Edible films from water soluble proteins in surimi wash water

Abstract

This research was to test the methodology involved in recovery of water-soluble fish proteins in surimi wash-water by freeze-drying, shifting the pH and ethanol and development of edible films from water-soluble proteins from different recovery methods. Water-soluble fish proteins were recovered in decreasing concentration with each successive wash. The amounts of proteins were highest for wash stage I (WS-I), followed by wash stages II (WS-II), and III (WS-III). For WS-I, most of the proteins had molecular weights (MW) ranging between 23.2 and 71.6. WS-II and-III also had proteins with MW between 23.2 and 71.6 kDa; however, the protein yield was relatively small. Maximum protein precipitation was obtained at pH 3.5 (66.30 %) and 60 % v/v of ethanol (64.98%), however, precipitated proteins had lowest solubility. There was direct correlation between percentage of precipitation and reaction temperature, which reversed with protein solubility. Reaction time for shifting the pH, and ethnol had little or no effect (p > 0.05) on precipitation. Water-soluble fish proteins film from three different recovering methods (freeze-drying, shifting the pH and ethanol precipitation) were developed and effects of pH, heating temperature, heating time and additive variable on various film properties were determined. The impact of pH and heating temperature was most significant, overall, on the films properties than heating time. Tensile strength (TS) and elongation at break (E) were highest at pH about 10.0 and heating temperature, 70 ํC for freeze-dried proteins and pH 2.0 and heating temperature, 80.0 ํC for proteins precipitated by shifting the pH and pH 11.50 and heating temperature 60 ํC for proteins precipitated by organic solvent. In contrast, at this same condition, the water vapor permeability (WVP), oxygen permeability (OP), films solubility (FS) and proteins solubility (PS) values were at their lowest. Film color was darker and more yellow with increase in pH and heating temperature of film solutions. The surface hydrophobicity and content of disulfide bond increased with increase in pH and heating temperature, while the available sulfhydryl group decreased. Increase of the protein concentration provided the film with higher TS but lowers E, WVP, OP, FS and PS and development of darker and more yellowish films. The properties of edible films from water-soluble fish proteins plasticized with different plasticizers were determined. Three plasticizers comprising sorbitol, glycerol and polyethylene glycol were studied over a range of concentration from 25 to 75%. Increasing in contents of these plasticizers resulted in decreased TS, but increased E, WVP, FS and PS. Sorbitol provided the films with the highest TS, FS and PS but lowest E, WVP, while glycerol and polyethylene glycol provided the films with high E, WVP, but low TS, FS and PS. The color of edible films changed with the plasticizer type. Mechanical properties of all three water-soluble fish protein films were pretty similar to those of various biomaterials based films. However, the films had substantially lower mechanical properties than polymeric materials. The water-soluble fish proteins films were characterized by relatively poor water vapor barrier properties, but showing lower oxygen permeability than values of other polysaccharide and common plastic films, such as low and high density polyethylene, polypropylene and polystyrene.