Several studies have indicated fortification of wheat cookies
with polyphenols from different ingredients such as grape,
blueberry, poppy seed flours, as well as pomegranate peel and tea
extract (Acun & Gül, 2014; Aksoylu, Çagindi, & K€ose, 2015; Ismail,
akhtar, Riaz, & Ismail, 2014; Mildner-Szkudlarz et al., 2009). In
this study, dark-red popping corn, blue popping corn and bluestandard
corn flours, which differ in the content of phenolic compounds,
were chosen as raw materials for cookie preparation. The
content of total phenolic compounds, flavonoids, anthocyanins, as
well as phenolic acids in both corn flours and cookies are given in
Tables 2 and 3. Dark-red popping corn flour had a considerably
higher total phenolic and flavonoid content (5293.9 mg GAE/kg
d.m. and 248.7 mg CE/kg d.m., respectively) than those from blue
popping corn, as well as blue-standard corn flour. On the other
hand, although not significantly different from red popping corn,
the highest content of anthocyanins was found in blue popping
corn flour (914.6 mg CGE/kg d.m.) (Table 1). In addition to total
flavonoids, phenolic acids had a high positive correlation with the
content of total phenolic compounds. Among the used corn flours,
the highest content of total ferulic and p-coumaric phenolic acids
was detected in dark-red popping corn flour (3314.1 and 337.3 mg/g
d.m., respectively) followed by blue popping corn and bluestandard
corn flour.
The control cookies were prepared from corn flours according to
the recipe described in AACC Methods 10e54 (2000) (Recipe 1) and
baked at commonly used temperature of 200 C for 7 and 10 min.
The content of phenolic compounds in the cookieswas significantly
affected by temperature and baking time (Tables 2 and 3). The data
were given per kg of cookies and also according to flour basis in
cookies (per kg of flour) to compare with the raw flour. The content
of total flavonoids, as well as anthocyanins, as free water-soluble
flavonoids, was reduced by applied baking conditions. The content
of anthocyanins in the dark-red popping corn, blue popping
corn and blue-standard corn cookies baked at 200 C for 10 minwas
decreased by 4, 5 and 3.5-fold, respectively, in relation to the
content in their flour (Table 2). On the other hand, in comparison
with the raw flour, the content of ferulic acid was increased by 48
and 22% after baking at 200 C for 10 min in cookies made from blue
popping corn and blue-standard corn flours, respectively (Table 3).
Similarly p-coumaric acid was increased by 55 and 24% in the same
cookies on flour basis, respectively. Baking process increased content
of total phenolic compounds by affecting the solubility of
bound forms of phenolic acids. It should be mentioned that Folin-
Ciocalteu reagent does not only measure phenolic compounds,
and it may react with any reducing substance. It therefore measures
the total reducing capacity of a sample, not just phenolic compounds.
Certain Maillard reaction products have also reductone
structures, which are Folin-Ciocalteu reactive substances. Therefore,
not only increase in free phenolic acids from bond forms but
also formation of Maillard reaction products contributed to increase
in total phenolic compounds measured by Folin-Ciocalteu
assay.
Recent studies have shown that the anthocyanins with acylating
substituents are more stable during processing and storage than
other natural pigments (Baublis, Spomer, & Berber-Jimenez, 1994;
Ba˛kowska-Barczak, 2005). These anthocyanins retain more color
at the higher pH values and show an improved resistance to other
factors such as heat and light than their unacylated analogs
(Brouillard, Chassaing, & Fougerousse, 2003). The stable acylated
anthocyanins are present in large amounts in pigmented corn
(Betran et al., 2000) and can be suitable for the application not only
in food with a low pH but also for neutral and slightly alkaline
products. However, our results show that in the baking of food
system the anthocyanins have to be protected (Fig. 1).
In order to investigate the effect of citric acid on the stability of
anthocyanins from pigmented corn flour, 0.5 and 1 g/100 g of citric
acid, on flour basis, was added to dough of blue popping corn andblue-standard corn, respectively. At the same time, high-fructose
corn syrup, sodium chloride and ammonium bicarbonate as ingredients
enhancing the Maillard reaction and caramelization
(G€okmen, Serpen, Çetinkaya Açar, & Morales, 2008), were skipped
from the formulation. Furthermore, in order to obtain light and
purple color development on the surface and milieu, Recipe 2 and 3
were baked at a lower temperature than of control cookies. The
baking temperature above 180 C provides browning through the
decomposition of sugar and Maillard reaction (G€okmen, Açar,
Serpen, & Morales, 2008), while the baking time of 10 min or less
was found insufficient in terms of wheat cookies texture at temperatures
of 180e220 C (G€okmen, Serpen, et al., 2008). Therefore,
the baking conditions of 150 C for 12 min was used for cookies
prepared using Recipes 2 and 3. A lower baking temperature
generally had the same effect on the content of total phenolics in
cookies prepared by the modified recipes as a high temperature of
200 C had. Compared with the control cookies baked at 200 C for
7 min, the cookies prepared according to the Recipe 2 with 0.5 g/
100 g added citric acid and baked at 150 C for 12 min had higher
contents of total flavonoids and anthocyanins by 2.5 and 3.4-fold,
respectively. Our results show that in addition to the stabilizing
effect, citric acid improved accessibility of the anthocyanins which
is in accordance with the research of Delgado-Vargas et al. (2000).
