Physicochemical Properties of Sonicated Mung Bean, Potato, and Rice Starches

Koo Min Chung,1,2 Tae Wha Moon,3 Hyunjung Kim,4 and Jae Kun Chun5

ABSTRACT Cereal Chem. 79(5):631–633

Mung bean, potato, and rice starch solutions (5%, w/w) were sonicated sonication. The starch paste became more transparent, and the hot paste
for up to 5 min after heating, and their physicochemical properties were viscosity measured at 70°C decreased remarkably. Results indicate that
investigated. Alkaline viscosities, including the apparent and inherent changes in the physicochemical properties of starch were induced by the
viscosities of starches, decreased. The residues of the swollen starch disruption of swollen granules rather than the breakage of glucosidic
granules after pasting and centrifugation were also reduced prominently linkages with sonication.
by sonication. Average degree of polymerization did not change with

Ultrasonic waves generated by converting electrical energy into output control 10; manufacturer recommended setting below 7 when
mechanical vibration result in the intense agitation of the molecules using micro tips) using a sonifier (model 450, Branson Ultrasonics
in the medium. High-amplitude waves (10 kHz – 1 MHz) generally Corp., Danbury, CT) equipped with a tapered micro tip (end
are best suited for applications such as cleaning, drilling, emulsi- diameter of 3.2 mm). The end of micro tip was placed at the depth
fication, soldering, medical therapy, welding, and chemical and bio- of 1 cm from the surface of pastes. At the condition used for
logical applications, as well as sonar. On the other hand, low- sonication, the meter reading of output was  15 (max. 100) and
amplitude waves are most effective for applications such as security corresponded to the output energy of 30W according to the output
systems, medical instrumentation, and material testing (Anonymous chart in the instruction manual. After sonication, samples were
1976). In food processing, ultrasonication can be applied to cleaning, lyophilized.
emulsifying, mixing, alcohol fermenting, extracting, cutting, drying, Apparent viscosity was measured using a viscometer (LVDV-
spraying, degassing, and cell disruption (Sato 1993). II+, Brookfield Engineering Laboratories, Stoughton, MA) equipped
Jackson et al (1988, 1989) used sonication to dissolve corn and with a small sample adapter (SSA 31/13R). Starch (0.5 g, db) was
sorghum starch granules (at <1% solids) after heating instead of dispersed in 3 mL of water and completely dissolved by adding
solubilization in alkali or dimethyl sulfoxide (DMSO) for the 27 mL of 1% NaOH solution. Viscosity was measured at 25•C
analysis of molecular structure through high-performance size-exclu- and 100 rpm (Chung and Seib 1991).
sion chromatography. They reported that ultrasonic vibrations disrupt Determination of inherent viscosity was made with a No. 75
swollen granules, thereby releasing amylose and amylopectin from Cannon-Fenske capillary viscometer. Starch (1 g, db) was dis-
the granules, resulting in an increase in water solubility of starch. persed in 100 mL of water and completely dissolved by slowly
Increase in solubility implies that sonication may change other adding 100 mL of 2M NaOH solution with continuous stirring.
physicochemical properties of starch and, consequently, could be Starch solution was then gravity-filtered through a G-1 glass funnel,
used a method for starch treatment. The objective of this work and the viscosity was measured at 25•C (Myers 1964).
was to investigate the effect of ultrasonic on the physicochemical Paste clarity was measured as % transmittance at 650 nm with a
properties of three types of starches (rice cereal starch, potato spectrophotometer (model UV-1601PC, Shimadzu Corp., Kyoto,
tuber starch, and mung bean legume starch) at high concentration. Japan) (Craig et al 1989). Starch (100 mg, db) was suspended in
10 mL of water in screw-cap tubes, heated in a boiling water bath
MATERIALS AND METHODS for 30 min, then cooled to room temperature.
Average degree of polymerization (DPn) was determined by
Starch measuring both the total carbohydrate content using phenol-sulfuric
Mung bean starch was isolated from commercial mung beans acid method and the reducing power through the modified Park-
purchased at a local market using an alkaline steeping method Johnson method (Hizukuri et al 1981; Chung and Seib 1991). Dry
(Chung et al 2000). Potato and rice starches were purchased from starch (50 mg) with 1 mL of 1M NaOH added was stirred with a
Sigma (St. Louis, MO) glass rod until no clots were found. Starch was dissolved completely
through gradual dilution using  0.5–1 mL of water. The solution
Physicochemical Measurements was neutralized with 1M HCl and diluted to a total volume of 10
Starch samples were prepared as follows. Twenty-eight grams mL with water. The neutralized solution was kept in a 50•C water
of starch slurry (5% solids) were heated at 95•C for 5 min in a bath to avoid retrogradation until measurement.
Rapid Visco Analyser (RVA model 3D, Newport Scientific, Sydney,
Australia) for uniform heating. Starch pastes were then immediately Hot Paste Viscosity and Granule Disintegration
sonicated for 1, 3, and 5 min at the output control of 5 (max. For hot paste viscosity, 28 g of starch slurry (3%, w/w) was
heated at 95•C for 5 min in an RVA and sonicated for 0.25, 0.5, 1,
3, and 5 min as described previously. Starch paste was then trans-
1 School of Bioresource, College of Natural Science, Andong National University, ferred into a screw-cap tube and kept in a 70•C water bath for 30
Andong, Kyungbuk 760-749, Korea.
2 Corresponding author. Phone: 82 54 820 5492. Fax: 82 54 823 1627. E-mail: min. Viscosity was measured at the same temperature using a vis-
kmchung@andong.ac.kr. cometer (Brookfield) equipped with a small sample adapter (SSA
3 Department of Food Science and Technology, School of Agricultural Biotech-
18/13R).
nology, and Research Center for New Bio-Materials in Agriculture, Seoul National Granule disintegration was determined using a method to measure
University, Korea.
4 Research Center for New Bio-Materials in Agriculture, Seoul National University, the swelling power of starch (Schoch 1964). Starch (2 g for mung
Korea. bean and rice starches and 0.5 g for potato starch) was mixed with
5 Department of Food Science and Technology, School of Agricultural Biotech- 200 mL of water in a preweighed 250-mL centrifuge tube. The
nology, Seoul National University, Korea. slurries were heated at 65–95•C for 30 min while stirring at 200
Publication no. C-2002-0801-06R.
rpm with a rectangular paddle. The pastes were then sonicated for
© 2002 American Association of Cereal Chemists, Inc. 0.25, 0.5, 1, 3, and 5 min as described previously. The sonicated

