Preparation And Properties Of Menthol-loaded Hybrid Microcapsules

As one of the bulk spices,menthol is antipruritic,analgesic,antibacterial,antiinflammatory and also a penetration enhancer,and exerts a cooling sensation with fresh odor,which has been widely used in food,medicine,toothpaste and oral hygiene supplies,cosmetics and tobacco.However,its instablility,sensibility to light,heat and oxygen,degradation and high volatility and irritation to skin and eyes limit the applications and shelf life.Embedding/encapsulation with micro-and nano-carriers has been proved to be an effective way to prevent/reduce the loss caused by volatility for protection,sustained release and longlasting cooling.Polymeric microcapsules,cyclodextrin molecular inclusion complexes and nanoparticles are available methods employed for menthol encapsulation,existing the common problems of low loading,high surface oil and poor thermal stability.Moreover,the whisker growth resulted by menthol recrystallization is a vital problem for its applications and shelf life.In this work,a novel structure based on OSA starch-solid lipid hybrid microcapsules —stabilizing menthol in an amorphous form for long term — was proposed to enhance the thermal stability and loading capacity and prolong shelf life of menthol loaded system.The main research contents and results are as follows:(1)Menthol was firstly dissolved in mixed lipids generating menthol-loaded solid lipid nanoparticles(SLNs),then the menthol-loaded SLNs were further encapsulated by OSA starch using spray drying.And finally the OSA starch-solid lipid hybrid microcapsules were constructed.The encapsulation effects(loading amount,encapsulation efficiency and encapsulation yield)and thermal stability of hybrid microcapsules were significantly improved compared with traditional menthol embedded carriers — OSA starch-based microcapsules and solid lipid nanoparticles.(2)The preparation process of hybrid microcapsules was optimized by single factor experiments by taking loading amount,encapsulation efficiency,encapsulation yield and thermal stability as comprehensive indexes.The optimal preparation conditions were determined as follows:the ratio of shea butter to candelilla wax was 1:3,the ratio of core to wall was 0.875,and the homogenization was conducted at a pressure of 800 bar for five times.The operational conditions of spray drying were as follows: the inlet air temperature was 180 °C,the outlet air temperature was 80 °C and the feed rate was 450 m L/h.The resulting hybrid microcapsule was obtained with high loading amount(33.15 ± 0.12)%,high encapsulation efficiency(96.44 ± 0.08)%,high encapsulation yield(99.46 ± 0.36)% and superb thermal stability.Mass retention of menthol was 93.29% at an elevated temperature(60 °C for 2 h,80 °C for 5 h and 100 °C for 5 h)after 12 h.(3)The morphology of hybrid microcapsules was studied by SEM.The spherical microcapsules with smooth and dense surfaces were observed without cracks or holes,and there were occasional dents,folds and clumps,which affected the fluidity of microcapsule powder.The influences of hydroxyethyl cellulose,silica and gum arabic on the morphology of hybrid microcapsules were investigated.The results showed that taking silica in combination with hybrid microcapsules reduced the surface dents,folds and clumps.The internal structure of hybrid microcapsules was observed by SEM,TEM and CLSM.The main types were multiplecore microcapsules and a fraction of composite microcapsules.The thermo gravimetric analysis revealed that the decomposition temperature of embedded menthol was significantly increased and the decomposition rate was slowed down,which proved that hybrid microcapsules had a good embedding protection effect on menthol and significantly improved the thermal stability of menthol.(4)The feasibility for practical application of hybrid microcapsules was explored from three aspects of storage stability,release performance and application on lip balm.The storage stability experiment showed that the structures and properties of hybrid microcapsules kept stable after 300 days,and there were no menthol leakage and crystallization,maintaining excellent thermal stability.The outer shell of hybrid microcapsules breaks down to instantly release its contents when triggered with water.When applied to oil-based or powder products,menthol releases slowly and continuously under the trigger of saliva and air humidity,so as to achieve a long-lasting cooling effect.The release of menthol in hybrid microcapsules was slowly in 37 °C compared to the release of free menthol from a lip balm application,providing a long-lasting cooling sensation.