Evaluation of Hemp Seed Oils Stability under Accelerated Storage Test

Abstract

The interest in hemp seed oil has recently increased, due to the latest regulations which allow its use as food. Hemp seed oil is characterized by a high content of polyunsaturated fatty acids, which are highly prone to oxidation. Accelerated thermal oxidation (60 °C, 18 days) has been applied to nine types of cold-pressed hemp seed oils to monitor the evolution of the samples during oxidative deterioration. The results showed that the only determinations of primary (peroxide value) and secondary (TBARs) oxidation products did not allow a sufficient or correct evaluation of the oxidative changes of hemp seed oils during storage. In fact, samples at the end of the test were primarily characterized by a high presence of oxidation volatile compounds and a significant decrease of antioxidants. Several volatiles identified before the accelerated storage, such as the predominant α-pinene and β-pinene, gradually decreased during the accelerated storage period. On the other hand, aldehydes (hexanal, (E)-2-hexenal, heptanal, (E,E)-2,4-hexadienal, (E)-2-heptenal, (E,E)-2,4-heptadienal, (E,Z)-2,4-heptadienal, 2-octenal, nonanal, nonenal, 2,4-nonadienal, (E,E)- 2,4-decadienal and 2,4-decadienal), ketones (1-octen-3-one, 3-octen-2-one, (E,E)-3,5-octadien-2- one and 3,5-octadien-2-one), acids (propionic acid, pentanoic acid, hexanoic acid and heptanoic acid) and 2-pentyl-furan increased during the accelerated storage, as principal markers of oxidation.

Keywords: accelerated storage; fatty acids; hemp seed oil; solid-phase microextraction; volatile compounds.

Figure 1

Results of the peroxide value expressed as mEqO2/kg of oil during the accelerated oxidation test (from T0 to T18, during 18 days of heating at 60 °C). Data are reported as mean ± standard deviation of 3 independent replicates. Different letters indicate statistically significant differences among Peroxide Values at different oxidation times for each sample (one-way ANOVA, Tukey’s HSD, p < 0.05).

Figure 2

Heat map comparing the content of the volatile compounds in the nine types of hemp seed oils during the accelerated storage test.

Figure 3

Cannabinoid content (µg/g) in the nine hemp seed oils at time 0 (T0) and time 18 (T18) of the accelerated oxidation test. Different letters between time 0 (T0) and time 18 (T18) in the same samples and for the same cannabinoid indicate statistically significant differences (one-way ANOVA, Tukey’s HSD, p < 0.05).

Figure 4

Ratio between cannabidiolic acid (CBDA) and cannabidiol (CBD) at the beginning (time 0/T0) and at the end (time 18/T18) of the accelerated oxidation test.

Figure 5

Representation of the principal component analysis (PCA) for volatiles identified in all the samples at each time of analysis (0, 3, 6, 9, 12, 15 and 18 days of accelerated storage). Observations are shown in blue dots and variables are shown in red font.