Effect of PEF pre-treatment coupled with osmotic dehydration on physico-chemical characteristics of organic strawberries

Summary

In the recent years the fruit organic production has been one the most growing sectors in food industry. Strawberries are a nonclimateric fruits, susceptible to mechanical injury and they are also highly perishable, especially the organic one. Therefore, there is a need to improve the processing of these fruits in order to obtain a semi-dried or osmodehydrated products with higher shelf-life.
The aim of this work was to evaluate the effect of PEF pre-treatment on mass transfer phenomena, water distribution and some physico-chemical parameters of strawberries subjected to osmotic dehydration. For the experiment the organic strawberries were purchased in a local market and stored at 4 ± 1 °C before analysing further processing. The fruits were washed and dried with absorbent paper and manually cut with a stainless steel knife into rectangular pieces (5 x 10 x 20 mm). For PEF treatments two strawberry pieces were placed in a 20 x 20 x 30 mm chamber and filled up with tap water. 100 near-rectangular shaped pulses, with fixed pulsed width of 100 µs and repetition time of 10 ms were used for all samples. Electric field strength applied was 200 and 400 V cm-1. Afterwards, the samples were subjected to OD treatments carried out in two different hypertonic solutions (40% w/w) one with sucrose and the other one with trehalose. The strawberry samples were analysed for mass transfer phenomena, water distribution by TD-NMR, colour and texture parameters. The results showed that PEF coupled with OD have a greater effect on mass transfer phenomena and water redistribution when sucrose solution was used for OD treatment compared to trehalose solution. Strawberry fruits treated with low PEF voltage better maintained their colour. However, the PEF-OD treated samples were softer than the untreated ones.