J. Agric. Food Chem. 2000, 48, 2625−2627
2625
Effective Dea cetyla tion of Ch itin u n d er Con d ition s of 15 p si/121 °C
Hong Kyoon No,*,† Young In Cho,† Hyeung Rak Kim,‡ and Samuel P. Meyers§
Department of Food Science and Technology, Catholic University of Taegu-Hyosung, Hayang 712-702,
South Korea; Faculty of Food Science and Biotechnology, Pukyong National University, Pusan 608-737,
South Korea; and Department of Food Science, Louisiana State University, Baton Rouge, Louisiana 70803
Deacetylation of chitin under autoclaving conditions (15 psi/121 °C) was evaluated for the preparation
of chitosan under different NaOH concentrations and reaction times. Deacetylation was effectively
achieved by treatment of chitin under elevated temperature and pressure with 45% NaOH for 30
min and a solids/solvent ratio of 1:15. Treated chitosan showed similar nitrogen content (7.42%),
degree of deacetylation (90.4%), and molecular mass (1560 kDa) but significantly higher viscosity
values (2025 cP) compared with those (7.40%, 87.6%, 1304 kDa, and 143 cP, respectively) of a
commercial chitosan. Reduction of the solids/solvent ratio from 1:15 to 1:10 did not affect degree of
deacetylation, viscosity, and molecular mass of chitosan.
Keyw or d s: Chitin; chitosan; deacetylation; autoclaving
INTRODUCTION
4, Thomas Scientific, Swedesboro, NJ ), sifted with 20 (0.841
mm) and 40 mesh (0.425 mm) sieves, placed in opaque plastic
bottles, and stored at ambient temperature. Chitin of 0.841-
0.425 mm particle size was used for deacetylation. Commercial
chitosan (Keumho Chemical Co.), prepared according to a
conventional method from the same source of chitin as used
in this investigation, was used for comparative purposes.
Dea cetyla tion by Au tocla vin g. Fifteen grams of chitin
in a 300-mL autoclavable bottle was deacetylated by pressure
of 15 psi for 5-30 min at 121 °C, using 40-50% NaOH and a
solids/solvent ratio of 1:10 or 1:15 (w/v). The autoclave was
preheated to 100 °C before introduction of the samples,
requiring about 12 min to reach 121 °C. The resulting
chitosans were washed to neutrality in running tap water,
rinsed with distilled water, filtered, and dried at 60 °C for 4 h
in a forced-air oven.
P r oxim a te An a lyses. Nitrogen was determined in tripli-
cate using an elemental analyzer (EA 1110, CE Instrument,
Rodano-Milan, Italy). Moisture content was determined using
a halogen moisture analyzer (HG53, Mettler Toledo, Greif-
ensee, Switzerland).
Solu bility. Percentage of solubility of chitosan was deter-
mined in duplicate at a 0.5% chitosan concentration in 1%
acetic acid.
Degr ee of Dea cetyla tion (DD). The DD of chitosan was
determined in duplicate according to a colloid titration method
(Kim, 1996) using N/400 potassium polyvinyl sulfate (PVSK;
f ) 1.006; Wako Pure Chemical Industries, Osaka, J apan).
Viscosity. Viscosities of chitosan samples were determined
with a Brookfield viscometer, model RVT (Brookfield Engi-
neering Laboratories, Inc., Stoughton, MA). Chitosan solutions
(500 mL) were prepared by dissolving chitosan for 4 h in 1%
acetic acid at a 1% concentration on a moisture-free basis; the
mixture was allowed to stand for 3 h at room temperature to
remove air bubbles. Measurements were made in duplicate
using a no. 2 spindle at 5 rpm on solutions at 20 °C with values
reported in centipoise (cP) units.
Molecu la r Weigh t. Weight-average molecular weight (Mw)
of chitosan was measured using multiangle laser light scat-
tering (Dawn DSP-F, Wyatt Technology, Santa Barbara, CA)
and refractive index (RI; model 7021, Rheodyne, Cotati, CA)
detectors operated in a high-performance size exclusion chro-
matograph following procedures described by You et al. (1999).
Operation conditions were as follows: column, TSK G5000PW
(7.8 × 300 mm, Tosoh Corp., Tokyo, J apan); RI detector
temperature, 35 °C; flow rate, 0.4 mL/min; eluent, 0.2 M
A variety of chemical processes have been developed
and proposed for the preparation of chitosan (No and
Meyers, 1995). This biopolymer generally is prepared
by treating raw chitin with 50% sodium hydroxide
solution, usually at 100 °C or higher to effectively
remove the acetyl groups (No and Meyers, 1995). During
deacetylation, conditions must, in a reasonable time,
sufficiently deacetylate the chitin to yield a final chito-
san product that is soluble in dilute acetic acid without
significant degradation. A limited number of alternative
techniques for chitin deacetylation have been proposed.
These include application of thermo-mechano-chemical
technology (Pelletier et al., 1990), an alkali impregna-
tion technique (Rao et al., 1987), use of water-miscible
organic solvents as diluents (Batista and Roberts, 1990),
and use of thiophenol to trap oxygen during deacetyla-
tion processes (Domard and Rinaudo, 1983).
Although a variety of methods have been developed
for chitosan preparation, few attempts have been made
to evaluate a combination of feasible elevated pressure
and temperature conditions for rapid deacetylation.
Earlier, Pelletier et al. (1990) tried thermo-mechano-
chemical treatment using a cascade reactor unit operat-
ing (90 s at 230 °C) under reduced alkaline conditions
of 10% (w/v) NaOH. However, this process required
prior mercerization of chitin in 50% NaOH for 24 h at
4 °C.
The present research reports on the development of
a relatively simple and inexpensive process for effective
deacetylation of chitin.
EXPERIMENTAL PROCEDURES
Ma ter ia ls. Commercial chitin was obtained from Keumho
Chemical Co. (Seoul, South Korea). To obtain a uniform size
product, the chitin was ground through a Wiley mill (model
* Author to whom correspondence should be addressed
(telephone/fax
cuth.cataegu.ac.kr).
+82-53-850-3219;
e-mail
hkno@
† Catholic University of Taegu-Hyosung.
‡ Pukyong National University.
§ Louisiana State University.
10.1021/jf990842l CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/05/2000
No, Hong Kyoon
