The rapid growth of the global population and changes in lifestyle have led to a significant increase in food waste from various industrial, agricultural, and household sources. Nearly one-third of the food produced annually is wasted, resulting in severe resource depletion. Food waste contains rich organic matter, which, if not managed properly, can pose a serious threat to the environment and human health, making the proper disposal of food waste an urgent global issue. However, various types of food waste, such as waste from fruit, vegetables, grains, and other food production and processing, contain important bioactive compounds, such as polyphenols, dietary fiber, proteins, lipids, vitamins, organic acids, and minerals, some of which are found in greater quantities in the discarded parts than in the parts accepted by the market. These bioactive compounds offer the potential to convert food waste into value-added products, and fields including nutritional foods, bioplastics, bioenergy, biosurfactants, biofertilizers, and single cell proteins have welcomed food waste as a novel source. This review reveals the latest insights into the various sources of food waste and the potential of utilizing bioactive compounds to convert it into value-added products, thus enhancing people’s confidence in better utilizing and managing food waste.

The green extraction of total phenolic compounds, flavonoids, anthocyanins, and tannins from grape marc was optimized using response surface methodology. The extracts were characterized and analyzed using LC-ESI-QTOF-MS/MS, and free radical scavenging capacity was evaluated. An efficient green extraction method is crucial for improving the recovery rates of these high-value phytochemicals and for sustainably reusing wine by-products. Our study optimized parameters for both conventional and ultrasound-assisted extraction methods, including solution pH, extraction temperature, liquid-to-solvent ratio, and ultrasonic amplitude. The optimized conditions for conventional extraction were identified as 60% ethanol with a pH of 2, a solvent-to-solid ratio of 50:1, extraction time of 16 h at a temperature of 49.2 °C. For ultrasound-assisted extraction, the optimized conditions were determined as 60% ethanol with a pH of 2, a solvent-to-solid ratio of 50:1, and an amplitude of 100% for 5.05 min at a temperature of 60 °C. We also demonstrated that lowering the temperature to 49.5 °C improves the energy efficiency of the extraction process with a minor reduction in recovery rates. Considering all factors, ultrasound-assisted extraction is more suitable for efficiently recovering bioactive compounds from grape marc.

Fish oils are widely consumed around the world to increase omega-3 fatty acid intake. Due to negative impacts on marine resources and ecosystems from an increasing demand for fish, alternative sustainable sources are under investigation. Squid viscera contains up to 10% oil by mass and is available as a byproduct from squid processing. Squid viscera oil is a source of EPA and DHA and contains the xanthophyll carotenoid astaxanthin, known for its significant anticancer, antioxidant, antidiabetic, and cardiovascular properties. In the raw form, squid viscera oil has a high free fatty acid (FFA) content, so conventional alkaline refining results in low yield and loss of astaxanthin. As a higher-yielding alternative, the current study optimized lipase-catalyzed glycerolysis of squid viscera oil to convert FFA into acylglycerol using a custom-built one-liter immobilized enzyme reactor. To monitor the reaction progress and assess its impact on the oil, we analyzed lipid classes, fatty acid composition and astaxanthin levels. Under optimized conditions, FFA was reduced from 40% to 2.7% in 10 h and 1.7% in 24 h, with no significant effect on EPA and DHA levels, and astaxanthin being retained. Squid viscera presents a safe and sustainable additional source of marine-derived EPA and DHA oil.

Grape marc (GM), a winemaking byproduct, has excellent antioxidant properties. Using GM as a lactic acid bacteria (LAB) fermentation medium could contribute to health benefits while managing waste volume. This study optimised a LAB fermentation system using GM and investigated different strains' impact on phenolics content and antioxidant capacity during fermentation and simulated gastrointestinal digestion. Our findings indicated that while raw GM could support growth, its intrinsic carbon limitation and high phenolic load necessitated yeast and glucose to 'prime' the metabolic pathways toward efficient homofermentative lactic acid production and biotransformation. During fermentation, flavonoids and tannins were significantly degraded, while the recovery and release of measurable anthocyanins was enhanced through enzymatic modification of the matrix. LC-ESI-QTOF-MS/MS analysis revealed changes in specific phenolics during degradation and transformation. In vitro digestion increased the total phenolic content and antioxidant activity of fermented GM compared to unfermented samples. These findings indicate that fermentation enhances the functionality of phenolics, making LAB-fermented GM a promising phenolic-rich functional ingredient for health-promoting applications in food, pharmaceuticals, and cosmetics, while also contributing to sustainable development. Furthermore, this biotransformation strategy demonstrates significant potential for extending to other phenolic-rich agro-industrial residues, such as olive mill wastewater, supporting broader circular economy goals.

Squid viscera, a waste product from squid processing, is a marine source of omega-3 fatty acid–rich oil suitable for nutritional supplement use. Squid visceral oil requires extraction and neutralisation of free fatty acids prior to consumption. Immobilised lipase (Lipozyme RMIM) is suitable for green neutralisation with high acylglyceride yields, high oxidative stability and retention of the antioxidant astaxanthin. Long-term utility of this method depends on lipase stability and reusability over multiple reaction cycles. To assess stability, this study monitored the performance of immobilised Lipozyme RMIM over 35 successive cycles of reuse in a custom-built one-litre reactor. This effectively reduces enzyme cost to 2.9% compared to single cycle use costs. We found a maximum of 97% free fatty acids in the crude oil were converted to acylglycerols under optimised reaction conditions in the first cycle, reducing to 86% after 35 reaction cycles. The partial loss of enzyme activity after each cycle appears to be a combination of enzyme unfolding and aggregation with a physical fracturing and breakdown of the resin, particularly after 30 cycles. Key points: • Immobilised Lipozyme RMIM neutralises squid oil effectively for 32 repeat cycles • Fatty acid composition of re-esterified squid oil is consistent over repeat cycles • Enzyme denaturation and carrier breakdown led to changes in lipase performance