Study on the variability of fucosidase activity in bovine milk by means of HPLC

Variability of α-l-fucosidase (FUC) activity in bovine milk was evaluated with respect to season, keeping conditions and location of herd. A HPLC method was firstly set up in order to overcome some limitations of both colorimetric and spectrophotometric assays. The HPLC method was capable of determining FUC activity lower than 3 nmoles mL−1 h−1 and, for higher values, it gave comparable results with respect to the reflectance colorimetric assay. Samples (n=125)(n=125) of raw bulk milk from 22 herds, consisting of 500–600 Holstein–Friesian cows each, were collected in a restricted area of Northern Italy from January to June 2004. The average enzyme activity in each month was in the range 47.5–51.0 nmoles mL−1 h−1. FUC activity in milk from different herds did not vary to a large extent during the 6-month period since average values from 44.8 to 53.4 nmoles mL−1 h−1 were recorded. Only milk samples from 2 herds presented significantly (P<0.05) lower (41.1 nmoles mL−1 h−1) or higher (55.7 nmoles mL−1 h−1) activity, respectively. The effect of location of herds was studied on raw bulk milk samples (n=85)(n=85) collected at cowsheds located in 8 districts of Northern Italy during March 2004. Samples from 7 districts presented average FUC activity in the range 41.9–55.5 nmoles mL−1 h−1. Higher activity (60.8 nmoles mL−1 h−1) characterized milk samples produced by cows of Rendena and Brown Swiss breeds in the other district. This feature could support the hypothesis that the enzyme activity is also genetically based. In general, FUC activity was from 32.8 to 66.2 nmoles mL−1 h−1 (mean=49.4) when all raw milk samples of this investigation were taken into account. On this basis, a minimum threshold level of 30 nmoles mL−1 h−1 was considered as characteristic of raw milk (P<0.001). Heat processing of raw milk at industrial-scale (55–70 °C for either 1 or 15 s) confirmed FUC to be sensitive to time/temperature conditions adopted in thermization. Nevertheless, the application of the residual activity as an indicator of raw milk thermization appeared not fully feasible. Indeed, false negative response (i.e. activity >30 nmoles mL−1 h−1) can be expected when raw milk with FUC activity >50 nmoles mL−1 h−1 is submitted to mild thermization conditions (i.e. 57–58 °C for 15 s). This problem was not overcome even when the evaluation of FUC activity was coupled with the determination of alkaline phosphatase.