Vol. 79, No. 5, 2002 631

pastes were immediately cooled to room temperature in a water and respectively, for potato starch and from 42.2 cP and 1.85 dL/g to
ice bath and centrifuged at 7,000 rpm for 15 min. The precipitated 6.9 cP and 0.88 dL/g, respectively, for rice starch after 5 min of
portion was weighed and expressed as the degree of granule dis- sonication. Reduction in alkaline viscosity was also reported for
integration. acid-thinned starch (Rohwer and Klem 1984; Chung and Seib
1991). As the acid concentration or treatment time increased, the
Statistical Analysis viscosity decreased. In addition, reduced alkaline viscosity was
All measurements were done at least in duplicate and the Statis- observed in oxidized starches (Chung and Seib 1991) and extru-
tical Analysis System (SAS Institute, Cary, NC) was used to analyze ded starches (Colonna et al 1984, 1989; McPherson and Jane
data and to calculate Fisher’s least significance differences (a = 2000). In all cases, molecular degradation by the cleavage of gluco-
0.05). sidic linkages results in low alkaline viscosity.
However, in the present study ultrasonic did not degrade the
RESULTS AND DISCUSSION glucosidic linkages. All treatments showed no statistically significant
changes (P < 0.05) in the average DPn (Table I). On the contrary,
Alkaline Viscosities and DPn of Sonicated Starches Jackson et al (1988) reported that extensive sonication appeared
Sonication reduced both the apparent and the inherent to depolymerize amylopectin. You and Lim (2000) also showed
viscosities of starches (Table I). Apparent and inherent viscosities alkaline-dissolved starch was degraded by sonication. The starch
of native mung bean starch were 81.6 cP and 2.92 dL/g, and concentration they used for experiments appears to have caused
decreased to 13.3 cP and 1.35 dL/g, respectively, after 5 min of different results. They treated starches at relatively low concentration
sonication. The decreases in alkaline viscosities were also observed ( 1%) for measuring molecular characteristics through high-per-
with potato and rice starches. Apparent and inherent viscosities formance size-exclusion chromatography. In our experiment, the
diminished from 59.6 cP and 2.74 dL/g to 10.1 cP and 1.30 dL/g, starch concentration was somewhat higher (5%, w/w), while the
energy applied to the starch was lower.

