Green Tea Extract Enhances the Oxidative Stability of DHA-Rich Oil

Abstract

Docosahexaenoic acid (DHA) is one of the most important omega-3 polyunsaturated fatty acids, with proven health-promoting properties. However, oils with a very high content in DHA (DHAO) are extremely susceptible to oxidation, which affects shelf stability and limits incorporation in food products. Green tea extracts (GTE) are potential candidates for the protection of these oils, but their use in such oils has not been previously reported. This study investigated the effect of GTE (160 ppm, 400 ppm, 1000 ppm) and α-tocopherol (80 ppm, 200 ppm, 500 ppm) on the oxidative stability of a DHAO over a 9-week storage at 30 °C. The oxidative status was monitored during storage by the measurement of peroxide value (PV) and p-anisidine value (p-AV). Changes in eicosapentaenoic acid (EPA) and DHA content, as well as in catechins and tocopherol contents, were also evaluated. The addition of GTE enhanced the oxidative stability of DHAO by reducing the formation of peroxides and secondary oxidation products, whereas α-tocopherol had no significant effect on the PV of oil during storage but led to a significantly higher p-AV. The EPA and DHA content of DHAO was stable in GTE-supplemented samples whereas a decrease was observed in the control and α-tocopherol-supplemented samples. GTE also delayed the degradation of tocopherols initially present in the oil, while catechins resulting from the addition of GTE decreased progressively during the storage period.

Keywords: DHA-rich oil; alpha-tocopherol; catechins; green tea extract (GTE); natural antioxidants; oxidation.

Figure 1

Peroxide value (PV) (A) and p-anisidine value (p-AV) (B) of DHA-rich oil (DHAO) with or without antioxidant during an oven storage test at 30 °C. Values are mean ± SD (n = 3); Different capital letters (A–D) indicate significant differences (p ≤ 0.05) during storage within a sample; different lower-case letters (a–e) among samples indicate a significant difference (p ≤ 0.05) at a specific storage time. Control = DHA-rich oil without added antioxidant; Toco80, Toco200 and Toco500 = DHA-rich oil supplemented with 80 ppm, 200 ppm and 500 ppm of α-tocopherol, respectively; GTE160, GTE400, GTE1000 = DHA-rich oil supplemented with 160 ppm, 400 ppm and 1000 ppm of green tea extract, respectively.

Figure 2

Catechins in DHA-rich oil supplemented with green tea extract at 1000 ppm and stored over 9 weeks at 30 °C. Values are presented as mean ± SD (n = 3). Different letters (a–d) for each catechin indicate a significant difference (p ≤ 0.05) during storage. EGC = epigallocatechin, EC = epicatechin, EGCG = epigallocatechin gallate, ECG = epicatechin gallate.

Figure 3

Tocopherol content of DHA-rich oil during 9 weeks of storage at 30 °C. (A) α-tocopherol; (B) γ-tocopherol; (C) δ-tocopherol; (D) Total tocopherols. Values are presented as mean ± SD (n = 3). Different letters (a–d) indicate a significant difference (p ≤ 0.05) during storage for each sample.