Steryl Sinapate as a New Antioxidant to Improve Rapeseed Oil Quality during Accelerated Shelf Life

Abstract

In recent years, steryl esters have become an attractive for the cosmetic, pharmaceutical, and food industries. Hence, the effect of exogenous antioxidant, β-sitosteryl sinapate on oxidative stability and antioxidant activity (AA) of refined rapeseed oil was evaluated by the accelerated shelf-life test. Oxidative parameters of refined rapeseed oil-peroxide value (PV), anisidine value (p-AnV), acid value (AV), and spectrophotometric indices (K₂₃₂, K₂₆₈)-increased during storage. However, the addition of β-sitosteryl sinapate caused a decrease of the primary and secondary oxidation products in the supplemented oils in comparison with the control sample. Moreover, oils with steryl ester had higher AA than oil without the synthetic antioxidant. The accelerated storage negatively affected the antioxidant potential of refined and enriched oils causing the AA decrease by 25-54% and 7-15%, respectively. Studies have consistently demonstrated beneficial associations between the presence of β-sitosteryl sinapate in oil samples and the inhibition of their oxidative degradation under the accelerated conditions. Additionally, the possibility of using the synchronous fluorescence (SF) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy for identification and observing changes in main fluorescent components present in non-supplemented and supplemented rapeseed oils during the accelerated storage was attempted.

Keywords: antioxidant activity; fluorescence spectroscopy; oxidative degradation; rapeseed oil; β-sitosteryl sinapate.

Figure 1

Structure of β-sitosteryl sinapate.

Figure 2

Position of oil samples in incubator.

Figure 3

Synchronous fluorescence spectra of refined rapeseed oils without and with β-sitosteryl sinapate diluted in n-hexane (c = 1%) and recorded at Δλ = 30 nm after storage at accelerated conditions.

Figure 4

Synchronous fluorescence spectrum recorded at Δλ = 30 nm (a) and excitation-emission matrix (b) of β-sitosteryl sinapate diluted in n-hexane (c = 0.1%).

Figure 5

Excitation–emission matrices of refined rapeseed oils without β-sitosteryl sinapate (a–e) and refined rapeseed oils with β-sitosteryl sinapate (f–j) after 0, 1, 2, 3 and 4 weeks of storage at accelerated conditions.

Figure 6

Bi-plot of scores and loadings of data obtained from fluorescence spectra, oxidative, and antioxidant parameters of refined rapeseed oils without and with β-sitosteryl sinapate stored during during 4 weeks.