Recovery of bioactive compounds from artichoke brines by nanofiltration
Introduction
Globe artichoke (Cynara scolymus L.) is a traditional component of the Mediterranean diet. According to FAO estimation, Italy was the world's largest artichoke producer in 2011, with a production of 474,550 metric tons (MT), followed by Egypt, Spain and Perù (FAO, 2014).
The artichoke has many nutritional qualities being rich in water (91% of edible portion) and minerals, but also of vitamins, carotenoids and polyphenols (Christaki et al., 2012). The phenolics include cynarin (1,3-di-O-caffeoylquinic acid), luteolin, cynaroside (luteolin-7-O-glucoside), scolymoside (luteolin-7-rutinoside); phenolic acids such as caffeic, coumaric, hydroxycinnamic, ferulic, caffeoylquinic acid derivatives; mono- and dicaffeoylquinic acids, including chlorogenic acid; alcohols and flavonoid glycosides, among others (Abu-Reidah et al., 2013, Chen and Ho, 1997, Lattanzio et al., 2009, Mulinacci et al., 2004). These substances exhibit an important scavenging activity against reactive oxygen species (ROS) and free radicals, and perform as a protective shield against oxidative damage to biological molecules, such as proteins, lipids and DNA. Several studies have demonstrated their health-protective potential in terms of hepatoprotective (Adzet et al., 1987, Gebhardt and Fausel, 1997), antimicrobial (Kukić et al., 2008), hypocholesterolemic (Clifford and Walker, 1987, Rondanelli et al., 2013) and anticarcinogenic (Clifford, 2000) activity.
In the course of artichoke processing and packaging a large amount of wastes and residues (leaves, stems, water blanching) is produced, which can reach up to 60% of the weight of the vegetable crop. In particular, the production of canned artichoke is based on the use of acidulated brines at pH values lower than 4.6 in order to limit the growth of Clostridium botulinum and make a pasteurization treatment at temperatures lower than 100 °C possible to obtain the microbiological stability. On average the brine is composed of water, citric acid (0.2%), ascorbic acid (0.05%) and salt (22–23%). Artichokes are preserved and stored in this solution for 50–60 days; after that they are removed from the brine and submitted to the blanching step before packaging.
The production of exhausted acidulated brines represents a serious environmental problem for the processing industry that must withstand high treatment costs and disposal. Some applications have been studied for animal foodstuff and fiber production (Femenia et al., 1998, Martínez Teruel et al., 1998). However, considering their content of health-promoting antioxidant compounds (Llorach et al., 2002), researches are oriented in obtaining phenolic-rich extracts from artichoke byproducts.
Membrane filtration processes offer very interesting perspectives and key advantages, in terms of low energy consumption, greater separation efficiency and improved product quality, over conventional technologies in the treatment of wastewaters from food processing industries. Pressure-driven membrane operations, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO), are well-known established technologies for the treatment of high strength wastewaters aimed at the production of purified water for recycle or reuse and the recovery of valuable compounds (Galanakis et al., 2010, Galanakis et al., 2014, Muro et al., 2012, Suárez et al., 2006, Tylkowski et al., 2011). Among these processes NF can also applied for applications involving fractionation rather than purification. Its potential in the food industry related to the production of high quality food, water softening, wastewater treatment, vegetable oil processing, beverage dairy and sugar industry has been recently reviewed (Salehi, 2014).
In a previous work an integrated membrane process has been investigated in order to recover from separated fractions enriched in sugar and phenolic compounds from artichoke wastewaters (Conidi et al., 2014). To the best of our knowledge, the extraction of phenolic compounds from artichoke brines has not been previously reported.
In this work a membrane-based process for the fractionation of artichoke brines was investigated in order to separate flavonoids and caffeoylquinic acids from salt compounds. Therefore, the performance of different commercial spiral-wound nanofiltration (NF) membranes in the treatment of clarified artichoke brines was evaluated in terms of productivity and selectivity towards bioactive compounds in selected operating conditions. Membranes of different polymeric material (polyethersulphone, polyammide) and molecular weight cut-off (MWCO) (from 200 to 1000 Da) were tested.
Section snippets
Artichoke brines
Artichoke brines were supplied by Indena SpA (Milan, Italy). They were stored at room temperature and prefiltered with a nylon cloth before ultrafiltration.
Pretreatment of artichoke brines
Artichoke brines were submitted to a preliminary UF process in order to remove suspended solids and macromolecular compounds and to reduce fouling phenomena in the subsequent NF process. UF experiments were performed by using a laboratory pilot unit equipped with a cellulose triacetate hollow-fiber membrane module (FUC 1582, Microdyn-Nadir,
Results and discussion
Preliminary NF experiments were carried out in batch mode at a TMP of 6 bar and room temperature (20 ± 2 °C). Fig. 2 shows the evolution of permeate flux along the concentration experiments for all the investigated NF membranes in the selected operating conditions. The permeate flux decreased gradually by increasing the WRF due to concentration polarization and membrane fouling. The Jp vs WRF curves show a rapid decrease of the permeate flux in the initial step; a second period, up to WRF 1.5,
Conclusions
NF membranes were investigated to recover and concentrate phenolic compounds from artichoke brines after a preliminary UF step. Among the NF membranes investigated those with MWCO of the order of 200 Da produced the best results in terms of recovery and concentration of phenolic compounds. In particular, the NF200 and Desal DL membranes allowed an effective separation of salt components from caffeoylquinic acid derivatives. For this type of membranes a low rejection of the dry residue (between
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