Natural materials such as chi-tosan, gelatin, alginate, and poly(l-lactide) have biodegradability
and environment-friendly properties and they have been utilized
for the sustained-release system of unstable drugs or specific ingredients
in food (Gao and others 1984; Moretti and others 2002;
Chang and Dobashi 2003; Sanna-Passino and others 2004; Chang
and others 2006; Hsieh and others 2006; Maji and others 2007).
However, most microcapsules composed of natural polymers have
low mechanical properties, poor heat stability, and short-term release
properties compared with synthetic polymers in severe environment.
For this reason, the application of natural polymers in
the food packaging industry has been restricted. Synthetic polymers
include melamine, urea, and so on. Although synthetic materials
are toxic for direct application to food products due to
crosslinking agent, which was combined with synthetic polymers,
it ensures high mechanical properties, thermal stability, and longterm
release properties (Park and others 2001; Jang and others
2005; Scarfato and others 2007). Such characteristics are suitable
for indirect application to food packaging processes like printing
and coating progress. Melamine resin in many synthetic materials
has been already investigated by many researchers. In a study, fragrant
oil was encapsulated successfully by in situ polymerization of
melamine resin (Hong and Park 1999; Hwang and others 2006).
Lee and others (2002) studied about the effect of pH and formaldehyde/
melamine molar ratio on encapsulation. As pH increased,
the mean size of microcapsules decreased. A high molar ratio of
formaldehyde/melamine caused low hardness and high flexibility.
Thermal properties of melamine–formaldehyde (M–F) microcapsules
were found to depend on the feature of the core material and
synthesis conditions (Sala¨un and Vroman 2008). Most researchers
have mainly studied the manufacturing conditions and mechanical
properties of microcapsules in papers related to melamine
resin