| Phytosterol(PS)is a kind of functional component naturally existing in plants,especially in vegetable oils.PS plays an important role in reducing plasma cholesterol,and can also prevent cardiovascular disease,anti-inflammatory,anti-cancer and participate in immune regulation.Therefore,PS is usually added to vegetable oils as food additive or nutritional fortifier.Vegetable oil is an indispensable substance in human daily drinking,but in the process of production,processing and cooking,it is easy to contact light,heat and other factors that are easy to lead to lipid oxidation,resulting in corruption and deterioration.Because of the double bonds existing in PS,it is prone to similar oxidation reactions to produce phytosterol oxidation products(POPs)that are potentially harmful to human body.Taking PS in lipid system as the research object,this paper systematically carried out the research on the photooxidation characteristics of PS in lipid system initiated by light and photosensitizer,and explored the effects of different kinds of light sources,different color temperature light sources,different color packaging materials and different kinds and concentrations of photosensitizers on the photooxidation of PS from multiple angles.The test results are as follows:1.Different kinds of light sources,different light intensities and different color temperatures affect PS photooxidation.(1)LED,fluorescent lamp and xenon lamp obviously caused PS photosensitive oxidation.When the light intensity is 10000 Lux,the degradation rate of PS caused by xenon lamp is significantly higher than that of LED and fluorescent lamp.LED is the light source with the least impact on oil oxidation.(2)In the system without photosensitizer,LED light will also lead to PS oxidation,and the higher the light intensity,the higher the degree of oxidation of grease and PS,and the greater the amount of POPs.When the light intensity was 15000 Lux,PS degraded 1922μg/g,POPs generated 420 μg/g。(3)The light source with different color temperature contains different proportion of light of each wavelength,which will also lead to the difference of photosensitive oxidation.After illuminating the sample with 3000 K,4000 K and 6000 K LED light sources(light intensity is 10000 Lux)for 7 d,the oxidation degradation of PS caused by 6000 K light source is the most obvious,and the most oxidation products are generated,with the amount of 943 μg/g.Secondly,the oxidation degree of PS caused by 4000 K light source is higher than that of 3000 K light source,and 738 and 655 μg/g POPs are generated after 7 d of illumination,respectively。2.Place a PET packaging between the light source and the sample to slow down the oxidation of oil and PS.The effect of different color baffles on photosensitive oxidation of different photosensitizer systems is different.In the chlorophyll-oil system,after adding brown,blue,red,yellow,green and transparent baffles,the total PS in the system decreased to 8110,7985,7918,7602,6658 and 5275 μg/g from 9126 μg/g respectively.The results show that red,yellow,blue and brown baffles can greatly reduce the oxidation degree of PS,while green plays a certain role,but the effect is not as good as other baffles.In the methylene blue-oil system,red and blue baffles had better effect on reducing oxidation,but yellow and green played little role.The four baffles reduced the content of PS to 7755,7483,6515 and 6881 μg/g respectively.The main reason for the difference is that the yellow baffle absorbs the light of 350 ～ 450 nm required by chlorophyll and transmits the light of 600 ～ 700 nm required by methylene blue.3.The addition of chlorophyll,quercetin and curcumin had an effect on the photosensitive oxidation of lipids and PS.Different concentrations of chlorophyll play different roles in promoting the oxidation of lipid system.When the chlorophyll concentration is 10 μg/g,the oxidation degree of oil and PS was significantly higher than that of the blank control group,and increased to 100 μg/g and 1000 μg/g with the increase of chlorophyll concentration,the degradation rate of total PS increased from21.4% to 25.5% and 33.2% respectively.Curcumin also promoted the photosensitive oxidation of oil and PS,and the concentration of curcumin was 10 μg/g and 100 μg/g,there was little difference in the promotion of PS and oil oxidation,and the total PS degraded to 7060 μg/g and 6866 μg/g from 9126 μg/g respectively.When the concentration is 1000 μg/g,the total PS content in the system decreased to 6536 μg/g,significantly different from the other two groups.When quercetin was added to the system,the oxidation degree of oil and PS decreased significantly,and the higher the concentration,the more obvious the inhibition effect on the oxidation of the system.In conclusion,both chlorophyll and curcumin can promote the photosensitive oxidation of lipid system,while quercetin inhibits the oxidation.And the higher the concentration of photosensitizer,the more obvious its promoting or inhibiting effect. |
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