Study On The Browning Mechanism And Control Of Minimally Processed Lily Bulbs

Yixing Lily bulbs cultivated Lilium lancifolium Thunb.were used as materials.The changes of physiological,the cell vitality,ultrastructural,membrane lipid and energy metabolism and the role of browning substrates of phenols in postharvest minimally processed lily bulbs were investigated.Heat and AIP treatment were subjected to minimally processed lily bulbs to assess its effect on browning control.These results will provide some theoretical basis for further study the browning mechanism in minimally processed lily bulbs.The main results were as follows:(1)Physiological and biochemical changes of minimally processed lily bulbs during storage at 4? were measured and compared.The results showed that with the prolongation of storage time,the color of the scale epiderm of lily bulbs turned brown and cell activity weakened.Membrane permeability and MDA content increased during storage.The activity of SOD,CAT and LOX increased first and then decreased.The browning degree of different parts in lily bulbs was in the order of internal scales>external scales>middle scales.The browning degree was significantly correlated with L*,a*,b*values,cell membrane permeability,MDA content,CAT activity and LOX activity(p<0.01),and was significantly correlated with SOD activity(p<0.05).The correlation coefficient of MDA content and browning degree was the highest(r=0.991),indicating that the increase of browning degree of lily bulbs was closely related to the lipid metabolism of cell membrane.(2)The changes of total phenol,PPO,POD,PAL activities and phenolic composition during the storage of minimally processed lily bulbs were studied and their effects on Browning were evaluated.The results showed that the total phenol,PPO,PAL and POD were significantly correlated with the browning of lily bulbs,and the correlation coefficient was 0.928,0.850 and 0.497,respectively.PPO was the key enzyme in browning of lily bulbs,followed by PAL and POD.The total phenol content of lily bulbs was lower than that of outer layer and inner layer,and the change trend of total phenol content was consistent with the change of PPO and PAL activities.The types and contents of phenol compounds increased gradually during storage.The content of regalosides K,regalosides D,regalosides B and 4,7-dimethoxy puerarin were higher in storage period.The correlation coefficient between regalosides F and browning degree was the highest(r=0.853).In addition,regalosides C,regalosides E,regalosides A,4,7-dimethoxy puerarin and regalosides K were closely related to lily bulbs browning.(3)The content of ATP,ADP,AMP and energy charge,mitochondrial energy metabolism related indexes including SDH,COX,H+K+-ATPase,Ca2+-ATPase were studied in minimally processed lily bulbs during storage,and the relationship between the energy metabolism and the browning of the bulb of the lily bulbs were analyzed.The results showed that the content of ATP,ADP and the total energy charge decreased during the storage of lily bulbs,while the content of AMP increased gradually.The occurrence of browning in lily bulbs was closely related to energy charge(r=-0.967).The activity of mitochondrial energy metabolism related enzymes gradually declined,indicating that the mitochondrial function was damaged and the lily scales were gradually senescent.The level of energy in middle scales decreased slowly,and the activity of mitochondria related enzymes in which was significantly higher than that of the internal scales.There was a significant correlation between browning degree and mitochondrial enzyme activity.Browning degree was used for dependent variable,other indexes were used for independent variables,and linear regressive analysis was presented.The simplified regression model was BD=2.056+0.417x5-0.085x13-0.009x12(x5:MDA,x13:ATP,x12:PAL).The regression analysis showed that browning degree was closely related to MDA,ATP and PAL activity.(4)The effects of HT(50 ?,3 min)and AIP(0.5 mmol/L,5 min)alone or combined treatment on the browning of lily bulbs during storage were studied.HT and AIP combined treatment resulted in lily bulbs with the lowest browning degree.HT +AIP treatment lily bulbs also showed the lowest TP content,PPO,POD and PAL activities,and kept cell vitality well.Combined treatment preserved higher SOD and CAT activities than control.These treatments could effectively delay the browning process of minimally processed lily bulbs.The browning degree was significantly correlated with L*,a*,b*,total phenol content,PPO activity,POD activity,PAL activity,cell membrane permeability,MDA content,CAT activity and LOX activity(p<0.01),and significantly correlated with SOD activity(p<0.05).The correlation coefficient of 4,7-dimethoxy puerarin and browning degree was the highest(r=0.727).In addition,(-)-epicatechin gallate-3"-O-methyl,regalosides C,regalosides K,regalosides F,regalosides A and hyperoside were closely related with browning degree.