Effects of Particle Size, Soybean Oil and Water
Content during Cooking on the In Vitro Resistant
Starch of Cornmeal
Kelly C Massarolo1*, Cláudia F J Ferreira1, Larine Kupski2 and Eliana Badiale-Furlong1
1Laboratório de Micotoxinas e Ciência de Alimentos, Universidade Federal do Rio Grande- FURG, Brasil
2Laboratório de Análises de CompostosOrgânicos e Metais, Universidade Federal do Rio Grande -FURG, Brasil
Submission: May 11, 2018;Published: July 05, 2018
*Corresponding author: Kelly Cristina Massarolo, Laboratório de Micotoxinas e Ciência de Alimentos, Escola de Química e Alimentos, Universidade Federal do Rio Grande - FURG, Avenida Itália km 8, Campus Carreiros, Rio Grande, RS, Brasil, Tel: +55 5332336796; Email: email@example.com
How to cite this article:Kelly C M, Cláudia F J F, Larine K, Eliana B F. Effects of Particle Size, Soybean Oil and Water Content during Cooking on the In
VitroResistant Starch of Cornmeal. Nutri Food Sci Int J. 2018; 7(1): 555703. DOI:10.19080/NFSIJ.2018.07.555703.
Resistant starch has attracted interest due to conferring functional properties to foods. Cornmeal is consumed after being submitted to some processing and preparation, which can affect the resistant starch content in the final product. The aim of this work was to find the interference of cornmeal’s particle size on resistant starch content and to establish the conditions of cooking that promote the highest resistant starch content when preparing cornmeal based foods, such as cornmeal:water proportion and the amount of soybean oil used. To achieve the aim, the in vitro starch digestibility of hydrothermal treated cornmeals was evaluated by experimental design CCD 22, carried in order to optimize the cornmeal:water proportion and the amount of soybean oil conditions that promote the major resistant starch formation. The best condition of hydrothermal treatment was applied in cornmeals with different particle sizes. The fine-ground cornmeal showed the highest resistant starch content (201.6mg/g). Applying hydrothermal treatment in the cornmeal:water proportion of 1:5w/v and 3% of soybean oil, the content of resistant starch has increased significantly (21.9%). Under these conditions, the resistant starch content was increased 39.8% and 45.4% for medium-ground and coarse-ground cornmeals, respectively. These findings can inspire other studies with different cooking conditions and starch and other ingredients interactions during processing, to obtain starch-based foods with lower glycemic inde
Corn (Zea mays) is used for human nutrition due to its specific physicochemical properties, such as high levels of starch, proteins with low levels of gliadin fraction, gluten free, dietary lipids, hypoallergenics, phytochemicals, dietary fiber and a delicate flavor .
The use of cornmeals has been increased by the demand to produce gluten free products, a protein found in the endosperm of some cereals such as wheat, barley and rye , which can cause harm to health, in some individuals in population. Cornmeals are obtained by corn milling processes  and have different particle sizes, that can affect physicochemical characteristics and the product quality [4,5].
The main cornmeal component is starch , which digestibility is modified by hydrothermal treatment . Starch digestion and absorption are crucial for the control of blood sugar levels in metabolic disorders . Therefore, resistant
starches to digestive enzymes have been recommended for diets that prevent the damage of the syndrome.
Resistant starch is not digested in the small intestine, it goes to the large intestine where it is fermented by bacterial microflora . Its content in food is related to properties such as amylose content [9,10], amylopectin branch chain length , amylose/amylopectin ratio , processing conditions such as milling, fermentation, quantity of water, time and temperature storage and its interactions with other compounds in food [9,13].
Studies shown that extrusion cooking process increases the resistant starch content in foods, with positive correlation with humidity, storage time  and amylose/amylopectin ratio ; hydrothermal treatment of corn starch also promotes formation of resistant starch , particularly when preformed with lipid addition associated to high moisture contents .
Interactions between starch and other compounds such as
lipids have been in focus of researches due to their impacts on
food properties and nutrition [15,16], as starch-lipid complexes
and other similar compounds shown resistance to hydrolysis
by amylases [17,18].
There is an interest on developing products with low
glycemic index carbohydrates. In this context, resistant
starch emerges as an alternative to reduce energy availability,
therefore, the increase on its contents in food promotes
benefits on health and on food functional properties .
