The United Nations (UN) has set as one of its sustainable development goals to reduce food waste by half by 2030 (1). Food waste is the term used to refer to both food loss that occurs earlier in the food chain and waste of food that is intended for human consumption. A closer look at this key issue of sustainability reveals that in rich societies, most of the food waste is produced by consumers (2, 3). Educating customers about sustainable food practices is therefore essential to reduce food waste in the future. Records show that consumers can reduce their emissions by 12 % if they avoid all food waste at home (4). Waste can be classified based on the industry that produces it into agricultural, farming, brewing, dairy, fattening, etc. (5). An environmentally friendly way to tackle food waste and shortages in the food sector is upcycling. Reducing debris and its negative effect on the environment is achieved by upgrading and recycling waste. Food security, both domestically and globally, is improved by repurposing nutrients from food waste (6).

The increasing need for renewable technologies in the food industry is supported by policies like United States Department of Agriculture (USDA) and United States Environmental Protection Agency (USEPA), aiming to reduce and recover food waste (7). In various food industries, one of the main problems is recycling of food waste streams. Worldwide, South Korea and Japan have been the leading countries in upcycling food industry waste (6). Without a doubt, one of the biggest industries that produces enough waste to negatively affect the environment is the food security sector (6). According to Mirabella et al. (8), 42 % of food waste in developed countries is caused by households, 39 % by food processing industries, 14 % by the food service industry (restaurants and catering) and the remaining 5 % by retail and distribution. These wastes are recognised as an important source of nutrients, particularly polyphenols and bioactive chemicals that have a major impact on human health, according to many studies conducted in recent years. However, since they are thrown out with the trash, it is necessary to retrieve them (9).

The Food and Agricultural Organization (FAO) of the United Nations estimated that food waste accounts for approx. 30 % of the world's food output (10). The Food Index Report states that over 930 million tonnes of sold food were wasted in 2019 (11). Melikoglu et al. (12) stated that “the amount of food that is wasted globally is enough to feed the whole world’s hungry population”. Furthermore, food waste is predicted to cost $310 billion in underdeveloped countries and $680 billion in industrialized countries, according to FAO (13). Creative solutions must be developed to transform the issue of food waste into an economic opportunity (14).

More initiatives are being taken to mimic and replace animal supplies including meat, milk and eggs with plant-based food ingredients and products. This trend is linked to consumer preferences for wholesome, environmentally friendly food and the exponential growth of the vegetarian and vegan sector (26). Customers are willing to change their habits and address the issue of climate change by reducing their carbon footprint. This includes choosing plant-based foods over those derived from animals (27, 28). Pulses contain 20–30 % protein high in lysine, such as lentils, chickpeas, faba beans, dried beans and dried peas. Consequently, pulses, edible dry seeds derived from legumes, can be quite helpful in replacing animal protein in the diet (26).

Recently, plant proteins have been increasingly favoured as potential substitutes for animal proteins (29). The food business and contemporary consumers both have a greater understanding of sustainability and health, which has sparked this interest. In the last 15 years, the production of legumes and pulses has increased significantly. India produced 13.75 million tonnes of chickpeas during 2021–2022 (fourth estimate) with a productivity of 12 600 kg/ha on 10.91 million ha of land (30). India's chickpea production accounts for almost half of the pulse production with a global market growing at a 7.0 % compound annual growth rate from USD 13.93 billion in 2022 to USD 14.9 billion in 2023. The market is forecast to reach USD 19.19 billion by 2027. India accounted for 73.46 % of chickpea production in 2020.

Coffee is one of the most popular foods and the second most traded commodity after petrol (39). Coffee grounds and coffee silver husks are the most volatile residues in the world, containing high concentrations of tannin and caffeine. They can pose environmental hazards if disposed improperly. After the beans are separated, dried, ground and dehulled, coffee silverskin is obtained as a by-product (40, 41).

