Mailo Virto

Coagulating and lipolytic activities of artisanal lamb rennet pastes

Lamb rennet pastes were prepared by the procedure most commonly used by Idiazabal cheese manufacturers. We studied the effects on their coagulating and lipolytic activities of the state of the stomach at the time of death (full of milk or empty), the amount of NaCl added, the origin of the lambs and paste storage time. Coagulating activities were generally between 155 and 363 units/g tissue. Pastes prepared from stomachs of lambs from slaughterhouse flocks had significantly higher coagulating activities than those of lambs from separate flocks. No significant decrease in coagulating activity was observed after 1 year storage at 4 degrees C. Chymosin represented 75-80% of the total coagulating activity with the remainder being pepsin. Rennet paste extracts with pH < 4.7 did not have increased coagulating activities when their pH was lowered to 2.0, while those with pH > 5.2 had activities 1.5-fold those before treatment. Lipase activity was higher in extracts of rennet pastes prepared using the stomachs of lambs that arrived at the slaughterhouse in the morning just prior to slaughter than in those prepared with the stomachs of lambs that had arrived on the previous evening. However, the reverse was the case for esterase activity. Activating the coagulating activity by pH cycling completely destroyed both lipolytic activities. Storage at 4 degrees C for > 1 year did not affect esterase activity but lipase activity decreased substantially after 4-5 months. Lipase, but not esterase, activity was responsible for the liberation of short-chain free fatty acids from ovine milk fat.

Determination of free fatty acids in cheese: comparison of two analytical methods

Two methods were compared for the determination of free fatty acids (FFA) from acetic to long-chain acids in samples with a large excess of triacylglycerols (TG) (1[ratio ]200, w/w), such as cheese and other dairy products. In method 1, after fat extraction, FFA were separated from TG by aminopropyl-bonded phase chromatography, injecting the fraction containing FFA directly into the gas chromatograph. In method 2, extracted fat was treated with tetramethylammonium hydroxide, the methyl ester derivatives being formed in the injector. Cheese samples and standard mixtures of FFA and TG in different proportions were analysed by both methods. The cheese sample contained 2·4 times more FFA when analysed by method 2 as compared with the result obtained with method 1. The composition of the standard mixtures analysed by method 1 closely reflected that of the original mixture and gave 90–100% recovery of FFA, regardless of their chain length and the ratio of FFA[ratio ]TG (1[ratio ]1 or 1[ratio ]200, w/w). The composition of samples with a FFA[ratio ]TG ratio of 1[ratio ]200 (w/v) was severely distorted (as compared with the original composition of the sample) when analysed by method 2. Varying recoveries of FFA were also obtained, the largest differences being found for the shorter-chain components. We conclude that the FFA fraction should be separated from the TG fraction before derivatization and chromatographic analysis, particularly for samples in which the FFA represent a minor fraction of the TG.

Seasonal changes in the composition of bulk raw ewe's milk used for Idiazabal cheese manufacture

Seasonal changes in the composition of bulk raw ewes milk used for Idiazabal cheese manufacture and its influence on the cheese yield are reviewed. This review is based on biochemical and microbiological data previously published on the composition of a bulk raw ewes milk collected at three different times of the year. In order to characterize, in a more extensive perspective, the seasonal changes in the composition of this bulk raw ewes milk and its influence on actual cheese yield, multivariate statistical analyses were applied to the compositional data of the milk and the actual cheese yield obtained at the factory. The results show pronounced seasonal changes in the composition of bulk raw ewes milk. Changes in cheese yield, lipolytic activity and microbiological quality of the bulk raw ewes milk are the principal aspects seasonally affected during the cheesemaking period. Also, the seasonal changes observed in the bulk raw ewes milk composition strongly affect the quality of Idiazabal cheeses manufactured over the cheesemaking period.

Winter/Spring Changes in Fatty Acid Composition of Farmhouse Idiazabal Cheese Due to Different Flock Management Systems

Typically, two different flock managements are employed by basque sheepherders in winter and spring. Thus, seasonal changes in the fatty acid (FA) composition of Idiazabal PDO farmhouse cheeses were studied. Ewes raw milk cheeses elaborated in winter and spring were collected after 120 days of ripening from 10 Idiazabal PDO farmhouses. In winter, concentrate and conserved forages were fed, whereas a part-time grazing system was adopted from spring onward. Spring cheeses had less (P <or= 0.05) saturated FA and higher (P <or= 0.05) content of unsaturated FA, including trans-FA (mainly trans-vaccenic acid) and conjugated linoleic acid (CLA), branched-chain FA (BCFA), and n-3 FA. Principal component analysis (PCA) separated winter and spring cheeses into two groups by the combination of two principal components (84.2% of variance). Fresh pasture in the diet enhanced desirable FA and lowered atherogenicity index in cheeses, supporting the benefits of using a part-time grazing system for the consumer.

Rapeseed and sunflower oilcake as supplements for dairy sheep: animal performance and milk fatty acid concentrations

The influence of different amounts of oilseed cake (rapeseed and sunflower) on animal production parameters and fatty acid (FA) concentrations of the milk was studied in a Latxa dairy sheep experimental flock, both in winter (50% oilcakes; indoor feeding) and in spring (30% oilcakes; part-time grazing). The two different levels of the oilcakes tested did not affect animal production parameters or milk yield. Milk fat content and the fat/protein ratio decreased significantly with 30 and 50% sunflower cake. Yet, fat/protein ratio values were within the range for cheesemaking. Both levels of either type of oilcake tested significantly increased the concentrations of nutritionally interesting FA (CLA isomer C18:2cis-9, trans-11, vaccenic, oleic, and total unsaturated FA), while simultaneously decreasing the concentration of atherogenic FA. The atherogenicity indexes of milks from ewes fed 50 or 30% of either oilcake were significantly lower than those of their corresponding control. The use of cakes in winter increased the concentration of nutritionally interesting FA to the values obtained with part-time grazing.