Eriobotrya japonica seed as a new source of starch: Assessment of phenolic compounds, antioxidant activity, thermal, rheological and morphological properties

Abstract

Investigating non-conventional starch sources is essential because different chemical compositions, granular sizes and shapes, and amylose and amylopectin ratios, reveal new technological features. The loquat (Eriobotrya japônica), which is from the Rosaceae plant family, has a high amount of starch in its seeds (≅ 20%). Thus, this study aimed to characterise the physicochemical, thermal, rheological and structural properties, as well as the bioactive compounds, of loquat seed starch (LSS) derived from urban afforestation and commercial fruits at two stages of maturity: ripe (RI) and unripe (UN). Scanning electron micrographs showed oval- and cylindrical-shaped LSS granules. Using X-ray diffraction patterns it was possible to classify the LSS as having a C-type crystalline structure. The LSS (RI and UN) exhibited a higher thermal stability range in relation to degradation than conventional starches in the thermogravimetric assays (TG/DTG). Using differential scanning calorimetry it was possible to suggest a correlation between the peak temperatures with the gelatinisation temperatures obtained by the oscillatory shear test of the LSS. The rheological assays revealed that the LSS gels present pseudoplastic behaviour, with a high degree of thixotropy. Furthermore, higher content of polyphenols and higher antioxidant capacity were observed for the UN unpurified starch samples. Seven bioactive compounds were quantified in the raw starches by Ultra-High Performance Liquid Chromatography, with major concentrations of kaempferol (up to 330.46 μg/kg) and 5-caffeoylquinic acid (up to 135.00 μg/kg). The LSS showed compatible characteristics for industrial usage as an alternative to chemically modified starches.