Sustainable Exploitation of Apple By-Products: A Retrospective Analysis of Pilot-Scale Extraction Tests Using Hydrodynamic Cavitation

Apple by-products (APs) consist of whole defective fruits discarded from the market and pomace resulting from juice squeezing and puree production, which are currently underutilized or disposed of due to the lack of effective and scalable extraction methods. Bioactive compounds in APs, especially phlorizin, which is practically exclusive to the apple tree, are endowed with preventive and therapeutic potential concerning chronic diseases such as cardiovascular diseases, metabolic diseases, and specific types of cancer. This study investigated the exploitation of APs using hydrodynamic cavitation (HC) for the extraction step and water as the only solvent. High-temperature extraction (>80 °C) was needed to inactivate the polyphenol oxidase; a strict range of the cavitation number (around 0.07) was identified for extraction optimization; less than 20 min were sufficient for the extraction of macro- and micro-nutrients up to nearly their potential level, irrespective of the concentration of fresh biomass up to 50% of the water mass. The energy required to produce 30 to 100 g of dry extract containing 100 mg of phlorizin was predicted at around or less than 1 kWh, with HC contributing for less than 2.5% to the overall energy balance due to the efficient extraction process.