structure of the polymer that makes it biodegradable. To be
biodegradable, some parts of the polymer main chain must be
similar to naturally occurring substances; therefore, microbes
can use their existing enzymes to break the polymer chain at
those specific locations and use them as a source of energy.
For example, microorganisms break down starch to use the
glucose, which is broken down to two molecules of pyruvic
acid, which can be further fermented into lactic acid or aerobically
converted into CO2 to generate energy. Portions of
polymers that are small enough are transferred into microbial
cells and consumed as a food source. Chemical structures of
pyruvic acid and lactic acid are similar to that of polylactic
acid (Fig. 5).