Pasting and viscoelastic properties of starches isolated from tropical fruits

The exploration of new starch sources has increased due to the demand to develop green materials. In this sense, diverse polysaccharides, including starch, can be isolated from fruits due to their significant postharvest loss in many countries with vast fruit biodiversity. The present work examined the chemical composition, morphology, and rheological properties of starches isolated from tropical fruits in Mexico, namely: (1) stenospermocarpic mango (Mangifera indica L.) 'Ataulfo', which is considered a postharvest loss due to its small size and no commercial value; (2) 'Pera' banana (Musa ABB), a low commercial value fruit; and (3) soursop (Annona muricata L.), a highly perishable fruit. The research concerning the morphological and rheological properties of those starches is scarce to date. The starches presented amylose contents ranging between 24.7 and 29.4% (w/w), congruent with the amylose content in most normal native starches. During pasting, the viscosities of the 7% fruit starch suspensions were higher than those of the normal corn starch (reference). Mango and soursop starches are rapid-swelling starches; their pasting temperatures were 66.3 and 69.5 degrees C, respectively. Banana starch showed the highest peak viscosity value (0.89 Pa s), and soursop starch pastes exhibited the lowest retrogradation tendency (setback viscosity = 0.168 Pa s). After cooling, the starch pastes exhibited soft gel-like viscoelastic behaviour. Accordingly, the rheological characterisation of the pastes and gels of the isolated starches allows us to propose them as new starches for diverse food and biotechnological applications.