Biomedical Engineering Reference
In-Depth Information
Chapter
2
E
NZYMATIC
S
YNTHESIS OF
A
CYL
A
SCORBATE
AND
I
TS
F
UNCTION AS A
F
OOD
A
DDITIVE
Yoshiyuki Watanabe
1
,*
and Shuji Adachi
2
1
Department of Biotechnology and Chemistry, School of Engineering, Kinki University,
1 Umenobe, Takaya, Higashi-Hiroshima 739-2116, Japan
2
Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto
University, Sakyo-ku, Kyoto 606-8502, Japan
Abstract
Acyl ascorbates were synthesized through the condensation of various fatty acids with L-
ascorbic acid using immobilized lipase in a water-soluble organic solvent, and their properties
as food additive were examined. The optimal conditions, which were the type of organic
solvent, reaction temperature, the initial concentrations of substrates and the molar ratio of
fatty acid to ascorbic acid, for the enzymatic synthesis in a batch reaction were determined.
The continuous production of acyl ascorbate was carried out using a continuous stirred tank
reactor (CSTR) and plug flow reactor (PFR) at 50
o
C, and each productivity was
ca
. 6.0 x 10
for CSTR and 1.9 x 10
3
g/(L-reactor
·
d) for PFR for at least 11 days, respectively. The
temperature dependences of the solubility of acyl ascorbate in both soybean oil and water
could be expressed by the van't Hoff equation, and the dissolution enthalpy, Δ
H
, values for
the soybean oil and water were
ca
. 20 and 90 kJ/mol, respectively, irrespective of the acyl
chain length. The decomposition kinetics of saturated acyl ascorbate in an aqueous solution
and air was empirically expressed by the Weibull equation, and the rate constant,
k
, was
estimated. The activation energy,
E
, for the rate constant for the decomposition in both
systems depended on the acyl chain length. The surface tensions of acyl ascorbates in an
aqueous solution were measured by the Wilhelmy method, and the critical micelle
concentration (CMC) and the residual area per molecule were calculated. The CMC values
were independent of temperature but dependent on the pH. The effect of pH of aqueous phase
on the stability of O/W emulsion prepared using acyl ascorbate as an emulsifier was
examined, and the high stability at pHs 5 and 6 was ascribed to the largely negative surface-
charge of droplets in the emulsion. The addition of saturated acyl ascorbate, whose acyl chain
length was from 8 to 16, lengthened the induction period for the oxidation of linoleic acid in a
*
E-mail address: wysyk@hiro.kindai.ac.jp. telephone to: +81-82-434-7000; fax: +81-82-434-7890; (Author to
whom correspondence should be addressed).
