Effects of Sodium Chloride, Potassium Chloride, and Calcium

Article pubs.acs.org/JAFC

Effects of Sodium Chloride, Potassium Chloride, and Calcium Chloride on the Formation of α‑Dicarbonyl Compounds and Furfurals and the Development of Browning in Cookies during Baking Tolgahan Kocadağlı and Vural Gökmen* Food Quality and Safety (FoQuS) Research Group, Department of Food Engineering, Hacettepe University, 06800 Beytepe Campus, Ankara, Turkey S Supporting Information *

ABSTRACT: Effects of NaCl, KCl, CaCl2, NaHCO3, and NH4HCO3 on the formation of glucosone, 1-deoxyglucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, diacetyl, 5-hydroxymethyl-2-furfural, and 2-furfural and browning were investigated in cookies. The presence of 1.5% NaCl, 1% KCl, and 1% CaCl2 on flour basis had no effect on α-dicarbonyl compounds, except 1-deoxyglucosone increased in the presence of KCl and CaCl2. The increase in 5-hydroxymethyl-2-furfural formation in the presence of NaCl, KCl, and CaCl2 did not relate to 3-deoxyglucosone formation and pH changes. NaCl, KCl, and CaCl2 increased browning in cookies. Model reaction systems indicated that NaCl, KCl, and CaCl2 enhance browning by increasing furfurals in caramelization. NaCl, KCl, and CaCl2 decreased browning intensity in a heated glucose−glycine system. Use of CaCl2 in cookies may considerably increase furfurals but not α-dicarbonyl compounds. Sodium reduction can be obtained by replacement with potassium without sacrificing the desired consequences of caramelization in sugar-rich baked goods. KEYWORDS: cookie, baking, α-dicarbonyl compounds, furfurals, nonenzymatic browning, calcium chloride, potassium chloride, sodium chloride, leavening agents

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INTRODUCTION Cookies comprise mainly cereal flour, fat, sugar, and water together with baking aids such as leaving agents, flavorings, and table salt. Viscoelastic dough transforms to a solid product after moisture removal via a thermal process. Heating produces a baked product, which is characterized by the generation of surface browning and flavor. These desirable aspects are provided by Maillard reaction and caramelization reactions to various degrees. The degradation of Amadori products (or Heyns products) in the Maillard reaction produces α-dicarbonyl compounds, which are important reactive intermediates in the formation of flavor and browning.1−5 Caramelization reactions of sugars also comprise same α-dicarbonyl compounds.6 In sugar-rich products caramelization may predominate, such as in baking and roasting where the surface of the product reaches elevated temperatures.6 1-Deoxyglucosone and 3-deoxyglucosone are formed by elimination of a water molecule from a hexose sugar.7,8 Glucosone is formed by oxidation of hexoses.8 Fragmentations of these α-dicarbonyl compounds may produce shorter chain α-dicarbonyl compounds including mainly glyoxal, methylglyoxal, and diacetyl.9 Dehydration reactions are faster in acidic conditions, and more deoxyosones and furfurals are formed.10 Under alkaline conditions fragmentation of the carbon chain predominates and shorter chain α-dicarbonyl compounds are formed.10 Dehydration of hexose sugars yields 5-hydroxymethyl-2-furfural (HMF) and that of pentoses yields 2-furfural.11 HMF formation from sucrose under dry conditions may proceed through the cleavage of glycosidic bond, yielding a fructofuranosyl cation, which eliminates © XXXX American Chemical Society

a proton and dehydrates easily to HMF through an intact furan ring.11,12 Occurrence of α-dicarbonyl compounds might be a concern due to their reactive nature both in foods and in vivo. Lysine and arginine residues in the presence of reactive carbonyl compounds are covalently modified, leading to advance glycation end products, which are linked to various health consequences.13−15 Cytotoxic effects of α-dicarbonyl compounds have also been reported.16,17 α-Dicarbonyl compounds found in foods may possess health risks, causing dicarbonyl stress mainly in the gastrointestinal lumen.18 It has been shown that dietary exposure to glyoxal has tumor growth-promoting properties in the small intestine in mice.19 Moreover, α-dicarbonyl compounds are involved in the formation of other toxigenic compounds during food processing, such as acrylamide, furan, heterocyclic aromatic amines, and 4(5)-methylimidazole.20−23 High amounts of 3-deoxyglucosone, 3-deoxygalactosone, methylglyoxal, and HMF have been reported in cookies and cereal products.24 A linear correlation between baking time and glyoxal and methylglyoxal formation has been previously observed.25 It has been indicated that commercial cookies made from ammonium bicarbonate and fructose show higher levels of methylglyoxal.25 It has been demonstrated that several cations facilitate dehydration of hexose sugars to form furfurals and limit Schiff base formation between hexose sugars and Received: August 30, 2016 Revised: September 25, 2016 Accepted: October 2, 2016

