Study On Variation Pattern Of 'Tarocco' Blood Orange Phenolic Compounds During Cold Storage And On-tree Storage

Citrus fruit,the world's first major fruit,is favored by consumers for its refreshing taste and rich nutrition.China is the main produce country of citrus,the planting area and yield are among the top of the world.The majority citrus varieties are medium ripening varieties in China,but few varieties of early and late ripening citrus.Blood orange [(Citrus sinensis)L.Osbeck],a late-ripening citrus,is the only species containing anthocyanin in commercial citrus fruits.It is in bright shiny appearance,subtle flavor and abundant polyphenols,which endows it with the activities of antioxidation,anti-inflammatory and anti-cancer,and the functions of a reduction of morbidity or slowing down the progression of various type of neurodegenerative disease.With the development of citrus industry,the problem of supply continuity caused by the imbalance of planting varieties is becoming increasingly serious,while it can be effectively improved by strengthening the fruit storage technology.Cold storage is a method commonly used to extend the commercial life of fresh citrus fruits,while on-tree storage is a preservation method used in late-ripening citrus.For the phenolics of blood orange,there is no research on the change of phenolics under on-tree storage.Therefore,in this paper,'Tarocco'blood orange was used as research materials.In order to explore the mechanism of phenolics enrichment in blood orange under cold storage and on-tree storage and provide a theoretical basis for blood orange production from the nutritional perspective,the effects of cold storage and on-tree storage on the edible quality and storage quality of blood orange fruit were studied;the phenolics in blood orange pulp were qualitatively and quantitatively analyzed;the change of phenol components during storage were tracked and analyzed;the changes of enzyme activities related to polyphenol synthesis pathway(phenylpropanoid pathway)were measured and the expression level of key enzyme gene in phenylpropanoid pathway were determined.The main results were as follows:(1)Both cold storage and on-tree storage had different degrees of regulating and controlling effects on blood orange fruit qualities.Both methods could effectively extend the fruit supply period to 12 weeks,improved the sensory quality of the fruit and could also significantly promote the increase of soluble solids,the degradation of titratable acid,the increase of solid-acid ratio,and the synthesis of ascorbic acid(P<0.05).At the same time,cold storage could effectively inhibit the water loss and rot of blood orange fruits.In addition,the blood orange fruit contained 7 soluble sugars and 5 organic acids.Under the action of various sugar and acid components,the total sugar and total acid content did not change significantly during storage and preservation.(2)‘Tarocco' blood orange fruit was rich in phenolics.Cold storage and on-tree storage could promote the synthesis and accumulation of polyphenols during the storage and preservation of blood orange fruit.Both methods significantly promoted the increase of total phenol content in fruits and effectively maintain the level of flavonoids in fruits.A total of 16 polyphenols were identified by HPLC-DAD,including 8 phenolic acids,6 flavanones,and 1 flavone and 1 flavonol.The contents of these phenolic substances were successively: flavanones > phenolic acids >flavanols > flavonoids.Both cold storage and on-tree storage significantly promoted the accumulation of various polyphenols(P<0.05),and mainly increased the total phenol by stimulating the synthesis of phenolic acids,followed by flavanones.Compared with the cold storage group,the on-tree storage group could significantly increase the content of phenolic acids in fruits(P<0.05),thereby promoting the accumulation of total phenols in fruits.(3)Blood orange fruit polyphenols have certain antioxidant activity,and free phenols are stronger than bound phenols.Both cold storage and on-tree storage could significantly promote the increase of free phenol and bound phenol antioxidant activity in blood orange fruit.The DPPH free radical scavenging activity of phenolics in the cold storage group fruit increased first and then decreased during storage,while ORAC of bound phenolics decreased first and then increased,and there was no significant change in free phenolics.The DPPH free radical scavenging activity of free phenolics in the on-tree storage group increased first and then decreased,and the bound phenolics was relatively stable,and ORAC of free phenolics gradually increased,and the bound phenol showed a bimodal change.Compared with the coldstorage group,the on-tree storage group had a more significant promotion effect on the polyphenol antioxidant activity of blood orange fruit(P<0.05).(4)The activity of phenylpropane pathway related enzymes could be activated by cold storage and on-tree storage.The activities of PAL,C4 H,4CL,CHI,FSI and FLS in blood orange pulp were significantly increased during cold storage and on-tree storage,but there was no significant effect on CHS enzyme.Compared with cold storage group,on-tree storage significantly induced the advance appearance of the peak of enzyme activity related to phenylpropane pathway,and had a more significant promoting effect on the improvement of enzyme activity(P<0.05).(5)According to the results of PCR,both cold storage and on-tree storage could induce the expression of key genes of the phenylpropanoid pathway.In addition to CHS gene,both methods significantly promoted the expression of PAL,C4 H,4CL,CHI,and FLS genes in blood orange pulp(P<0.05).The expression levels of other genes in cold storage group continued to increase during storage except PAL gene.For on-tree storage,the expression levels of the other genes increased first and then decreased during storage,except C4 H gene.Compared with on-tree storage group,the promoting effects of cold storage on the expression of key enzyme genes of the phenylpropanoid pathway was more significant(P<0.05).