Investigation On The Mechanism Of Natural Waxes Regulating Fat Crystallization And Partial Coalescence Of O/W Emulsion

Whipped cream is widely used in the baking industry because of its easy availability,stable properties and low cost.Currently,the oil used in whipped cream is hydrogenated vegetable oil,which has perfect crystallization properties and can form the partial coalescence of fat globules in the O/W emulsion,giving the whipped cream satisfactory plasticity.However,its trans fatty acids are harmful to the health.Therefore,how to develop the non-hydrogenated whipped cream based on the design of fat crystallization and partial coalescence has attracted much attention.Natural wax is an underutilized and green natural resource in the food industry.It has the potential to modify the fat crystallization,but the mechanism which wax modifies the fat crystallization and the partial coalescence of fat globules is still unclear.Herein,we propose a strategy for improving the crystal properties of tropical vegetable oils by compounding triglycerides(TAG)and adding natural waxes.The regulation mechanism of crystal properties on the partial coalescence of fat globules was also revealed.The effects of partial coalescence of fat globules on the micro-and macroscopic structure of whipped cream were systematically investigated.Our findings provide a theoretical basis for the development of low-fat,room-temperature non-hydrogenated whipped cream.The conclusions were as follows.(1)The lipid composition and crystallization properties of 8 tropical vegetable oils were investigated,using fully hydrogenated palm kernel oil(FHPKO)as control.Palm kernel oil and its fractions,coconut oil and FHPKO mainly contain La La La and La La M,showing?'crystal form,fine and uniform granular crystals;palm oil and its mid-melting point fractions mainly contain POP and OPO,showing?'crystal form,fine and uniform spherical crystals;palm stearin mainly contains PPP and OPO,showing?'crystal form,coarse spherical crystals.High-SFC palm stearin(POs)was added to the palm kernel oil and its fractions,whose solid fat content(SFC)was 0 at 35°C.A pseudo-phase diagram of binary and ternary blends was constructed to optimize the TAG composition of blends.Combination 1(palm kernel oil(PKO):palm stearin(POs):palm kernel stearin(PKS)=5:15:80)and combination 2(POs:PKS=15:85)showed similar properties with FHPKO.The application evaluation of whipping cream showed that combination 2(PKS85)achieved similar properties with FHPKO.It suggested that PKS85 could be used as the base oil of non-hydrogenated whipped cream.(2)The effects of beeswax(BW),candelilla wax(CLW),carnauba wax(CW)and rice bran wax(RW)on crystal properties of PKS85 were investigated.Based on the Avrami model,it was found that the addition of 2?8 wt%CLW and CW significantly increased the K value of PKS85 and reduced the t_1/2 value(P<0.05),which promoted the crystallization of PKS85;when samples crystallized at 4°C and 20°C,the n values were 2.220 and 2.992 respectively,showing a two-dimensional disc growth mode and a three-dimensional spherical growth mode,respectively;The n values of PKS85 were reduced with the addition of waxes during crystallization at 20°C.The n values at 20°C of samples with waxes were similar with PKS85at 4°C,which suggested the similar crystal growth pattern.In addition,waxes could induce a new hydrocarbon chain with the lengths of 3.70?and 4.15?during the TAG crystallization.Waxes could reduce the lamellar thickness(d₀₀₁)by 1.4?to 4.0?.The lamellar thickness(d₀₀₁)and nanoplatelets thickness (?) were positively related to the length of the wax alkyl chain.PKS85-BW,PKS85-CW and PKS85-RW were observed larger needlelike,feather,and linear crystals,respectively,while PKS85-CLW was observed smaller needlelike crystals.(3)The effects of natural waxes on lipid crystallization and partial coalescence of O/W emulsions were investigated.The waxes induced the formation of a new hydrocarbon chain distances of 3.70 and 4.15?and slightly decreased the lamellar thickness(d₀₀₁)and nanoplatelets thickness (?) in emulsions.PKS85-BW,PKS85-CW and PKS85-RW were observed larger needlelike,feather,and linear crystals,respectively,while PKS85-CLW was observed smaller needlelike crystals in emulsions.The crystals in droplets induced by waxes tended to penetrate the interface film,forming the crystal bumps on the droplet surface and facilitating partial coalescence.Finally,the rheology strongly supported that waxes enhanced the crystalline droplet-droplet interaction and strengthened the network in O/W emulsions.In summary,natural waxes displayed a high efficiency in modifying the crystallization behavior,partial coalescence,as well as the overall structure of emulsions,which play a significant role in structure of whipped cream.(4)Based on above,whipped cream was fabricated with PKS85 containing 4 kinds of natural waxes.the effects of natural waxes on the structure of whipped cream were explored.The surface tension values of O/W emulsion with the addition of 4 kinds of waxes were 34.5-35.7 m N/m.To further investigate the properties of the bubble interface film,PLM,Cryo-SEM and expansion rheology were used.It is found that partial coalesced fat globules form a stable elastic interface film of bubble(elastic modulus(E?)>viscosity modulus(E??)),and the addition of waxes could enhance its elasticity.Meanwhile,the rheology further confirmed that the addition of wax could strengthen the overall structure of whipped cream.In addition,the addition of waxed increased the viscosity,slowed down drainage,and improved the stability of whipped cream.The basic indicators and macrostructure of low-fat whipped cream(15 wt% oil)prepared with BW were consistent with those of the control whipped cream(25 wt%oil);The basic evaluation indicators and macrostructure of room-temperature whipped cream prepared with BW were consistent with the low-temperature group.In summary,natural wax can participate in the assembly of triglycerides,modify its crystal properties,inducing fat globules to form irregular interface protrusions,and promoting the formation of partial coalescence.Based on the findings,the low-fat non-hydrogenated and room-temperature non-hydrogenated whipped cream were sucessfuly developed,respectively.The defects in whipped cream including hydrogenated,high-fat and low-temperature storage were improve in this study.