Thermal inactivation and variability of γ-glutamyltransferase and α-l-fucosidase enzymatic activity in sheep milk

- Thermal inactivation of EC 2.3.2.2 and EC 3.2.1.51 is presented in sheep milk.
- No differences in both enzymatic activities were ascribable to the animal diet.
- Enzymatic activity of EC 2.3.2.2 is roughly constant over the whole lactation cycle.
- Enzymatic activity of EC 3.2.1.51 increases linearly during lactation cycle.
- Enzymes can be used as reliable markers of low thermal treatments in sheep milk.

We present a study of the thermal inactivation and variation of activity of two enzymes in sheep milk: γ-glutamyltransferase and α-l-fucosidase. We find that the thermal treatment of milk causes inactivation of α-l-fucosidase between 57 °C and 68 °C, and γ-glutamyltransferase between 68 °C and 80 °C. In untreated sheep milk, the highest level of enzymatic activity (EA) for these two enzymes is in the pH range 5.5-6.0 and 8.0-8.5, respectively. Skimming treatment causes the loss of 35% of the activity of γ-glutamyltransferase. No differences in the EA were ascribable to the diets evaluated in this study. We observed EAs of α-l-fucosidase and γ-glutamyltransferase over the entire lactation cycle, noting that the EA of the former increased from 81 to 207 U mL−1 (average 159 ± 30 U mL−1) while the EA of the latter from 3.12 to 4.89 U mL−1 (average 3.83 ± 0.34 U mL−1). Relationships between both enzymes and selected milk parameters (lipids, proteins, lactose, urea and somatic cells) are highlighted by Principal Component Analysis.