Determination of the Oil Content of Sunflower Seeds Using Natural Samples of Sunflower Oil: on the Example of the Calibration of a Pulsed NMR Analyzer

Abstract

One of the main parameters of sunflower seeds is its oil content. This characteristic is mandatory for certifica[1]tion of agricultural products and assessment of their value. IR spectroscopy and pulsed NMR methods are widely used to determine the oil content.The purpose of the research was to scientifically and practically substantiate the possibility of using sunflower oil samples for calibrating NMR analyzers, identifying and assessing the quality of oilseeds and products of their processing based on the NMR method. The comparison of the results of various options for the calibration of a pulsed NMR analyzer for determining the oil content of sunflower seeds was carried out. The first option was to measure the NM relaxation characteristics of oil protons from prepared samples of sunflower seeds, followed by determination of their oil content by exhaustive extraction in a Soxhlet apparatus, construction of a calibration equation based on the obtained data, and entering its coefficients into the program of NMR analyzers.The resulting calibration was the base one, with which other calibration options were compared. The second option was to use for calibrating the NMR analyzer various samples of sunflower oil obtained by pressing from sunflower seeds of the same varieties and hybrids, that were used for the first calibration option, as well as sunflower oil samples purchased in a commercial network. Five samples evenly distributed in the range from 2.000 g to 7.000 g with an accuracy of 0.001 g were taken from each oil sample using laboratory scales, and the amplitudes of proton NMR signals were measured in them. The dependency between the oil mass of the analyzed samples and the amplitude of proton NMR signals in them was graphed. Comparison of the obtained calibration dependences showed their close nature. Mathematical calculations have shown that the use of sunflower oil for the calibration of NMR analyzers does not lead to an increase in the error in the measurement results of the oil content of sunflower seeds compared to the first option of the calibration.The practical significance of the research will considerably simplify the calibration process, reduce the calibration time from 3–4 days to 3–4 hours, and eliminate the use of toxic solvents and additional expensive equipment without a significant change in the error in determining the oil content of sunflower seeds by NMR.