Pressure, shear, thermal and interaction effects on quality of raw milk treated by Continuous High Pressure Processing system

Research poster
Jerish Joyner Janahar
V.M. Balasubramaniama
Department of Food, Agricultural and Biological Engineering

Continuous high pressure processing (HPP) involves pressurization of foods upto 400 MPa and subsequent depressurization by passage through tiny clearance. This study evaluated the effect of process parameters viz., pressure, shear, temperature and their interaction during continuous HPP on quality attributes of raw milk. For continuous HPP, raw milk equilibrated to 25±2°C and 15±2°C were pressurized to 400 MPa and depressurized via shear valve under low and high flow rates, at process temperatures of 70°C and 40°C respectively. Batch HPP was performed at 400 MPa and 42°C for 1s and 3 min, to study the effect of pressure (only). Untreated raw milk served as control. The quality attributes were evaluated using particle size, viscosity, pH, creaming rate and protein profile. Treatments and analyses were run in triplicate and ANOVA was performed to determine statistical significance.
The particle diameter and polydispersity of samples decreased from 3511.8 nm and 0.420 respectively for raw milk to 335.89 nm and 0.242 respectively during continuous HPP (at 70°C) demonstrating effect of pressure associated shear. Pressure only treatment did not cause apparent particle size reduction, but increased the viscosity of samples upto 3.08 cP as compared to 2.68 cP for raw milk. Creaming rate of raw milk samples were 14 mL/100 mL. No creaming in continuous HPP samples indicated shear effect on cream prevention. Batch HPP and continuous HPP at 70°C samples induced formation of protein aggregates, demonstrating the pressure and thermal impact on protein respectively. This knowledge is essential for equipment developers and food processors.