Effect of potassium hydroxide on rheological and thermo-mechanical properties of semi-refined carrageenan (SRC) films

Abstract

KOH is widely used for extraction of semi-refined carrageenan (SRC). The concentration levels of KOH used in extraction can significantly influence SRC qualities and edible films developed. SRC extracted from red seaweeds ‘Kappaphycus alvarezii’ at different concentration levels (using KOH at 6%, 12%, 18% and 24%) were used to develop an edible films with 20% glycerol as a plasticizer. Results showed that the total yield of SRC ranged from 28.1% to 37.5%. A decreased sulfate level was obtained beyond 12% KOH extraction resulting in increased 3,6-anhydrogalactose (ranged from 26.4% to 32.5%). Functional groups were confirmed using FT-IR-spectrum, which mainly showed ester sulfate groups and with a shift in the peak values measured at higher concentrations of KOH. All the formulated films were opaque and flexible with a thickness between 30.5 and 34.1 µm (moisture: 11.4–14%). All of the films had good viscoelastic properties (power law exponents (n′) being 0.34–0.98) and showed a ‘gel like’ behavior. The X-ray-diffractogram peak showed 2 theta at 28.4°, 37.2°, and 50.4° and was consistent with an amorphous structure. The endothermic peaks varied between 119 and 131 °C. Higher solubility was obtained in SRC films prepared with 24% KOH. Among all the formulated films, water vapor permeability ranged between 8.5 and 12.2 × 10−10 g Pa−1 s−1 m−1 and with high tensile strength ranging between 38.1 and 47.5 MPa. Results showed optimization of KOH extraction for SRC can produce edible films with potential food packaging applications.