Rheological and microstructural properties of native cassava starch-low methoxyl pectin in a fruit filling gel system

Abstract

Two native cassava starches (Mentega starch, MS; Adira-4 starch, AS) were isolated using the water extraction method, and their physicochemical properties were characterised. The starch gelation behaviour was assessed in a fruit filling system where addition of low methoxyl pectin (LMP) was varied at different concentrations (0, 5, 10, 20, 30 g/kg). MS was rich in amylose (260 g/kg) with average granule size of ~17 μm, while AS had lower amylose content, smaller particle size of ~190 g/kg and ~13 μm, respectively. MS had a higher overall molecular weight than AS. In the fruit filling system, the rheological properties indicated that the LMP addition to starch had increased the gel G’ and G” values. The gel mechanical spectra exhibited less frequency dependence. Both moduli also increased when calcium was added, demonstrating the starch and pectin molecules associated with calcium ions. However, starch-LMP gels showed a loss in elasticity when the strain percentage increased due to the disruption of starch gel alignment by pectin gel. There was no occurrence of syneresis observed for all gels. Overall, the work suggested that addition of calcium and LMP could be a promising technique for improving the gel strength of starch-based fruit filling.