Encapsulating materials

After sonication of whey protein dispersions at 20 kHz and 750 W, it was observed that particle size distribution curve shifted to the left for more diluted dispersions. It was also reported that longer time of ultrasound treatment resulted in the formation of smaller particles when compared to short time processing (Gordon & Pilosof, 2010).

In another study by Leong et al. (2009) it was shown that ultrasonication (400 W, 20 min) of triglyceride oils in water resulted in the production of transparent nano-emulsion with mean particle size less than 40 nm.

Among the key parameters of emulsification using ultrasound, special attention should be paid to the optimization of applied power. Kentish et al., (2008) performed a study in which they showed that droplet particle size decreased with increasing power then particle size reached its minimum at an intermediate power application and after that increased at higher power levels. The same phenomenon was also observed and described as “over-processing” in the studies performed by Desrumaux & Marcand (2002) and Jafari et al. (2006).

1.3.3 Encapsulating materials

There are many different types of encapsulating/entrapping materials used in encapsulation of food ingredients. They can be used separately or in the mixture of two or more different materials. Coating material used for the encapsulation should meet the required criteria, such as compatibility with the food product, mechanical strength, appropriate thermal or dissolution release, and appropriate particle size (Gharsallaoui et al., 2007). Wall materials can be composed of sugars, gums, proteins, natural and modified polysaccharides, lipids and synthetic polymers (Gharsallaoui et al., 2007;

Gibbs et al., 1999). Generally, encapsulating materials used in food industry are

14

considered as biomolecules. There are different sources of biomolecules, such as plants, animals, and microorganisms. Overview of coating materials with their origins is given in the Table 1.4. The most commonly used materials such as maltodextrins and gum arabic belong to the polysaccharides category (Wandrey et al., 2010).

Table 1.4 Microencapsulating materials overview and their sources (Wandrey et al., 2010)

15 1.3.3.1 Maltodextrin

Maltodextrin is a functional derivative of starch. It is formed by hydrolysis of starch (usually corn or potato starch in US and wheat starch in Europe) by acid, enzyme, or acid/enzyme combinations (Wandrey et al., 2010). Dextrose equivalent (DE) of maltodextrin is less than 20. DE term is defined as a measure of reducing power of a starch derivative compared with D-glucose on a dry-weight basis and is higher for greater extent of starch hydrolysis (Wang & Wang, 2000). Starch and some starch derivatives with their DE are shown in the Fig.1.1.

Fig. 1.1 Classification of starch hydrolysates based on the dextrose equivalent (DE) value (Wandrey et al., 2010).

16

Maltodextrins are cold-water soluble, easily digestible, creamy white powders which are tasteless or moderately sweet. Klinkesorn et al. (2004) studied stability and rheology of oil-in-water emulsions which contained maltodextrins with different DE.

They found that, minimum amount of maltodextrin required to promote rapid creaming decreased as the DE of maltodextrin decreased. They also reported that, at high concentrations maltodextrins with lower DE cause higher relative viscosity. Wang &

Wang (2000) reported DE values of 8.2, 5.9 and 14.2 for commercial corn, potato and rice maltodextrins, respectively. They emphasized that, high concentrations of high molecular weight saccharides (low DE) in maltodextrins contributed to higher viscosity and freezing temperature, less water sorption and greater tendency to retrogradation.

Maltodextrin with 10 DE had higher phenolic retention when compared to 20 DE in the study performed on encapsulation of açai pulp by spray drying (Tonon et al., 2009).

Cactus pear (Opuntia streptacantha) was encapsulated by spray drying using two types of commercial maltodextrin with DE of 10 and 20, and better binder properties were reported for maltodextrin 10 DE when compared to maltodextrin 20 DE which resulted in greater capacity of retention of vitamin C after encapsulation (Rodriguez-Hernandez et al., 2005). Microencapsulated powders of cloudberry (Rubus chamaemorus) phenolics prepared with maltodextrin 5-8 DE were remarkably better in the encapsulation yield and efficiency when compared to powders which contained maltodextrin 18.5 DE (Laine et al., 2008).

1.3.3.2 Gum arabic

Gum arabic (GA) is naturally occurring, edible and gummy exudate collected from the stems and branches of Acacia senegal and, to a lesser extent, from Acacia seyal that is rich in non-viscous soluble fiber (Ali et al., 2009; Yadav et al., 2007). Gum arabic is composed of arabinogalactan oligosaccharides, polysaccharides, and glycoproteins and

17

its chemical composition is dependent and may vary due to the factors such as source, climate, season, age of trees, rainfall, time of exudation, etc. (Wandrey et al., 2010). It is colorless, odorless and tasteless and does not add any odor, taste or color to the product it is added. Gum arabic is both cold- and hot-water soluble and it is a good emulsifying agent. Gum arabic is used as a stabilizing, emulsifying and thickening agent in the food industry (in beverages, candy, confections, etc.) and it is also used in pharmaceutical, textile, cosmetics, pottery and lithography industries (Verbeken et al., 2003).

Shiga et al. (2001) reported that blending of gum arabic and cyclodextrin in the feed liquid in the encapsulation of flavors by spray drying resulted in an increase of flavor retention. Microcapsules of cinnamon oleoresin obtained by spray drying and prepared with gum arabic:maltodextrin:modified starch (4:1:1) were spherical and had smooth surface, whereas microcapsules prepared from gum arabic had some dents and capsules prepared from maltodextrin and modified starch were broken and not complete (Vaidya et al., 2006). Better emulsion stability and better stability against environmental factors such as NaCl concentration and thermal treatments has been reported for the soybean-stabilized oil-in-water emulsion in the presence of gum arabic (Wang et al., 2011).

Gum arabic was successfully used in the production by spray drying of açai powder and particles produced with it exhibited the lowest mean diameter when compared to maltodextrin and tapioca starch (Tonon et al., 2009). It was also used as a carrier agent in the encapsulation by microfluidization and spray drying of red rasberry (Rubus idaeus) puree (Syamaladevi et al., 2012). Maltodextrin and gum arabic were used separately as carrier agents in the production of lemon juice powders (Martinelli et al., 2007).

18