Technological Insights into Apple Purée: Assessing Colour Variation Across Production, Cooling Techniques and Shelf-Life

Enzymatic browning is a chemical process resulting in the conversion of phenolic compounds into dark-coloured polymers. In apple-based products, this reaction affects shelf life and organoleptic properties, thereby elevating the potential for product non-conformity. To block enzymatic activity, heat is typically employed. The present work aims to evaluate the variation in the colour of apple purée in relation to different stages of the production process. Three case studies have been analysed, assessing colour variation: I) during the production process, sampling in-line at 8 distinct stages; II) due to different cooling methods: no cooling, standard cooling system with room-temperature water, and instant cooling system with cold water; III) during 16-months conservation. Colour analysis was performed based on CIELAB methodology. In the second case study, focused on the cooling system, temperature and global heat transfer coefficient were also measured. First, results showed that the largest increase in browning occurs in the apple grinding step. Second, the instant cooling system is more efficient than no cooling and the standard cooling system in hindering the browning process. The analysis of the colour parameters demonstrated a visually significant difference among the apple purées subjected to the three cooling treatments. Finally, results highlighted that browning increases exponentially in the first months after packaging and then stabilises. The study supported the adoption of physical preventative methods in apple processing to reduce enzymatic browning of apple purée, favouring product safety and quality. It provides significant insights for enhancing apple purée productive plants and implementing suitable process control systems.