Effect of electric field and osmotic pre-treatments on quality of apples after freezing–thawing

• Pre-treatment of apple by pulse electric fields (PEF) and ohmic heating (OH) was done.
• Osmotic (O) treatment of pre-treated samples in aqueous glycerol solution was studied.
• Distribution of osmotic solution was practically homogeneous inside PEF-treated apple.
• PEF-treatment has a positive impact on freezing and thawing and texture strengthening.
• There is a good potential of practical applications of PEF + osmotic assisted freezing.

This work discusses the effects of pulsed electric field (PEF), ohmic heating (OH), and osmotic (O) treatments on the structure of apple tissue and its freezing/thawing behaviour. Apple discs were treated at electric field strength E = 800 V/cm (PEF, isothermal regime) and E = 40 V/cm (OH, non-isothermal regime) to a high level of tissue disintegration (conductivity disintegration index Z was ≈ 0.98) and then were subjected to osmotic (O) treatment in the aqueous solution of glycerol (20 wt.%). The distribution of osmotic solution was practically homogeneous inside the disc of PEF-treated tissue and highly inhomogeneous in untreated and OH-treated samples. The freezing–thawing (FT) experiments (+ 20 °C → − 40 °C → + 20 °C) were done in order to reveal the effects of combined modes of treatment on the structure of apple tissue. The most pronounced reducing of both freezing and thawing times and strengthening of the apple texture were observed for PEF treatment.Industrial relevanceFreezing-assisted preservation of plant materials in the most natural-looking state with near-original texture and colours requires thorough optimization of freezing operation. In this study, the research of the impact of pulsed electrotechnologies combined with osmotic pre-treatment on the structure of apple tissue, its freezing/thawing behaviour and texture quality, is provided.