Study On The Variation Of The Crystal Network Structure And Macroscopic Physical Properties Of Palm Oil-based Shortenings During Storage

With the development of the national economy and food industry, and the rising percapita consumption, as a new type of edible oils and fats for products in the modern foodindustry, a large number of plastic fats with higher product quality are required.The impropertemperature or the fluctuant temperature during storage will induce deterioration in the qualityof plastic fats such as consistency and plasticity, which is related to the change of the internalstructure in plastic fats. Learning the variation of the quality and internal structure of plasticfats has an important guiding role on the production of high-quality plastic fat. Two kinds ofpalm oil-based shortening were employed to explore the effect of storage temperature andtime on the composition, physical properties, thermal characteristics, the structure of crystalnetwork under different storage modes for28days including constant temperatures (0°C,10°C,20°C,30°C,40°C, repectively) and fluctuant temperatures (0°C12h-20°C12h,10°C12h-20°C12h,30°C12h-20°C12h,40°C12h-20°C12h, repectively for a cycle), as wellas their relations. In addition, mathematic model between the microstructure and physicalproperties of palm oil-based shortenings during storage has been further built to proposescientific theory foundation for control administration production and storage of plastic fatswith high quality. The main contents and results of this study were as follows:(1) The variation of the triglyceride (TAG) composition, solid fat content, texture andrheological properties of two model palm oil-based shortenings during storageThe TAG composition, solid fat content, texture and rheological properties of two modelpalm oil-based shortenings stored at constant and fluctuant temperatures for28days wereanalyzed by pNMR, TA and Hakee rheometer. The results indicated that the TAG compositiondid not change during constant and fluctuant temperature storage. When stored at constanttemperature, as the temperature increased, the solid fat content values of two palm oil-basedshortenings have been found to decrease linearly, the hardness decreased in an exponentialmanner, the elasticity modulus decreased with the rising temperature; with the extension ofthe storage time, the solid fat content values and the elasticity modulus of the two modelshortenings did not change, the hardness increased when the temperature≤20°C anddecreased when the temperature>20°C. When stored at fluctuant temperatures, as the temperature increased, the solid fat content values of two model palm oil-based shorteningswere constant in the temperature range from0°C to20°C and then decreased (30°C-40°C),the hardness decreased when the temperature was higher than10°C, the elasticity modulusdecreased initially when the temperature was lower than10°C and then turned to be stable;with the extension of the storage time, the solid fat content values and the elasticity modulusof the two model shortenings did not change and the hardness decreased in a logarithmicmanner.(2) The variation of the thermal characteristics and crystal form of two model palmoil-based shortenings during storageThe thermal characteristics and crystal form of two model palm oil-based shorteningsstored at constant and fluctuant temperatures for28days were analyzed by DSC and XRD.When the model shortenings were stored at constant and fluctuant temperatures, the peaktemperature in the melting curves shifted to higher temperature, suggesting higher content ofhigh-melting TAG in the crystals of the two model shortenings. When storing at constanttemperatures, the content of the β form crystal increased with the increasing storagetemperature and time. When the two model shortenings were stored at fluctant temperatures,the content of the β form crystal increased with the extension of the storage time. Comparedwith the constant temperature storage, the β-type crystal conversion rate of the twoshortenings stored at fluctuant temperatures was faster.(3) The variation of the crystal network structure of two model palm oil-basedshortenings during storageThe crystal morphology, size, and fractal dimensions of the crystal network in the twomodel palm oil-based shortenings stored at constant and fluctuant temperatures for28dayswere analyzed by PLM and SEM, and the mechanisms of the crystal network variation underdifferent temperatures were summarized. When the two model shortenings were stored atconstant temperatures, with the extension of the storage time, the crystal size increased, somecrystal aggregates appeared, resulting in the increasing of the crystal network inhomogeneity,the fractal dimensions Dbincreased when the temperature was higher than20°C anddecreased when the temperature was lower than20°C. When the two model shortenings werestored at fluctuant temperatures, with the extension of the storage time, the different crystal aggregates appeared, and the size of the crystal aggregates increased. Meanwhile, the fractaldimensions Dbof the two model shortenings decreased as the fluctuant temperature increased.Compared with the constant temperature storage, the fluctuant temperature storage showed agreater impact on the crystal network and crystal size.(4) The relationship between the crystal network structure and macroscopic physicalproperties of the two model palm oil-based shortenings during storageThe relationship between the crystal network structure and macroscopic physicalproperties of the two model palm oil-based shortenings were discussed and the artificialneural network models were built. The results indicated that the solid fat content, the crystalnetwork structure and the content of β form crystalline had an important fluence on themacroscopic physical properties of the model shortenings whether during constanttemperature storage or fluctuant temperature storage. Meanwhile, two artificial neuralnetwork models with a high precision between the crystal network structure and macroscopicphysical properties of the two model palm oil-based shortenings during storage wereestablished, and the models could be used to relate and predict the crystal network structureand macroscopic physical properties of the shortenings.