Construction Of Cookie Oleogel And Its Influence Mechanism On Cookies Quality

Cookies are popular baked food,but the overuse of plastic fat such as traditional shortening in cookies results in high levels of saturated fatty acids and trans fatty acids,which are harmful to human health.Oleogels have zero-trans,low-saturation health properties,making them an ideal alternative to traditional shortening.At present,oleogels have not been applied in cookie industry,and the influence of its microstructure and physicochemical properties on cookie quality is not clear.Therefore,this paper takes the special oleogel for cookies as the research object,compares the effects of different types of oleogel on cookies quality,determines the type of oleogel suitable for cookies,and studies the effect of its microstructure and physical properties on the quality of cookies.And from the perspective of dough structure,the mechanism of oleogel affecting the quality of cookies was elucidated,and then,the medium and long chain triacylglycerols（MLCT）oleogel was constructed and its application in cookies was evaluated.This provides a theoretical basis for the development of special oleogel for healthy cookies and the quality control of oleogel cookies.The main research contents are as follows:The effects of three different types of food grade gelators including polysaccharide,emulsifier and wax on the quality of cookies were investigated.The result indicated that wax oleogels containβ′crystals,emulsifier oleogels containαcrystals orβcrystals,while polysaccharide oleogels formed an amorphous structure,indicating that the crystal structures of the three different types of oleogels are different.Wax and emulsifier based oleogels exhibited excellent rheological properties similar to shortening,with non-linear decreases in G′,G″and shear viscosity with increasing temperature,while G′,G′,and shear viscosity of polysaccharide based oleogels remain unchanged.Compared with the hardness（42.6 N）and overall acceptability（4.1）of shortening cookies,polysaccharide based oleogel cookies showed significantly higher hardness（～63N）and lower overall acceptability（2.9-3.1）,while the hardness（40.9-47.5N）and overall acceptability（3.4-4.3）of wax and emulsifier oleogel based cookies were similar to those of shortening cookies,indicating that wax and emulsifier based oleogels could replace shortening in cookie making.Wax and emulsifier oleogels have different crystal structures,but the hardness of cookies prepared by them was similar,indicating that wax and emulsifier oleogels have different mechanism on cookie quality.Rice bran wax（RBW）,beeswax（BW）,candelilla wax（CDW）and carnauba wax（CRW）were used to construct oleogels.And the relationship between the structure and physical properties of wax based oleogels and the quality of cookie was studied.The results showed that5%-9%（m/m）RBW and CDW could produce cookies with good texture,ductility and color.The results of nuclear magnetic resonance（NMR）and X-ray diffraction（XRD）showed that compared with shortening,wax oleogels with lower SFC（4.5%-11.0%,20℃）and higherβ′crystals（2.19%-7.62%）had similar cookie hardness to that of shortening（p>0.05）.Polarized light microscopy（PLM）and texture analysis showed that the cookie hardness was lower when wax oleogels had more crystals.The correlation analysis showed that the SFC and relative content ofβ′crystals in wax oleogels was the main determinant of cookie quality,and was negatively correlated with cookie hardness.The effect of wax based oleogels on dough moisture state,oil distribution and gluten network structure were further studied.It was found that the wax oleogels dough with SFC of4.5%-11%（20℃）andβ′crystal relative content of 2.19%-7.62%had a similar extensibility values to the shortening dough.The results of laser confocal microscopy（CLSM）showed that with the increase of SFC andβ′crystals relative content,the fat distribution in the dough changed from non-uniformly dispersed droplets to uniform film,and the structure of gluten network changed from dense to relatively sparse.The starch particles on the surface of the gluten matrix of the dough prepared from oleogel with high SFC andβ’crystals were partially exposed,indicating that the starch particles were not gelated,the continuity between the gluten protein and the starch particles was broken,and the gluten was weakened.The wax oleogel cookies with moreβ′crystals showed uniformed porous structure,indicating that moreβ′crystals made the dough have better ability to absorb and stabilize bubbles.Wax based oleogels with high SFC andβ′crystals mainly through promoting the