Quality Improvement By Emulsifiers In The Palm Kernel Oil Based Whipped Cream And The Mechanism

Whipped cream,a widely used product in the baking industry,is a system where air bubbles are dispersed in water and surrounded by a complex network.Hydrogenated palm kernel oil(HPKO)is the most commonly used fat to stabilize whipped cream by contributing to the crystals of the interface.However,growing health concern over trans and saturated fatty acids have been raised over the past decade.It is of great interest to seek alternatives of HPKO without changing the physical properties of the modified product.The objective of this study was to develop an alternative way to replace hydrogenated palm kernel oil in whipped cream using palm kernel stearin(PKS)coupled with different emulsifiers.The main findings are as follows:A potential alternative PKS with similar crystallization kinetics as HPKO was used as ingredient oil in whipped cream.In the first experiment,a variety of emulsifiers were screened to study the effect of emulsifier on the properties of whipped cream.The results showed that the pure protein stabilized emulsion as a control showed poor physical stability and the particle size was 1659.3 nm.The turbiscan stability index(TSI)of emulsion after storage for 30 min was 2.7.Fat structure couldn't form during whipping.The low-molecular-weight emulsifiers promoted fat structuring for whipped cream.The TSI value of glyceryl monostearate(GMS),polyglycerol ester(PGE)and sorbitan monostearate(Span 60)samples decreased and the particle size of the emulsions decreased to 822.0,881.3 and 1053.3 nm,respectively.The cream showed more compact partial coalescence fat network adhered to the air-serum interface,which provides the cream good stabilities.Conversely,large aggregates and clumpy structures in emulsions were induced by the addition of lactic acid ester of monoglyceride(LACTEM),propyelene glycol monostearate(PGMS),sorbitan monooleate(Span80)and sucrose ester(SE).They promoted the process of fat partial coalescence,providing stiff crystal structures to stabilized air bubbles during whipping.But the irregular distribution of the air bubbles provided poor stability for whipped cream.Next,the effects of emulsifiers on crystallization behavior of fat and the competitive adsorption at interface were explored to understand the influence of emulsifiers on the properties of whipped cream.It was found that emulsifiers with high melting point(GMS,PGE and Span60)affected the crystallization behavior by decreasing induction time,increasing crystallization rate and elevating number concentration of crystals,generating compact crystal networks.In contrary,LACTEM,PGMS and Span80 slowed crystallization rate and lengthen induction time,forming loose crystal networks.No difference in the polymorphism of fat was observed among different treatments.Subsequently,a relationship between oil/water interfacial properties and the whipping performance was investigated for GMS,LACTEM and SE which showed different properties.It was found that emulsifiers could lower surface tension.While SE exhibited higher surface activity and it was more effective than LACTEM,GMS in displacing protein molecules at oil-water interfaces.With the addition of emulsifiers at low concentrations(0.05% to 0.25%),the improvement of emulsion stability was achieved in a dose-dependent manner.However,adverse effect was observed at higher SE,LACTEM concentrations where large aggregates were formed.It was inferred that different emulsifiers affected the whipped cream in different ways.Oil-soluble emulsifiers with high-melting point induced interface heterogeneous nucleation and volume heterogeneous nucleation in emulsions.The crystals oriented parallel to the oil-water interface increased the stability of emulsions,leading to a lower tendency to coalesce by preventing the piercing of the fat crystals through the film connecting together.But better spreadability was due to even distribution of fat crystals with smaller sizes and larger quantities.Conversely,the oil-soluble emulsifiers with lowmelting point or water-soluble emulsifier decreased the strength of protein membrane,which increased the emulsion susceptibility to fat crystal mediated partial coalescence of the interface.While the coarse crystalline network of PKS was unfavorable for trapping air efficiently,resulting in inter-bubble coalescence and finally collapse of foam.Finally,the multiple emulsifiers usually create more stable cream than single emulsifiers due to the synergistic effect.Therefore,an emulsifier with low HLB value(GMS)was used together with an emulsifier with high HLB value(SE)to optimize the functional properties of whipped cream.It was found that the emulsions had high thermodynamic stability in the HLB range of 3.8~10.0.As HLB value went up to 10.0,the overrun arised to 317% after 5min whipping.When the HLB value was above 10.0,the stability of emulsion decreased and larger fat globules aggregation were formed.Morever,the emulsions became more sensitive to shearing and the whipping time decreased sharply,indicating the emulsion droplets were more susceptible to partial coalescence.Meanwhile,the firmness of cream increased and emulsion stability reduced with higher HLB values.As a result,the optimum whipping properties can be achieved by the HLB value of 10.