Abstract
In this study, membrane-based methods were evaluated for the recovery of FucoPol, the fucose-rich exopolysaccharide (EPS) secreted by the bacterium Enterobacter A47, aiming at reducing the total water consumption and extraction time, while keeping a high product recovery, thus making the downstream procedure more sustainable and cost-effective. The optimized method involved ultrafiltration of the cell-free supernatant using a 30 kDa molecular weight cut-off (MWCO) membrane that allowed for a 37% reduction of the total water consumption and a 55% reduction of the extraction time, compared to the previously used method (diafiltration-ultrafiltration with a 100 kDa MWCO membrane). This change in the downstream procedure improved the product’s recovery (around 10% increase) and its purity, evidenced by the lower protein (8.2 wt%) and inorganic salts (4.0 wt%) contents of the samples (compared to 9.3 and 8.6 wt%, respectively, for the previously used method), without impacting FucoPol’s sugar and acyl groups composition, molecular mass distribution or thermal degradation profile. The biopolymer’s emulsion-forming and stabilizing capacity was also not affected (emulsification activity (EA) with olive oil, at a 2:3 ratio, of 98 ± 0% for all samples), while the rheological properties were improved (the zero-shear viscosity increased from 8.89 ± 0.62 Pa·s to 17.40 ± 0.04 Pa·s), which can be assigned to the higher purity degree of the extracted samples. These findings demonstrate a significant improvement in the downstream procedure raising FucoPol’s recovery, while reducing water consumption and operation time, key criteria in terms of process economic and environmental sustainability. Moreover, those changes improved the biopolymer’s rheological properties, known to significantly impact FucoPol’s utilization in cosmetic, pharmaceutical or food products.
Highlights
Extracellular polysaccharides (EPS) are carbohydrate biopolymers secreted by the cells of many microorganisms that are released to the surroundings of the cells, remaining only loosely attached to them [1]
The resultant cell-free supernatant was subjected to a thermal treatment to inactivate bacterial enzymes [11,23], and the treated cell-free supernatant was used for testing FucoPol recovery using membranes of two different molecular weight cut-off (MWCO), namely, 100 kDa and 30 kDa
The results obtained in this study show that Method 2 reached the best performance in terms of operation time and water consumption, together with good FucoPol recovery (Table 5)
Summary
Extracellular polysaccharides (EPS) are carbohydrate biopolymers secreted by the cells of many microorganisms that are released to the surroundings of the cells, remaining only loosely attached to them [1]. Many microbial EPS (e.g., xanthan and gellan gums, hyaluronic acid [2], and pullulan [3]) are utilized in high-value applications such as pharmaceutical, food, and cosmetic products [2,4,5] due to their biodegradable, biocompatible, and usually nontoxic nature [6,7] Given their extracellular nature, EPS recovery from the culture broth involves rather simple downstream procedures that usually consist of cell removal, followed by biopolymer precipitation from the cell-free supernatant by addition of a precipitating agent (e.g., methanol, ethanol, isopropanol, acetone) and drying [1,8,9]. For high-value applications, in which a higher purity degree is often a prerequisite, specific procedures must be used to reach highpurity products Such procedures include, for example, reprecipitating the EPS from dilute aqueous solutions, deproteinization by chemical or enzymatic methods, and membrane processes, such as dialysis, ultrafiltration and diafiltration [11,14,15]. Process optimization should at least maximize the following criteria: recovery, highest purity, polymer performances adopting simple, rapid and green procedures. [1,18–20]
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