Expressed per kg of flour, the content of anthocyanins in the blue
popping corn cookies with 0.5 g/100 g citric acid was increased by
1.11-fold in relation to that in their flour (Table 2). However, 1 g/
100 g of citric acid added to the cookies prepared by the Recipe 3
and baked at 150 C for 12 min had no effect on the anthocyanins
extraction. Li et al. (2011) showed that the content of total
anthocyanins was increased in baked corn cookies with the addition
of citric acid, as well as that their retention reached an
apparent plateau at about 1.5e2 g/100 g of acid. Citric acid affected
total anthocyanins in corn cookie dough and final cookies by
lowering their pH in the dough system and by acylation of their
sugar residues or flavylium cation. pH values of blue popping corn
and blue-standard corn cookie dough were 7.86 and 8.05, respectively,
while with the addition of 0.5 and 1 g/100 g citric acid, pH
values of dough were reduced to 4.59 and 3.72, respectively
(Table 4). The increased temperature and baking time slightly
decreased the pH values of both control and acid-modified cookies
in relation to their dough.
Amic, Baranac, and Vukadinovic (1990) reported that the redcolored
flavylium cation is the predominant anthocyanin species
in strongly acidic media (pH 1). Between pH values of 2 and 4, the
uncharged blue quinonoidal unstable species prevails, while at pH
5 and 6, unacylated anthocyanins are unstable and decolorize
quickly by hydration at the position 2 of the anthocyanidin skeleton
forming the carbinol pseudobase and chalcone structures. According
to our results, blue popping corn and blue-standard corn
cookies with citric acid had pH values of 4.41 and 3.55 and
appeared to be pink and pale pink (Fig. 1), respectively. In addition,
lightness (CIE L*) and redness (CIE a*) of blue popping corn and
blue-standard corn cookies with citric acid were increased as
compared to color of their dough (Table 4). Due to decolourisation
of anthocyanins at pH above 7.8, color of control doughs of red
popping corn, blue popping corn and blue-standard cornwas black
and gray, while the brown surface of the control cookies was a
result of thermal anthocyanins degradation, as well as the formation of brown polymers of the Maillard reaction called melanoidins.
The usual trend for CIE L* is to decrease, and for CIE a* and
CIE b* to increase during browning proceeds (Romani, Rocculi,
Mendoza, & Dalla Rossa, 2009), which is in agreement with our
results. The decrease in pH along with the lower temperatures
restricted Maillard reaction and thus non-enzymatic browning was
avoided during baking of corn cookies. In low pH media amino
groups found in amino acids and proteins present in protonated
form and their reactivity towards carbonyl compounds become
limited. Therefore the rate of Maillard reaction becomes lower. On
the other hand higher pH enhances the Maillard reaction providing
remarkable browning.
In order to determine the effect of the high pH value of dough
and ammonium bicarbonate on the phenolic compounds stability
and the color formation in blue-standard corn cookies, the concentration
of ammonium bicarbonate, as often used leavening
agent, was increased from 0.5 (Recipe 1) to 1.25 g/100 g on flour
basis (Recipe 4). No significant increase in the pH of the dough was
observed however increased concentration of ammonium bicarbonate
had a negative effect on both stability and content of total
flavonoids and anthocyanins. Expressed per kg of flour, the content
of the total flavonoids and anthocyanins in the blue-standard corn
cookies with 1.25 g/100 g of ammonium bicarbonate baked at
150 C for 12 min was decreased by 35 and 7%, respectively, in
relation to that in control cookies with 0.5 g/100 g of ammonium
bicarbonate baked at 200 C for 7 min. Moreover, decrease in total
flavonoids and anthocyanins were found to be 65 and 51%,
respectively, compared to that in raw flour (Table 2). Our results are
in agreement with study of Cortes, Salinas, San Martín-Martinez,
and Martínez-Bustos (2006), who analyzed the effect of pH value
by different concentrations of calcium hydroxide on anthocyanins
stability after nixtamalization. However, combined with the temperature,
the leavening agent increased