The effect of microencapsulation on characteristics of orange peel essential oil of extracted from by- product of orange juice factories

Orange peel essential oil is used in various industries as a flavoring component due to its excellent organoleptic properties. These compounds are generally rich in active and sensitive components (antioxidant and antimicrobial compounds). These compounds typically have low physicochemical stability and lower solubility in water. Therefore, the use of a method that can protect these compounds against environmental factors is of particular importance. Microencapsulation is one of the methods of protecting chemical compounds with biological activity. Since the microencapsulation process of the active compounds is influenced by the core and wall material and drying method, it is expected to use suitable wall materials such as sodium alginate and beta-cyclodextrin with a suitable drying method such as freeze drying lead to the production of stable microcapsules. The aim of this study was to produce microencapsulation of orange peel essential oil extracted from Thomson cultivar with walls of sodium caseinate and beta cyclodextrin by freeze-drying method and to investigate its quantitative and qualitative characteristics.

Orange peel was subjected to ultrasound at a frequency of 20 kHz with 60% intensity for 19 minutes at 35 °C and then its essential oil was extracted by Clevenger method. The extracted essential oil was finely Microencapsulate using beta-cyclodextrin and sodium caseinate at concentrations of 5 and 10% by freeze-drying method at -70 ° C for 19 hours and then transferred to a freeze-dried dryer. Samples were dried in a freeze-dryer at -55 ° C with a pressure of 0.15 mm Hg (Azarpazhooh et al. 2018). Then the properties of capsulate essential oil including Microencapsulate efficiency, particle diameter size were used using laser light refraction method. moisture was measured using an infrared hygrometer at 105 ° C until reaching a constant weight. To determine the mass density, a specific volume of the sample, its weight and density were calculated by dividing the weight (g) by the volume of the sample (ml) in g/ cm3. The glass transition temperature was determined using a differential scanning calorimeter with a liquid nitrogen cooling system. To determine phenolic compounds, Folin–Ciocalteu method was used. The antioxidant activity of the samples was also measured using the DPPH test. Scanning electron microscopy was used to observe the microstructure of the prepared microcapsules. Stability kinetics of microcapsules were performed under different temperature and humidity conditions (temperature, 4 and 25 °C; relative humidity, 52 and 75% and storage time of 0, 7, 14, 21, 28, 35 and 42 days) in three replications. The results were analyzed using a completely randomized statistical design with 3 replications and MSTATC software.

The results of statistical analysis of data showed that the effect of wall material on all properties of microcapsules was significant (p <0.05). Thus, all the characteristics of microcapsules prepared with beta-cyclodextrin wall except mass density were significantly higher than the characteristics of microcapsules prepared with sodium casinate wall. The low production efficiency of microcapsules containing sodium caseinate is probably due to the instability of the initial emulsion. Also, the lower moisture of these microcapsules is another reason for the low efficiency. Microcapsules with 10% beta-cyclodextrin and 5% sodium caseinate had the highest and lowest moisture and efficiency, respectively. Therefore, the type and concentration of wall material effectively affects the efficiency and final moisture of the microcapsules. The bulk density of microcapsules with beta-cyclodextrin wall was lower than that of sodium caseinate. Because of their greater porosity, beta-cyclodextrin-containing microcapsules will take up more volume than sodium caseinate microcapsules. As a result, their bulk density is lower. The small particle size of microcapsules containing sodium caseinate is related to the effective emulsifying properties of sodium caseinate and its hydrophobic and hydrophilic components (Moghimi et al. 2016). The large particle size of beta-cyclodextrin-containing microcapsules may be due to the lack of ionization of beta-cyclodextrin, which tends to accumulate in water, there is no repulsive force to prevent particle aggregation (Torres-Alvarez et al. 2020). Moisture and efficiency of microcapsules increased with increasing concentration of beta-cyclodextrin but decreased with increasing concentration of sodium caseinate. Also, with increasing the concentration of both walls, the density of the mass increased and the glass transition temperature and free radical scavenging decreased (p <0.05). Also, the glass transfer temperature of all microcapsules is higher than the ambient temperature. Therefore, none of the microcapsules prepared at ambient temperature reach the glass transition temperature, so it is not possible to release and transfer the core material out of the wall. As the concentration of both walls increased, the glass transition temperature decreased (p <0.05). The results of determining the microstructure of the microcapsuleed particles by electron microscopy showed that the resulting microcapsules did not have a definite geometric shape, which is probably due to the drying mechanism. Spherical capsules containing beta-cyclodextrin had a large indentation and pore, and microcapsules containing sodium caseinate had thin, uniform, non-porous walls. The results of the study of the stability of microcapsules indicate that during storage the amount of DPPH increased with increasing relative humidity but decreased with increasing temperature from 4 to 25 °C.

Orange peel essential oil capsules prepared with 10% beta-cyclodextrin wall had better physicochemical properties than other walls.