material includes high solubility, effective emulsification, low viscosity at high level of solids, low hygroscopicity, easy release of core material and efficient drying properties. (Lee et al., 2003) a) Gum arabic (Acacia) It is one of the oldest and traditional wall materials or carriers used in spray drying. It is a natural exudate from the trunk and branches of leguminous plants of the family Acacia. Although it is one of the most preferred wall materials, alternative carriers are being used for dry flavouring and other core materials due to its low production (300g/plant/year) and high cost. b) Modified starches: Chemically modified starches most closely reproduce the functional properties of gum arabic. Natural starches virtually have no emulsifying property. Esterification with cyclic dicarboxylic acid anhydride imparts emulsifying power to partially hydrolysed starches. This technique is practiced on a commercial scale to have the wall material tailor made. The modified starches are found to be superior to gum acacia in emulsifying properties and in retention of volatile flavours during spray drying (Varavinit, 2001).
93 c) Hydrolyzed starches: This is one of the most common wall or carrier materials. The hydrolysed starches are available in dextrose equivalent (DE) ranging from 2 to 36.5 and offer good protection against oxidation. These are low in viscosity at high total solid contents. However, they lack in emulsifying properties. It is therefore used along with gum acacia or other emulsifying agents like protein, whey protein concentrates and whey protein isolates. Maltodextrin and low dextrose equivalent (DE) corn syrup solids (CSS) when dried, show matrix forming properties important in the wall system. (Kenyon & Anderson, 1998). When Maltodextrins or CSS are used as wall constituents, it is necessary to incorporate other wall material such as gelating agent, sodium caseinate, whey proteins, lecithins etc. for improving emulsifying characteristics. (Lin, et al . 1995). d) Whey proteins: As starch and related products lack emulsification properties, they are used as wall materials alongwith surface active wall constituents (Lin, et al 1995). Whey protein owing to their structure gives functional properties desired for effective microencapsulation of anhydrous milk fat. Whey protein in combination with maltodextrins and corn syrup solids are reported to be the most effective encapsulation material during spray drying (Kenyon and Anderson, 1998). 2. Spray Chilling In spray chilling, the material to be encapsulated is mixed with the carrier and atomized by cooled or chilled air as opposed to heated air used in spray drying (Risch, 1995). The outer material is usually vegetable oil in the case of spray cooling (45 to 122°C) or a hydrogenated or fractionated vegetable oil in the case of spray chilling (32 to 42°C). Frozen liquids, heat-sensitive materials and those not soluble in the usual solvents can be encapsulated by spray chilling / spray cooling. It is the least expensive encapsulation
You've reached the end of your free preview.
Want to read all 18 pages?
- Summer '17