| Pecan kernels are thick and sweet in taste,containing rich nutrients such as fats,proteins,and carbohydrates,and are highly favored by consumers.However,pecan kernels are prone to oxidation and rancidity during storage and processing,which can reduce their quality.Currently,most research attributes the oxidation of pecan kernels to the oxidation reaction of internal fats,but neglects the fact that fats exist in the form of oil bodies in pecan kernels,and changes in oil body structure can also affect the oxidation process of pecan nuts.It is not yet clear whether the rupture of oil bodies will exacerbate the oxidation of pecan kernels and the mechanism of oil body rupture.Therefore,this study aimed to thoroughly analyze the mechanism of pecan kernel oxidation and rancidity from the perspective of oil body structure,clarified the mechanism of oil body damage,and explored the optimal heat treatment methods and conditions for pecan kernels to reduce oil body damage,improve their oxidation stability,and preserve their flavor and texture characteristics.This provided theoretical guidance and data support for the industrial application of pecans and other nut industries.The main research content and results of the paper included:1.The oxidation of pecan kernels at 60°C for 0 ～ 50 days was studied,and the changes in various oxidation indicators and internal oil body structure during different storage periods of pecan kernels were investigated.At the same time,the relationship between pecan kernel oxidation and oil body structure was verified by constructing an oil body system.The results showed that after 20 days of storage,the various oxidation indicators of pecan kernels increased significantly,entering a stage of chain growth in auto-oxidation.Meanwhile,there was extensive rupture and aggregation occurring within the oil bodies of pecan nuts,indicating a temporal correlation between oil body rupture and pecan nut oxidation.Subsequently,the oil bodies with structural ruptures had significantly higher peroxide value(PV)and thiobarbituric acid reactive substances(TBARS)values than the intact oil bodies.Therefore,it can be concluded that the damage to oil body structure can accelerate the oxidation of internal lipids in pecan kernels,thereby accelerating the oxidative rancidity of pecan kernels.2.Oil bodies were extracted from pecan kernels that underwent accelerated oxidation for0 ～ 50 days,and were prepared into emulsion to study the particle size,microstructure,composition,and changes in membrane proteins of oil bodies during different storage periods,with the aim of identifying the cause of oil body rupture.The results showed that with increasing storage time of pecan kernels,the particle size of oil bodies inside gradually increased,and the oil bodies underwent rupture and recombination.Oil body rupture led to a decrease in the lipid content from 96.34% to 91.89%,an increase in the content of free fatty acids and oxidized triacylglycerols,and a decrease in the content of polyunsaturated fatty acids from 17.531% to15.541%.Meanwhile,the results of gel electrophoresis indicated that the hydrolysis of oleosin and caleosin was a key factor causing oil body structure rupture.3.By studying the effects of sodium chloride,temperature,and different thermal treatment methods on the stability of oil body structure,the key factors that caused oil body structure damage due to hydrolysis of oil body membrane proteins during processing of pecan kernels were clarified.The results showed that sodium chloride did not have a significant destructive effect on oil body membrane proteins.Temperature was the key factor influencing the hydrolysis of oil body membrane proteins and causing oil body rupture,and the higher the temperature,the greater the degree of oil body damage.Different heat treatment methods had varying degrees of impact on oil body disruption.Based on the comprehensive analysis of microstructure,particle size,and membrane protein composition,the order of oil body structure disruption from weakest to strongest was infrared,oven,and microwave heat treatment,respectively.This was associated with the heating principles and heat transfer efficiency of the three heat treatment methods.4.Through studying the effects of three heat treatment methods on the structure of oil bodies,degree of lipid oxidation,antioxidant capacity,protein oxidation,texture,and flavor of pecan nuts,the optimal heat treatment conditions that can reduce oil body rupture,inhibit pecan nut oxidation,and preserve its texture and flavor were further clarified.The results showed that under the corresponding oven(100°C,40 min),microwave(160 W,60 min),and infrared(80°C,75 min)heat treatment conditions,the degree of oil body structure damage was the weakest.Among them,infrared heat treatment had the least impact on oil body structure.At the same time,the pecan kernels after infrared heat treatment had the weakest degree of oxidation,further verifying the conclusion that the smaller the degree of oil body rupture,the lower the degree of oxidation.In addition,pecan kernels after infrared and microwave heat treatment had strong antioxidant capacity,with polyphenol contents reaching 6.173 mg GAE/kg and 6.044 mg GAE/kg,respectively.The protein carbonyl content of pecan nuts after infrared heat treatment was the lowest,at 1.681 nmol/mg prot.The flavor and texture of pecan nuts obtained by the three heat treatments did not differ significantly from those of commercially available pecan nuts.It can be seen that infrared heat treatment was expected to become the best way to reduce pecan nut oxidation and ensure its quality. |
PDF Full Text Request