Research On Fresh-keeping Technology Of Post-harvest Broccoli

Broccoli(Brassica oleracea var.italica)is known as the ’vegetable crown’ with significant contents of vitamin C,glucosinolates,and minerals.However,it has a strong respiratory metabolism after harvest,and deteriorates very quickly.It is very easy to decay and turn its color to yellow at normal temperature.In China,most vegetable farmers and vegetable merchants cannot achieve pre-cooling in time after harvesting broccoli.Therefore,research on safe,effective and low-cost fresh-keeping methods in the transportation of broccoli is extremely necessary for vegetable farmers and vegetable vendors.In this test,’Su Qing’ No.6 broccoli was used as the test material.The physiological and biochemical indexes were measured to study the fresh-keeping effect of pre-cooling and low temperature and pre-harvest 1-MCP,and pre-harvest CaCl2 treatment on the transportation of broccoli,and the results were analyzed by transcriptomics Reveal the molecular regulatory mechanism of broccoli during the transportation.The main findings are as follows:1.The effects of pre-cooling and low temperature(0±1℃)storage on broccoli color,vitamin C content,respiration,antioxidant capacity,total phenol and total glucosinolate content were studied.The results showed that the pre-cooling broccoli maintained lower respiration,MDA content,POD activity,chlorophyllase activity and higher content of vitamin C,chlorophyll,total phenol,glucosinolate and isothiocyanates;maintained higher APX activity,CAT activity and DPPH free radical scavenging ability,and maintained better color during the transportation and storage.The results showed that pre-cooling and low temperature treatment could effectively prolong the shelf life of broccoli.The color of broccoli is closely related to chlorophyll metabolism.In addition to the chlorophyll content,it is also significantly related to POD activity.The content of glucosinolate and isothiocyanates is closely related to the degree of cell damage.There is a certain relationship between various indicators of vegetables,which can provide scientific basis for the utilization and analysis of the nutritional value of broccoli.And the chlorophyll content,CAT activity,glucosinolate content,chlorophyllase avtivity,respiration and MDA content can be used as key indicators for evaluating the quality characteristics of broccoli.2.The effects of pre-harvest 1-MCP and CaCl2 treatment on broccoli color,vitamin C content,respiration,antioxidant capacity,total phenol,total glucosinolate and isothiocyanate content were studied.It was found that 400 μL/L 1-MCP solution and 10mmol/L CaCl2 solution could effectively prolong the shelf life of broccoli.1-MCP and CaCl2 delays the degradation of chlorophyll by inhibiting chlorophyllase activity,and inhibits the increase of respiration,a*and b*values.1-MCP and CaCl2 treatment increased the total phenol content and the activities of antioxidant enzymes such as APX and CAT,maintained higher DPPH free radical scavenging rate and the content of vitamin C,glucosinolate and isothiocyanates and lower accumulation of MDA.The fresh-keeping effect of 1-MCP is better than CaCl2.And pre-harvest 400 μL/L 1-MCP treatment is a good alternative way when vegetable farmers and vendors fail to achieve precooling in time.3.The postharvest metabolic pathway and chlorophyll metabolism mechanism of precooling and low temperature treatment and pre-harvest 1-MCP treatment at the transcription level was studied.A total of 79.74 Gb of Clean Data was obtained.The Clean Data of each sample reached 5.94 Gb,and the percentage of Q30 bases was 93.49%and above.The GO function enrichment analysis of differentially expressed genes found that the 1-MCP group significantly changed response to cytokinin,photosynthesis,light harvesting in photosystem I,light-harvesting complex,and xyloglucan:xyloglucosyl transferase activity.The precooling and low temperature group significantly affected microtubule-based movement,oxidation-reduction process,response to salicylic acid,microtubule,light-harvesting complex,microtubule binding,microtubule motor activity and so on.KEGG enrichment analysis found that the metabolic pathways significantly changed in the 1-MCP group were Carbon metabolism,Linoleic acid metabolism,Glyoxylate and dicarboxylate metabolism,Alanine,aspartate and glutamate metabolism,and 2-Oxocarboxylic acid metabolism.Significantly changed pathways in the pre-cooling and low temperature group include Phenylpropanoid biosynthesis,Linoleic acid metabolism,Glucosinolate biosynthesis,Flavonoid biosynthesis,Alanine,aspartate and glutamate metabolism,and so on.It was also found that 1-MCP and pre-cooling treatment significantly affected genes expression related to key enzymes(GluTR,PBDG,UROD,CPOX,MgCh,MgMT,CS,POR,CBR,CLH,PPH and PaO)of chlorophyll metabolism pathways.The mechanism of 1-MCP and pre-cooling treatment for broccoli was obtained by preliminary sorting.