Effect of Zinc Excess on Sinapis alba L. Seed Yield, Biochemical Parameters, and Potential for Further Processing

Excess zinc (Zn) has an important effect on seed yield and quality, as well as the possibility of subsequent processing. In this study, we investigated the effect of excess Zn concentrations (50, 100, and 150 mg kg^-1) in the substrate on the seed yield and selected biochemical parameters of white mustard (Sinapis alba L.) seeds. The following parameters were investigated: seed yield, individual lipid classes were analyzed using high-performance thin-layer chromatography (HPTLC); gas-liquid chromatography with mass-selective detection (GS-MS) was used to analyze the fatty acid (FA) profile; and trace elements were detected using inductively coupled plasma-mass spectrometry (ICP-MS). It was found that Zn at concentrations of 100 and 150 mg kg^-1 caused a decrease in the number of S. alba pods, and the 1000-seed weight also decreased at a Zn concentration of 150 mg kg^-1. The Zn concentration in seeds from plants grown on contaminated substrate was higher than the control values and government standard thresholds. Zn at concentrations of 100 and 150 mg kg^-1 caused a slight increase in the content of triacylglycerols (up to 1.35-1.36% dry weight) and the total content of unsaturated FAs along with a decrease in saturated and total FAs. Zn at a concentration of 50 mg kg^-1 stimulated an increase in the total FA content. A high erucic acid content in S. alba seeds was observed in all studied variants. A mathematical model was used to evaluate the physicochemical properties of biofuels. The parameters relating to the FA composition of seeds of plants grown on a Zn-contaminated substrate did not deteriorate, and in the case of the kinematic viscosity coefficient, they were even improved compared to the control plants and complied with American (ASTM D6751) and European (EN 14214) standards for biofuels. The obtained data indicate a negative effect of high Zn concentrations on seed yield. Changes in the FA composition of S. alba seeds may reduce their value for the production of edible oils due to the high content of erucic acid, but they could be used to produce technical oils (biofuel).