Utilization of Plant-Based Wastes for a Sustainable Preparation of Xanthophyll Esters via Acid Anhydrides Using β-Pinene as a Bio-Derived Solvent

Abstract

A new valorization strategy for selected plant-based waste materials has been put forward. We have shown that avocado peels (fruit waste) and green leaves of Japanese knotweed (plant waste) are good sources of free xanthophylls such as antheraxanthin (9 mg/100 g dry weight) and lutein (106 mg/100 g dry weight), respectively, which can be converted into xanthophyll esters, a process inspired by nature to regulate the physicochemical properties of these bioactive species such as solubility and chemical stability. To this end, we developed the first environmentally friendly and economically viable synthetic platform and critically evaluated it by preparing 55 different xanthophyll esters (combining 5 model xanthophylls with 11 structurally and electronically distinct acid anhydrides). These esters were synthesized using β-pinene as a bio-derived solvent at ambient temperature and pressure with excellent selectivity (median 97%) and finally isolated in high yields (median 81%) and with high purities (median 97%). The integration of this technology with xanthophyll-containing wastes contributes to the zero-waste principle, and new valorization pathways for invasive alien plant species (such as Japanese knotweed) are particularly welcome as they help to control their rapid spread which causes great economic damage and loss of biodiversity around the globe.

Esterification of Lutein from Japanese Knotweed Waste Gives a Range of Lutein Diester Products with Unique Chemical Stability

“… 44 − 46 By using sc-CO 2 , cleaner carotenoid extracts can be obtained with less potential chemical interferences compared to extracts obtained with other common solvents such as acetone, EtOAc, EtOH, and similar. 19 For the synthesis of the 13 model lutein diesters in the next step, the sc-CO 2 extract was used without further purification to avoid the generation of additional waste; from the perspective of economic and environmental sustainability, this is very important during scale-up and industrial implementation. After completion of the reaction, the lutein diester products were purified and excess reagents were quantitatively removed, but a moderate chemical background derived from the Japanese knotweed matrix remained.…”

“…Afterward, carotenoids were extracted from the processed plant material by supercritical CO 2 (sc-CO 2 ) extraction as described previously. 19 To summarize, 5 kg of dried pulverized plant material was loaded into an extraction cell and was then extracted with sc-CO 2 for 24 h at 150 bar, 65 °C, and at a flow rate of 120 g CO 2 /min. The extract, taking the form of a viscous paste, was being collected in a separator held at 80 bar and 45 °C.…”

“…For the synthesis and purification of lutein diesters, a recently developed green procedure was followed with minor modifications. 19 Briefly, ethanolic standard solution of lutein (0.5 nM; 500 μL) was transferred into a reaction vessel (an amber 4 mL storage vial), the solvent was evaporated under a stream of argon, and the solid residue was redissolved in EtOAc (250 μL). Then, EtOAc solutions of a corresponding acid anhydride (37.5 nM; 200 μL) and 4-dimethylaminopyridine (DMAP) (75 nM; 200 μL) were added at a molar stoichiometric ratio of lutein/acid anhydride/DMAP = 1:30:60.…”

“…These were made clean of any dirt or particulate matter, air dried, and finally pulverized. Afterward, carotenoids were extracted from the processed plant material by supercritical CO 2 (sc-CO 2 ) extraction as described previously . To summarize, 5 kg of dried pulverized plant material was loaded into an extraction cell and was then extracted with sc-CO 2 for 24 h at 150 bar, 65 °C, and at a flow rate of 120 g CO 2 /min.…”

“…This genuine sensitivity not only of xanthophylls but also of carotenoids, in general, has sparked numerous research studies, and consequently there is now a whole arsenal of mature technologies that can be used for their stabilization, such as encapsulation in various protective shell materials, emulsification, complexation with macromolecules, and micelle and liposome formation. − There is accumulating evidence that the chemical stability of xanthophylls bearing at least one hydroxyl group could also be improved by esterification with various carboxylic acids, an approach that offers multiple advantages . Recently, green leaves of Japanese knotweed have been used as a source of lutein to produce a structurally diverse series of lutein diesters with potentially improved physicochemical properties such as chemical stability . However, can the improvement be generally attributed to any given lutein (or xanthophyll) ester and under any given condition?…”