A

DOI: 10.1021/acs.jafc.6b03870 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Article

Journal of Agricultural and Food Chemistry asparagine.26,27 Increment of HMF formation in the presence of sodium and calcium cations in cookies has been reported.28,29 Even though there is considerable knowledge about the effect of sodium and calcium on furfurals and acrylamide formations during heating of foods, effects of cations on the formation of α-dicarbonyl compounds in foods are not known.30 Sodium salts are commonly added to cereal products mainly for flavor (sodium chloride) and technological purposes (sodium bicarbonate, sodium acid pyrophosphate). There is an increasing demand for sodium reduction in staple foods due to the adverse health effects in higher consumption. Because the presence of cations changes the fate of caramelization reactions, there is a need to reveal the formation of α-dicarbonyl compounds in bakery products. In this study, it was aimed to understand the formation of α-dicarbonyl compounds, furfurals, and browning development in cookies formulated with NaCl, KCl, NaHCO3, CaCl2, and NH4HCO3; furthermore, to reveal the predominating nonenzymatic browning mechanism in cookies, glucose and glucose−glycine model systems were investigated in the presence of NaCl, KCl, and CaCl2.

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All ingredients were mixed thoroughly in accordance with the AACC Method 10-54 procedure using a KitchenAid 5KSM150 dough mixer. The dough was rolled out on aluminum foil, and disks were formed to a diameter of 5 cm and a height of 3 mm. Two disks of dough were baked in an oven (Memmert, UN 55) at 200 °C for 7 min under full convection mode. Two disks from a baking batch were ground together and used for the analysis. All baking experiments were performed twice and separately analyzed. Preparation of Model Reaction Systems. To simulate caramelization and Maillard reaction, glucose and glucose−glycine model systems were prepared and heated in the presence or absence of NaCl, CaCl2, and KCl. Aqueous equimolar solutions of (0.1 M each) glucose (Glc), Glc−NaCl, Glc−KCl, Glc−CaCl2, Glc−Gly, Glc−Gly− NaCl, Glc−Gly−KCl, and Glc−Gly−CaCl2 were prepared. One milliliter of solution from each, containing 100 μmol of equimolar reactants, was transferred to glass tubes. The tubes were frozen at −80 °C and freeze-dried to observe dry heating conditions. The tubes (dried) were sealed with PTFE screw caps and heated in an oil bath (Memmert, Germany). The tubes with glucose and glucose−salt were heated in duplicates at 180 °C for 15 min. The tubes with Glc−Gly and Glc−Gly−salt were heated at 180 °C for 3 min and also at 140 °C for 2 min in duplicates. After the tubes had cooled to room temperature, the reaction mixtures were dissolved with 5 mL of water by vortexing and shaking the tubes for 1 min. After centrifugation of the dissolved mixtures, they were used for the analysis of α-dicarbonyl compounds, furfurals, pH, and color as described below. Analysis of α-Dicarbonyl Compounds. Extraction of Cookies. One gram of ground cookie was extracted with 20 mL of deionized water in three stages (10, 5, 5 mL) by mixing for 3 min in a shaker. After centrifugation at 5000g for 5 min in each step, the extract was collected in a test tube. Before separation of the supernatant in each step, the fat was removed from the top. The combined extract was used for the analysis of α-dicarbonyl compounds, sugars, and furfurals as described below. Derivatization. A part of the extract (0.5 mL) was mixed with an equal amount of acetonitrile and centrifuged at 7000g for 5 min to precipitate coextracted colloids. Derivatization of α-dicarbonyl compounds was carried out with o-phenylenediamine according to a published procedure with minor modifications.24 The derivatization of 0.5 mL of supernatant was performed by adding 150 μL of 0.5 M (pH 7) phosphate buffer and 150 μL of 0.2% o-phenylenediamine in 10 mM DETAPAC. The mixture was immediately filtered through a syringe filter into an autosampler vial and kept in the dark at room temperature for 3 h before analysis. HPLC-ESI-MS Measurement. The quinoxaline derivatives of glucosone, 3-deoxyglucosone, 1-deoxyglucosone, glyoxal, methylglyoxal, and diacetyl were quantitated by using by LC-ESI-MS as described previously.32 Analysis of Furfurals. A part of the extract was precipitated by Carrez clarification and centrifuged at 5000g for 5 min. The supernatant was filtered through a 0.45 μm syringe filter into an autosampler vial prior to analysis. The quantitation was performed by using HPLCDAD as described previously.32