The coffee processing industry should explore its by-products for environmental sustainability, as food waste can generate revenue, increase food security and combat hunger. Bioactive compounds like phenolic compounds, organic acids, proteins and polysaccharides can be extracted and reused as functional food ingredients. Novel extraction methods can preserve the quality of the active ingredients (42, 43). Over 50 % of coffee fruit is discarded during processing, making it a potential source for incorporating coffee bioactive compounds into new functional foods (39).

Coffee roasting produces a by-product called coffee silverskin, which contains insoluble dietary fibre and high levels of antioxidant activity (44). Coffee silverskin consists of cellulose and hemicellulose, as well as significant amounts of glucose, monosaccharides, proteins and extractives, making it a valuable material for nutraceutical and cosmetic applications. On a dry mass basis, it contains 7.3 % moisture and is particularly rich in proteins, which make up 18.7 % of its composition. The fat content is between 2.2 and 3.8 %, while the ash content, which indicates its mineral content, is between 5 and 7 %. Carbohydrates form the largest content at 62.1 %, and it is also abundant in dietary fibre, particularly cellulose and hemicellulose, which together account for 16 to 23 % of the total content. This nutrient-rich profile emphasises the potential of coffee silver skin as a functional ingredient in both food and animal feed products (39).

The biological detoxification of coffee silverskin by solid-state fermentation leads to the production of phenolic compounds by fungal strains like Aspergillus, Mucor, Penicillium and Neurospora (45). The food industry is looking for ways to reduce sugar, fat and salt content in food while meeting consumer demands. Phytochemicals of coffee silverskin could be a functional ingredient to address issues like colour change and nutrient loss during food processing, potentially offering useful food applications (46). The researchers successfully developed high-quality bakery products like bread by adding coffee silverskin in combination with hydrogen peroxide to extend the shelf life (47). The scientists also describe a positive correlation between coffee silverskin and the water hydration, rheological properties, nutritional value and sensory properties of cookies (48). Minor phenolic compounds in coffee silverskin have antioxidant potential that may be a result of the Maillard reaction (44).

The results obtained by Ateş and Elmacı (49) showed that coffee silverskin treated with water can be used perfectly to replace 30 % of fat while maintaining physicochemical and sensory properties of the cake. However, the high fibre content of coffee silverskin makes it a low-calorie cake, which can extend the health benefits of the cake. The use of coffee silverskin as a substitute for wheat flour in the composition of cakes with better mechanical and colour properties has been reported (49). Coffee silverskin can be used in the development of functional beverages by promising fat reduction and mass control (50). Researchers reported that coffee silverskin is one of the functional ingredients for snacks, breakfast cereals, bread and biscuits and prepared a report proposing coffee by-products as a new food in the European Union (51, 52). Coffee silver skin has been used in food formulations as a substitute and replacement in the bakery and beverage industry, which has been studied by various researchers (47, 49, 50).

Instant coffee production involves treating coffee powder with steam or hot water, which produces a by-product called spent coffee grounds (SCG). Spent coffee grounds are produced in quantities up to 6 000 000 tonnes per year, usually as a result of instant coffee production (40). Despite their industrial importance, SCG have not been widely used. Solid-state fermentation (SSF) can minimise the amount of tannins and alkaloids in spent coffee grounds and thus reduce soil pollution. Despite the complexity and low economic feasibility of the extraction process, as well as the low triglyceride content of coffee oil, the lipids in spent coffee grounds have significant emulsifying properties (39).

Spent coffee grounds have a diverse and nutrient-rich composition that offers potential for various value-added applications. They contain 14.7 % minerals, which contribute to their inorganic nutrient content, and 17.4 % protein, which is a relatively high protein profile for a food by-product. The ash content is modest at 1.3 %, indicating a limited amount of residual inorganic matter. A notable feature of spent coffee grounds is their high polyphenol content of 17.8 %, which has an antioxidant effect and makes them attractive for use in functional foods, cosmetics or nutraceuticals. Additionally, polysaccharides make up the majority of the composition at 51.5 %, indicating a significant amount of complex carbohydrates that could be used in dietary fibre formulations or as a substrate in biotechnological processes (53).

