A Way to Close the Loop: Physicochemical and Adsorbing Properties of Soybean Hulls Recovered After Soybean Peroxidase Extraction

Abstract

Soybean hulls are one of the by-products of soybean crushing and find application mainly in the animal feed sector. Nevertheless, soybean hulls have been already exploited as source of peroxidase (soybean peroxidase, SBP), an enzyme adopted in a wide range of applications such as bioremediation and wastewater treatment, biocatalysis, diagnostic tests, therapeutics and biosensors. In this work, the soybean hulls after the SBP extraction, destined to become a putrescible waste, were recovered and employed as adsorbents for water remediation due to their cellulose-based composition. They were studied from a physicochemical point of view using different characterization techniques and applied for the adsorption of five inorganic ions [Fe(III), Al(III), Cr(III), Ni(II), and Mn(II)] in different aqueous matrixes. The behavior of the exhausted soybean hulls was compared to pristine hulls, demonstrating better performances as pollutant adsorbents despite significant changes in their features, especially in terms of surface morphology, charge and composition. Overall, this work evidences that these kinds of double-recovered scraps are an effective and sustainable alternative for metal contaminants removal from water.

Recovering the Soybean Hulls after Peroxidase Extraction and Their Application as Adsorbent for Metal Ions and Dyes

“…The first extract showed peroxidase activity of 200 U/ml, while after the third cycle of extraction, the peroxidase activity within sample SH-PO was below the level of detection. Furthermore, from the examined samples FE-SEM microphotographs (see Figure 2), it is evident that the soybean hull’s surface partially collapses after the enzyme’s extraction (SH-PO) being more compressed than before the extraction (SH+PO), which is in accordance with the literature [34]. It is worth mentioning that peroxidase’s removal also contributes to a smoother soybean hull surface morphology compared to the rough SH+PO surface with pronounced pores (see Figure 2, sample SH+PO).…”

“…Such differences could be explained by the changes in the soybean hulls’ surface physico-chemical properties that occurred after the peroxidase removal. Tummino et al [34] ascribed the higher adsorption potential of SH-PO to the effect of the intrinsic metal ions present in the enzyme competing with metal ions for adsorbent active sites. Furthermore, the surface chemistry of the soybean hulls is modified after peroxidase extraction in terms of the availability of the groups that are capable and preferential for metal binding.…”

“…A low-intensity band at 1726 cm –1 appears from stretching vibrations of characteristic C=O groups. Due to the complexity of the soybean hulls’ surface chemistry, a relatively wide band centered at 1602 cm –1 could be ascribed to different vibrations ranging from C=O peptide, C=C, and COO – stretching vibrations [35] and absorbed water [34]. After peroxidase extraction, the band at 3300 cm –1 becomes intensified, while the band at 2907 cm –1 is sharper (see Figure 3(a)).…”

Immobilized Soybean Peroxidase Hybrid Biocatalysts for Efficient Degradation of Various Emerging Pollutants

“…As can be seen in panels A-C ( Figure S3 ), immobilization of SBP on TiO 2 led to the appearance of a new peak around 1200 cm −1 , corresponding to the C-N vibration, typically observed when proteins are immobilized on TiO 2 [ 38 ]. The same C-N peak was also observed for ZnO-SBP sample (panel F, Figure S3 ), in addition to the “Amide I” C = O peak (from SBP) at around 1650 cm −1 , as well as the N-H (stretch) around 3400 cm −1 [ 39 , 40 ], thus confirming the immobilization of SBP onto ZnO as well. The other expected characteristics peaks for the APTES-mediated functionalization of ZnO and TiO 2 (e.g., the N-H (bending) peaks around 1550 cm −1 ) are also indicated (panel E).…”

Soybean peroxidase immobilised on cellulose-alginate hydrogels for removal of recalcitrant organic pollutants in water

“…[10][11][12][13] Moreover, this protein is very interesting because it maintains its catalytic activity over a wide range of pH and temperature. 14,15 Cellulose, which makes up about 40-50% of Soybean hulls, 16 is a biopolymer suitable for various chemical modifications, for different environmental applications and also for enzyme immobilization. [17][18][19] Herein, hybrid hydrogels were obtained by introducing SBP immobilised on chemically modified-cellulose inside sodium alginate beads.…”