Starch Recovery Process from the Tiger Nut Horchata Processing Waste

Tiger nut horchata solid residue (HSR) has high starch content (about 23%, dry basis) that can be recovered to valorise this waste, together with other valuable components, such as oil, fibres, or phenolic compounds. In this study, a chemical-free, sustainable process was proposed to obtain starch with good yield and purity. This consists of a high-speed homogenisation step with distilled water, followed by filtration and phase separation by density in the slurry to obtain a starch-rich sediment that can be isolated by decantation. Five minutes of homogenisation at 10,200 rpm allows for obtaining 14.5 g of starch powder per 100 g of dried HSR, with a purity of about 85% and WI of 94.97. Applying 1 washing cycle to the filtering residue increased the starch powder yield up to 17 g/100 dried HSR, without notable losses in starch purity, whereas centrifugation at 15,000 g for 1 h in the phase separation step highly reduced separation time, increasing starch purity up to 92%. Thus, it was possible to recover up to 70% of the starch present in the HSR. The obtained starch had similar morphological characteristics, crystallinity degree, and gelatinisation behaviour to that present in the tiger nut tubers, exhibiting similar thermal stability to that reported for other native starches. Therefore, HSR can be used as a starch source for different uses.