Chlorogenic acid reduces body mass and waist circumference, promotes insulin secretion and controls blood pressure. It also reduces the accumulation of liver fat and increases lipase reactivity. Young people with degenerative diseases benefit from improved cognitive function by coffee. In mice with Alzheimer's disease, trigonelline improves brain function, memory and neuron activity. Melanoidins can trigger gene-protective pathways in several cell lines and have antioxidant and antibacterial properties. In addition, they support the fermentation of gut bacteria, the activation of antioxidant pathways and the population management of gut bacteria (54).

Spent coffee grounds have diverse applications because of their nutritional and functional properties. In the food industry, they improve dietary fibre content in bakery products, cookies and sponge cakes, and are used in fermented and distilled beverages. Coffee oil from spent coffee grounds is used as a butter substitute and flavouring in syrups. Spent coffee grounds also provide bioactive peptides and beneficial compounds like caffeine and chlorogenic acid. In cosmetics, they are valued for their anti-aging, sun protection and hydration effects. In addition to food and cosmetics, spent coffee grounds are also used in construction, bioenergy and as a material for biodegradable containers. However, variability, allergies, sanitation and high extraction costs continue to pose challenges (55).

Propolis, a resinous substance produced by bees in their hives, has a potential use in food and health industries (56). The propolis market is predicted to expand at a compound annual growth rate (CAGR) of 4.90 % during the forecast period, from a value of USD 622.64 million in 2023.

Propolis, a plant-based food, is a complex substance with various biomolecules, including phenols, esters, terpenes, sugars and minerals. It contains varying amounts of components, including 45–55 % resins, 8–35 % wax, 5–10 % aromatic and essential oils, 5 % fatty acids, 5 % pollen and 5 % other organic components. The colour of propolis varies from greenish-yellow to brown, depending on maturity and origin. The characterisation of individual constituents like cinnamic acid and gallic acid can provide information about the health benefits of propolis (57).

Propolis extract, which is obtained by extraction from crude propolis (Fig. 3), is widely used in food technology because of its significant antibacterial and antioxidant properties (58). When propolis extract is mixed with foods including fish, meat, milk, honey, fruit juice and beer, it reduces the total bacterial count, including Staphylococcus and Listeria, while protecting antioxidant food components. Soaking or washing fruits, vegetables and seafood in propolis extract reduces yeast, mould and bacterial infection, slows down ripening, minimises water loss, and preserves firmness, improving overall food quality. Furthermore, the addition of propolis extract to meat, fruit and vegetable packaging films significantly reduces microbial counts, including mesophilic and psychrotrophic bacteria and pathogens such as Enterobacteriaceae, thereby improving food preservation and safety in a wide range of food products (59, 60). Coating and immersion techniques have been found to reduce the number of saprophytic and other microbiota in food (61).

Propolis, a healthy food, is categorised as a food supplement in different countries, including Brazil, the USA and the EU. However, because of differences in formulation and production site, the European Food Safety Authority (EFSA) has not yet released health statements for propolis on food labels, despite its potential health benefits (62).

The sediment produced during winemaking, i.e. fermentation, filtration, centrifugation and other additional processing during storage, is called wine lees, which constitutes 1.3–1.5 kg per litre of wine production (63). The components of wine lees, i.e. yeast, tartaric acid, phenolic compounds and other inorganic substances and enzymes, are of great importance in the food industry (64).

Wine lees, the sediment from wine fermentation, are nutritionally rich and promising for use in food, feed, cosmetics and agriculture. They contain 10.5–10.6 % ash, 21.2–21.9 % dietary fibre, 5.0–5.9 % lipids and 14.5–15.7 % proteins. Their polyphenol content (1.9–16.3 g/kg) offers antioxidant and antimicrobial benefits. The mineral content is significant, with high mass fractions of copper (1187 mg/kg), iron (84–1756 mg/kg) and potassium (17.6–158.1 g/kg) as well as zinc, phosphorus, magnesium, manganese and calcium. This composition shows that wine lees are a valuable resource for sustainable and functional applications (63). The phenolic compounds extracted from wine lees were studied (65). In this procedure, the preliminary treatment of wine less for conversion to powder for further use in food products and other studies was presented.

