Impact of indirect and ohmic heating sterilization processes on quality parameters of apple puree: application in a real industrial line

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.