Preparation of foods with higher resistant starch contents
from cornmeals is important, therefore the aim of this work
was to verify the cornmeal particle size (fine, medium and
coarse), moisture conditions and amount of soybean oil that
promotes a higher content of resistant starch during food
preparation from cornmeals.
Cornmeals with different particle sizes (fine, medium and
coarse) and soybean oil where obtained on Rio Grande - RS,
Brazil’s local market. Fungal alpha-amylase enzyme (30U/mg)
produced by Aspergillus oryzae was obtained from Novozymes
Corp., Sigma-Aldrich Co., Switzerland, fungal protease enzyme
(500U/g) produced by Aspergillus oryzae was obtained from
Novozymes Corp., Sigma-Aldrich Co., Denmark and fungal
amyloglucosidase enzyme (6U/mL) produced by Aspergillus
niger was obtained from Sigma-Aldrich Co., Germany.
Particle-size distribution of fine, medium and coarse
grounded cornmeals was determined using sieve openings of
0,71; 0,50; 0,35; 0,25 e 0,14mm. Composition was determined
by protein, ash and lipid content, according to AOAC methods
Amylose content was determined according to colorimetric
method by Martinez and Cuevas , with adaptations.
Extraction of cornmeal’s amylose was performed with ethyl
alcohol 95% (v/v) and NaOH 1M solution. Colorimetric reaction
was performed with iodine 2% solution (w/v) and the amylose
content was determined using amylose standard curve (4-
24μg/mL) in a spectrophotometer with a wavelength of 620nm.
The total starch content of the solution of each gelatinized
sample was determined by iodometry and the starch-iodine
complex was quantified in a spectrophotometer at 620nm
using a starch standard curve (0.05-0.21mg/mL) .
Amylopectin was estimated by the difference between total
starch and amylose.
The hydrothermal treatment was performed by electric
plate cooking, according to Giacomelli et al. . The fine
cornmeal was added in boiling water with salt (1%) and
homogenized until the end of the treatment. The electric
plate temperature was maintained at 120 °C for 40 min. The
variables cornmeal:water proportion and amount of soybean
oil were defined by CCD 22 (Table 1), with the RS content as the
X1:Soybean oil amount (g); X2: Proportion of cornmeal:water
The determination of available and RS was performed
according to AOAC method 996.11 modified by Walter, Silva and
Perdomo . The in vitro method quantifies the RS after the
removal of starch digestible fraction by enzymatic treatment,
simulating the hydrolysis that occurs in the digestive tract
(mouth, stomach and small intestine), with α amylase,
protease and amyloglucosidase enzymes. The remaining
starch (resistant) was solubilized with dimethylsulfoxide and
again hydrolyzed by amylolytic enzymes
The determination of the starch fractions (available and
resistant) after hydrolysis was performed by quantifying the
glucose released in each step using the 3,5 dinitrosalicylic acid
(DNS) reduction  and using a conversion factor of 0.9, to
convert free glucose into starch.
The particle-size distribution for the 3 types of cornmeals
is as described on the packaging by the supplier. The coarse
grounded presented 78.6% of the particles larger than 0.35
mm, the medium had 58.7% of the particles with sizes between
0.25 and 0.50 mm and the fine 88.8% of the particles smaller
than 0.35 mm (Table 2).
Results expressed as mean (RSD) n=3. RSD= relative standard
In addition to the difference in particle size, cornmeals
present a difference in its composition. The fine cornmeal had a
higher content of ash (0.9%) and lipids (2.8%) when compared
to other cornmeals (Table 3).
Results expressed as mean (n=3). Different superscript letters in the same column indicate significant differences (p<0.05). AS=amylose,
AP=amylopectin, AT=total starch
There is no significant difference (p> 0.05) in the protein
content of the cornmeals, in the study by Shi et al.  similar
results were verified since the milling process does not affect
the primary structure and the protein content in cornmeal.
The coarse cornmeal has the highest content of
amylopectin (66.0%). The same cornmeal had the lowest
amylose/amylopectin ratio (0.36), the medium cornmeal had
the highest value (0.55), followed by the fine cornmeal (0.50).
The amylose/amylopectin ratio in the cornmeal composition
may contribute to changes in RS content . In this way, the
fine and medium cornmeal, because of the higher amylose/
amylopectin ratio, have a higher potential to form a higher RS
The results of RS in the CCD for the 2 variables under study
(soybean oil amount, and proportion of cornmeal:water) are
shown in (Table 1).
In this design, the RS content ranged from 83.2 to
240.1mg/g, however the best result for the RS was found in
trial 2, which showed less proportional cormeal:water, at level
-1 (1:5) and more soybean oil amount at level +1 (0.3g).
The proportional cornmeal:water was found to be the
most relevant variable for RS content (Table 4). The RS
content decreased on an average of 119.4% by increasing the
proportional cornmeal:water from 1:5 to 1:15. The combined
effect of soybean oil amount and proportional cornmeal:water
resulted in an average decrease of 37.5% in the RS. The soybean
oil amount did not present any significant effect (p>0.05)
A variance analysis (ANOVA) was performed using the
significant effects only (Table 5)
Based on the F-test, the model is predictive, since its
Fcalculated (327.28) was greater than Ftabled (19.25); and
significant, once the regression coefficient (0.88) is close
to unity. The coded model was used to generate the contour
diagram (Figure 1).
The greater values of the significant variables were not
determined (X2 and interaction X1 and X2) because there is no
possibility to reduce water in the hydrothermal treatment,
which simulates the cornmeal domestic cooking process.
Therefore, the proportion of cornmeal:water was defined as
1:5 and soybean oil amount 3%.
These hydrothermal treatment conditions were applied for
the 3 cornmeals (fine, medium and coarse) and also treatment
without oil were realized to evaluate the soybean oil addition
effect on the RS content. Factor analysis showed that both the oil
addition and cornmeal particle size had a significant difference
(p<0.05). When the treatment without oil was carried out, the
fine cornmeal showed higher RS content (201.6 mg/g) and the
coarse cornmeal lower content (142.7mg/g) (Figure 2).
Lower digestibility of starch with smaller particles
(greater RS) was also verified in the study by Guo et al. ,
in which the in vitro starch digestibility from milled durum
wheat grains with different particle sizes was evaluated. In it,
the digestibility was greater for the cooked flour with larger
granules (0.25-0.50mm) than for the flours with smaller
particle sizes (0.15-0.25mm and less than 0.15mm). Therefore,
higher interactions between the components of the cornmeal
during heating occur in flours with the smaller particle size
Besides the particle size, the fine cornmeal composition
may contribute to the higher RS content, since this cornmeal
had higher lipid content (Table 2) that can interact with the
starch during the hydrothermal treatment and form an
amylose-lipid complex, forming RS type 5.Figure 2
For the 3 cornmeals, the highest RS content was verified in
the treatment with oil addition (Figure 2), with higher content
of RS to fine cornmeal (245.7mg/g) and medium (249.3mg/g)
and lowest to coarse (207.5 mg/g), increases were 21.9%,
39.8% and 45.4%, respectively.
A study with different food lipids (triglycerides,
phospholipids and free fatty acids of different chain-lengths
and numbers of double bonds) showed that all lipids, after
cooking with starches, promoted a significant decrease in
starch hydrolysis, except for corn starches waxy low amylose
. In the study by Chen et al.  the addition of corn oil and
soy protein decreased the rapidly digestible starch content
and increased the sum of the slowly digestible starch and RS
content. It has been demonstrated that the physical barrier of
corn oil, amylose-lipid complex and protein-starch matrix can
promote resistance to starch digestion [15,17]. This fact can be
interesting for the elaboration of food products with reduced
The cornmeal particle size interferes in the RS content,
however the proportion cornmeal:water was the variable
more relevant, followed by combined effect of oil amount and
proportion cornmeal:water. All cornmeals, after hydrothermal
treatment with soybean oil, showed an increase in the RS
content in the final product, it can be associated the production
of RS type 5. The interaction between starch and oil may
contribute to obtaining carbohydrate-based food with low
The authors acknowledge the support of Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil),
Conselho Nacional de Desenvolvimen to Científico e Tecnológico
(CNPq, Brazil) and Fundação de Amparo à Pesquisa do Estado
do Rio Grande do Sul (FAPERGS, Brazil).