Avocado, a nutrient-rich fruit, is a popular choice because of its nutritional value (74). Mexico is the leader in the cultivation and export of avocado, with a production of 2.4 million tonnes in 2022. The fruit consists of pulp, seed and peel, which contain essential nutrients such as fibre, protein, healthy fats, vitamins C and E, phenolic compounds, carotenoids, chlorophyll and minerals (75). However, the increasing global demand for avocado production and processing leads to increased waste generation, causing environmental problems like greenhouse gas emissions, soil and water pollution and the attraction of pests. Urgent action is needed to address these environmental challenges (76, 77).

Green valorisation can be used to turn avocado waste, which is rich in nutrients and compounds, into valuable products for the culinary, cosmetics or pharmaceutical industries (78). This strategy minimises the environmental impact and promotes resource efficiency by using the concepts of the circular economy. Composting, anaerobic digestion and the production of value-added products are sustainable methods of managing avocado waste that reduce adverse environmental effects and generate revenue (79-81).

Sustainable utilisation of avocado waste can improve farmers' lives and increase agricultural output. Promoting resource efficiency and reducing waste output through this method is in line with the sustainable development goals (SDGs). Focusing on the prospects and difficulties of setting up a biorefinery, the researchers explore the possibility of transforming avocado by-products into useful goods through biotechnological and environmentally friendly processes. The aim is to support sustainable practices in the avocado business and promote the avocado waste biorefinery as a sustainable way to treat processing by-products (82-86).

Approaches to valorisation of avocado waste: in recent years, a number of methods have been developed to valorise avocado waste. One strategy uses methods like microwave-assisted extraction and supercritical fluid extraction to extract bioactive chemicals and antioxidants from the waste material, including polyphenols, flavonoids and carotenoids. The anti-inflammatory and antioxidant properties of these chemicals make them ideal candidates for use in the food and cosmetics industries. Another method is to use avocado waste, which has a high protein and fibre content, to produce animal feed for pigs, poultry and ruminants, as shown in Fig. 5 (75) and investigated in numerous studies (81, 82, 87-90). Persenone A is the most abundant acetogenin in avocado, accounting for 46 % in peel. These chemicals have been reported to have antioxidant effects by decreasing the formation of nitric oxide and superoxide but further studies are needed (91).

Avocado seeds can be used to develop ready-to-eat extruded snacks, with freeze-drying reducing potentially harmful compounds like persin and amygdalin to non-toxic levels. Cereal snacks enriched with 6–18 % avocado seed powder had negligible amounts of these compounds, while they had increased dietary fibre and polyphenol content, with 6 % leading to a fivefold increase in polyphenols. Snacks containing 20 % avocado seed flour and maize also had notable antioxidant activity. Avocado peel and seed extracts have proven effective, especially the ethanolic peel extract, which showed greater antimicrobial activity than ascorbic acid in mayonnaise. Additionally, avocado seeds are rich in starch with functional properties, a gelatinization temperature of 56–74 °C, a solubility of 19–20 % and a swelling power of 28–30 g/g, which emphasise their potential as an ingredient in functional food formulations (75).

The sustainable development goals (SDGs) can be significantly supported by the valorisation of avocado waste. By producing bio-products like food ingredients, biodegradable plastics, biogas and biofuels, waste production is reduced and resource efficiency is increased. Additionally, avocado waste can be used as a fuel for the production of bioenergy, supporting the use of renewable energy sources and reducing greenhouse gas emissions. Because jobs are created, this also strengthens employment and the local economy. Achieving the SDGs requires collaboration between government agencies, businesses and academic institutions (92-94).

