Kinetics studies of chemical reactions in conjugated linoleic acid (CLA) enriched milk treated with high-pressure sterilization

Abstract Text:

Conjugated linoleic acid (CLA), a bioactive lipid naturally found in milk, is degraded through oxidation during thermal processing. Application of pressure-assisted thermal processing (PATP) reduces the thermal exposure during processing, protecting a variety of bioactive compounds. This study evaluated the impact of PATP on the CLA content at conditions where commercial sterilization has been achieved. In addition, the effect of PATP on some quality indicators was evaluated, including lactulose formation, inactivation of alkaline phosphatase, and retention of CLA during storage. At 600 MPa and 120˚C for 15 min, ~78% of the CLA was retained while only ~20% was retained at 0.1 MPa and 120˚C. The Weibull model was used to predict the retention kinetics of CLA. Temperature and pressure accelerated the formation of lactulose, with a maximum value of 650 mg L^-1 at 120˚C, 600 MPa and 15 min. The PATP conditions needed to reduce 7-log of B. amyloliquefaciens endospores in inoculated milk were determined as well as the effect of adding nisin (4-64 mg L^-1 milk). A reduction of 7-log was obtained after 5 min at 600 MPa and 120˚C in milk with nisin added. Milk treated at 600 MPa and 120˚C for 5 min was selected to evaluate the impact of PATP on the CLA retention and formation of hydroperoxides during storage. Milk with nisin added and treated with PATP delivered higher CLA retention and lower hydroperoxides concentration compared with the UHT equivalent process. The kinetic information obtained was used to build pressure-temperature diagrams for CLA retention and lactulose formation. The outcomes of this study are considered as a step further for the development of shelf-stable milk processed by PATP.

Keywords: Conjugated linoleic acid, kinetics, modeling,