Study On The Correlation Between Crystallization Behavior And Ductility Of Industrial Sheet Margarine

With the rapid development of baking industry,the demand of sheet margarine,one of the most important raw materials of pastry production,has been on the rise.However,existing sheet margarines on the market are still laden with problems,such as high content of trans fatty acids（TFA）and poor plasticity,which result in premature breakage of the fat layer during the folding and sheeting process,further resulting in unsatisfactory quality of the final baked products（i.e.poor appearance and taste）.Therefore,an in-depth understanding of the formation mechanism and influencing factors behind the plasticity of low TFA sheet margarine is crucial for ensuring a practical industrial production.From the perspective of industrial-scale production,shea olein,which contains high stearic acid（C18:0）,was introduced to modify the molecular composition in the system further to improve the crystallization based on the previous studies which focused on the crystallization speed resulted from staturated fatty acids.The correlation between this change of fatty acid composition and crystallization network of the fat was revealed,and the mechanism of the crystallization and texture of sheet margarine under different process parameters of chilling,kneading and tempering was systematically investigated.The correlation between the crystal network structures of sheet margarine and macroscopic application characteristics was established,which can provide theoretical guidance for industrial sheet margarine production.The key findings are as follows:1.The impact of the crystallization mechanisms and characteristics on the plasticity of sheet margarine was studied under the condition of changes in fatty acid composition（FAC）and triacylglyceride（TAG）of the recipe resulting from the addition of shea olein and chemical interesterification（CIE）process.The results showed that there was an increase in C18:0 fatty acids and a decrease in C16:0 fatty acids.For the TAG compositions,there was a decrease in tripalmitin（PPP）and 1,3-palmitic acid-2-oleic acid triacylglyceride（POP）with an increase in triolein（OOO）when replacing palm olein（POL）with SHOL in palm-based formula（PST:PKOL:POL=50:15:35,w/w/w）.Theβ’crystal content of the sheet margarine was observed to increase from 70.86%to92.29%.A corresponding decrease in both solid fat content（SFC）and product hardness were observed.The observed changes inβ’crystal content,SFC,and hardness are consistent with an overall improvement in the plasticity of the sheet margarine product.After CIE,the crystallization rate was accelerated due to the further decrease of PPP,POP and OOO triglyceride content alongside with the increase of S₂U（mainly POS）triglyceride content.Polarized light microscope（PLM）analysis in the sheet margarine with increasedβ’crystal content（93.72%）revealed finer and more uniformed crystals and a more viscoelastic crystal network.These observations are parallel to the enhanced plasticity and improved bending characteristics of the products after transesterification.2.The effects of different chilling intensity,kneading intensity and stirring speed and their combined matrixes on the crystal network and textures of sheet margarine were explored.2.3 tons industrial sheet margarine were manufactured in the margarine plant based on the formulation of CIE（50%PST+15%PKOL+35%SHOL）and the pipeline configuration of industrial-scale production.A relatively high kneading speed（300 rpm）should be followed when the condition of strong cooling was implemented on the 1^st and 2^nd cooling tubes（-5℃,-5℃）.Increasing the kneading speed can effectively disperse a large number of crystals generated by the intensive cooling,preventing their aggregation into large crystals,thus preventing the transformation of crystals fromβ’crystal toβcrystal.This effectively reduces the hardness of products and confer improved plasticity to the product.When weaker cooling（0℃,0℃）was implemented on the first and second tubes with reduced kneading speed（100 rpm）,the X-ray diffraction（XRD）pattern showed a small diffraction peak at 4.6（?）besides the diffraction peaks at 3.8（?）,4.2（?）and 4.3（?）,indicating thatβcrystals are present in the product althoughβ’is still predominant.As long as the chilling and kneading parameters are well optimized,no matter weak cooling or intensive cooling implemented on the 1st and 2nd cooling tubes,both products had predominantβ’crystal types with fine and uniform textures The DSC melting curves,texture（hardness）,bending and plasticity characteristics were found to be similar.3.The effects of tempering temperatures（10℃,15℃,20℃,25℃and 30℃）on crystal transformation,crystal networks and textures were investigated by optimizing the cooling and kneading based on the CIE formulation.The results show that the tempering temperature has a great influence on the crystallization network characteristics and operational performance of sheet margarine.At relatively low tempering temperatures（10℃and 15℃）,it is easier to form stronger intermolecular primary bonds which increase the solid fat content of the product.Hardness via texture analyzer（TA）was found to be high（>700 g）in the product.After CIE,Differential scanning calorimeter（DSC）shows that the melting peak is relatively wide and the crystal network has a more uniformed distribution.The tempering process helps to further stabilize the crystal network.At lower tempering temperatures,the crystal network is predominantly consisting ofβcrystals,which significantly increases the hardness of the product.However,too high of a maturing temperature（30℃）can easily result in the melting of the low melting point TAGs（i.e.POO,SOO）.Synonymous with the X-ray diffraction（XRD）results,the increase in tempering temperatures will destabilize the crystal network,resulting in crystal migration and aggregation to form coarse crystal particles ofβcrystals,thus leading to hard and brittle textures and poor plasticity.Appropriate tempering temperatures（20℃and 25℃）is conducive for inhibiting the transformation ofβ’intoβcrystals,forming relatively fine and uniform crystallization,which in turn gives the product improve bending and sheeting application properties.4.Based on the above transesterification formula containing SHOL,combined with appropriate processing and tempering conditions,the relationship between the physical properties and the macro application performance was established by investigating the changes of the physic-chemical properties of sheet margarine in different formulas under different storage conditions.The results show that there is no relationship observed between the structure of the crystal network and the hardness or plasticity of the sheet margarine.the rheological tanδvalues of all the samples were low（tanδ<1）,indicating that they were viscoelastic dominated by solid properties.The value of tanδfor the samples stored at 20℃after CIE was the lowest,implying that the solid properties of the samples were the most obvious.The distribution image of dough and fat layers during the folding and sheeting process generated from confocal Raman microscopy（Raman）showed that the crystal network will be fractured during the sheeting process,which will then reduce the consistency of sheet margarine.The presence of a certain amount ofβcrystals in the product is beneficial to maintain the hardness of the sheet margarine.If the sheet margarine is too soft（hardness is less than 200 g）,it can easily be absorbed into the dough during the sheeting process,undesirably reducing the volume of the baked goods.According to the Specific Capacity（SC）analysis the of baked goods,the higher SC value of product stored at 20℃is related to theβ’+βcrystals.With the presence ofβcrystal at less than 20%,the sheet margarine is able to maintain a certain ideal hardness,and also allow for relatively even distribution of the fat in the dough.The continuous and complete fat layers have an improved retention of gases produced during fermentation and baking,and thus ensure a greater volume in the final baked pastry products.