Quality Control Of Hydroponic Lettuce Grown In Plant Factory By Combination Of LED Lighting And Nutrient Solution Supply Prior To Harvest

Leafy vegetables are important nutrient sources for human beings and play an important role in safeguarding health maintenance.Lettuce as a model leafy vegetable is widely used to produce in plant factory under LED lighting combined with hydroponics for high yield and quality production.However,unfortunately leafy vegetables contained higher nitrate content is disturbing the whole food chain with severe threats to human life.Therefore,LED lighting and nutrient solution adjustment prior to harvest were used to reduce nitrate content of hydroponic lettuce grown in plant factory for value-added plant production in this study.The target of this study is to reduce the nitrate content of hydroponic lettuce without losing yield for controlling the lettuce quality.The main results and conclusions in this study are as follows.Interactive effects of light quality and nitrogen supply before harvest on quality formation of hydroponic lettuce(Lactuca sativa L.cv.Frill ice,Ziwei,and Luzhu)were conducted in plant factory under LED lighting.Light sources including LED lamp with R:B ratio of 1.2 and fluorescent lamp with R:B ratio of 1.8 were used to provide lighting intensity of 250 ?mol m-2 s-1 and photoperiod of 16 h d-1 for hydroponic lettuce growth.At the three days prior to harvest,lighting intensity improved from 250 ?mol m-2 s-1 to 350?mol m-2 s-1 and nutrient solution based on Yamasaki formula decreased to half concentration were used to reduce the nitrate content of the hydroponic lettuce.The gradual decrease in nitrate content of hydroponic lettuce was accompanied by an increased concentration of nutritionally carbohydrates and keep same level of fresh weight of leaves at half concentration of nutrient solution and increasing lighting intensity.The vitamin C contents in three cultivars observed significantly higher with lowing nitrate content and same fresh weight in LED lighting compared to fluorescent lamps.The fresh and dry weights of leaves were decreased in same lighting intensity combined with half concentration of nutrient solution.Further,presented results disclosed that to avoid high accumulation of nitrate in leafy vegetables,the strategy of lowering nitrogen supply and increasing light intensity prior to harvest benefiting growers and consumers by improving quality of the product also making it consumer friendly.In different temperature such as 20 ?,22 °C and 24 °C in photoperiod with +4°C temperature difference between photoperiod and dark period,high performance of quality control in lowing nitrite content without losing fresh weight for hydroponic lettuce were found at half concentration of nutrient solution and increasing lighting intensity.Light quality strongly impairs lettuce growth and quality due to inhibition of thylakoid multiprotein complex and photosynthetic metabolism under LED lighting environment.Therefore,a comparative proteomic study of lettuce leaf using multidimensional protein identification technology in response to light quality in plant factory was conducted.Our results demonstrated that the light quality had a significant effect on altering the proteomic level and expression pattern in lettuce leaves,in addition,light quality had marked striking effects on functional,molecular and biological level among treatments.The study successfully identified seventy-one proteins for plants treated with fluorescent lamps,fifty and forty-one for LEDs,respectively,which were involved in energy metabolism and regulation of morphogenesis.Our data will provide the foundation for future detail study to unlock the advantages of this next generation lighting technology to strengthen the connection between light quality and multi-complex protein(CB23_HORVU)of LHC family in highly energy-efficient horticulture.Therefore,to produce high quality of leafy vegetables with low nitrate content,quality control methods during multi-selves cultivation including light quality,light intensity and nutrient solution can add value to the product.It is expected that our study recommendations can be suitable for the improvement of aesthetic and heath values of leafy vegetables.