capillary zone electrophoresis (CZE) in isoelectric, acidic buffers (50 mM imino diacetic acid, IDA, pH = pI 2.3). The cheese samples were extracted with a 20:80 v/v ethanol-water mixture in presence of 3 M urea and 1% beta-mercaptoethanol for 1 h. After centrifugation and lipid extraction, the samples were dissolved in 50 mM IDA, 6 M urea and 0.5% hydroxyethyl cellulose and analyzed by CZE at 700 V/cm. A total of 18 characteristic peaks were resolved among the three types of cheeses and 18 variables were defined as their respective areas. There was excellent similarity among the electrophoretic patterns obtained with cheeses of a given type of milk, while cheeses made with different types of milk were easily distinguishable. Most peaks were common to all cheeses, but the profile differed depending on the type of milk used. Principal component analysis, linear discriminant analysis, and partial least squares regression (PLS) were used for statistical analysis of the data obtained by CZE. In particular, by using PLS multivariate regression, the contents of cow's milk in presumably pure goat and ewe cheeses, as well as in binary and ternary mixtures, could be predicted with relative standard deviations of ca. 6-7%. In addition, the ripening time in goat and ewe cheeses could also be predicted.

Gel electrophoresis and immunoblotting for the detection of casein proteolysis in cheese

The whole N fraction of six samples of hard and semi-hard pressed cheeses was analysed using PAGE, polyacrylamide gel isoelectric focusing and immunoblotting with polyclonal antibodies against beta- and alpha s1-casein. The origin of some electrophoretic bands corresponding to peptides produced from the enzymic degradation of the casein fractions was established. A number of these peptides were also present in the in vitro hydrolysates of casein with plasmin and chymosin. Thus, it was also possible to determine which casein was the source of each peptide and which enzymes were active in cheese. Compared with the traditional Coomassie staining procedures, immunoblotting is more sensitive and specific, making the interpretation of each electrophoretic profile easy. Thus, it was also possible to obtain a clear picture of the state of each casein fraction in a cheese variety. Two main peptides were isolated from the pH 4.6-insoluble N fraction of Parmigiano-Reggiano using DEAE-cellulose chromatography and identified, from the amino acid sequence of the N- and C-terminal ends, as gamma 3-casein (beta-casein(f108-209)) and alpha s1-PL1 (alpha s1-casein(f80-199). In both cases, a Lys-X bond was hydrolysed, indicating the action of a trypsin-like enzyme in beta- and alpha s1-casein hydrolysis during the ripening of this variety of hard pressed cheese.

Application of PhastSystem to the resolution of bovine milk proteins on urea-polyacrylamide gel electrophoresis

Optimal conditions were established for alkaline urea-PAGE using modified precast, ultrathin gradient gels on the automated PhastSystem. Profiles of milk proteins showed that the caseins and whey proteins resolved extremely well. Major bands were observed for alpha s1-casein and beta-casein, and alpha s2-casein appeared as a well-resolved doublet. In contrast, kappa-casein separated from other caseins as a faint doublet, and purified kappa-casein appeared as one major and one minor band. Whey proteins (serum albumin, alpha-lactalbumin, beta-lactoglobulin) separated into broad bands resolved from each other and from the caseins. Partially (40%) dephosphorylated whole casein showed multiple bands for alpha s1-casein and beta-casein at different levels of phosphorylation. Separation of genetic phenotypes was observed for beta-lactoglobulin A and B; alpha s1-casein A, B, and C; and beta-casein A, B, and C. Electrophoretic patterns of milk proteins extracted from cheese samples varied among the different types of cheeses. Our modified procedure provides researchers with a rapid technique to separate both caseins and whey proteins on the same urea gel according to their charge to mass ratios.

[Analysis of proteins in food with electrophoretic and chromatographic methods]

The efficiency of electrophoretic methods (gel electrophoresis, isoelectric focusing, twodimensional techniques) and of chromatographic methods (size exclusion and ion exchange chromatography, reversed phase HPLC) to analyze proteins in foods is reviewed. Several selected applications are discussed in detail. The large diversity of proteins in a particular food results in a unique electrophoretic or chromatographic pattern, that can be used for identification purposes, by means of the so called indicator proteins. The adaptability and resolving power of the methods assure their extended application to many protein containing foods. The uniqueness of the patterns obtained warranties differentiations of even closely related animal or plant foods as well as mixtures of them. The methods also allow quantitative determinations of mixtures of foods. Their ease of handling and good reproducibility and reliability favours their use in routine analyses. Numerous investigations on fish, meat and derived products, non-meat proteins in meat products, milk, cheese, cereals and products made of cereals, oilseed proteins, legumes, fruits and vegetables described in the literature are here presented.