Free Amino Acids and Water-Soluble Nitrogen As Ripening Indices in Montasio Cheese*
Total Page：16
File Type：pdf, Size：1020Kb
Lait (1997) 77, 359-369 359 © ElsevierlINRA Original article Free amino acids and water-soluble nitrogen as ripening indices in Montasio cheese* N Innocente Dipartimento di Scienze degli Alimenti, Università di Udine, 33100 Udine, Italy Summary - Traditionally, in semi-hard and hard cheeses the development of proteolysis is fol- lowed by the increase of water-soluble nitrogen (SN) as a percentage of total nitrogen (TN), but the characterisation of proteolysis for each particular cheese must con sider ail the processes that lead to the formation of peptides, free amino acids and products of their catabolism. In Montasio cheese, a considerable variability in the SN values and the amino acid profiles of cheeses at the same stage of ripening was recorded. This variability was probably due to the different traditional technologies adopted. Therefore, no chemometric model could be set up to evaluate the typical nature of Monta- sio cheese. On the other han d, a relationship between the total free amino acid content and the SNrrN ratio was demonstrated and it was found that certain amino acids cou Id be used as an index for deter- mining the level of proteolysis reached by the Montasio chee se. proteolysis / free amino acid / total nitrogen / water-soluble nitrogen / Montasio cheese Résumé - Les acides aminés libres et l'azote soluble dans l'eau pour la caractérisation du fromage Montasio. Traditionnellement, dans les fromages à pâte dure et semi-dure, le développe- ment de la protéolyse est suivie d'une augmentation du rapport en pour cent entre l'azote soluble dans l'eau et l'azote total. Toutefois, pour caractériser la protéolyse dans chaque fromage particulier, il faut considérer l'ensemble des processus qui mène à la formation de peptides, acides aminés libres et produits de leur catabolisme. Dans le fromage Montasio, on a remarqué au même stade de matura- tion une forte variabilité des valeurs d'azote soluble dans l'eau, ainsi que des profils d'acides aminés. Cette variabilité est probablement due aux différentes technologies traditionnelles. Ainsi, aucun modèle chémométrique ne peut être créé pour déterminer la nature caractéristique du fromage Mon- tasio. D'un autre côté, on peut établir une relation entre le contenu total d'acides aminés et le rapport azote soluble dans l'eau/azote total. Certains acides aminés peuvent être aussi utilisés comme indice pour déterminer le niveau de protéolyse dans le fromage Montasio. protéolyse / acide aminé libre / nitrogène total/azote soluble dans l'eau / fromage Montasio * Oral communication at the lOF Symposium 'Ripening and Quality of Cheeses', Besançon, France, February 26-28, 1996. 360 N Innocente INTRODUCTION teolysis is the most commonly used index for maturity. Proteolysis occurs in ail cheese Many Italian cheeses have particular fea- varieties and is considered to be a prereq- tures related to the milk employed, the par- uisite for good f1avour development, so that ticular technology applied and the geo- attention has been focussed on the parame- graphical environment. These typical ters that quantify and characterise proteolysis characteristics allow such chee ses to be (McSweeney and Fox, 1993). Traditionally, legally designated as 'DOC' (controlled proteolysis is monitored by the increase in denomination of origin) if they conform water-soluble nitrogen (SN) as a percent- with the local milk production regulations, age of total nitrogen (TN), but the charac- the traditional cheese manufacturing tech- terisation of proteolysis for each particular niques and the cheese ripening process. Nev- chee se must consider ail the processes that ertheless, to ensure that these regulations lead to the formation of peptides, free amino and transformations are effective in prac- acids and the products of their catabolism tice, it is necessary to define methods for (Creamer, 1970). In fact, the first level of evaluating the qualitative characteristics of proteolysis results from enzymatic action typical cheeses (Corradini and Innocente, on curdled milk and the consequent release 1995). The organoleptic qualities of chee se of amino acids, but later the se amino acids are generally determined by the physical are further broken down by enzymes and che mi cal changes that occur during involved in deamination, decarboxylation, ripening. In fact, the basic composition and transamination and/or demethiolation structure of cheese are determined by the (Hemme et al, 1982; Bech, 1992). The curd-producing operations, but it is during amino acids that are subjected to a more ripening that the individuality and unique rapid degradation are methionine (Strecker characteristics of each chee se variety degradation) and tyrosine (degraded to tyra- develop, and these are influenced by the mine by tyrosine decarboxylase, produced composition of the curd and other factors, by Streptococcus faecalis and only inacti- such as the microflora established during vated by the pasteurisation of the milk), manufacture (Fox et al, 1993). The bio- while