Thermal processing of kale purée: The impact of process intensity and storage on different quality related aspects

This study focused on investigating quality changes of thermally processed kale purée using an integrated targeted and untargeted approach. Low, medium, and high processing intensities (carried out at 70, 90, and 128 °C) were selected based on predetermined shelf-life targets: frozen-thawed, refrigerated, and ambient storage, respectively. The results show that that physicochemical properties determining consumer acceptability were largely dependent on the treatment intensity. The high intensity treatment resulted in the least favorable quality characteristics (distinct brown color, chlorophyll and vitamin C destruction as well as a phase separation after storage). Enzymes were inactivated with increasing thermal load. Regarding taste related compounds, there was no clear effect of processing and storage on acidity and sugar profiles. The untargeted GC–MS approach showed that increasing the processing intensity resulted in an increase of the formation of furans and sulfides. Storage clearly affected the formation of volatiles that could be, depending on the thermal treatment, attributed to lipid and/or carotenoid oxidation, continuation of Maillard reactions, and enzyme catalyzed reactions.
Industrial relevance

Compared to other Brassicaceae vegetables such as as broccoli, cauliflower and different types of cabbages, kale so far has received little attention from an industrial processing point of view. However, kale has been reported to contain high nutritional value due to its important content of minerals, bioactive compounds and fibre. With the growing health awareness of consumers and increasingly busy lifestyles, the demand for more convenient fruit and vegetable products with high nutritional content has increased. Therefore, research to obtain more insight on the effect of processing and storage on kale purée is important.