Green extraction techniques are more and more relevant due to major sustainable goals set by the United Nations. Greener extraction processes are being designed through the use of unconventional extraction techniques and green solvents, resulting in less hazardous processes which, consequently, reduces environmental impacts. This is also in line with the main principles of green chemistry. Additionally, greener extraction techniques intend to solve different drawbacks that are often related to conventional extraction techniques such as the high environmental impact. Biorefineries are a major player in developing greener extraction processes. These facilities take full advantage of several biomass sources, such as food waste, microalgae, and lignocellulosic biomass, in order to create high-value products, energy, alternative fuels, and bioactive compounds. Herein, a state-of-the-art review is presented, focused on presenting the greenest and least hazardous extraction processes that have been reported on the main biomass sources of a biorefinery—food waste, microalgae, and lignocellulosic biomass. Bioactive compounds such as phenolic compounds, bioactive pigments, and fatty acids are important in several sectors, mainly, the health, pharmaceutical, and agro-food sectors. Moreover, the bioactive compounds obtained through the aforementioned biomass sources and the different extraction procedures used will be presented and the authors will attempt to discuss, compare, and provide information about the most effective extraction techniques for each compound. Therewith, this review article should serve as a guide for industries, academics, and biorefineries in the future development of optimized and greener extraction procedures. Such analysis is lacking and could be very helpful for future research biorefinery projects since it tackles all of the major biomass sources of a biorefinery in a review article. To the best of our knowledge, this brings a novelty to the scientific community.

Chlorella sp. and Spirulina (Arthrospira) sp. account for over 90% of the global microalgal biomass production and represent one of the most promising aquiculture bioeconomy systems. These microorganisms have been widely recognized for their nutritional and therapeutic properties; therefore, a significant growth of their market is expected, especially in the nutraceutical, food, and beverage segments. However, recent advancements in biotechnology and environmental science have led to the emergence of new applications for these microorganisms. This paper aims to explore these innovative applications, while shedding light on their roles in sustainable development, health, and industry. From this state-of-the art review, it was possible to give an in-depth outlook on the environmental sustainability of Chlorella sp. and Spirulina (Arthrospira) sp. For instance, there have been a variety of studies reported on the use of these two microorganisms for wastewater treatment and biofuel production, contributing to climate change mitigation efforts. Moreover, in the health sector, the richness of these microalgae in photosynthetic pigments and bioactive compounds, along with their oxygen-releasing capacity, are being harnessed in the development of new drugs, wound-healing dressings, photosensitizers for photodynamic therapy, tissue engineering, and anticancer treatments. Furthermore, in the industrial sector, Chlorella sp. and Spirulina (Arthrospira) sp. are being used in the production of biopolymers, fuel cells, and photovoltaic technologies. These innovative applications might bring different outlets for microalgae valorization, enhancing their potential, since the microalgae sector presents issues such as the high production costs. Thus, further research is highly needed to fully explore their benefits and potential applications in various sectors.

The United Nations 2030 Agenda for Sustainable Development has created more pressure on countries and society at large for the development of alternative solutions for synthetic and fossil fuel derived products, thus mitigating climate change and environmental hazards. Food wastes and microalgae have been studied for decades as potential sources of several compounds that could be employed in various fields of application from pharmaceutical to textile and packaging. Although multiple research efforts have been put towards extracting rich compounds (i.e., phenolic compounds, tocopherols, and tocotrienols) from these sources, they still remain overlooked as two major sources of bioactive compounds and pigments, mainly due to inefficient extraction processes. Hence, there is a growing need for the development of optimized extraction methods while employing non-organic solvent options following the main principles of green chemistry. This review will focus on delivering a clear and deep analysis on the existing procedures for obtaining bioactive compounds and pigments from food wastes derived from the most consumed and produced fruit crops in the world such as apples, oranges, cherries, almonds, and mangoes, and microalgal biomass, while giving light to the existing drawbacks in need to be solved in order to take full advantage of the rich properties present in these two major biorefinery sources.