catabolic products are œ-aminobu- chemical events involved in cheese ripen- tyric acid and y-aminobutyric acid, formed ing are traditionally assessed from a sen- by decarboxylation of glutamic acid, and sory evaluation of f1avour, body, texture and ornithine, which is derived from the enzy- typical eyes, finish and overall quality by matie degradation of arginine (Hemme et experienced judges or trained consumer pan- al, 1982). These reactions may be introduc- els (Lavanchy et al, 1994). However, sen- tory to the development of important and sory analyses are subjective, and although at specifie f1avours (Griffith and Hammond, present the best index of consumer accept- 1989). Thus, the typical nature of cheese ability, they provide data that are difficult can be evaluated by means of the relative to evaluate scientifically and compare content of certain amino acids, and their between laboratories or studies (Boume et al, increase and/or degradation or formation as 1975). Therefore, chemical and physical products of amino acid catabolism (Reiter et analyses of cheese are used to objectively al, 1969; Weaver et al, 1978; Aston et al, monitor ripening and to assess quality, usu- 1983; Amantea et al, 1986). This is partie- ally to complement sensory evaluation. ularly important in cheeses with character- Although it may never be possible to assess istic eyes, such as Montasio. Montasio is a cheese quality by chemical criteria alone, semi-hard cheese cooked at 44-46 "C, pro- they can provide valuable indices of quality. duced from unpasteurised (raw or thermised) For most hard and semi-hard cheeses, pro- milk in Friuli Venezia-Giulia and the Veneto Ripening indices in Montasio chee se 361 (north-east Italy) and is consumed as a table Reagents cheese after at least 2 months of ripening, whereas 8-9-month-old cheese is used for The amino acid standards used were from Sigma grating. One of the characteristics of Mon- (L-amino acid kit). The calibration standard solu- tasio cheese is the typical eyes, which tion contained alanine, a-aminobutyric acid (Aaba) and y-aminobutyric acid (Gaba), alanine depend on the use of natural milk culture in (Ala), glycine (Gly), valine (Val), threonine (Thr), which the heterofermentative microorgan- leucine (Leu), isoleucine (Ile), serine (Ser), pro- isms are not excessively dominant over the line (Pro), methionine (Met), aspartic acid + homofermentative microbes. However, at asparagine (Asx), phenylalanine (Phe), glutamic present, to limit the development of defects acid + glutamine (Glx), tyrosine (Tyr), omithine commercial starters can also be used sorne- (Om), lysine (Lys) and homoserine (Hom) (inter- naI standard) in 7% ammonia. The final amino times combined with thermal treatments of acid concentration was 1 mg/mL. Other reagents the milk. Consequently, it is possible that of analytical grade were from Carlo Erba the characteristic eyes and the typical taste (ethanol, 28% ammonia solution, isobutanol, sul- and f1avour could be excessively changed. phuric acid, sodium hydroxide pellets), Fluka (heptafluorobutyryl anhydride, > 99% purity, a To evaluate the typical nature of Monta- gas chromatography reagent) Aldrich-Chemie sio cheese by chemical parameters, prote- (Dowex 50W x 8 100-200 mesh) and Janssen olysis during ripening and the free amino (methylene chloride). acid composition in ripened cheese were determined. A high correlation between the intensity of f1avour and the concentration Methods of free amino acids had already been demon- strated in sorne Italian cheeses (Resmini et Determination of free amino acid al, 1993; Pellegrino et al, 1995). The quantitative analysis of amino acids, as their N-heptafluorobutyryl iso-but yi ester derivatives, MATERIALS AND METHODS was achieved by high resolution gas chro- matography using a Varian Model 3700 instru- ment equipped with a HD detector, a Hewlett- Materials Packard 3396 A integrator and a 25 m x 0.32 mm id fused silica capillary column coated with a Cheese samples 0.2-llm thick OV 170 1 film. The carrier gas was helium with a column flow rate of 1.6 mUmin at 80 "C. Both inje ctor and detector temperature The first phase of the experimental work involved were 280 oc. The column temperature ranged the analysis of cheeses from four different cheese- from 80 to 280 -c, with an 8 OC/min rate. The makers located in the typical production zone. cheese samples were prepared, purified and At the time of sampling, a sensory evaluation derivatised as described by Bertacco et al (1992). forrn was filled out, which included a graphie representation of the arrangement of the typical holes. Later, the cheeses from a single producer Determination of nitrogen content were considered. These were manufactured by the genuine traditional method, the only variable The water-soluble extract was prepared by grind- being the different storage temperature for mat- ing 4 g grated cheese in a mortar with water at uration, thereby demonstrating the influence of 50 "C until a homogeneous sample was obtained, this processing parameter on the proteolytic trend and the paste then diluted to 100 mL (Stadhouders, during maturation.