Changes in soluble nitrogenous compounds, caseins and free amino acids during ripening of artisanal prato cheese; a Brazilian semi-hard cows variety

Abstract

Proteolytic changes, during ripening (1–60 days) of 12 batches of artisanal Prato cheese, a Brazilian semihard cows’milk variety, were evaluated by determining the soluble nitrogenous compounds, caseins and their degradation products and free amino acids. Levels of pH 4.4-soluble nitrogen (pH 4.4-SN) and 12% TCA-soluble N, expressed as% TN, at the end of ripening were 21.4 and 12.5, respectively.% Aminoacid nitrogen/TN increased significantly (P<0.05) during ripening to final values of 4.32. The degradation patterns of α_s1- and β-caseins were similar in all cheese batches and α_s1-casein was hydrolysed more extensively than β-casein during ripening. The total content of free amino acids increased aproximately 8 times throughout ripening with average final values of 2454 mg/100 g total solids. γ-Amino butyric acid, leucine, lysine, glutamic acid, tryptophan and phenylalanine were the most abundant free amino acids in all batches studied, representing of 62% of total free amino acids.

Introduction

Of all the dairy products made in Brazil, cheese is the most traditional. Cheese production in Brazil is currently running at approximately 470,000 metric tonnes a year (Leite Brazil, 2001). Some 78% of the production of cheese is done under Federal inspection, while the remaining 22% is carried out by small craft producers working outside the legal framework. In Brazil two groups of cheeses are distinguished: common cheeses (95% of the total produced), covering widely-consumed varieties such as Mozzarella, Prato, Requeijao, Minas Frescal, Parmesan and Ricota; and fine or special cheeses (5% of the total) which include types such as Tilsit, Gouda, Gruyère, Gorgonzola and Camembert. Fine cheeses are those the better prospects in the Brazilian market. Nonetheless, common cheeses are those in greater demand by consumers, basically through being eaten indirectly as an ingredient, e.g. in pizzas (Mozzarella), sandwiches (Prato) and pasta dishes (grated Parmesan).

The Southern Region in Brazil (Rio Grande do Sul, Santa Catarina and Paraná states) is the second largest producer of milk in Brazil with approximately 4841 million litres output yearly (Milkbizz, 2002). Rio Grande do Sul state is the third largest milk producer in Brazil and the first by size in the Southern Region.

The dairy trade in Rio Grande do Sul is made up, for the most part, of small businesses, using family members as staff. Around 80% of these producers have associated to form co-operatives that make cheeses of the highest quality. However, the remaining 20% make and sell raw-milk cheeses of poor and inconsistent quality that can be a health risk for consumers. Hence, improvements in the quality of artisanal cheeses entail investments in hygiene, technology and production control with the aim of making consistent, safe cheeses with a traditional aspect. Achievement of this would yield, not merely health and technology improvements, but also financial advantages, as it would allow viable sales routes for small artisanal producers.

Among the craft cheeses most widely present in Rio Grande do Sul are the Minas Frescal and Prato varieties. The second of these is the subject of this characterization study.

Prato variety is a ripened cheese made by enzymatic curdling with a smooth, thin rind and an elastic, compact consistency. It is rectangular in shape and has a normal weight of 1.6–1.8 kilogrammes.

Characterization of artisanal Prato cheese includes, as one part, a study of the technological procedures for its production and of the chemical and physico-chemical parameters during its maturation (Cichoscki, Valduga, Valdaga, Tornadijo, & Fresno, 2002). A second part involves the biochemical changes in the principal components during maturation, with proteolysis the most important feature in bacterially-ripened varieties.

Proteolysis in cheese during ripening plays an important part in determining texture and flavour and has been the subject of several reviews (Fox & McSweeney, 1996). Hydrolysis of caseins by rennet and alkaline protease, in the initial stages of maturation releases a considerable quantity of peptides of large or intermediate molecular size. These peptides are substrates of peptidases of the starter and contaminating flora, giving rise to smaller peptides and free amino acids. These contribute directly to the flavour or in some cases indirectly by acting as precursors of aromatic substances (amines, acids, thiols, thioesters, and the like).

The aim of this work is to study proteolytic changes during the ripening of artisanal Prato cheese by the assessment of soluble nitrogenous compounds, casein and their breakdown products and free amino acids to establish a scientific basis for improvements in the quality of this variety of cheese.