formation of barrier films of fat crystals,uniformly encapsulating starch particles,weaken the interaction between gluten protein and water/starch molecules,and prevent the formation and cross-linking of gluten networks;at the same time,a large number of smallβ′crystals transfer more crystal interface to the surface of expanding bubbles,improve the stability of bubbles,form more open pores,and improve the quality of cookies.Four emulsifiers,monoglycerides（MAG）,Sodium stearyl lactate（SSL）,polyglycerol fatty acid esters（PGE）and sorbitan monostearate（SPAN 60）,were used to construct oleogels.The relationship between the quality of cookies and the structure and physical properties of emulsifiers oleogels was studied.The results showed that the hardness and L*,a*,b*of the oleogels cookies were similar to those of the shortening cookies when the concentration of MAG and SPAN were 6%-15%and 12%-18%（m/m）,respectively.Emulsifier oleogels containsαcrystals orβcrystals,but noβ′crystals.The cookie hardness of oleogel with highαcrystal content was similar to that of oleogel withoutαcrystal,indicating thatαcrystal content did not affect cookie quality.The amount of crystals in SSL9-15 oleogel was much higher than that in SSL6,but there was no significant difference in their cookie hardness,indicating that the amount of crystals is not the key factor affecting cookie hardness.Rheological analysis showed that when the shear viscosity was 6.8-35.1 Pa·s,the cookie hardness was similar to that of shortening.Correlation analysis showed thatαcrystal content and SFC of emulsifier oleogels had no significant correlation with cookie hardness,while shear viscosity was negatively correlated with cookie hardness（r=-0.401*）,and shear viscosity was related with SFC content.In conclusion,shear viscosity of emulsifier oleogel is a key determinant of cookie quality,and SFC can affect shear viscosity to a certain extent.The influence of emulsifier oleogels on dough moisture state,oil distribution and gluten structure were further studied.The result showed that the dough extensibility values prepared by emulsifier oleogels with shear viscosity of 6.8-35.1 Pa·s was similar to shortening,and with the increase of shear viscosity,the fat in emulsifier oleogel dough changed from small balls dispersed in single phase to relatively uniform extension shape,and the gluten network changed from regular compact structure to relatively loose.With the increase of shear viscosity,the starch particles in the oleogel dough gradually become exposed,indicating that the interaction between gluten protein and starch particles is weakened.The dough prepared by oleogel with high shear viscosity had lower density,and the corresponding cookies had large pores and more channels,indicating its better ability to maintain the number and stability of bubbles.The low field nuclear magnetic resonance（LF-NMR）analysis showed that with the increase of shear viscosity,T₂ increased significantly,and the mobility of water molecules increased,indicating that the binding effect between water molecules and gluten proteins of dough components was greatly weakened.High shear viscosity emulsifier oleogel mainly through the strong polar group of emulsifier competes with the gluten protein to combine with water,reducing the hydration ability of gluten protein,weaken the structure of gluten;at the same time,a certain amount of emulsifier adsorbed on the liquid thin layer composed of protein lipids to compensate the weak area caused by bubble deformation,prevent bubble rupture,form loose porous structure,and improve the quality of cookies.Finally,with MAG as gelator,three MLCT synthesized by transesterification of corn oil,rapeseed oil and flaxseed oil with medium-chain triglyceride were used as low-calorie base oils to construct three MLCT oleogels,and to prepare cookies and evaluate their quality.The results showed that the content of MLCT in three MLCT all reached 70%,the color of the three MLCT oleogel cookies was similar to that of shortening cookies,and the texture and spread of the three MLCT oleogel cookies had no significant difference with that of shortening cookies（p>0.05）.Sensory evaluation results showed that the appearance,color,flavor,crispness and overall acceptability of the three MLCT oleogels cookies were similar to those of shortening cookies,and the overall acceptability scores of corn oil and rapeseed oil MLCT oleogels cookies was 7.55 and 7.05,respectively,reaching the level of high-quality butter cookies（7.65）,indicating that the MLCT oleogel with MAG as gelators can completely replace shortening for cookies preparation.