Effect of aqueous and ethanolic extracts from pinhão coats on the properties of corn and pinhão starches

Abstract

The Araucaria angustifolia seed, named pinhao, has a high content of carbohydrates, and it is considered an unconventional starch source. Its coats are rich in phenolic compounds, which can be easily extracted with some solvents. This study presents a method of aqueous and ethanolic extraction of phenolic compounds from pinhao coats and its incorporation into corn and pinhao starches. Thermogravimetry, differential scanning calorimetry, X-ray powder diffractometry, Fourier-transform infrared spectroscopy and field emission gun-scanning electron microscopy were applied to evaluate the thermal, structural and morphological properties of starches. The control samples were prepared under the same conditions, with deionised water and ethanol/water 55:45 v/v, without extracts. Starches incorporated with both extracts showed lower thermal decomposition temperatures than the native ones. The gelatinization enthalpy (ΔHgel) of corn starch decreased after incorporation with extracts. The ΔHgel of native pinhao starch was 7.3 J g−1. A higher ΔHgel was observed after treatment with ethanolic extract, while the aqueous extract caused a decrease in this value. Treatments did not change the diffraction patterns but change the relative crystallinity (RC) of starches, except to the samples treated with ethanol/water 55:45 v/v that maintained RC similar to the native ones. There was a good correlation of FTIR data with RC and ΔHgel. After incorporation with ethanolic extract, the pinhao starch showed superficial peeling. No change was observed in morphological characteristics for the other samples. Results indicate that there is an interaction between the phenolic compounds of the pinhao coats and the starch.