MATERIALS AND METHODS

Chemicals and Consumables. 3-Deoxyglucosone (75%), quinoxaline (99%), 2-methylquinoxaline (97%), 2,3-dimethylquinoxaline (97%), o-phenylenediamine (98%), diethylenetriaminepentaacetic acid (DETAPAC) (98%), sucrose (>99%), D-glucose (>99.5%), D-fructose (>99%), L-glycine (>99%), methanol (HPLC grade), and acetonitrile (HPLC grade) were purchased from Sigma-Aldrich (Steinheim, Germany). 5-Hydroxymethyl-2-furfural (HMF) (98%), 2-furfural (99%), and sodium bicarbonate were purchased from Acros (Geel, Belgium). Formic acid (98%) was purchased from J. T. Baker (Deventer, The Netherlands). Potassium hexacyanoferrate, zinc sulfate, disodium hydrogen phosphate anhydrous, sodium dihydrogen phosphate dihydrate, sodium chloride, calcium chloride, and potassium chloride were purchased from Merck (Darmstadt, Germany). Deionized water (5.8 μS/m) was used throughout the analysis and sample preparation. Syringe filters (nylon, 0.45 μm) and Oasis HLB solid phase extraction cartridges (30 mg, 1 mL) were supplied by Waters (Milford, MA, USA). Preparation of Cookies. All-purpose wheat flour, shortening (refined palm oil), icing sugar (sucrose), nonfat dry milk, ammonium bicarbonate, and high-fructose corn syrup (HFCS; 42%) used in the formulation of cookies were obtained from a local market. Cookies were formulated according to AACC Method 10-54 with certain modifications as given in Table 1.31 The control cookie recipe R1 was formulated with 1% NaCl on flour basis instead of 1.25% as in the AACC recipe. In addition to that, HFCS was increased from 1.5 to 2.5% on flour basis to increase the amount of reducing sugars to monitor changes clearly. Various formulations comprising NaCl, CaCl2, and KCl with or without NH4HCO3 or NaHCO3 were tested.

Table 1. Composition of Recipes Used To Prepare Cookies recipe

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

R13

R14

R15

R16

flour (g) fat (g) sucrose (g) HFCS (g) milk powder (g) water (mL) NH4HCO3 (g) NaHCO3 (g) NaCl (g) CaCl2 (g) KCl (g)

