Effect of protease addition for reducing turbidity and flocculation of solid particles in drainage water derived from wheat-flour noodle boiling process and its electrostatic properties

Abstract We describe the effect of enzyme (protease M) addition on reducing turbidity and self-flocculating of solid particles (mainly starch) in the drainage water after boiling a type of wheat-flour noodle (DWBWN) without the addition of flocculants to decrease waste-water-treatment costs to reuse the content of such drainage water. Reduction in turbidity and flocculation/sedimentation of solid particles in DWBWN are highly dependent on enzyme addition/concentration and pH level. We conducted experiments to determine the effect of adding protease to DWBWN. A decrease in turbidity of over 90% was observed in protease-added DWBWN. A decrease in total carbon (TC) of approximately 40% in the clear upper portion of DWBNW was also observed after protease addition and sedimentation. This TC was almost the same as with the supernatant of stock DWBWN without protease addition after centrifuging. Adding protease to DWBWN decreased the protein content, strengthened the negative surface electron charge, and decreased the isoelectric point of the solid particles. To determine the dissociation of phosphate ions in relation to reduction in turbidity and flocculation/sedimentation of solid particles, these processes were observed at the same pH level of a specific dissociate form of phosphorylated (mono-ester phosphates) starch in solid particles. This suggest that the strong negative zeta-potential of solid particles formed in DWBWN reduce turbidity, and flocculation/sedimentation of solid particles depends on the electrostatic properties.