Development of methods and technologies for the specific inhibition of enzymes relevant for low colour stability of fruit juices and nectars.

This thesis explores the development of methods and technologies for the specific inhibition of enzymes relevant to the low colour stability of fruit juices and nectars. This research was carried out in collaboration with the HiStabJuice project, funded by the European Union’s Horizon 2020 program. This research project comprises five articles on inhibiting enzymes and maintaining colour stability in strawberry nectars. One of these articles details how certain enzymes are deactivated and focuses on polyphenol oxidase, peroxidase, pectin methylesterase, and polygalacturonase. It also explores methods, for inhibiting these enzymes. Manuscript 2 analysed how thermal and nonthermal methods impact the quality of strawberry nectar in terms of factors, like viscosity, colour, enzymatic activity and microbial content. In the following, third, manuscript the comparison was extended over a six-week timeframe showing that processed nectars retained their colour better than non-processed ones. A fourth manuscript studied the determinants of low colour stability in strawberry nectars by multilinear regression analysis. The results of the analysis revealed that storage time is the primary factor affecting the lightness of strawberry nectars and sugar content plays a key role in the preservation of red colour and overall colour saturation. The final manuscript compared the energy consumption of thermal and non-thermal technologies in strawberry nectar production. Non-thermal treatments were less energy-consuming than thermal treatments, especially at increased packaging volume. This thesis gives insights into the enzymes responsible for the low colour stability of strawberry nectars and other factors that contribute to the low colour stability of strawberry nectars. The findings inform how the product quality and shelf-life extension of strawberry nectars can be achieved.