| Red and blue LED irradiation on fruits and vegetables has the advantages of no pollution,which has been widespread concerned. In this paper,,in order to explore the mechanism of red and blue LED irradiation on fruits and vegetables quality impacts,combination of red and blue LED light irradiation preservation technology is used as the core; we established a red and blue LED light irradiation on fresh fruits and vegetables testing system,which based on optical principles. The distribution of light intensity of flat are measured,which distance of 30 cm, 40 cm and 50 cm away from the LED light, and according to the measurement results, the test cabinets light irradiation uniformity are analysed. The temperature distribution at the plane of 50 cm are measured under the light intensity of 20μmol·m-2 ·s-1, the effect of heat transfer under LED light irradiation are analysised based on the above results. The weight loss rate, chlorophyll content, VC content, hardness and color of the celery are measured to explore the impact of humidity under the condition of a combination of red and blue LED light irradiation,which determined the reasonable humidity of follow-up experimental studies. The weight loss rate, chlorophyll content, VC content, hardness and color of the celery and broccoli are measured under the light intensity of 10 μmol·m-2·s-1,20μmol·m-2·s-1 and 30μmol·m-2· s-1. Analysis the effects of celery and broccoli harvest quality under different light intensity respectively,and explored the mechanism of quality indicators changes. The best recipe of celery and broccoli for the post-harvest preservation technology of red and blue LED light irradiation are determined according to the above results.Specific conclusions are as follows:1. Red and blue LED light irradiation of fresh fruits and vegetables test system:(1) Light uniformity are differ from the distanceof the LED light, which illumination are gradually improved with increasing distance,and 30 cm away from the ligh is the worst while 30 cm away from the ligh is the best.(2) Temperature fluctuates with the temperature fluctuations in the test box, and the Plane temperature of 50 cm are almost the same while the cold storage temperature is maintained at 4oC,the heat transfer of red and blue LED light had no significant effect on the temperature of the text box.2. Different humidity and light intensity on the post harvest quality of celery changes:(1) Humidity impact quality changes of celery under the condition of red and blue LED irradiation significantly,and 90% relative humidity helps to reduce water loss of celery,but the delay of chlorophyll content and VC content of celery is not due to degradation of excessive water loss, because of the LED light.(3) For the same light intensity, light intensity group compared with backlighting group,three kinds of light intensities of red and blue light treatment may help to slow the degradation of chlorophyll and VC content of celery, the loss rate of chlorophyll content under 10 μmol·m- 2·s-1,20μmol·m-2·s-1 and 30μmol·m-2·s-1 light intensities is respectively 0.54, 0.57 and 0.24 times of the condition of same batch experiments without light, while VC content loss rate was 0.54, 0.31 and 0.29 times under no light conditions.(4) For the comparison of three different light intensity, the content of chlorophyll loss ratio of celery under 30μmol·m-2·s-1 light intensity are 0.9 and 0.54 times under the condition of 10μmol·m-2·s-1 and 20μmol·m-2·s-1 light intensity; VC content loss ratio are 0.36 and 0.36 times under the condition of 10μmol·m-2·s-1 and 20μmol·m-2·s-1 light intensity. Overall, 30μmol·m-2·s-1 light intensity preservation best.3. Different light intensity treatments on broccoli postharvest quality:(1) Red and blue light treatment may help to slow degradation of chlorophyll and VC of broccoli, the loss rate of chlorophyll content under 10 μmol·m- 2·s-1, 20μmol·m-2·s-1 and 30μmol·m-2·s-1 light intensities is respectively 0.73, 0.53 and 0.22 times of the condition of same batch experiments without light, while VC content loss rate was 0.84, 0.52 and 0.75 times under no light conditions. The light intensity 30μmol·m-2·s-1 is the best in terms of keeping the chlorophyll, while the light intensity 20μmol·m-2·s-1 is the best in terms of keeping the VC content.(2) Pros and cons of different intensity light treatment has different impact of each indicator,with the increase of light intensity, weight loss trends to slowly increasing,and 10μmol·m-2·s-1 light intensity has the minimum rate of weight loss; chlorophyll content loss ratio increased with the light intensity gradually decreased, 20μmol·m-2·s-1 light intensity has the minimum rate of VC loss rate; color loss in 10μmol·m-2·s-1 light intensity lower than the other conditions.To sum up, red and blue LED irradiation treatment has significant effect on postharvest preservation of fruits and vegetables, and the changes differ with the different intensity of light. 90% humidity environment more conducive to maintaining the water content of fruits and vegetables taken in the light of LED, nutritional quality of celery and broccoli has been significantly improved under different lighting conditions than the condition of the same batch experiments without light. For celery, 30 μmol·m-2·s-1 light intensity preservation best, and 20 ~ 30μmol·m-2·s-1 is the best for broccoli. |
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