High pressure assisted thermal processing of pumpkin purée: Effect on microbial counts, color, bioactive compounds and polyphenoloxidase enzyme

• HPTP is an adequate alternative to preserve low acid vegetables.
• HPTP maintained or increased the bioactive compounds content of pumpkin.
• HPTP are also effective to reduce PPO activity.
• Processed pumpkin at these conditions needs the storage at low temperature.

The effect of high pressure assisted thermal processing (HPTP) to preserve the pumpkin purée was evaluated. Pumpkin cv. Butternut purée was submitted to 9 different combinations of pressure and temperature of HPTP (300, 600, 900 MPa/60, 70, 80 °C/1 min). Native microorganisms’, instrumental color, polyphenol oxidase (PPO) enzyme activity, carotenoids content, total antioxidant activity and individual and total polyphenols content were examined after processing and compared to non-processed purée. In treated purées, the inactivation of native microorganisms increased proportionally with pressure and temperature; CIE L* increased while CIE a* decreased respect to control purée. Moreover, most of the treatments applied reduced markedly the PPO activity, although the treatment at 600 MPa/70 °C was the most effective to reduce its activity. All treatments applied were effective to maintain or increase the content of carotenoids and phenolic compounds in the purée. The combination of 600 MPa/70 °C would be the treatment of choice since it increased the contents of bioactive compounds and the antioxidant activity of the purées, while caused the largest reduction of PPO activity.