Green valorization of avocado waste comes with a number of problems, including scale-up, regulatory framework, logistics and environmental impact (95). Handling Perishable waste must be handled carefully to prevent spoilage and to preserve its quality. Scaling up the process can be challenging since the composition, quality and quantity of waste varies greatly. Converting avocado waste into value-added products can consume energy and water resources, creating waste streams. It is essential to take sustainable measures to reduce these effects. There are still many unanswered questions regarding the authorisation procedures for food, cosmetics and pharmaceuticals within the legal framework for avocado waste valorisation (75).

The quantitative microbiological risk assessment (QMRA) approach has been refined with two new definitions: the appropriate level of protection (ALOP), which defines the level of health protection for foodborne pathogens, and the food safety objective (FSO), which defines the maximum hazard level in food at consumption to meet the ALOP. These definitions are complex and intended for use within the QMRA framework for global microbiological risk management. Policy makers and researchers recognise the need to engage society and promote consumer acceptance, particularly for novel foods produced from by-products. Addressing consumer concerns and preferences is crucial but requires further analyses and innovative approaches. The REPRO (Reducing Food Processing Waste project) consortium, funded by the European Commission, is transforming vegetable waste and cereal by-products into valuable food, feed and related ingredients (96). Using advanced bioprocesses and extraction technologies, the aim is to create safe, marketable products while ensuring compliance with regulations and consumer acceptance through risk assessments. This initiative targets the substantial waste from the EU vegetable and brewing industries and emphasises sustainability and innovation. Synthetic biology combined with advanced tools like tunable solvents (e.g. supercritical fluids) and microfluidic devices will drive the development of novel bioproducts such as biomaterials, bioenergy and biopharmaceuticals (Table 1; (97-108)). By integrating genetics into these technologies, biological engineers can create more functional biosystems for in vitro and in vivo applications, such as targeted drug delivery. With the growing interest in biofuels and environmental clean-up, supercritical extraction and synthesis techniques are expected to play a key role, including in biodiesel production and heavy metal removal. The future of these technologies depends on creativity at the intersection of science and engineering (97).

Biotechnology plays a central role in the production of single-cell proteins (SCP), single-cell oils (SCO) and single-cell polysaccharides (SCP) as it can optimise microbial systems and increase production efficiency. Biotechnology is indispensable for the production of SCP, SCO and SCP and contributes to sustainable solutions for global challenges. It increases efficiency, enables resource utilisation and reduces environmental impact, making these bioproducts essential for future food, health and industrial needs (109).

Microorganisms, including bacteria, fungi and yeasts, are being studied for their ability to produce single-cell oils (SCO) that could be used as a sustainable feedstock for biodiesel synthesis. These oleaginous microorganisms, which include yeasts such as Lipomyces and Yarrowia, can store 20–25 % of their biomass as lipids, which are often high in polyunsaturated fatty acids (PUFA). Lipid build-up is regulated by parameters such as the C/N ratio and nutrient depletion, and cultivation methods such as batch, fed-batch and continuous culture are used to increase production (110). SCO, which are used in animal feed, aqua feed and biodiesel, provide benefits such as regional independence and consistency in quality. However, high production costs, limited production capacity and competition from plant oils are barriers to commercialisation. Enzymatic techniques and waste substrates such as glycerol are being investigated to increase production efficiency, while research is focussing on the production of strains with high lipid accumulation and modified microbes (111). Biodiesel, a renewable and ecologically beneficial fuel, is typically produced from plant and animal oils, but energy demand and resource scarcity limit this strategy, making microbial oils a potential substitute. Extraction technologies such as solvent extraction make production easier, but customer acceptability and cost remain an issue. The "biorefinery concept", which uses low-cost substrates such as sugar cane and industrial fats, promises to reduce prices and increase SCO production for biodiesel, opening the door for a bio-based economy (112).

