Effect of Processing on the Rheological Properties and Water Uptake of Plasma Protein Superabsorbent Materials

Abstract

As porcine plasma protein is mostly used as ingredient in foods (e.g. frankfurters) where water holding capacity is required, the feasibility of using it in the development of superabsorbent materials is considered in the present work. Plasma protein is blended with glycerol, which acts as plasticizer, at a 1:1 ratio, and subsequently injection-moulded at different mould temperatures, ranging from 60 to 120 °C. Moreover, the effect of pH is studied submitting the plasma protein to a pH modification procedure, involving aqueous dispersion, followed by pH modification and lyophilization. Following that procedure, bioplastics with pH equal to 3, 8 and 9 are produced. A reinforcement in the rheological properties was observed when plasma protein-based bioplastics are produced at higher moulding temperatures, resulting in a lower water uptake capacity. It is remarkable that at temperatures lower than 100 °C, superabsorbent materials are produced. Additionally, the highest water uptake is displayed by the sample prepared at pH 3, showing an apparent effect of pH on the properties of the samples. The estimation of the protein isoelectric point (IEP) is possible through zeta-potential and solubility tests performed on plasma protein aqueous dispersions at different pH values. The IEP is estimated to be around 5, which determines the positively charged character of the protein when processed at the acidic pH.