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Research Project: Commercial Flocculants from Low-Value Animal Protein

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Title: Chemical and enzymatic protein cross-linking to improve flocculant properties

item ESSANDOH, MATTHEW - Orise Fellow
item Garcia, Rafael
item Nieman, Christine

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2018
Publication Date: 8/28/2018
Citation: Essandoh, M., Garcia, R.A., Nieman, C.M. 2018. Chemical and enzymatic protein cross-linking to improve flocculant properties. ACS Sustainable Chemistry & Engineering. 6(10):12946-12952.

Interpretive Summary: Flocculants are substances that are used for removing contaminants from water. The most commonly used flocculants are synthetic polymers. This type of flocculant is facing rising health and environmental concerns. Proteins are natural polymers that have some similarities to flocculants; indeed, some proteins can serve as less-potent substitutes for synthetic flocculants, but many other proteins do not have this property. Synthetic flocculants are extremely big molecules, much larger than proteins. In this project, researchers linked many protein molecules together, so that the overall size of the group of linked proteins is comparable to that of a synthetic flocculant. The results showed that cross-linking could give flocculant properties to proteins that do not have it, and enhance the potency of proteins that already have flocculant properties. The research was conducted using proteins from farm animal blood, collected at slaughter. This work provides the opportunity to transform an under-utilized agricultural by-product into a biobased, biodegradable product and a new revenue stream for meat processors.

Technical Abstract: Some proteins promote the flocculation of aqueous suspensions, but proteins are much smaller than modern polymeric flocculants, and they are often not as potent. In this study, two globular proteins, hemoglobin (Hb) and bovine serum albumin (BSA), were crosslinked through either chemical or enzymatic means. The degree of crosslinking was approximately 95%. Compared to the native proteins, the crosslinked proteins had a 20-30 fold increase in molecular weight and a reduced isoelectric point. Crosslinked proteins appear to have lost the secondary structures present in their native counterparts, and do not go through organized structural transitions upon heating. The crosslinked Hb sample showed a higher peak clarification efficiency (KCE = 2.96) compared to its BSA counterpart, indicating its potential to be used as a bioflocculant. Interestingly, native BSA has no flocculant activity (KCE = 0, 0% clarification) but crosslinked BSA has substantial activity (peak KCE=1.85, or ~98% clarification).