Effect of pretreatments and freezing rate on the firmness of potato tissue after a freeze-thaw cycle

The texture of potato tissue after a freeze-thaw process using different freezing rates and different pretreatments was analysed, in order to select the best strategy for optimum preservation of the textural characteristics of pre-frozen potato. Ten blanching conditions were tested and a two-step blanching process with calcium chloride (0.07 g mL^-1) proved the most effective in protecting the tissue after a freeze-thaw process (maximum load force around 10-55% of the raw tissue, depending on potato batch, for air-blast freezing and 20-60% for immersion freezing). Vacuum impregnation at 100 and 400 mbar, even when followed by different pre-drying treatments to remove excess water, was very detrimental to resistance to a freeze-thaw process (maximum load force below 10% of the raw tissue for air-blast freezing and below 20% for immersion freezing). Microstructure analysis confirmed better tissue integrity retention with ethyleneglycol immersion freezing instead of air-freezing. Differences were found between batches with a 6-month difference in storage time, indicating that the fresher batch was more suitable for freezing.