Irma Veronica Wolf

Influence of milk pretreatment on production of free fatty acids and volatile compounds in hard cheeses: Heat treatment and mechanical agitation

This work aimed to identify technological steps that can increase fat hydrolysis and volatile compounds production in hard cheeses; these biochemical events have been related with improved piquant taste and development of genuine flavor during cheese ripening. For that purpose, 2 different pretreatments of cheese milk were tested: heat treatment and mechanical agitation. Both factors were assayed at 2 levels: milk was either batch pasteurized or nonthermally treated, and mechanical agitation was either applied or not applied. For all combinations, hard cheeses (Reggianito type) were produced in a pilot plant and ripened for 90 d. In all cheeses the degree of lipolysis, assessed by gas chromatography, increased similarly during ripening. However, the proportion of short-chain fatty acids was higher in the cheeses made with unpasteurized milk, suggesting a higher activity of lipases with positional specificity toward the sn-3 position of the triglyceride, among which milk lipoprotein lipase is found. Similar results were found for most of the volatile compounds, determined by solid-phase microextraction-gas chromatography flame-ionization detector/mass spectrometry, which constitute the groups of ketones, alcohols, esters, and the group of acids. On the contrary, no effect of mechanical agitation was observed, although some interactions between factors were found. In the conditions of the study, results suggest that heat treatment had a higher effect on cheese lipolysis and volatile compounds production than partial destabilization of the fat emulsion produced by the agitation method applied.

SPME/GC-MS Characterization of the Volatile Fraction of an Italian PDO Sheep Cheese to Prevalent Lypolitic Ripening: the Case of Fiore Sardo

A specifically aimed SPME/GC-MS method has been assessed in order to describe the volatile fraction of intense flavoring cheeses like Fiore Sardo PDO, a prevalent lipolytic ripening sheep cheese from Sardinia, Italy. A DVB/CAR/PDMS 50/30 µm fiber and a 3-min exposure time showed to be the best compromise between the possibility to extract compounds with a wide range of polarity and molecular mass and the need to avoid competition and displacement effects among analytes. The volatile compound profile of Fiore Sardo PDO sheep cheese was largely characterized by carboxylic acids (about 68% of the total area of recognized peaks), whereas esters (14%), ketones (9%), and alcohols (8%) represented other abundant classes of low molecular weight species. A number of low-smelling threshold trace compounds were also identified as likely contributors of aroma of the Fiore Sardo PDO cheese.

Composition and volatile profiles of commercial Argentinean blue cheeses

BACKGROUND A first approach was made to acquire knowledge of the global composition, proteolysis, lipolysis and volatile profile of Argentinean blue cheeses. A total of 20 samples belonging to six leading commercial brands were analysed. A comparison of the results with bibliographical data on other blue cheeses was performed and the variability among and within dairy plants was also evaluated. RESULTS Values of global composition were intermediate in relation to those reported for mould-ripened cheeses. Levels of proteolysis and lipolysis were lower than those of other blue cheeses. Volatile compound profiles were characterised mainly by short-chain fatty acids, methyl ketones and secondary alcohols, as reported previously for blue cheeses. Wide-ranging values of physicochemical parameters, lipolysis and proteolysis levels as well as volatile compound areas of cheeses produced by each dairy plant were observed. Owing to this high variability in the chemistry and volatile profile of cheeses, principal component analysis of the data did not show groupings by commercial brands. CONCLUSION On the whole, Argentinean blue cheeses were characterised both by gross intermediate composition values and by proteolysis and lipolysis levels lower than those of blue cheeses of different origins. A typical volatile compound profile of blue cheeses was observed. The high variability found within each commercial brand could reflect the lack of standardisation of the technological processes used in blue cheese manufacturing in Argentina.

Production of flavour compounds from fat during cheese ripening by action of lipases and esterases.

The milk fat is an essential component for the development of correct flavour in cheese. The lipolysis and catabolism of fatty acids are two biochemical events very important on flavour development of some cheese varieties. The role and characteristics of various lipolytic agents during cheese ripening is reviewed and discussed. Before starting with the specific study about formation of flavour compounds from milk fat during cheese ripening, a brief review of the technological aspects of cheese production is needed.

