Wall Material

After the encapsulating certain target materials("core materials") into the liquid based-system such as an emulsion, the complex system is dried into powder form to minimize water content and extend shelf life. Spray drying has been the conventional method to do so. However this may cause damage to the core due to the inevitable heating process. A more recent technology to minimize the damage is lyophilization, or freeze drying. In this process, liquid sample is frozen up to -70 C in a deep freezer and the ice in the system is entirely removed through sublimation. This allows the wall materials cover the droplet or form inclusion complexes, protecting them from the environmental stresses as well as controlling the release of incorporated bioactive compounds from inside to outside.

Fig 1. Schematic diagram of encapsulation by drying

Wall material is a substance that encapsulates and protects vulnerable core materials by surrounding them and acts as a physical barrier between the core and the outer system. One of most commonly used wall materials in the food industry is carbohydrate-based compound such as maltodextrin, gum Arabic, and modified starch. Starch is a source of a plant so that they are nature-friendly and inexpensive compared to protein-based wall materials. Chemically or enzymatically modified starches usually have lower molecular weight than native starch so that they efficiently cover the surface of the droplets containing bioactive core material(eg. phytochemical). They also have unique rheological properties and texture profiles depending on the variation of carbohydrate components, which may also attribute to other desirable characteristics of the system as a whole. Therefore, development of a noble wall material is necessary.

Fig 2. SEM image of spray dried B-carotene with polysaccharide-based wall material

In our lab, various carbohydrate sources, mainly rice starch, are modified using various enzymes such as Thermus aquaticus 4-alpha-glucanotransferase, cyclodextrin glycosyltransferase, and isoamylase in order to alter molecular characteristics including branched chain distribution, amylose content, molecular weight, and gelation properties and make them suitable as wall materials. The molecular characteristics and rheological properties are measured by High Performance Size Exclusion Chromatography (HPSEC), rheometer and Texture Profile Analysis (TPA) respectively.

The main objective of our study includes:

1) To develop modified novel starch wall materials using various starch sources and enzymes

2) To analyze the stability of the capsules in various environmental conditions

3) To analyze physicochemical properties of the emulsion encapsulated with modified starch wall materials

4) To develop the emulsion system that enables stable and well-controlled release of the core substances with modified starch wall materials

5) To develop the powdered emulsion system using modified starch wall materials