Examples of bioactive compounds from plant- and animal-derived by-products and the applied extraction techniques.
Food represents as one of the most basic human needs, providing our physical integrity. The entire planet is facing an alarming issue, regarding the amount of edible food and by-products, which are wasted in an increasingly manner. Moreover, food manufacturing requires resources such as soil and water and involves various processes, which generate huge amounts of food waste. As the production of food is resource-intensive, food losses and wastes are strongly correlated with a broad range of environmental problems, such as water and air pollution, soil erosion, and greenhouse gas emissions; all of these undesirable effects occur in all stages of production, storage, and transportation as well as in the case of adopting a deficient management system .
The generation of food waste is inevitable, especially during the pre-consumption stage. It is estimated that up to 42% of food waste is generated from household activities, 39% occur from the food manufacturing industry, and 14% occur from the food service sector (catering and restaurants), while 5% is lost during storage and distribution. This problem is intensified by the global population growth leading consequently to an increasing demand for natural resources like food and energy [2, 3].
Nowadays, the biggest challenge of the scientific world is to provide viable alternative models that combine food production with an efficient valorization strategy of waste and by-product, minimization of energy consumption, and environmental protection. In this context, the exploitation of food waste or by-products for the recovery of valuable functional compounds can be considered as being one of the most feasible approaches .
In order to implement a circular economy in any industrial sector, two main strategies are needed: reducing waste levels and finding the most sustainable solution to manage the remaining waste. In particular, the waste management of new strategies focus on the following actions: waste prevention, reuse, recycling, energy recovery, and, lastly, disposal .
Until a few decades ago, food waste was considered neither a cost nor a benefit being usually discarded to landfills, sent for composting, or used as animal feed. The negative perception on these by-products and implicitly the application of a deficient management lead to environmental degradation and especially to significant loss of valuable material that could otherwise be exploited as food, fuels, and a great variety of additives .
At present, the attitude has changed radically, the researches being intensely oriented toward the identification and extraction of valuable compounds from residues and their reintegration in the food industry but also in other fields such as cosmetics, pharmaceuticals, or agriculture (Figure 1).
Using the recovered bioactive molecules as functional ingredients represents a sustainable alternative of food waste exploitation as an inexpensive source of valuable compounds while developing innovative food and nonfood products with health-promoting benefits and at the same time contributing to an efficient waste reduction management.
2. Extraction technologies for bioactive compounds from food waste
Most of the wastes generated by the agri-food industries are difficult to store, transport, and process because of the biological instability, pathogenic potential, high levels of nutrients or enzyme activity, high water content, and the potential for self-oxidation.
The new aspects concerning the use of agri-food wastes as by-products for further exploitation in the production of various functional products must be environmentally friendly and sustainable from the economic point of view [7, 8, 9]. Therefore, it is imperative to identify the most feasible and optimized stabilization methods in order to ensure a flow of biomass with a constant composition and reduced storage and transport costs.
For this purpose, technological innovation has favored the development of many effective exploitation methods, with cogeneration of electricity and thermal biogas, also called green energy. In addition, the implementation of a biorefinery concept offers remarkable opportunities to valorize biomass by converting it to a wide range of chemicals with many applications in food, cosmetic, and pharmaceutical industries [10, 11].
The innovative approach of converting food waste in new generation of useful products involves the application of unconventional methods and advanced techniques in order to model the most appropriate and sustainable recovery system (Figure 2).
Nevertheless, the extraction protocols cannot be used indiscriminately, and their choice depends on the type of bioactive compounds and matrix structure, the processing scale (pilot or industrial level), the balance between processing costs and economic income of the recovered component, and their new assigned destinations .
In the last years, the researches focused on the development and optimization of the methods for the recovery and purifications of the functional compounds; some of them are based on new emerging techniques, but some are effective by applying and modeling the existing conventional method. In both situations, the extraction of the high-value components must be environmentally friendly and economically feasible to perform.
The applied parameters have a major impact on the release of the bioactive compounds from the matrix but also on their structure and functionality. Therefore, selecting the most suitable extraction protocol is a decisive step for the recovery of the valuable component [6, 9, 12].
