| As a typical cold-sensitive fruit and vegetable,green pepper fruit is bound to face the problem of chilling in low temperature storage and cold chain transportation.The commercial,edible and economical types of green pepper fruits after chilling injury were reduced to varying degrees.The short-time heat treatment method has the advantages of safety,high efficiency,no pollution,and easy operation.Therefore,this study is suitable for short-term heat treatment conditions of frozen green pepper fruits before storage,and explores the storage quality of green pepper fruits of each group under different short-term heat treatment conditions.The changes in a series of systems such as active oxygen metabolism and ASA-GSH(ascorbic acid-glutathione)cycle further explored the mechanism of chilling damage.The main findings are as follows:1.Short-term hot water treatment to reduce the chilling injury of green pepper fruits in cold storage.The fruit of"Luojiao"green pepper was used as the test material,and the weight loss rate was the target.The short-term hot water treatment temperature and short-time hot water treatment time were respectively carried out.The single factor test is used to determine the temperature and time range of short-term hot water treatment.Combined with the quadratic regression orthogonal rotation combination design,the regression equation of the short-time hot water treatment temperature and time with the weight loss rate as the evaluation index is obtained:Y=0.426918-0.018074x1-0.001552 x2+0.000205 x12-0.00000357 x1×x2+0.000064812 x22.The optimized short-term hot water treatment temperature was 44.05°C and the time was 11.97 min.Finally,the verification test was carried out,and the temperature and time of short-term hot water treatment under optimal conditions were selected,and the weight loss rate was determined to be 2.07%.The results show that the measured values and theoretical values are in good agreement.2,short-term forced convective hot air treatment to reduce the chilling injury of cold green pepper fruit,the experimental study,"Luojiao"green pepper fruit as test material,with electrolyte permeability as an indicator,through a short period of forced convection hot air temperature and time of the single Factor tests to determine temperature and time range.Combined with the quadratic regression orthogonal rotation combination design,the regression equation of the short-time forced convection hot air treatment temperature and time with electrolyte permeability as the evaluation index is obtained:Y=411.608703-14.682192x1-2.197679 x2+0.147453 x12+0.000646 x1×x2+0.05015 x22.The optimized short-term forced convection hot air treatment temperature was 49.74°C and the time was 19.68 min.Finally,the verification test was carried out,and the value of the electrolyte permeability measured under the optimal short-time forced convection hot air treatment condition was 25.37%,which was in good agreement with the theoretical value.3.Effects of different short-time heat treatment time on storage quality,active oxygen metabolism and ASA-GSH cycle of frozen green pepper fruits.In this test,the green pepper fruits and the control group were stored in a cold storage(temperature:4°C;relative humidity:85%)for 21 days after short-term hot water treatment.The chilling injury index,chlorophyll,and chlorophyll of the green pepper fruits of each treatment group were measured every 2 days.Titration acid,electrolyte permeability,malondialdehyde(MDA),superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),hydrogen peroxide(H2O2),superoxide anion(O2-),reduced glutathione(GSH),glutathione reductase(GR),ascorbic acid(ASA),and ascorbate peroxidase(APX)activity.The test results showed that the changes of various indexes of green pepper fruits under different short-term hot water treatment conditions were different during cold storage.Under the hot water treatment at 44°C,the chilling injury symptoms of the green pepper fruits in the 12min group were the lightest and the chilling injury time was delayed.The electrolyte permeability and MDA content in the green pepper fruit of this group were the lowest in each treatment group.The activities of SOD,POD and CAT were higher than other groups in the same period,and the ASA-GSH cycle was effective.Among them,2,7 and 17 minutes can also alleviate the chilling symptoms of green pepper fruit to some extent and maintain its storage quality.For the 22min treatment group,the effect of delaying chilling injury was not achieved,and the storage quality of the green pepper fruit of this group was not much different from that of the control group.The results showed that in each treatment group,the hot water treatment at 44°C for 12 min not only effectively delayed the occurrence of chilling injury of the frozen green pepper fruit,but also reduced the symptoms of chilling injury.The electrolyte permeability value which reflects the integrity of the cell membrane is kept at a low level,and the MDA content of the membrane lipid peroxidation accumulation is also low.The content of active oxygen scavenging enzyme activities(SOD,POD,CAT)and non-enzymatic substances(GSH,ASA)remained at a high level,thereby controlling the active oxygen species(H2O2,O2-)in the cells to be in a safe range.Reduce the adverse damage of the frozen green pepper fruit.4.Effects of different short-term forced convection hot air time on storage quality,active oxygen metabolism and ASA-GSH cycle of frozen green pepper fruits.The strong heat convection air treatment was carried out in a constant temperature and humidity chamber at 50°C for 5,10,20,30,40 min,and the green pepper fruit without any treatment was set as a control group.The chilling injury index,chlorophyll,titratable acid,electrolyte permeability,malondialdehyde(MDA),H2O2,O2-,GSH,ASA content and SOD,POD,CAT,GR and APX activities of green pepper fruits were determined every 2 days.The test results show that the storage effect of green pepper fruits under different forced convection hot air treatment time is different.From theorderofoccurrenceofchillinginjury,ck>40min>30min>5min>10min>20min,and the severity of chilling symptoms also showed this relationship.Forced convection hot air treatment at 50°C for 20 min can not only delay the increase of chilling injury index of frozen green pepper fruit,but also control the electrolyte permeability and malondialdehyde content.The activity of SOD,POD,CAT,GR and APX in the active oxygen defense system can be maintained,and the contents of active oxygen scavenging substances GSH and ASA are also much higher than other groups.For the 30min and 40min treatment groups,the effect of delaying the occurrence of chilling injury of green pepper fruit was not obvious,and the treatment effect was similar to that of the control group.In general,the forced convection hot air treatment at50°C for 20 min has a good preservation effect on the storage quality of the frozen green pepper fruit,and the chilling symptoms of the green pepper fruit of the group are alleviated.5?Effects of different short-term heat treatment conditions on the storage quality and antioxidant defense system of frozen green pepper fruits.The chilling injury index,chlorophyll,titratable acid,electrolyte permeability,MDA,H2O2,O2-,GSH of the frozen green pepper fruit were studied by heat treatment at 44°C for 12 min and forced convection hot air at 50°C for 20 min without any treatment.,ASA content and SOD,POD,CAT,GR and APX enzyme activities.The test results show that the hot water treatment conditions can better alleviate the chilling symptoms of green pepper fruits and delay the occurrence of chilling damage.It also plays a good role in scavenging the accumulation of membrane lipid peroxidation products,thereby protecting the integrity of the cell membrane of green pepper fruit.In addition,hot water treatment can control the rate of generation of active oxygen,improve the antioxidant activity and antioxidant enzyme activity of green pepper fruit,and the effect is better than forced convection hot air treatment. |
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