The current world population of 8.2 billion (2024) is expected to grow to 9.5 billion by 2050, leading to an increasing demand for food, especially meat. Currently, 370 million tonnes of beef are produced worldwide each year, but this figure will have to increase to 470 million tonnes by 2050. Traditional meat production is resource intensive, as almost 6 kg of plant protein is needed to produce 1 kg of meat protein. To solve this problem, single-cell protein (SCP), also known as microbial protein, has proven to be a promising solution. SCP is obtained from microorganisms such as algae, yeasts, fungi or bacteria and provides a protein-rich biomass. SCP was first developed in the 1960s as the "protein-from-oil process" and became widely recognised due to its promise to minimise dependence on traditional agricultural proteins (113). SCP has several advantages. It has fast production cycles, with microorganisms like bacteria and algae producing biomass within hours. It is environmentally friendly, requires less water and land, and has a smaller climatic impact than traditional agriculture. Furthermore, SCP can be genetically manipulated to improve amino acid content and utilise biodegradable industrial waste, reducing costs and environmental impact. However, there are also obstacles. The production of SCP is costly and requires strict sterilisation procedures. The high concentration of RNA can lead to gout and kidney stones as well as allergic reactions, poor digestion and taste or colouring problems. The production and quality of SCP depend on the microbial strains, environmental conditions (temperature, pH and light) and nutrient availability. To improve safety, the downstream manufacturing process includes isolation of the microbial cells by filtration or sedimentation, dissolution of the cell walls by mechanical, enzymatic or chemical processes and removal of nucleic acids (114). The final products, such as SCP concentrates, isolates and hydrolysates, are sterilised and dried. As the demand for sustainable protein sources increases, SCP present a viable option for meeting global nutritional demands, despite production and acceptability issues. Technological developments and further research can help solve these challenges, making SCP a feasible alternative in the future. Recombinant strains of nonconventional GRAS (Generally Regarded as Safe) yeasts and fungi should also be developed as part of the research. These strategies have a significant potential to improve the quality of meals, which is promising. It is necessary to thoroughly investigate the use of by-products from the food industry for the production of SCP (115).

Single-cell polysaccharides (SCP) are microbial polymers produced by bacteria, fungi and algae and have a wide range of commercial and biological uses because of their diverse properties, which include thickening, gelling and stabilisation. Bacterial polysaccharides such as xanthan gum and curdlan, fungal polysaccharides such as pullulan and chitosan, and algal polysaccharides all have antioxidant and immunomodulatory properties (116). SCPs are highly sustainable since they can be produced from renewable substrates such as agricultural and industrial waste and are biodegradable, making them environmentally friendly alternatives to synthetic polymers. However, obstacles to large-scale commercialisation include high production costs, the need for optimised bioprocesses and strict regulatory requirements (117). Recent research has focused on the use of low-cost substrates and genetic engineering to increase yield and functionality, and establish SCPs as important contributors to a sustainable bioeconomy in the food, health and industrial sectors. With continued innovation, SCPs are expected to play an important role in long-term development (118).

Most of the by-products are reportedly derived from the food industry, which are rich in bioactive compounds and can be used in various industrial applications to promote health and nutritional benefits. A novel step in sustainable application is the use of these inexpensive by-products from the agri-food industry to create value-added products. Different patents are available in the field of food and biotechnology for the utilisation of by-products in the agro-food industry.

The waste and by-products generated during the production of coffee, tea, fruit juices and alcoholic beverages have a vast potential for utilisation by industry. However, the large amounts of waste and by-products are underutilised. They can be made more valuable by conducting extensive research and development to identify and derive key bioactive molecules that will help in the creation of new value-added products with more affordable prices and health-promoting properties. Novel products that have the potential to reduce environmental pollution with excess by-products are needed.

Research is needed to standardise the conditions for aquafaba extraction and demonstrate its characteristics for consistent quality and functional properties. This is crucial for the innovation in chickpea waste recovery. Coffee silver skin has health-promoting properties for humans and contributes to sustainable health. Further studies are needed on spent coffee grounds as a food ingredient and the metabolic activity of their microbiota. Propolis needs to be standardised for therapeutic and medicinal purposes in dentistry, oral health and medicine. Further research is needed to recommend propolis as a dietary alternative for the treatment and prevention of chronic diseases. The influence of the components of wine lees on wine ageing needs further clarification. A study on the removal of tannins in avocado seed flour is recommended to improve flour quality.