The Influence of Different Pre-Treatments on the Quality and Nutritional Characteristics in Dried Undersized Yellow Kiwifruit

Featured Application Industrial application of the pre-treatments used prior to convective drying should take into account the time required for the pre-treatments themselves. In the case of osmotic dehydration (OD), the processing time could be relatively long (up to 120-150 min to reach a pseudo-equilibrium of the mass change), but it offers the possibility to handle underripe and very sour fruits and it could be carried out in batch or continuous lines with fair simple technologies. Moreover, it can be performed at near ambient temperature before drying to bring the partially dewatered products to the convective drying. The spent solution management can also be easily performed. On the other hand, the industrialization of PEF pre-treatment can be easily introduced also in a continuous process since the required time for PEF application is very short (in the present work-10 s) and nowadays there are several equipment suppliers able to scale-up industrial plants from laboratory scale. Undersized kiwifruits are considered waste; therefore, there is a need to develop sustainable processing technologies for their valorization, in order to have a positive economic impact on their entire production chain. Therefore, the aim of this study was to apply pulsed electric fields (PEF) combined with osmotic dehydration (OD) and air drying (AD) to develop a novel yellow kiwifruit dried snack with high nutritional functionality. In particular, the effect of the different pre-treatments, PEF (200 V/cm) and/or OD (trehalose at 40%), on the color, bioactive compounds content and antioxidant activity (AA) was evaluated on kiwifruit chips air-dried at three different temperatures (50, 60, 70 degrees C). The results showed that better color maintenance was observed at the drying temperature of 60 degrees C. Concerning the bioactive compounds, a good retention in total polyphenols (TP), vitamin C content and AA with the DPPH method was obtained on OD and PEF kiwifruit dried snacks, similar to that of control samples. Instead, the ABTS method showed the best AA in PEF and OD/PEF samples. In general, a shorter drying time in the OD- and PEF-treated samples could contribute to the higher sustainability of the process.