CONICET | Buscador de Institutos y Recursos Humanos

Incorporation of exogenous lipases in cheese-making is usually used as a resource to develop the production of volatile compounds or to accelerate ripening process. The aim of this work was to evaluate the effect of the addition of an esterase on the lipolysis and volatile compounds profiles of semi-hard cheeses. EST2 is a thermophilic pure esterase isolated from Alicyclobacillus acidocaldarius with moderated esterase and thiosterase activities. Semi-hard cheeses (like Pategras variety) were made at pilot plant scale according to a standard process, using four levels of enzymes, 2, 5, 10 and 20 mg/L of milk (experimental cheeses, EI-EIV) and without enzyme (control cheese, C). The cheeses were ripened at 12ºC during 60 days. Lipolysis and volatile compounds profile were analysed at the end of ripening. Free fatty acids (C4:0 to C18:2) were extracted from fat by solvent and quantified by GC-FID as ethyl esters, and concentrations were expressed in mg/Kg of cheese. Analysis of the volatile fraction was performed by SPME-GC-FID/MS obtaining semiquantative data (peak areas in arbitrary units) by GC-FID. Global composition and degree of ripening were assessed according to IDF methods and the protein profiles were investigated employing the ProteinChip SELDI system. Sensory analysis was performed by a triangle test. The degree of lipolysis (sums of 10 FFA concentrations) for experimental cheese with highest level of enzyme (EIV) was 1.5 fold higher than C cheese. Relative increases of 54% and 33% in short- (C4:0-C8:0) and medium- (C10:0-C12:0) chain fatty acids, were observed for EIV cheese in relation to control cheese. This fact suggests the preferential release of short chain fatty acids by EST2. Twenty seven and thirty one volatile compounds were identified respectively in control and experimental cheeses. They belonged to different chemical families such as ketones, alcohols, esters and acids. Experimental cheeses showed higher areas values than control cheeses for almost all volatile compounds. In particular, it was interesting to notice that the EIII cheese showed the greatest values in spite it had not the highest enzyme level. In sensorial analysis significant differences among cheeses made with and without enzymes were observed. Global composition and degradation of protein did not reveled significant differences between experimental and control cheeses, indicating that the enzyme had not a proteolytic activity. Taking into account that the use of EST2 in cheese-making intensified the production of flavour compounds, specially those related with lipolysis and FFA catabolism, this esterase could be an interesting technological strategy to improve the sensory quality or accelerate the ripening process of cheeses.