Characterization of volatile compounds produced by Lactobacillus helveticus strains in a hard cheese model

Starter cultures of Lactobacillus helveticus used in hard cooked cheeses play an important role in flavor development. In this work, we studied the capacity of three strains of L. helveticus, two autochthonous (Lh138 and Lh209) and one commercial (LhB02), to grow and to produce volatile compounds in a hard cheese extract. Bacterial counts, pH, profiles of organic acids, carbohydrates, and volatile compounds were analyzed during incubation of extracts for 14 days at 37 ℃. Lactobacilli populations were maintained at 106 CFU ml−1 for Lh138, while decreases of approx. 2 log orders were found for LhB02 and Lh209. Both Lh209 and LhB02 slightly increased the acetic acid content whereas mild increase in lactic acid was produced by Lh138. The patterns of volatiles were dependent on the strain which reflect their distinct enzymatic machineries: LhB02 and Lh209 produced a greater diversity of compounds, while Lh138 was the least producer strain. Extracts inoculated with LhB02 and Lh 209 were characterized by ketones, esters, alcohols, aldehydes, and acids, whereas in the extracts with Lh138 the main compounds belonged to aromatic, aldehydes, and ketones groups. Therefore, Lh209 and LhB02 could represent the best cheese starters to improve and intensify the flavor, and even a starter composed by combinations of LhB02 or Lh209 with Lh138 could also be a strategy to diversify cheese flavor.

Response of Leuconostoc strains against technological stress factors: Growth performance and volatile profiles

The ability of twelve strains belonging to three Leuconostoc species (Leuconostoc mesenteroides, Leuconostoc lactis and Leuconostoc pseudomesenteroides) to grow under diverse sub-lethal technological stress conditions (cold, acidic, alkaline and osmotic) was evaluated in MRS broth. Two strains, Leuconostoc lactis Ln N6 and Leuconostoc mesenteroides Ln MB7, were selected based on their growth under sub-lethal conditions, and volatile profiles in RSM (reconstituted skim milk) at optimal and under stress conditions were analyzed. Growth rates under sub-lethal conditions were strain- and not species-dependent. Volatilomes obtained from the two strains studied were rather diverse. Particularly, Ln N6 (Ln. lactis) produced more ethanol and acetic acid than Ln MB7 (Ln. mesenteroides) and higher amounts and diversity of the rest of volatile compounds as well, at all times of incubation. For the two strains studied, most of stress conditions applied diminished the amounts of ethanol and acetic acid produced and the diversity and levels of the rest of volatile compounds. These results were consequence of the different capacity of the strains to grow under each stress condition tested.

Influence of lactose hydrolysis on galacto‐oligosaccharides, lactose, volatile profile and physicochemical parameters of different yogurt varieties

BACKGROUND Different types of reduced-lactose yogurt, obtained by lactose hydrolysis using β-galactosidase enzyme, are commercially available. The breakdown of lactose modifies the carbohydrate profile, including the production of prebiotic galacto-oligosaccharides (GOS), which could affect the survival and activity of starter and probiotic cultures and the parameters of yogurt quality. The extension of these changes is dependent on the yogurt matrix composition. This study aimed to evaluate the influence of lactose hydrolysis on GOS, lactose, volatile profile and physicochemical parameters of different yogurt varieties during storage. RESULTS The presence of β-galactosidase enzyme did not affect either the global composition or the survival of cultures. Overall, the hydrolyzed products had lower acidity than traditional ones. GOS were found at similar levels in fresh hydrolyzed yogurts, whereas in traditional yogurts they were not detected. The proportion of ketones, acids and aldehydes seems to be more dependent on yogurt variety than on addition of the enzyme. Likewise, the storage period affected the volatile fraction to different degree; the increase in acid compounds was more pronounced in hydrolyzed than in traditional yogurts. CONCLUSION This work shows that it is possible to obtain different varieties of reduced-lactose yogurt, some of them with additional benefits to health such as reduced fat, reduced calories, added with probiotic/inulin and enriched in GOS, with similar characteristics to traditional products.