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

  • Author / Creator
    Martinez, Sergio I.
  • Conjugated linoleic acid (CLA), a bioactive lipid naturally found in milk, is thermally degraded through oxidation during thermal processing. Finding alternatives to enhance the retention of CLA is challenging. In this thesis, high-pressure sterilization (HPS) was used to enhance CLA retention in milk. In addition, the effect of HPS on some quality indicators was evaluated, including lactulose formation, inactivation of alkaline phosphatase, and retention of CLA during storage. When HPS was applied (600 MPa and 120˚C), 78% of the CLA was retained after 15 min, while only 20% was retained after 15 min at 0.1 MPa and 120˚C. The retention kinetics was represented with Weibull model. To further improve the retention of CLA in milk, seven antioxidants, mainly phenolic acids, were evaluated. Gallic acid and catechin resulted in the highest retention of CLA after treatments at 600 MPa and 120˚C. 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 HPS conditions needed to reduce 7-log of Bacillus amyloliquefaciens endospores in inoculated milk were determined as well as the effect of adding nisin (4-64 mg L-1 milk). The inactivation kinetics of alkaline phosphatase was determined. Results showed that the addition of nisin (≥16 mg L-1) significantly enhanced the inactivation of Bacillus amyloliquefaciens (7-log reduction) after 5 min of treatment at 600 MPa and 120˚C, while without nisin 10 min were required to achieve the same log reduction. For storage, milk treated at 600 MPa and 120˚C for 5 min was selected to evaluate the impact of HPS on the CLA retention and formation of hydroperoxides. During storage, milk with nisin added and treated with HPS 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. These data can be further used to design HPS processes, achieving high CLA retention.

  • Subjects / Keywords
  • Graduation date
    Spring 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.