Several examples of bioactive compounds recovered from food processing by-products and the selected extraction methods are presented in Table 1.
|Recovered compounds||Waste source||Extraction method||Ref.|
|Polysaccharide/dietary fibers||Fruits pomace, sugar beet, sunflower heads||Solid-liquid extraction|||
|Citrus peel and apple pomace||Subcritical water extraction|||
|Cereal by-products||Enzymatic treatment and sequential extraction|||
|Apple pomace||Hot-compressed water|||
|Olive mill wastewaters||Ultrafiltration and nanofiltration|||
|Rice bran||Microwave treatment and microbial fermentation|||
|Phenolic compounds||Apple pomace||Microwave-assisted extraction|||
|Electric field-assisted extraction|||
|Tomato pomace and skin||Enzymatic-assisted extraction/solvent extraction|||
|Potato peels||Microwave-assisted extraction|||
|Olive cake||Ultrasound-assisted extraction|||
|Avocado peel and seeds||Solvent extraction|||
|Wheat beans||Ultrasound-assisted extraction|||
|Tea by-products||Supercritical fluid extraction; microwave-assisted extraction/solvent extraction||[27, 28]|
|Bran and germs||Ultrasound-assisted extraction|||
|High-voltage electrical discharges and ultrafiltration|||
|Supercritical fluid extraction|||
|Solvent extraction/microwave-assisted extraction/ultrasound-assisted extraction|||
|Blueberry residue||Supercritical fluid extraction and pressurized liquids|||
|Flax seeds||Solid-liquid extraction|||
|Caffeine||Tea waste||Microwave-assisted extraction/solvent extraction|||
|Oils||Rice bran||Supercritical carbon dioxide extraction and compressed liquefied petroleum gas/solid-liquid extraction||[36, 37]|
|Essential oils||Citrus peel||Solvent extraction/hydrodistillation|||
|Steam explosion at high temperature and pressure|||
|Proteins||Brewers’ spent grain||Sequential extraction of proteins and arabinoxylans; enzymatic-assisted extraction||[15, 41]|
|Rice by-products||Enzymatic hydrolysis and membrane filtration technique|||
|Hazelnut meal||Solvent extraction (water, acetone)|||
|Rapeseed by-products||Ultrasound-assisted aqueous extraction|||
|Carotenoids||Tomato pomace and skin||Enzymatic-assisted extraction|||
|Supercritical fluid extraction/solvent extraction|||
|Supercritical fluid extraction|||
|Citrus peel||Ultrasound-assisted extraction|||
|Sea buckthorn seeds||Supercritical carbon dioxide fluid extraction|||
|Proteins and bioactive peptides||Whey wastewater||Membrane separation/ultrafiltration/microfiltration/nanofiltration/reverse osmoses|||
|Mild enzymatic hydrolysis|||
|Fish and chicken||Isoelectric solubilization and precipitation|||
|Sardine solid waste||Enzymatic hydrolysis and ultrafiltration|||
|Shellfish||Enzymatic hydrolysis and micro-, ultra-, and nanofiltration/ion exchange chromatography|||
|Sugars||Whey wastewater||Membrane separation and spray drying|||
3. Food preservation for minimizing food waste
Beside the possibilities mentioned before for the proper management of food waste and its valorization through the recovery of the bioactive compounds, we also need to consider the role of food preservation to reduce food waste. Following harvest, slaughter, or manufacture, all foods start to lose quality. The rate at which food quality is lost is dependent on food type, composition, the way it was processed, packed and storage conditions. On the other hand, the lost of quality and safety attributes of the foods may occur at any stage in the food chain generating food waste: raw material storage; product formulation; processing; packaging; storage in the factory; distribution to depots and storage; distribution to retail outlets; display in stores; sale to the consumer and further storage; preparation for consumption. Nonetheless, by applying conventional, highly advanced or hurdle preservation techniques (Figure 3), one can impede the chemical or microbiological deteriorations, thus preventing outbreaks of foodborne illness and at the same time limiting the food waste. As it is illustrated in Figure 3, in the food industry, beside the commonly used preservation techniques, a number of new ones are being developed to satisfy the current demands of economic preservation and consumer satisfaction in safety, nutritional and sensory aspects. Also, as the preservation of foods is often a multicomponent issue, the “hurdle” concept was introduced, highlighting the complex interaction between the factors that are significant for food safety and stability [56, 57, 58].
4. Concluding remarks and future trends
The idea of converting the agri-food waste into functional ingredients is an area of research with huge potential and opportunities. Many researches in biotechnology have already shown that agri-food by-products are no longer regarded as a waste but rather a valuable substrate for producing a new range of useful compounds. Based on this, it is an undeniable fact that, through compatible biotechnological processes, every food processing by-product possesses a relevant potential for a sustainable reuse.
The recent findings, presented in the chapters of this book, highlighted the potential reuse of food industry by-products and led to the idea that multidisciplinary approaches should be implemented in order to achieve the most effective exploitation protocol or to develop integrated biorefineries
This work was supported by three grants of Ministry of Research and Innovation, CNCS - UEFISCDI, project number PN-III-P1-1.1-PD-2016-0869, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2016-0973 and CNCS-UEFISCDI Projects for Financing the Excellence in CDI, Contract no. 37PFE/06.11.2018.