## 4 Enzyme-Assisted Extraction for the Recovery of Carotenoids and Betalains  
The application of enzymes for the breakdown of the plant cell-wall barrier is an interesting and promising field for the green extraction of high added-value molecules from unsold fruits and vegetables, avoiding the use of solvents [12]. Enzyme-assisted extraction (EAE) is based on the selective hydrolysis of the plant cell-wall polysaccharides (e.g., cellulase, hemicellulose, pectinase and protease) [58], which leads to parietal lysis, thus improving the extraction of bioactive components [59]. For this reason, preliminary knowledge of the exact cell wall composition of each plant source (e.g., fruits or vegetables) is crucial for selecting one or more enzymes useful for the extraction process [60]. For example, [PERSON] et al. [61] reported that in enzyme-assisted aqueous extraction, the interaction of different enzymatic activities leads to the breakdown of polysaccharide-protein colloids in the cell wall, creating an emulsion that promotes extraction. Synergism resulting from the combined use of cellulase and pectinase has been highlighted in several studies (Figure 3). In addition to identifying the most suitable tailored enzymatic mix, it is essential to understand the catalytic properties, the mode of action and the optimal operating conditions (temperature, pH, time and dosage) of each enzyme in order to maximize the extraction yield [12]. EAE results in several benefits, such as a reduction of extraction time, minimization of the use of organic solvents and an increase in yield and product quality. Reducing the use of solvents during extraction is particularly important for both regulatory and environmental reasons, providing a more environmentally friendly option than traditional non-enzymatic extraction [62]. The main drawback of this approach is the high cost of the biocatalysts. This problem could be partially solved by reducing the enzymatic dosage used. In turn, this issue may be addressed by developing a tailored mix formulated on the basis of the polysaccharide composition of the matrix to be treated [12]. Studies using EAE of carotenoids from vegetable waste are schematically reported in Figure 3.  
The schematic representation in Figure 3 suggests only a few works exploited the synergistic action of multiple enzymes for the recovery of carotenoids from vegetable waste [63]. However, the enzymatic dosages used were considerably high [63] even though many process parameters have been optimized (e.g., temperature and pH), and the yields were quite low, only 15%. In other works, commercial multi-enzymatic preparations have been used [64; 65; 66; 67; 68], which do not allow researchers to selectively balance the individual activities according to the vegetable tissue composition. This has, above all, implications on the extraction efficiency, as it appears by the rather prolonged extraction times (4 or 5 h) even though, in many cases, the temperature and pH are those suggested by the manufacturing sheets. The positive aspects that emerge from the review of these works are that, in any case, the extraction yields are generally high, about 77-90% [69; 70; 71]. However, the non-balancing enzymatic activities in such commercial multi-enzymatic preparations make it impossible to modulate pigment extraction, also involving the destruction of the cytoplasmic organelles (e.g., chromoplasts, in which carotenoids are protected against alterations). Only a few studies (Figure 3 focused on the chromoplasts' isolation from plant tissues, where carotenoids are stable because they are still incorporated into their natural medium (lipoproteins). A green extraction protocol for the recovery of lycopene enclosed in the chromoplast (therefore protected from oxidation) from tomato peels was developed using hydrolytic enzymes (Cellulyve 50 LC, Peclyve LI and Prolyve 1000) and pH variations [64]. In this way, an increase of about 20-30 times in lycopene recovery was achieved. [PERSON] et al.