The first ever nanofibers produced by the electrospinning of polyvinyl alcohol (PVA) and Spirulina platensis extracts are presented in this article. Spirulina platensis extracts were obtained by ultrasound-assisted extraction (UAE) using two different solvents: a glucose/glycerol-based natural deep eutectic solvent (NADES) and water. Through spectrophotometry analysis, it was possible to determine the pigment yield of the extractions for both extracts: phycocyanin = 3.79 ± 0.05 mg/g of dry biomass (DB); chlorophylls = 0.24 ± 0.05 mg/g DB; carotenoids = 0.13 ± 0.03 mg/g DB for the NADES/Spirulina extracts, and phycocyanin = 0.001 ± 0.0005 mg/g DB; chlorophylls = 0.10 ± 0.05 mg/g DB; carotenoids = 0.20 ± 0.05 mg/g DB for water/Spirulina extracts. Emulsions were formed by mixing the microalgae extracts in PVA (9%, w/v) at different concentrations: 5, 20, 40, and 50% (v/v). Electrospinning was carried out at the following conditions: 13 cm of distance to collector; 80 kV of applied voltage; and 85 rpm of electrode rotation. After the nanofibers were collected, they were checked under a scanning electron microscope (SEM). ImageJ was also used to determine fiber diameter and frequency. SEM results showed the formation of nanofibers for 5 and 20% (v/v) of NADES/Spirulina extract content in the electrospinning emulsions, presenting diameters of 423.52 ± 142.61 nm and 680.54 ± 271.92 nm, respectively. FTIR confirmed the presence of the NADES extracts in the nanofibers produced. Overall, the nanofibers produced showed promising antioxidant activities, with the NADES/Spirulina- and PVA-based nanofibers displaying the highest antioxidant activity (47%). The highest antimicrobial activity (89.26%) was also obtained by the NADES/Spirulina and PVA nanofibers (20%, v/v). Principal Component Analysis (PCA) revealed positive correlations between both the antioxidant and antimicrobial activities of the electrospun nanofibers, and extract content in the emulsions. Moreover, PCA also indicated positive correlations between the viscosity and conductivity of the emulsions and the diameter of the nanofibers produced.

Millions of tons of wool waste are produced yearly by textile industries, which may become a serious environmental hazard in the near future. Given this concern, it is crucial to explore strategies to reduce the amount of wool waste generated worldwide and adopt more sustainable practices for dissolving and regenerating wool keratin (WK) from textile waste. Most traditional methods involve the use of expensive, toxic, harmful, and poorly biodegradable compounds. To overcome these limitations and facilitate the reuse of wool waste through a cascade valorization strategy, researchers have started testing the use of deep eutectic solvents (DES) as a more sustainable and eco-friendly alternative for WK dissolution and regeneration. In this study, the potential of two different DES mixtures, Choline chloride (ChCl): Urea and L-Cysteine (L-Cys): Lactic acid (LA), was explored for dissolving wool waste. Subsequently, the gels obtained based on DES-WK were blended with polyvinyl alcohol (PVA) in different ratios to produce nanofibers using the electrospinning technique. The PVA/L-Cys: LA DES-WK proved to be the most effective DES mixture for fabricating WK gel-based nanofibers. Furthermore, their antioxidant and antimicrobial abilities were evaluated, thus confirming their bioactivity. The results obtained revealed that this approach to valorizing textile waste offers a unique avenue for the development of sustainable functional materials with potential applications in various biomedical and industrial fields.

Millions of tons of wool waste are produced yearly by textile industries, which may become a serious environmental hazard in the near future. Given this concern, it is crucial to explore strategies to reduce the amount of wool waste generated worldwide and adopt more sustainable practices for dissolving and regenerating wool keratin (WK) from textile waste. Most traditional methods involve the use of expensive, toxic, harmful, and poorly biodegradable compounds. To overcome these limitations and facilitate the reuse of wool waste through a cascade valorization strategy, researchers have started testing the use of deep eutectic solvents (DES) as a more sus-tainable and eco-friendlier alternative for WK dissolution and regeneration. In this study, the potential of two different DES mixtures, Choline chloride (ChCl): Urea and L-Cysteine (L-Cys): Lactic acid (LA), was explored for dissolving wool waste. Subsequently, the obtained gels based on DES-WK were blended with polyvinyl alcohol (PVA) in different ratios to produce nanofibers using the electrospinning technique. The effect of pH and the properties of the electrospinning solutions, namely electrical conductivity and viscosity, on the morphology of the gel solutions were evaluated. Moreover, the morphological features of the produced gel-based electrospun PVA/DES-WK nanofibrous membranes were analyzed using scanning electron mi-croscopy (SEM). Additionally, the PVA/L-Cys: LA DES-WK, which proved to be the most effective DES mixture for fabricating WK gel-based nanofibers, were characterized through Fourier transform infrared spectroscopy (FTIR) and tensile tests. Furthermore, their antioxidant and an-timicrobial abilities were evaluated. The results obtained revealed that this approach to valorize textile waste offers a unique avenue for the development of sustainable functional materials with potential applications in various biomedical and industrial fields.