Integrated processes for the recovery of valuable compounds from artichoke wastewaters

In recent years, the recovery of antioxidant compounds from natural sources is a focus of great interest due to their potential use as natural ingredients in food, pharmaceutical and cosmetic formulations or as substitutes of synthetic products in the food industry. The artichoke-based industry generates huge amounts of agricultural waste (up to 60% of the harvested product) consisting mainly of the leaves, stems and the external parts of the flower which are not suitable for human consumption. Blanching waters represent additional residues of the canning artichoke industry. These by-products are suitable for ensiling, with pleasant smell, good silage characteristics, crude protein content 88 g/kg, dry matter and fiber content 509 g/kg dry matter [1]. An alternative approach is their use as sources of natural antioxidant compounds, mainly phenolic compounds, which, in some cases, have activities comparable to those of synthetic antioxidants [2]. Membrane operations are recognized as powerful tools for the purification and concentration of various solutions (e.g., juices, extracts, whey) and the separation of valuable compounds from by-products of the agro-food industry. The combination of membrane processes with conventional separation technologies (i.e. adsorption, precipitation, crystallization) offers new and interesting perspectives in order to increase the selectivity of the process [3]. This work aims at giving an overview of integrated processes based on the use of membrane operations such as ultrafiltration (UF) and nanofiltration (NF) and macroporous resins, in a sequential form, for the selective purification of polyphenols with desirable bio-functional properties, from artichoke wastewater. In particular, a preliminary UF step was investigated to remove suspended solids from artichoke wastewaters. The clarified solution was then submitted to different NF spiral-wound membranes characterized by different molecular weight cut-off (MWCO) (from 200 to 1000) and different polymeric material (polyethersulphone (PES) and polyamide (PA)) in order to produce concentrated fractions enriched in antioxidant compounds. Finally, the NF retentate was submitted to an adsorption/desorption treatment by using three different macroporous resins based on polystyrene (LewatitS 6328 A, Lewatit S 2328 and Lewatit S 7968) in order to purify phenolic compounds, such as chlorogenic acid (CA) and apigenin 7-O-glucoside (AOG) from sugars. Samples produced in UF, NF and adsorption-desorption tests were assayed for phenolic composition (chlorogenic acid and apigenin 7-O-glucoside), sugar composition (fructose, glucose and sucrose) and antioxidant activity in order to evaluate the selectivity of each step toward compounds of interest. The performance of UF and NF membranes was also evaluated in terms of productivity (permeate fluxes) in selected operating conditions. All the different NF membranes presented a very high retention toward phenolic compounds and TAA: no phenolics compounds were detected in the NF permeate allowing to verify the efficiency of the membrane concentration process [4]. Among the three different tested resins, the S 7968 offered the best performance in terms of adsorption/desorption ratio for chlorogenic acid, with a total adsorption/desorption yield (TADY) of 63.39%; for the apigenin 7-O-glucoside the S 7968 and the S 2328 resins showed a TADY in the range 68.31-78.45% [5]. The obtained results indicated that the integration of membrane operations with adsorbents resins can be an interesting approach for the purification of phenolic compounds from artichoke wastewaters producing a more purified fraction of phenolic compounds if compared to an integrated system fully based on the use of membranes. References [1]M.D. Me