Contribution of Chlorophyll to Photooxidation of Soybean Oil at Specific Visible Wavelengths of Light

Abstract

Photosensitizers in foods and beverages are important considerations when selecting packaging materials. Chlorophyll is found at low concentrations in many food products. The objective of this study was to determine the photosensitizing effect of chlorophyll on soybean oil (SO) using broad-spectrum light and 3 visible wavelength regions of light. SO with added chlorophyll (0, 1, or 2 μg chlorophyll added/mL SO) was exposed to 5 light conditions, using a photochemical reactor (10 °C; 4 h). Light treatments included broad-spectrum (BS; no filter; 157.6 ± 4.7 mW intensity), 430 nm (10 nm; 1.8 ± 0.7 mW), and 660 nm (10 nm; 0.332 ± 0.05 mW) wavelengths compared to a no-light control. Chlorophyll a (but not b) absorbs light in the selected visible wavelength regions. Chlorophyll degradation was evaluated. Oxidative changes in SO were assessed by peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) assay, which measures malondialdehyde (MDA). Chlorophyll was completely degraded at BS and 430 nm conditions and degraded to 36% of original concentration at 660 nm wavelength. PV and MDA concentration significantly increased with chlorophyll addition (1 μg/mL) at BS and 430 nm wavelengths compared to no-light control. Lower light intensity at 660 nm initiated oxidation reactions as measured by PV, but not significantly. There were differences in PV (BS, 430 nm) and TBARS (BS) between the no-light and light-exposed SO without chlorophyll added. There was very little effect at 450 nm. This study suggests that broad-spectrum light and at least light wavelengths at or near 430 nm and 660 nm excite chlorophyll, resulting in initiation of oxidation reactions. Packaging material selection for foods and beverages should consider blocking excitation wavelengths of photosensitizing molecules, including chlorophyll, to protect product quality.

Contribution of the Ratio of Tocopherol Homologs to the Oxidative Stability of Commercial Vegetable Oils

“…Whereas the term “loss” describes the decline in bioactive tocopherol homologs during autoxidation of lipids, atmospheric triplet oxygen reacts with lipid alkyl radicals, whose formation is accelerated in the presence of transition metals or heat [ 15 ], while photosensitized oxidation of vegetable oils is based on the direct reaction of singlet oxygen (Type II) or superoxide (Type I), released by sensitizers, such as chlorophyll, with unsaturated fatty acids in the presence of light. Both mechanisms, autoxidation as well as photooxidation, result in the formation of primary lipid peroxidation products (lipid hydroperoxides) and, subsequently, to various secondary lipid peroxidation products, such as lipid hydroxides, aldehydes and ketones [ 16 , 17 ]. In one of our previous studies, a substantial loss of α-tocopherol (−58 ± 1.5%), γ-tocopherol (−77 ± 3.5%), and δ-tocopherol (−23 ± 0.7%) was demonstrated in commercial soybean oil after 56 days of retail/household storage (22 °C, 12 h exposure to cold fluorescent light per day) [ 13 ].…”

(−)-Epigallocatechin Gallate Stability in Ready-To-Drink (RTD) Green Tea Infusions in TiO2 and Oleic-Acid-Modified TiO2 Polylactic Acid Film Packaging Stored under Fluorescent Light during Refrigerated Storage at 4 °C

“…Chlorophyll has light absorption peaks at wavelengths of 430 and 660 nm [12]. As a result, chlorophyll might have acted as a photosensitizer in our model system.…”

“…Chlorophyll is a green pigment in green tea, and its amount decides the final color of green tea infusion [23]. Light may degrade chlorophyll in RTD green tea infusions during storage because light absorptions of the photosensitizer chlorophyll are at the wavelength of 430 and 660 nm [12,23]. Hence, the light may reduce the green color of RTD green tea infusions in the packaging during storage.…”

“…Fresh tea leaves contain mainly photosensitized pigments such as chlorophylls (0.2-0.6% dry weight) and carotenoids [11]. Chlorophylls absorb light at wavelengths of 430 and 660 nm [12]. Light has a detrimental effect on green tea flavor; when green tea was exposed under 2000 lux light for one month, the green tea infusion had unacceptable off-flavors [11].…”

“…TiO 2 is well known as a low-cost, nanostructured filler for polymer nanocomposites in food packaging applications due to enhancing barrier properties as well as providing color, UV-light protection and antibacterial effects under UV-light illumination [12][13][14]. TiO 2 has been added to biodegradable polylactic acid (PLA), which is classified as generally regarded as safe (GRAS), for direct-contact materials in food packaging application by the U.S. Food and Drug Administration [15].…”