40 16 16.8 1 0.4 8.8 0.2 0.4 0.4

40 16 16.8 1 0.4 8.8 0.2 0.4

40 16 16.8 1 0.4 8.8 0.2 0.4 0.6

40 16 16.8 1 0.4 8.8

40 16 16.8 1 0.4 8.8

40 16 16.8 1 0.4 8.8 0.2

40 16 16.8 1 0.4 8.8 0.2

40 16 16.8 1 0.4 8.8

40 16 16.8 1 0.4 8.8 0.2 0.4

40 16 16.8 1 0.4 8.8 0.2

40 16 16.8 1 0.4 8.8

40 16 16.8 1 0.4 8.8 0.2 0.4

40 16 16.8 1 0.4 8.8

0.4

40 16 16.8 1 0.4 8.8 0.2 0.4 0.4 0.4

40 16 16.8 1 0.4 8.8 0.2 0.4

0.4

40 16 16.8 1 0.4 8.8 0.2 0.4 0.4 0.2

0.2

0.4

0.4

0.4 0.4

0.4

0.4 0.4

B


Article

Journal of Agricultural and Food Chemistry Analysis of Sugars. Co-extracted colloids were precipitated by Carrez clarification and centrifugation at 5000g for 5 min. The clear supernatant was passed through a preconditioned HLB cartridge. The first 8 drops of the sample eluent were discarded, and the rest was collected into an autosampler vial. The cartridges were preconditioned by passing 1 mL of methanol and 1 mL of water subsequently. Analysis of sugars was performed on an Agilent 1200 HPLC system consisting of a quaternary pump, an autosampler, a column oven, and a refractive index detector. An isocratic elution of 5 mM H2SO4 in water at a flow rate of 1 mL/min was used in a Shodex Sugar SH-1011 column (300 mm × 8 mm i.d., 6 μm) (Tokyo, Japan) conditioned to 50 °C. The injection volume was 5 μL. Quantification of sucrose, glucose, and fructose was according to the external calibration curves built between the concentrations of 0.005 and 0.1%. Determination of Color and Browning Ratio in Cookies. Color measurements (CIE L*a*b*) and browning ratio (%) of cookies were acquired by using a computer vision-based image analysis technique as described previously.33 The surface color of cookies was given as average L* (lightness), a* (redness), and b* (yellowness) values. The browning ratio on the surface of cookies was obtained by segmentation of brown regions from the rest. The color and browning ratio of all four cookie replicates were individually determined, and data were reported as the average ± standard deviation. Determination of Color Intensity in Heated Model Reaction Systems. The browning intensities in the heated model systems were measured by using a Shimadzu 2100 UV/vis spectrophotometer (Shimadzu Corp., Kyoto, Japan) at 420 nm. The measurements were taken by appropriate dilution of the dissolved heated systems. The color intensities of the samples were given as absorbance values after multiplication with the dilution factor. Measurement of pH. Dough or ground cookies (0.5 g) were mixed with 10 mL of deionized water and vortexed for 1 min. To obtain an ionic equilibrium in the aqueous phase, the tubes were put on a horizontal shaker, which was set to rotate at 250 rpm for 1 h. After centrifugation (at 5000g for 5 min), the fat was removed from the top of the supernatant. The pH of supernatants was measured by using a pH meter (MeterLab PHM210, France). The pH values of unheated solutions of model reaction systems and dissolved heated systems were also measured by using the pH meter. Statistical Analysis. The analytical data are reported as the average ± standard deviation of two independent baking batches or model systems. Significance of difference between recipes was determined by analysis of variance according to the Duncan test.

becomes quantitatively significant after prolonged heating (10−11 min at 200 °C),28 and in the present cookies there was no change in 3-deoxyglucosone by addition of NaCl. Differences in the amounts of sucrose, glucose, and fructose were not statistically significant between these recipes (p > 0.05). However, a slight decrease in the concentration of sucrose was observed, and also glucose and fructose slightly increased in the presence of NaCl (p > 0.05). The results are in agreement with the previous findings that reaction rate constant of 3-deoxyglucosone formation from glucose decreases in the presence of NaCl.35,36 An increase in 3-deoxyglucosone concentration would be expected when considerable sucrose hydrolysis produces higher amounts of glucose and fructose, as was shown previously in cookies formulated with colored corn in comparison to wheat flour.37 It has been demonstrated that the interaction of NaCl with amino acids may produce sodium and chloride salts of amino acids and, upon heating, HCl can be formed, thereby increasing the acidity and the chlorinating potential of the Maillard reaction mixtures.38 In this study, the drop in pH was not considerable by addition of NaCl to cookies. The reason for not observing a pH change in cookies could be related to the low amounts of total free amino acids (ca. 10 mmol/kg of flour) in all-purpose wheat flour.37 Although addition of 1% NaCl on flour basis corresponds to 171 mmol of NaCl/kg of flour, which is in excess amount with respect to total free amino acids, it did not result in pH changes. Therefore, the increase in the levels of HMF was not related to pH of either dough or cookies (R1, R2, and R3) as dehydration of sugars is more pronounced under acidic conditions. It may be speculated that the pH drop effect of NaCl could be more pronounced during the baking process as the water evaporates at higher temperatures, therefore yielding more HMF. If so, the level of 3-deoxyglucosone would also increase, as it is a primary dehydration product of sugars, especially in acidic conditions, but there was no change. When leavening agents were eliminated (R4), the pH of the dough reduced 1.5 units and the pH of the corresponding cookie reduced 1 unit with respect to R2 (pH of R2 dough, 7.93 ± 0.07; pH of R2 cookie, 7.34 ± 0.05). In the R4 cookie, the concentration of HMF was found to be 12.4 ± 0.5 mg/kg. The concentration of HMF in the cookie with 1.5% NaCl (R3) was 11.2 ± 0.1 mg/kg (pH of R3 dough, 7.85 ± 0.07; pH of R3 cookie, 7.25 ± 0.13). This clearly indicated that the effect of NaCl on HMF formation might correspond to the effect of 1 unit of pH drop, without a pH change in cookies. Therefore, it is obvious that the effect of NaCl on the formation of HMF is not related to its pH lowering effect in cookies. This observation was also valid when the changes in 3-deoxyglucosone were considered. The drop in pH remarkably increased the level of 3-deoxyglucosone in cookie R4. However, addition of NaCl showed no change in the level of 3-deoxyglucosone as mentioned above, thereby discarding any pH-lowering effect of NaCl during baking of cookies at high temperatures. In the absence of leavening agents (both NaHCO3 and NH4HCO3), addition of NaCl (R4 to R5) increased the concentrations of 1-deoxyglucosone, 3-deoxyglucosone, and HMF, whereas the concentrations of glucosone and furfural reduced (p < 0.05) and others were not much affected (p > 0.05) (Table 2). Sucrose hydrolysis was significantly higher in recipe R5, containing 1% NaCl in the absence of baking agents. Because the absence of the leavening agents reduced the pH of the dough, hydrolysis of sucrose was apparent, and more 1-deoxyglucosone, 3-deoxyglucosone, and HMF was observed than in the

