RYEGRASS NANOSTARCH: PROSPECTION AND CHARACTERIZATION

Starches are homopolysaccharides widely used in the most diverse industrial sectors. Despite its versatility, it has limitations due to its botanical origins, such as instability to freezing and thawing cycles, acidic pH, cold insolubility, high shear, high temperatures and restricted viscosity range. This work aimed to investigate a new botanical source for starch extraction using ryegrass seed (Lolium multiflorum L.) of the Winter Star 3 variety, using four extraction methods (aqueous, reducing – 0.2% active SO2, alkaline – NaOH 0 .1M and combined - 0.2% SO2 + 0.1M NaOH). Starches were analyzed for chemical, morphological, structural and thermal properties. It was noticed that the samples did not differ in terms of extraction yield (31.55 to 37.81% based on flour), with ryegrass seed having 63.93% starch but being higher in absolute values for reducing method, where the disruption of the disulfide bonds of the protein matrix, favoring the leaching of the starch granules. The starches obtained by the alkaline and combined methods had the lowest protein contents (0.24 and 0.25%, respectively), although the ash content was higher in the alkaline method (1.16%) and similar to the other techniques (~0.75%). The apparent amylose content showed mean values of 16.69% and did not differ with the applied extraction method. The minerals Si, P, Ca, K, S, Fe, Cu and Ag were identified in the starches. Si and P were the major minerals in the starches obtained by the aqueous and reducing methods, and Ca and K were the most important in concentration in the alkaline and combined methods. In addition, the presence of Si, P and S was not detected in starch from the alkaline way. The residual presence of proteins and silicon was confirmed by Fourier transform infrared spectrogram, with characteristic peaks at 2250cm-1 (nitrile group stretching) and 720cm-1 (vibrations of Si-O-Si bonds from the silanol family). Scanning electron microscopy identified that the ryegrass starch granules were oval, polyhedral and irregular, classifying them as trimodal starch granules. The average size of the starch granules was similar between the extraction methods, with average values of 31.5 nm, placing ryegrass starch as the first native nanostarch identified in Brazil. The thermograms determine the temperature required for the endothermic processes of gelatinization and showed values of initial temperature (Ton), peak (Tpeak), final gelatinization (Tend) and gelatinization enthalpy (ΔH) of 58.13, 58.12, 62.63 and 60.09°C for Ton, 64.73, 64.51, 67.27 and 68.2 °C for Tpeak, 72.36, 74.19, 77, 64 and 80.22°C for Tend and 9.08, 6.14, 9.16 and 14.17 J.g-1 for ΔH, respectively for the starches obtained by the aqueous, reducing, alkaline and combined methods. The results indicate specific characteristics of ryegrass starch, as it has a nanoscale trimodal granular structure, low amylose content, high purity and, depending on the extraction method, the presence of silicon, making ryegrass nanostarch as a potential polysaccharide for use in food and non-food industry.