Pulsed electric field (PEF) pretreatment impact on the freezing and ultrasound-assisted atmospheric freeze-drying of butternut squash and yellow turnip

Abstract

This study explores the impact of the application of pulsed electric field (PEF) pretreatment in the freezing and in the power ultrasound-assisted (US) atmospheric freeze-drying (AFD) of two different products: butternut squash and yellow turnip. Two PEF pretreatments were applied, inducing cell disintegration indexes (CDI) of 0.25 and 0.75. The results showed that PEF pretreatments significantly altered the microstructure of butternut squash and yellow turnip, but in a different way. These changes led to a significant shortening of the freezing process by up to 11.6%. Although PEF pretreatments significantly affected the drying rate of AFD, the effect was maximum when combined with ultrasound-assisted AFD. However, the PEF treatment that most enhanced ultrasound-assisted drying kinetics varied between products: a moderate treatment (CDI of 0.25) was most effective for butternut squash (37.3% time reduction), while a more intense treatment (CDI of 0.75) was better in the case of yellow turnip (44.2% time reduction). These findings indicate an enhancement of the atmospheric freeze-drying process achieved through the combined application of PEF and US under adequate conditions.