TABLE I Degree of Disintegration of Starch Granules by Sonication

Apparent and Inherent Viscosities and Average Degree Instead of breakage of glucosidic linkages, sonication appeared
of Polymerization (DPn) of Sonicated Starchesa to disrupt the swollen starch granules (Table II). When mung bean
Sonication Apparent Inherent starch was sonicated for 5 min after cooking at 95°C, the weight
Time Viscosityb Viscosityb of precipitated swollen granules after centrifugation decreased from
Starch (min) (cP) (dL/g) Average DPnc 14.91 to 0.57 g/g of dry starch. Starch subjected to sonication
Mung bean 0 81.6 ± 1.3a 2.92 ± 0.00a 3,160 ± 220a
1 46.7 ± 0.2b 2.14 ± 0.01b 3,380 ± 520a
3 19.7 ± 0.2c 1.59 ± 0.00c 3,280 ± 650a
5 13.3 ± 0.1d 1.35 ± 0.00d 2,920 ± 410a
Potato 0 59.6 ± 0.6a 2.74 ± 0.01a 3,930 ± 450a
1 36.9 ± 0.0b 2.28 ± 0.00b 4,340 ± 1390a
3 14.3 ± 0.2c 1.60 ± 0.00c 4,220 ± 910a
5 10.1 ± 0.2d 1.30 ± 0.00d 3,490 ± 470a
Rice 0 42.2 ± 0.6a 1.85 ± 0.01a 1,710 ± 190a
1 12.3 ± 0.8b 1.24 ± 0.00b 1,790 ± 180a
3 8.4 ± 0.0c 1.03 ± 0.01c 1,560 ± 210a
5 6.9 ± 0.0d 0.88 ± 0.01d 1,600 ± 150a
a Means in the same column not followed by the same letter for each starch
are significantly different at P < 0.05.
b Mean value of duplicate measurements – standard deviation.
c Mean value of four measurements – standard deviation.

TABLE II
Disintegration of Starch Granules by Sonicationa–c

Sonication Precipitate Weight (g/g dry starch)

Starch Time 65•C 75•C 85•C 95•C
Mung bean Control 3.69b 6.21a 11.34a 14.91a Fig. 1. Clarity of sonicated starches.
15 sec 3.69b 5.65b 11.29a 15.10a
30 sec 3.61b 5.41b 10.38b 9.37b
1 min 3.89a 4.94c 6.74c 4.51c
3 min 3.68b 3.19d 1.23d 1.13d
5 min 3.03c 2.33e 1.01d 0.57d
Potato Control 20.26a 35.78a 49.29a 71.04a
15 sec 9.38b 16.28b 10.33b 8.34b
30 sec 7.49c 6.35c 4.48c 4.36bc
1 min 4.45d 3.32d 2.68c 3.06c
3 min 2.51e 2.20d 1.75c 1.87c
5 min 2.23e 2.35d 1.68c 2.37c
Rice Control 3.53a 5.00a 8.61a 9.57a
15 sec 3.49a 4.93a 8.03b 9.77a
30 sec 3.42a 4.79a 8.11b 8.90b
1 min 3.13b 4.57ab 7.89b 8.10c
3 min 3.02b 4.18bc 5.87c 3.80d
5 min 2.48c 3.77c 4.24d 1.97e
a Heated at 65–95•C for 30 min, sonicated, cooled, and centrifuged.
b Mean of duplicates.
c Means in the same column not followed by the same letter for each starch
are significantly different at P < 0.05. Fig. 2. Hot paste viscosity of sonicated starches.

632 CEREAL CHEMISTRY

treatment for 15 sec showed almost no difference from the control most remarkable in potato starch which had the highest swelling
starch. With sonication for 30 sec, the weight decreased to 9.37 g. ability among starches tested. Granular disruption by sonication
When the cooking temperature was lowered, the disruption in starch also induced the starch paste to become more transparent and less
granules decreased due to the low swelling degree. At 65•C, the viscous. Thus, sonication may be applied for the preparation of a
precipitate weighed 3.03 g for the starch sonicated for 5 min, physically modified starch that has good clarity and low viscosity
while the control weighed 3.69 g. Rice starch showed a trend very without decrease in chain length.
similar to that of the mung bean starch. Potato starch also showed
less disintegration with the decrease in heating temperature. But, ACKNOWLEDGMENTS
unlike other starches, potato starch granules were disrupted con-
siderably by sonication even after heating at 65•C due to the This work was supported by the Special Research Program for
relatively high swelling ability at this temperature. Potato starch Agriculture and Forestry funded by the Ministry of Agriculture and
Forestry in Korea. T. W. Moon was supported, in part, by the grant from
sonicated for 5 min had 2.23 g of precipitated swollen granules
National Research Lab Program funded by the Ministry of Science and
while the control had 20.26 g. Overall, the granular disruption was Technology of Republic of Korea.
the most remarkable in potato starch.
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[Received June 7, 2001. Accepted March 20, 2002.]

Vol. 79, No. 5, 2002 633