By Maja Berden Zrimec
Reducing food waste is a hot topic in the sustainability debate. But did you know that food waste is actually an important source of valuable compounds that can be used in various industries? Unfortunately, we are still not taking full advantage of the potential of agro-food waste. Most of it is still ending up in composting or biogas plants for anaerobic digestion. While this does produce biofuels and biofertilizers with high market potential and are economically sound (1), there is still much more we could get from it.
Many interesting substances that can be obtained from different types of food waste by various technologies (1-3). For example, fruit and vegetable waste can be processed to obtain sugars, cellulose, hemicellulose, lignin, pectin, and proteins. Waste cooking oil can be used to produce free fatty acids, glycerol, and biodiesel. Starch-rich food waste, such as bread, rice, and pasta, can yield glucose, ethanol, and biohydrogen. Dairy waste, like cheese whey and buttermilk, can produce lactose, lactic acid, and ethanol. Meat and fish waste can give us proteins, lipids, and amino acids. Shellfish waste, such as crab, shrimp, and lobster shells, can be used to obtain chitin and chitosan. And food processing waste, like distillery and brewery waste, and sugar industry waste, can yield ethanol, biogas, and biohydrogen.
What is more, many additional substances can be produced from waste. Agro-food waste and side-streams are also a rich source of bioactive compounds. Researchers have extracted a wide variety of compounds, including vitamins, minerals, carotenoids, glucosinolates, proteins, polysaccharides, dietary fibers, and flavoring compounds from shells, seed fractions, and molasses, among other sources (1-3). Antioxidant compounds, like hydroxycinnamic and hydroxybenzoic acids, anthocyanins, proanthocyanidins, flavanols, flavones, flavanones, isoflavones, stilbenes, and lignans, have attracted even more interest due to the high levels found in food waste (1-3).
To extract these valuable bioactive compounds, the most commonly used technique is liquid-liquid extraction or solvent extraction. Many interesting are produced also by different types of fermentation. Agro-food waste and by-products are typically composed of polysaccharides (like cellulose, lignocellulose, hemicelluloses, and lignin), sugars (such as glucose, xylose, galactose, mannose, and arabinose), and phenolic compounds (like organic acids). The extraction process is critical and can involve different solvents, acids, alkalis, steam diffusion, and hydrodistillation, depending on the type of extracted compound (3). However, conventional extraction processes can be expensive due to their high energy consumption. To address this issue, emerging technologies like ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), pressurized liquid extraction (PLE), supercritical fluid extraction (SFE), pulsed electric field (PEF), moderate electric field (MEF), high voltage electrical discharge (HVED), and membrane-based techniques (like microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF)) have been shown to be more efficient for recovering bioactive compounds from various sources, including agro-food waste and by-products (3).
The extracted bioactive compounds are interesting for because of potential health benefits. For example, antioxidants are known for their ability to protect against cell damage and inflammation, which are associated with various diseases. In addition, bioactive compounds have applications in various industries, like chitosan, that can be extracted from shellfish waste. It has antimicrobial properties and can be used in food packaging to extend shelf life. Polysaccharides like cellulose and hemicellulose can be used to produce bioplastics, which are biodegradable and can replace conventional plastics. And enzymes extracted from food waste can be used in various industrial processes, like the production of biofuels and food additives. Extracting these compounds from food waste could provide a sustainable and affordable way for their production. As technologies for extracting these compounds continue to develop, we can look forward to even more innovative and sustainable uses for food waste.
1. Usmani, Z., Sharma, M., Karpichev, Y., Pandey, A., Kuhad, R.C., Bhat, R., Punia, R., Aghbashlo, M., Tabatabaei, M., Kumar Gupta, V. (2020): Advancement in valorization technologies to improve utilization of bio-based waste in bioeconomy context. Renewable and Sustainable Energy Reviews 131:109965. DOI: 10.1016/j.rser.2020.109965
2. Kumar, K., Yadav, A.N., Kumar, V., Vyas, P., Singh Dhaliwal, H. (2017): Food waste: a potential bioresource for extraction of nutraceuticals and bioactive compounds. Bioresour. Bioprocess. 4:18. DOI: 10.1186/s40643-017-0148-63. Castro-Muñoz, R., Díaz-Montes, E., Gontarek-Castro, E., Boczkaj, G., Galanakis, C.M. (2022): A comprehensive review on current and emerging technologies toward the valorization of bio-based wastes and by products from foods. Compr Rev Food Sci Food Saf. 21:46–105. DOI: 10.1111/1541-4337.12894