Compositional Changes during Storage of Industrially Produced Olive Oils Co-Milled with Olive Leaves

Abstract

The possibility of enriching the oil produced from Leccino cultivar olive fruits with phenolic and volatile compounds by adding olive leaves (2.5%) during industrial-scale production were investigated. Furthermore, the influence of the addition of leaves on the oil quality, composition, and oxidative stability during storage for 6 and 12 months was studied. A slight negative impact on the oil quality after processing with leaves was determined. The addition of leaves had no influence on the total saturated, monounsaturated, and polyunsaturated fatty acids in oils, while it influenced increases in total phenolic compounds (+29.55%), total secoiridoids (+29.43%), chlorophylls (+47.59%), and the oil stability index (+18.70%), and their higher values were also determined in the stored oils. The addition of leaves increased C5 volatiles (+10.50%) but decreased C6 volatiles (-10.48%). The intensity of most of the positive sensory characteristics increased in fresh oils obtained with leaves, and the established improvements were also maintained in the stored oils. The extractability of olive paste was positively affected by the addition of olive leaves, which increased the oil yield (+27.17%). The obtained results significantly contribute to the knowledge about the possibilities of enriching olive oils with bioactive compounds.

Keywords: co-milling; olive leaves; olive oil; oxidative stability; phenolic compounds; sensory characteristics; volatile compounds.

Figure 1

Pigments (mg/kg), chlorophyll and carotenoids, determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage in oils of the Leccino cultivar (L) produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves. Results are expressed as mean values ± SD (n = 3). Means were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 2

Oxidative stability index (hours) determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage in oils of the Leccino cultivar (L) produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves. Results are expressed as mean values ± SD (n = 3). Meas were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 3

Total phenols (mg equivalents of galic acid/kg oil) determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage in oils of the Leccino cultivar (L) produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves. Results are expressed as mean values ± SD (n = 3). Means were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 4

Results of quantitative descriptive sensory analysis of odor characteristics in Leccino oils produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage. Results are expressed as mean values ± SD (n = 3). Means were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 5

Results of quantitative descriptive sensory analysis of taste characteristics in Leccino oils produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage. Results are expressed as mean values ± SD (n = 3). Means were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 6

Total sensory score in Leccino oils produced with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves determined immediately after processing (L-0) and after 6 (L-6) and 12 (L-12) months of storage. Results are expressed as mean values ± SD (n = 3). Means were compared separately for each storage time, and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between oils produced with or without the addition of olive leaves.

Figure 7

(a) Separation of Leccino cultivar olive oils according to the rate of leaf addition on PC1 and PC2 (red circles—oils produced without leaf addition (Control), green circles—oils produced with leaf addition (Leaf)). (b) Factor loadings of selected variables (the concentrations of individual phenolic compounds, the concentrations of individual volatile compounds, and the intensities of sensory attributes) along the directions of principal components PC1 and PC2.

Figure 8

(a) Separation of Leccino cultivar olive oils according to the duration of oil storage on PC1 and PC2 (red circles—fresh oils produced with and without leaf addition (Fresh); green circles—oils produced with and without leaf addition, stored for 6 months (Six months); blue circles—oils produced with and without leaf addition, stored for 12 months (Twelve months)). (b) Factor loadings of selected variables (the concentrations of individual phenolic compounds, the concentrations of individual volatile compounds, and the intensities of sensory attributes) along the directions of principal components PC1 and PC2.

Figure 9

(a) Oil yield (%) and (b) extractability index of Leccino cultivar olive paste obtained with (2.5%—L-L) or without (0%—L-cont) the addition of olive leaves. Results are expressed as mean values ± SD (n = 3), and different small letters show significant difference (Tukey’s test. p ˂ 0.05) between treatments.