M. Dolores Álvarez

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at -2 °C min -1 . The effects of variation in levels of temperature (57.93-72.07°C) and time (15.86-44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box-Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60-70 °C) and time (20-40min) in the first blanching step and steaming temperature (112-122°C) and time (1-3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22°C and 29.37min before freezing and 64.39°C and 28.02min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues.