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J Sci Food Agric 1998, 77, 103È108
Eþect of Acid Treatments and Drying Processes
on Physico-chemical and Functional Properties of
Cassava Starch
Manuel Plata-Oviedo and Celina Camargo*
Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas (UNICAMP),
Cx Postal 6121, CEP 13083-970, Campinas-SP, Brazil
(Received 24 October 1995 ; revised version received 12 August 1997 ; accepted 11 September 1997)
Abstract : The e†ects of acid treatments (HCl or organic acids) and drying processes (oven or sun) on the physico-chemical and functional properties of cassava
starch have been studied. The objective was to obtain modiÐed starches with
expansion properties similar to those of sun dried fermented cassava starch
(polvilho azedo) as produced by an empirical process. Expansion was evaluated
using a baking test. Independent of the drying method, organic acid-hydrolysed
cassava starch presented the same X-ray di†raction patterns (changes from C to
A) and similar intrinsic viscosity values. SEM observations showed no di†erences
between granule surfaces of sun dried and oven dried samples. However sun
dried organic acid-hydrolysed starches presented lower paste consistency values
at 30¡C when compared with oven dried ones. HCl-modiÐed cassava starches
were oven or sun dried, giving biscuits with low speciÐc volumes (2É5È
3É1 ml g~1). Similar behaviour was obtained using oven dried organic acid modiÐed cassava starches. When submitted to sun drying, organic acid modiÐed
starches showed great improvements in biscuit expansion (5È10 ml g~1). The
highest average speciÐc volumes were obtained using lactic acid modiÐed
starches. ( 1998 SCI.
J Sci Food Agric 77, 103È108 (1998)
Key words : cassava starch ; modiÐed starch ; hydrolysis ; lactic acid ; drying
process ; functional properties
INTRODUCTION
During starch fermentation, several organic acids are
produced (Cereda 1987). Observations made by scanning electron microscopy showed some holes on the
surface of the granules which are characteristic of enzymatic attack (Plata-Oviedo and Camargo 1995).
In order to simulate the fermentation e†ects observed
in fermented cassava starch, native cassava starch was
modiÐed by enzymatic or acid hydrolysis (Cardenas and
Buckle 1980 ; Camargo et al 1988) and dried in a conventional oven. These hydrolysed starches showed poor
expansion properties.
In this work, native cassava starch was treated with
HCl or organic acids. The e†ects of oven or sun drying
on some functional properties of these acid modiÐed
Sour cassava starch (polvilho azedo) is a typical Brazilian product obtained by natural fermentation of
cassava starch for a period of approximately 30 days
(Cereda 1987). The Ðnal product is sun dried for about
12 h. Sour cassava starch is used in the manufacture of
biscuit and “cheese breadÏ in which it is irreplaceable
due to its characteristic Ñavour and functional properties, mainly those of expansion. The biscuits have high
speciÐc volumes, alveolar structure and crispness,
similar to extruded snacks.
* To whom correspondence should be addressed.
103
( 1998 SCI.
J Sci Food Agric 0022È5142/98/$17.50.
Printed in Great Britain
M Plata-Oviedo, C Camargo
104
Fig 1. Biscuits made from sun dried (A) HCl-hydrolysed cassava starch, (B) native cassava starch and (C) sour cassava starch.
starches were investigated.
MATERIALS AND METHODS
Materials
Native industrial cassava starch and sour cassava starch
(polvilho azedo) were obtained from a local market in
Campinas (Brazil).
ModiÐcations of native industrial cassava starch
Native cassava starch batches (240 g DM basis) were
subjected to
HCl hydrolysis : 600 ml of 0É1, 0É3, 0É5 and 1É0 M
HCl for periods of 0É5, 1É0, 2É0 and 4É0 h at 40¡C.
I Organic acid hydrolysis : 600 ml of organic acid
solutions (pH 3É6, adjusted with 1É0 M NaOH)
containing 0É3 and 2É0% (v/w) of organic acid
(starch basis) for periods of 10 and 60 min at
30¡C. The organic acids used were : acetic (A),
propionic (P), lactic (L) and mixtures of AÈL,
AÈP, PÈL (1 : 1, v/v) and AÈPÈL (1 : 1 : 1).
I
After hydrolytic treatments, the modiÐed starches
were recovered by centrifugation (974 ] g, 3 min) and
Ðnally sun (12 h) or oven dried at 45¡C (18 h).
Baking test
The baking test was performed on native industrial
cassava starch, sour cassava starch and acid modiÐed
cassava starches, using the basic formulation described
by Cereda (1983) : 30 g starch, 7É5 g hydrogenated
vegetable fat, 0É9 g salt and water, the water absorption
values for the native starch, acid modiÐed starches and
sour cassava starch being 21 ml, 24 ml and 30 ml,
respectively.
The hydrogenated vegetable fat was Ðrst mixed with
the salt and 25% of the total water and boiled. This
boiling mixture was added to the starch, already moistened with another 25% of the total water, and all the
ingredients were mixed into a dough followed by the
addition of the remaining water (50%). The total mixing
time was 5 min. Portions of 4É0 ^ 0É1 g of the Ðnal
dough, having a creamy consistency and smooth
appearance were dropped onto metal sheets and cooked
for 20 min at 200È210¡C.
After cooling at room temperature for 30 min, the
biscuits were weighed (g) and the volume (ml) determined by the seed displacement method.
Physico-chemical properties and scanning electron
microscopy
The intrinsic viscosity of starch suspensions, dissolved
in 1É0 M KOH, was measured according to Leach
(1963), using a viscosimeter (Cannon-Fenske Number
50) maintained at 35¡C in a thermostatic bath.
The pasting properties were studied using a Brabender viscoamylograph with a 700 cmg sensitivity cartridge at 75 rpm. The starch dispersions at 6É2% (27É9 g
DM basis in 450 ml of water) were heated from 30 to
95¡C at 1É5¡C min~1, kept at this temperature for
15 min, and Ðnally cooled to 30¡C at 1É5¡C min~1.
X-ray di†raction patterns were determined using a
Shimadzu XD-3A unit with Cu radiation, K line, equal
to 0É154 02 nm (LiF as monochromator). The scanning
Physico-chemical and functional properties of cassava starch
105
Fig 2. Biscuits made from hydrolysed cassava starches. (A) Acetic acid (2É0% for 60 min) ; (B) lactic acid (2É0% for 10 min) ; (C)
aceticÈlactic acid mixture (0É3% for 10 min). Biscuits A, B and C : left (oven dried starch) and right (sun dried starch).
velocity was 1¡(2h) min~1 at 30 kV and 20 mA. All
samples had moisture contents of 13 ^ 0É2%.
The starch samples for scanning electron microscopy
observations were dehydrated by lyophilisation. The
starches were sprinkled onto a double-sided adhesive
tape attached to a circular specimen stub and coated
Ðrst with carbon followed by gold, and observed with a
JEOL-JSM T300 Microscope at an accelerating potential of 5 kV.
RESULTS AND DISCUSSION
HCl-modiÐed starches
Fig 3. E†ect of lactic acid on biscuit expansion (measured by
average speciÐc volumes) performed on sun dried organic acid
hydrolysed starches. * mixtures AÈL, PÈL and AÈP (1 : 1, v/v).
** mixture AÈPÈL (1 : 1 : 1, v/v/v).
TABLE 1
Intrinsic viscosities (dl g~1) of oven and sun dried organic
acid hydrolysed cassava starchesa
a
b
c
d
Samples
Oven dried
Sun dried
A, 2É0% : 60 minb
L, 2É0% : 10 minc
AÈL, 0É3% : 10 mind
2É25
2É20
2É44
2É18
2É15
2É21
Intrinsic viscosity of native industrial cassava starch : 2É57.
