Optimized strategy for simultaneous recovering bioactive oligosaccharides and reusable perlite from agar industrial waste residues

This study proposed a greener strategy for recovering bioactive agar- and cello-oligosaccharides via the enzymatic method, as well as reusable perlite via the acid-assisted method from the agar industrial waste residues. By using response surface methodology, the conditions for β-agarase digestion for the waste residues (4 g) were determined to be the enzyme amount of 40 U, temperature of 58 °C, pH 7.0, liquid-to-material ratio of 25.65 ml/g, stirring speed of 474 rpm, and reaction time of 4 h. In addition, the conditions for cellulase digestion of the waste residues (2 g) using single factor optimization were the liquid-to-material ratio of 50.0 ml/g, temperature of 50 °C, pH 5.0, enzyme amount of 300 U, stirring speed of 500 rpm, and reaction time of 3.5 h. The recovered oligosaccharides were confirmed by mass spectroscopy to be neoagarobiose, neoagarotetraose, cellobiose, and cellotriose. After the enzymatic digestion, the conditions for hydrochloric acid treatment of the waste residues were optimized using single factor optimization in terms of acid concentration, reaction temperature and time. After acid treatment, the physical and chemical properties revealed by parameter determination, Fourier-transform infrared spectroscopy, scanning electron microscopy and X-ray fluorescence spectroscopy assays indicated that the recycled perlite had similar properties to the commercial perlite implying its reusability. This study provides theoretical and technical reference for the comprehensive utilization of seaweed industrial waste residues by enzyme technology.