Effects of Curcumin on the Oxidative Stability of Oils Depending on Type of Matrix, Photosensitizers, and Temperature

Abstract

The photosensitizing activity of curcumin was tested in corn oil and oil‐in‐water (O/W) emulsion systems under visible light irradiation. In addition, the antioxidative/prooxidative properties of curcumin were evaluated in corn oil at 100 °C and in O/W emulsion at room temperature under riboflavin photosensitization or at 60 °C in the dark. Curcumin acted as a photosensitizer in corn oil and O/W emulsions . The oxidative stability of corn oil samples containing curcumin (0–5.0 mmol/kg oil) were not significantly different (p > 0.05) at 100 °C, implying curcumin did not act as an antioxidant nor a prooxidant in corn oil. However, curcumin inhibited lipid oxidation in O/W emulsions under riboflavin photosensitization at room temperature and 60 °C in the dark. The photosensitization and antioxidant abilities of curcumin were greatly influenced by matrix types and presence of riboflavin. Therefore, antioxidative or prooxidative characteristics of curcumin should be evaluated considering matrix type including bulk oil or O/W emulsions and presence of visible light irradiation.

Oxidative Stability in Oil‐in‐Water Emulsions with Quercetin or Rutin Under Iron Catalysis or Riboflavin Photosensitization

“…The antioxidant properties of rutin (from 0 to 1.0 mM) were not clear when compared to quercetin. RF photosensitization can induce the consumption of headspace oxygen and formation of lipid hydroperoxides and conjugated dienes through type I and type II pathways (Lee and Decker ;Yi and others ). The excited triplet state of RF can react with triplet oxygen to form singlet oxygen (type II pathway) or extract an electron or hydrogen atom from substrates to generate free radicals (type I pathway) (Min and Boff ).…”

“…O/W emulsions were prepared according to the method of Yi and others () with a slight modification. Tween 20 at 0.25% (w/w) was added to deionized water as an aqueous phase, and 2.5% (w/w) corn oil was combined with the aqueous phase.…”

“…Lipid hydroperoxides were measured by using a modified method of Yi and others (). A 0.2‐mL sample was mixed with 1.5 mL of isooctane/2‐propanol (3:2, v:v), vortexed three times for 10 s each, and centrifuged for 3 min at 2000 × g .…”

Antioxidant Properties of Astaxanthin in Oil‐in‐Water Emulsions with Differently‐Charged Emulsifiers Under Chlorophyll Photosensitization

“…The headspace oxygen in the air‐tight sample bottles was analyzed according to the method of Yi and others (). Thirty microliters of headspace gas were removed from a sample vial with an air‐tight syringe, and the oxygen content was determined using a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD).…”

“…Lipid hydroperoxides were determined using a method modified from previous reports (Yi and others , ). The sample (0.2 mL) was first mixed with 1.5 mL of isooctane/2‐propanol (3:2, v/v), before undergoing vortex‐mixing for 1 min each time.…”