Recovery, chemical, and bioactivity characterisation of polyphenols from fruits and by-products in food applications: a circular solution toward resilient food systems

The food industry is increasingly concerned with sustainable food production and the effective use of fruit and waste products. Food processors are known to generate substantial quantities of biological by-products and waste materials, which may have alternative applications. In 2021, the worldwide production of apples was around 93.14 million metric tons. China is one of the largest apple producers in the world, followed by Turkey, the United States, Poland, Turkey, India, and Iran (FAOSTAT, 2021). About half of all apples grown in China are estimated to be processed for apple juice concentrate production (Cheng et al., 2022). According to recent data, 25-30% of the fresh apples used for juice production result in fruit by-products, including apple pomace (AP), considered post-industrial organic waste (Ampese et al., 2023; Gołębiewska et al., 2022). According to data from 2019 and 2020, around 70%– 75% of apples were processed, with AP accounting for approximately 25% of the total weight (Lyu et al., 2020; Manzoor et al., 2022). AP is mainly composed of the skin and flesh of the apple (about 95%), as well as seeds (2-4%) and stems (1%) (Lyu et al., 2020; Pollini et al., 2022). In Ireland, apple production is estimated at around 45,000 tonnes, generating approximately 11,250 tonnes of AP. Although AP contains significant amounts of fiber (14.5- 42.5% on a dry basis) and phenolic compounds (2% on a dry basis), it is still considered a waste product by the industry, resulting in disposal costs and environmental concerns (Muzaffar et al., 2022). Currently, several million tonnes of AP, the leftover material after apple juice and cider production through pressing, is being generated (Barreira et al., 2019). There are several uses for AP in food science and biotechnology applications, such as for the production of enzymes (Satapathy et al., 2021; Wilkowska et al., 2019), animal feed (Z. Yang et al., 2022), pectins (Luo et al., 2019), citric acid (Dhillon, Brar, et al., 2013), and ethanol (Borujeni et al., 2022). Additionally, it can serve as a valuable source of dietary fibres and polyphenols, naturally occurring bioactive compounds in plants (Antonic et al., 2020).