Determination of the influence of high pressure processing on calf rennet using response surface methodology: Effects on milk coagulation

- HPP process increases the proteolytic and milk-clotting activities of calf rennet.
- Pressurization improves the stability of the rennet in solution.
- Protein aggregation is faster for gels clotted by the HPP enzyme.
- The milk gels produced using HPP processed calf rennet has higher consistency.
- HPP may be an interesting new tool for calf rennet modification.

This study investigated the influence of high pressure processing (HPP) on the proteolytic and milk-clotting activities of calf rennet and milk coagulation using processed enzyme by rheological assay and confocal microscopy. The process was carried out at 25 °C, using pressure range from 50 to 300 MPa and time between 5 and 30 min. It was found that HPP (175-285 MPa for 14-23 min) increased the enzyme proteolytic activity by up to 23% and the milk-clotting activity by up to 17%. Furthermore, the G' values obtained during milk coagulation were higher for calf rennet processed at 280 MPa for 20 min than for the non-processed enzyme, forming more consistent gels (25.8% higher G′ value after 90 min). The evaluation of the milk coagulation by confocal microscopy confirms the results obtained on the rheology. Pretreatment of calf rennet using HPP accelerates the coagulation of milk and produces firmer and more consistent gels.