catalyzed transesterification is performed to obtain high yield of
biodiesel. Both base and acid catalyzed reactions are affected by
moisture content [8]. In presence of water, base catalyzed reaction
lead to saponification instead of transesterification. Furthermore,
acid catalyzed transesterification lead to hydrolysis in the presence
of water. Both acid and base catalyzed reaction require high
reaction temeparture. It is a well know fact that acid and base are
corrosive and toxic towards the environment.
Enzymes are proteins. Enzymes can be used as an alternative to
chemical catalysts for biodiesel synthesis. Lipases are a class of
enzymes which are known to catalyze hydrolysis, esterification
and transesterification reactions [45,46]. Lipase catalyzed biodiesel
production is extensively reported as the reaction can be carried
out under mild conditions and no side products are formed [47–
51]. Moreover, lipases are moisture tolorent. Both free and
immobilized lipases can be used for biodiesel preparation.
Immobilized lipases are recovered after transesterification and can
be reused for many cycles [47–51].
Acid, base and enzyme catalyzed reactions are reported for the
production of biodiesel from food waste (Scheme 1). Yang et al.
studied the feasibility of biodiesel synthesis from oil obtained from
instant noodle waste. Both KOH and H2SO4 were used as catalysts
for the preparation of biodiesel. Under optimized reaction conditions
using KOH (2% w/v) and 1:8 methanol to oil molar ratio
98.5% of biodiesel can be achived at 60 °C in 2 h [42]. Whereas,
H2SO4 (5% v/v) catalyzed reaction gave 97.8% biodiesel in 3 h using
1:6 methanol to oil molar ratio at 80 °C [42]. In addition, Yang et al.
also used Novozyme-435 for the transesterification of oil obtained
from noodle waste. Four parameters were optimized viz. (i) effect
of different alcohols, (ii) oil to alcohol molar ratio, (iii) reaction
time, (iv) lipase amount and (v) water content for biodiesel