No abstract

This study will provide an overview and a description of the most promising alternatives to conventional thermal treatments for juice stabilization, as well as a review of the literature data on fruit and vegetable juice processing in terms of three key parameters in juice production, which are microbial reduction, enzyme inactivation, and nutrient-compound retention. The alternatives taken into consideration in this work can be divided, according to the action mechanism upon which these are based, in non-conventional thermal treatments, among which microwave heating (MWH) and ohmic heating (OH), and non-thermal treatments, among which electrical treatments, i.e., pulsed electric fields (PEF), high-pressure processing (HPP), radiation treatments such as ultraviolet light (UVL) and high-intensity pulsed light (PL), and sonication (HIUS) treatment, and inert-gas treatments, i.e., the pressure change technology (PCT) and supercritical carbon dioxide (SC-CO2) treatments. For each technology, a list of the main critical process parameters (CPP), advantages (PROS), and disadvantages (CONS) will be provided. In addition, for the non-thermal technologies, a summary of the most relevant published result of their application on fruit and vegetable juices will be presented. On top of that, a comparison of typical specific working energy costs for the main effective and considered technologies will be reported in terms of KJ per kilograms of processed product.

The aim of the present work is to investigate the impact of the production process and heat treatment technology to produce sterilized apple puree in the case of a real industrial production line. The technologies considered for the sterilisation process are traditional indirect thermal heating and ohmic heating, while the results will be expressed in terms of residual amount of vitamin C, Furfural content and finally HunterLab colour space (L, a, b value). The samples for the evaluation of the comparison parameters have been taken in 3 different steps of the production process, i.e. in the fresh product, after hot finisher (after extraction) and at the end of the line (after sterilization and bottling). It has been observed that both processes considered showed similar performance for all the various parameters evaluated, leading to a very similar final product. This result is somehow unexpected since the Ohmic technology has demonstrated in the last years to bring significant advantages in terms of preserving of nutrients and of colour stability. This could be since apple puree is a sort of homogeneous product, while the best advantages for the Ohmic heating are expected to be found in heterogeneous products containing pieces or particulate matter. But the main reason is related to the fact that in the present work the focus is on the whole process and not only on the heat treatment technology. One of the aims is to put the attention on the importance of specifically designing the whole production line: the adoption of ohmic heating or other innovative technologies to shield nutrients and colour will be wasted if the rest of the production line is not specifically designed to obtain such objectives.