The Quality of Red Bell Pepper Subjected to Freeze-Drying Preceded by Traditional and Novel Pretreatment

It has been demonstrated previously in the literature that utilization of PEF or a combination of a pulsed electric field (PEF) and ultrasounds (US) can facilitate dehydration processes and improve the quality of dried products even better than the application of thermal methods such as blanching. The aim of the study was to evaluate the quality of red bell pepper subjected to freeze-drying preceded by blanching or PEF or US treatment applied in a single and combined mode. Furthermore, the freeze-drying was preceded by shock freezing or vacuum freezing performed inside the freeze-dryer as a result of pressure drop during the first stage of freeze-drying. All of the analyzed technological variants enhanced the drying kinetics when compared to the intact material. Freeze-dried bell pepper subjected to non-thermal pretreatment exhibited higher vitamin C, total phenolic and carotenoids content than blanched material despite the fact that blanching reduced drying time the most compared to all other analyzed methods.

Comparison of the effect of freezing on the quality of ‘nam dokmai” mango fruit

This study evaluated effect of freezing methods on freezing rate and physical qualities of mango flesh before and after thawing. The method of freezing included still air freezing (at -20°C), air blast freezing (at -35°C, velocity 3 m/sec) and Air Blast Combined Vacuum Freezing (at -40°C, were configured core temperature 2 level is -5°C and -10°C) until the temperature reaches -20°C. The frozen flesh were thawed and evaluated for drip loss, pH, total soluble solid, colour, texture (firmness and %firmness decrease). The results showed that Air Blast Combined Vacuum Freezing (-5°C) Quality of mango frozen after thawing did not show significant effect on pH and total soluble solid of fresh mango. The frozen mango had highest lightness (L*) and the total colour differences (ΔE) had lowest and can maintain the maximum. Therefore, it's possible to introduce air blast combined vacuum freezing techniques applied to frozen mango industry as a result of significant increases freezing rate.