Acetic acid hydrolysed starches (2É0% for 60 min).
Lactic acid hydrolysed starches (2É0% for 10 min).
AceticÈlactic acid hydrolysed starches (0É3% for 10 min).
Oven or sun dried HCl-modiÐed starches gave hard and
dense biscuits, with no expanded structure, characterized by low speciÐc volumes (2É5È3É1 ml g~1), similar to
those obtained with native cassava starch. Sour cassava
starch gave highly expanded biscuits, characterised by
high speciÐc volumes (15 ^ 0É3 ml g~1, Fig 1).
Organic acid modiÐed starches
Baking tests performed on oven dried organic acid
modiÐed starches showed biscuits with low speciÐc
volumes (3É0È3É3 ml g~1). However, the same acid
modiÐed starches, when submitted to sun drying
showed great improvement in biscuit expansion (Fig 2).
Sun dried lactic acid starches gave the highest
average speciÐc volumes (Fig 3). When lactic acid was
added to the acetic acid, propionic acid and aceticÈ
propionic acid mixture used in the hydrolytic treatments, the sun dried modiÐed starches gave biscuits
106
M Plata-Oviedo, C Camargo
Fig 4. Brabender viscograms of native cassava starch (ÈÈÈ) and sun (È È È È) or oven (È Œ È Œ È) dried organic acid hydrolysed
starches. (A) Acetic acid hydrolysed starch (2É0% for 60 min) ; (B) lactic acid hydrolysed starch (2É0% for 10 min) ; (C) aceticÈlactic
acid hydrolysed starch (0É3% for 10 min).
with higher average speciÐc volumes than with the
acetic acid, propionic acid and aceticÈpropionic acid
mixture sun dried modiÐed starches. These results
showed the beneÐcial e†ect of lactic acid on biscuit
expansion.
Physico-chemical properties and scanning electron
microscopy of some organic acid modiÐed starches
The intrinsic viscosity of native industrial cassava starch
was 2É57 dl g~1. This value is higher than 2É30 and
2É45 dl g~1 reported by Franco et al (1988) and Ciacco
and DÏAppolonia (1976), respectively. The organic acid
hydrolysed starches showed lower viscosities suggesting
some starch degradation (Table 1).
The viscograms of native and organic acid hydrolysed starches are shown in Fig 4. Both sun and oven
dried hydrolysed starches, when compared with native
starch, showed a slight decrease at pasting peak consistency and higher peak consistency temperatures. The
initial consistency of organic acid treated starches at
95¡C was higher than the native cassava starch (Table
2). Sun and oven dried hydrolysed cassava starches had
lower Ðnal viscosity (at 30¡C) than industrial starch,
suggesting a decrease in tendency to retrograde. The difference between sun drying and oven drying starches
was small and not signiÐcant.
X-ray di†raction patterns of native and sun or oven
dried organic acid hydrolysed cassava starches are
shown in Fig 5. There were no di†erences between the
Physico-chemical and functional properties of cassava starch
107
TABLE 2
Pasting properties of native industrial cassava starch and sun or oven dried organic acid hydrolysed cassava starch
Samples
Native starch
A, 2É0% : 60 minb
Oven dried
Sun dried
L, 2É0% : 10 minc
Oven dried
Sun dried
AÈL, 2É0% : 10 mind
Oven dried
Sun dried
a
b
c
d
Initial
pasting
temp
(¡C)
Consistency (BUa)
Pasting
peak
temp
(¡C)
95¡C
30¡C
Peak
Initial
Final
63É0
71É3
885
330
240
700
62É0
62É0
73É0
74É0
860
830
410
400
280
270
580
495
62É8
62É8
73É5
73É5
795
790
350
370
220
205
425
390
62É8
62É8
73É0
73É5
825
840
395
410
275
275
560
510
BU, Brabender Units.
Acetic acid hydrolysed starch (2É0% for 60 min).