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RESULTS AND DISCUSSION Effect of NaCl on α-Dicarbonyls and Furfurals in Cookies. The concentrations of α-dicarbonyl compounds according to the different recipes are given in Table 2. Omitting 1% NaCl from the control cookie (R1 to R2) decreased the concentration of methylglyoxal from 15.1 ± 0.2 to 10.3 ± 0.0 mg/kg and 1-deoxyglucosone from 11.3 ± 0.3 to 6.7 ± 0.2 mg/kg; other α-dicarbonyl compounds were not influenced. Increasing the amount of NaCl to 1.5% on flour basis (R3) did not show any effect on α-dicarbonyl compounds, except a reduction in methylglyoxal concentration to the level of unsalted cookie (R2). On the other hand, concentrations of HMF and furfural gradually increased by addition of NaCl. The pH change was not statistically significant by addition of NaCl (p > 0.05). The effect of NaCl on HMF formation from sucrose in model systems was investigated previously.34 It was reported that the rate of sucrose degradation increased from 2.85 to 10.18 μmol/min in the presence of NaCl.34 Therefore, extensive degradation of sucrose yields considerable amounts of invert sugars, and in the reaction medium more 3-deoxyglucosone formation was observed together with higher amounts of HMF.34 However, in cookies sucrose degradation C


