Ultrasound Applications in Bioactive Peel Compounds: Enhancing Gut, Food, and Plant Health

The global food industry generates large amounts of fruit and vegetable residues, with peels accounting for up to 30-50% of total biomass in crops such as citrus, mango, and pomegranate. Once regarded as waste, peels are now recognized as rich sources of polyphenols, flavonoids, carotenoids, phenolic acids, and vitamins with antioxidant, antimicrobial, and anti-inflammatory properties. Efficient recovery of these compounds is essential for developing functional products that support human health, food preservation, and sustainable agriculture. Conventional extraction methods often involve high energy input, long processing times, and risk of degrading sensitive compounds. Ultrasound-assisted extraction (UAE) has emerged as a non-thermal, green technology that overcomes these limitations. By generating acoustic cavitation, ultrasound disrupts plant cell structures, enhances solvent penetration, and accelerates mass transfer, resulting in higher yields, reduced solvent use, and improved compound stability. These features position UAE as a key strategy for valorizing peel-derived bioactives. Applications of UAE-extracted peel compounds span three critical domains. In food systems, polyphenols such as quercetin, gallic acid, and naringin act as natural preservatives, antioxidants, and antimicrobials, extending shelf life and replacing synthetic additives. In gut health, microbiome studies demonstrate that peel-derived polyphenols promote beneficial bacteria such as Lactobacillus and Bifidobacterium while downregulating inflammatory mediators including TNF-α and IL-6, thereby improving metabolic regulation and immune resilience. In agriculture, extracts enriched in tannins, phenolic acids, and essential oils function as biostimulants by enhancing seed germination, root growth, and photosynthesis, while also suppressing pathogens such as Fusarium and Aspergillus. These multifunctional effects highlight the potential of peel extracts to improve crop productivity and reduce reliance on synthetic agrochemicals. This review examines recent advances in UAE optimization for peel-derived bioactives, evaluates their impacts on gut, food, and plant health, and identifies challenges in scaling, stability, and regulation. By integrating evidence from food science, microbiology, and plant physiology, the work underscores the pivotal role of ultrasound technologies in transforming peel waste into high-value products and advancing circular bioeconomy goals. Keywords: Fruit peel, valorization, polyphenols, gut microbiota, prebiotics, antioxidants, functional foods, biostimulants, circular bioeconomy.