Lactic acid hydrolysed starch (2É0% for 10 min).
AceticÈlactic acid hydrolysed starch (0É3% for 10 min).
di†raction patterns of sun and oven dried hydrolysed
starches. However, the organic acid treatments changed
the original C di†ractogram pattern of native starch to
A. Changes from B to A patterns in potato starch (Sair
1964) and from C to A pattern in cassava and arrowroot starches (Lorenz and Kulp 1982) were observed
when starches were heated at restricted moisture levels
(heatÈmoisture treatments).
SEM observations revealed a mild superÐcial corrosion on some granules (less than 1%) of organic acid
hydrolysed starches. There were no visual di†erences
between sun dried (B1) and oven dried (B2) samples
(Fig 6).
CONCLUSIONS
Fig 5. X-ray di†ractions patterns of native industrial cassava
starch and sun or oven dried organic acid hydrolysed cassava
starches. (A) Corn starch (A type) ; (B) native cassava starch (C
type) ; (C) oven dried acetic acid starch (2É0% for 60 min) ; (D)
sun dried acetic acid starch (2É0% for 60 min) ; (E) oven dried
lactic acid starch (2É0% for 10 min) ; (F) sun dried lactic acid
starch (2É0% for 10 min) ; (G) oven dried acetic-lactic acid
starch (0É3% for 10 min) ; (H) sun dried aceticÈlactic acid
starch (0É3% for 10 min).
Independent of drying method (sun or oven) organic
acid hydrolysed starches presented similar physicochemical properties (X-ray di†raction patterns, intrinsic
viscosities, Brabender viscograms). Furthermore, SEM
observations detected no di†erences between sun dried
and oven dried samples.
Baking tests demonstrated that sun dried organic
acid hydrolysed starches produced expanded biscuits
which was not observed when oven drying was used.
Unfortunately we could not relate the expansion property of sun dried organic acid hydrolysed starches with
the physico-chemical properties studied in this work.
Both fermented cassava starch (Dufour et al 1994 ;
Plata-Oviedo and Camargo, unpublished) and lactic
acid hydrolysed cassava starch (Nunes and Cereda
1994) showed the expansion property when irradiated
by UV-lamps. It is well known that UV radiation
catalyses photochemical reactions. Herold and Fouassier (1981) using a non-degassed system, grafting methyl
methacrylate on potato starch under UV radiation
M Plata-Oviedo, C Camargo
108
Fig 6. SEM observations on organic acid hydrolysed starches. (A1) Acetic acid hydrolysed starch (2É0% for 60 min), sun dried
(5000]) ; (A2) aceticÈlactic acid hydrolysed starch (0É3% for 10 min), sun dried (7500]) ; (B1) lactic acid hydrolysed starch (2É0%
for 10 min), oven dried (5000]) ; (B2) lactic acid hydrolysed starch (2É0% for 10 min), sun dried (5000]).
without photo-initiators. We believe that the expansion
property of sun dried organic acid hydrolysed cassava
starches results from some chemical interactions
between the organic acids and the starch, catalysed by
the UV segment of solar radiations. The same hypothesis could explain the expansion property of sun dried
fermented cassava starch (polvilho azedo). Model
experiments are being carried out to conÐrm this
hypothesis.
REFERENCES
Camargo C, Colonna P, Buleon A, Richard-Molard D 1988
Functional properties of sour cassava (Manihot utilissima)
starch : polvilho azedo. J Sci Food Agric 45 273È289.
Cardenas O S, Buckle T S 1980 Sour cassava starch : a preliminary study. J Food Sci 45 1509È1512, 1528.
Cerada M P 1983 PadronizacÓa8 o para ensaios de qualidade
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I-FormulacÓa8 o e preparo de biscoitos. Bol SBCT A 17 287È
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Cereda M P 1987 Tecnologia e qualidade do polvilho azedo.
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Ciacco C F, DÏAppolonia B L 1976 Characterization of
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