microencapsulation of spearmint (menthaspicata) oil using spray drying method

introduction: flavor plays a pivotal role in consumer satisfaction and further consumption of foods. most available aroma compounds are synthetic and most of consumers tend to avoid them as they are of the idea that the chemical flavors are toxic or detrimental to their health. recently, the market of flavors from natural sources is shifting its focus on application rather than synthetic flavors (badee et al, 2012). essential oils consist of sensitive compounds against environmental effects. microencapsulation is one of the methods which increases the stability of essential oils and flavors during storage and transportation. different methods which may be used for microencapsulation include spray drying, spray-cooling, spray-chilling, coaservation, extrusion, fluidized bed method (kashappagoud et al, 2003). however, spray drying method is preferred due to its high speed, high reliability, high flexibility and its being economical and the fact that it can be easily implemented in industry (kashappagoud et al, 2003). spray drying of essential oils requires homogenizer, spray dryer and chemical materials used for walls such as some types of emulsifiers and ingredients including maltodextrin, dried corn syrup, gum arabic, gelatin and milk protein (adamiec&kalemba;, 2004; badee et al, 2012). arabic gum (acacia gum) is a biopolymer which is derived from internal sap of acacia tree. it consists of a heteropolysaccharide complex with highly ramified structure (phisut, 2012). it is an effective emulsifier for flavor emulsions thanks to its high water solubility, low solution viscosity, good surface activity, and ability to form a protective film around emulsion droplets (chanamai&mcclements;, 2001). maltodextrins are products of starch hydrolysis, consisting of d-glucose units linked mainly by α(1→4) glycosidic bonds. they are described by their dextrose equivalence (de) which is inversely related to their average molecular weight. the greater the de is, the shorter the glucose chains are and the more water they absorb (phisut, 2012). materials and method: spearmint oil was produced by clevenger distillation from spearmint leaves (mohal khan et al, 2012). malthodextrin with de=18-20 from xiwang starch co. ltd., china, has a sweet taste and it is used in combination with emulsifiers, creates the walls and covers and causes thermal resistance and resistance to browning. solubility in water=min 98%, moisture=4.5-6%, ph=4.5-6.5 and ash=max 0.1%. arabic gum was prepared from slandwide corporation co., philippines, which is used as an emulsifier, stabilizer and the cover (moisture = max 10%, ash=max4% and ph =4-5).in making an emulsion, deionized double distilled water was used. a solution of maltodextrin/arabic gum (1:1) in ratios of 10%, 20% and 30% in deionized water were prepared at 45°c and 1200 rpm for 1h (by stirrer ika). the solution was kept in cool room temperature at 4°c overnight (badee et al, 2012; baranauskiene et al, 2007). then, 2.5% spearmint oil was added to an aqueous and homogenized (15000 rpm for 10 min) solution with an ultra turrax (model t25 digital, ika co, germany) (badee et al, 2012; baranauskiene et al, 2007; baranauskiene&venskutonis;, 2009; frascareli et al, 2012). then sonificasion (model ,hd3200, bandeline co, germany) for 1 minute by amplitude control 100%, frequency 20 khz at 45 °c. the emulsion was spray dried in a buchi b-190 spray dryer (badee et al, 2012; baranauskiene et al, 2007; baranauskiene&venskutonis;, 2009) where the inlet temperature was 180 °c, outlet temperature 60°c, pump speed 10 ml/min, air flow 600 l/h and pressure 4 bar. the powder was stored at -18°c until tested. results and discussion: the results of this research showed that during microencapsulation of spearmint oil at the fixed rate of 2.5%, wall concentration were effective in the stability of emulsions and in keeping menthol and d-limonene in microcapsule during drying and storage. by increasing wall material from 10% to 30% the most stability in emulsion was obtained and more half life and less release in microcapsules was achieved. also, temperature plays an important role in protecting the volatile components, so that the microcapsules stored at 4°c had about half life which was 80 days more than the the samples stored at 25°c.