96.6 ± 6.0 e

65.6 ± 0.7 c

30.8 ± 2.1 i

0.7 ± 0.1 a

2.2 ± 0.1 hij 17.6 ± 0.5 g

R5

R6

54.3 ± 0.9 a

7.7 ± 0.1 hi

1.9 ± 0.1 fgh 12.9 ± 0.7 cde

R9

D

70.1 ± 3.2 c

24.1 ± 0.9 h

39.8 ± 1.7 j

12.3 ± 0.5 cd

29.5 ± 1.5 i

R13 2.2 ± 0.2 j

R14 1.3 ± 0.2 cd

R15 1.0 ± 0.1 bc

R16 0.8 ± 0.1 ab

0.13 ± 0.03 ab

sucrose 254.3 ± 6.4 gh

251.2 ± 1.9 fgh

14.4 ± 0.7 d

11.9 ± 0.3 c 0.58 ± 0.03 c

0.59 ± 0.07 c

15.3 ± 0.4 de 0.55 ± 0.08 c

252.4 ± 0.7 fgh

0.11 ± 0.02 a

257.0 ± 3.4 h

0.30 ± 0.03 f 253.4 ± 3.8 gh

12.3 ± 0.5 c

0.24 ± 0.03 a

2.2 ± 0.1 ab

8.3 ± 1.3 a

0.22 ± 0.02 a

6.7 ± 0.3 efg 15.8 ± 0.6 de 0.90 ± 0.02 d

3.1 ± 0.1 b 15.1 ± 2.1 e

7.9 ± 0.7 b

83.9 ± 1.6 h

35.3 ± 0.5 g 236.5 ± 0.4 bc

229.4 ± 3.3 a

245.7 ± 3.3 def

14.7 ± 0.3 efg

13.0 ± 0.9 ab

20.2 ± 0.2 i

16.2 ± 0.2 h

250.2 ± 1.4 efgh 15.1 ± 0.4 g

0.23 ± 0.09 cdef 236.2 ± 1.0 b

0.18 ± 0.01 abc

0.71 ± 0.06 h

0.46 ± 0.01 g

0.28 ± 0.01 def

14.8 ± 0.4 fg

14.4 ± 0.9 cdefg

13.3 ± 0.0 abc

13.8 ± 0.3 bcdef

14.4 ± 0.4 cdefg

249.9 ± 1.3 efgh 13.5 ± 0.5 abcde

0.25 ± 0.05 cdef 243.3 ± 3.3 cde

9.2 ± 0.5 bc 0.30 ± 0.00 f 18.4 ± 0.2 f

13.4 ± 0.0 abcd

12.6 ± 0.5 a

fructose

dough

cookie

7.90 ± 0.08 de 7.17 ± 0.07 e

pH

7.31 ± 0.18 b

6.40 ± 0.06 a

6.50 ± 0.28 cd

6.13 ± 0.04 ab

6.28 ± 0.08 bc

7.25 ± 0.13 e

4.9 ± 0.1 g

2.9 ± 0.4 a

8.6 ± 0.1 i

5.6 ± 0.0 h

4.3 ± 0.1 ef

3.6 ± 0.0 cd

4.4 ± 0.2 fg

3.8 ± 0.4 de

7.33 ± 0.24 e 5.86 ± 0.13 a 6.33 ± 0.02 a

6.04 ± 0.01 ab

8.00 ± 0.07 de 7.38 ± 0.04 e

6.27 ± 0.01 a

7.73 ± 0.35 cd 6.24 ± 0.08 bc

8.40 ± 0.21 f

8.25 ± 0.25 ef 7.26 ± 0.03 e

8.23 ± 0.25 ef 7.27 ± 0.15 e

7.96 ± 0.13 de 7.23 ± 0.11 e

3.5 ± 0.3 bcd 7.38 ± 0.06 bc 7.27 ± 0.06 e

3.6 ± 0.1 bcd 7.44 ± 0.17 bc 6.60 ± 0.13 d

3.7 ± 0.0 cd

4.4 ± 0.6 fg

6.47 ± 0.04 a

3.4 ± 0.2 bcd 7.85 ± 0.07 d

3.2 ± 0.1 abc 7.93 ± 0.07 de 7.34 ± 0.05 e

3.1 ± 0.1 ab

250.4 ± 0.3 efgh 14.0 ± 0.4 bcdefg 4.3 ± 0.0 ef

8.3 ± 1.1 b 18.5 ± 0.1 f

glucose 13.6 ± 0.1 abcde

0.20 ± 0.00 abcd 241.6 ± 4.0 bcd 14.6 ± 1.0 defg

0.30 ± 0.02 ef

10.5 ± 0.8 cd 0.29 ± 0.03 def

14.6 ± 1.5 e

13.5 ± 2.3 e

12.4 ± 0.5 d

11.2 ± 0.1 cd 0.24 ± 0.02 cdef 251.4 ± 4.9 fgh

5.2 ± 0.3 a

furfural 0.18 ± 0.04 abc

g/kg cookie

Semiquantitated according to 3-deoxyglucosone calibration curve. Different letters in each column indicate statistically significant difference (p < 0.05). G, glucosone; 1-DG, 1-deoxyglucosone; 3-DG, 3deoxyglucosone; MG, methylglyoxal; HMF, 5-hydroxymethyl-2-furfural.

a

8.1 ± 0.4 i

96.6 ± 5.6 e

0.61 ± 0.01 c 0.52 ± 0.05 bc

6.0 ± 0.1 de 17.2 ± 0.6 ef 0.44 ± 0.01 b

6.3 ± 0.6 ef

51.6 ± 1.8 a

52.7 ± 0.4 a

13.1 ± 0.5 cde

R11 1.6 ± 0.1 ef

R12 1.9 ± 0.0 ghi 14.5 ± 0.5 def

56.0 ± 1.0 ab 8.1 ± 0.4 i

16.2 ± 0.3 fg

R10 2.2 ± 0.1 ij

54.2 ± 0.7 a

8.2 ± 0.1 a

18.4 ± 1.5 f

0.58 ± 0.02 c

0.17 ± 0.06 a

HMF 7.4 ± 0.7 b

6.9 ± 1.0 fgh 10.9 ± 2.3 bc 0.53 ± 0.02 bc 10.7 ± 0.2 cd 0.20 ± 0.05 bcde 249.2 ± 0.5 efg

62.2 ± 3.0 bc 5.5 ± 0.6 cd

62.5 ± 2.3 bc 4.7 ± 0.2 c

2.0 ± 0.3 hij 15.7 ± 0.4 efg

130.7 ± 3.4 f

7.5 ± 0.3 a

9.4 ± 0.1 ab 0.20 ± 0.01 a

11.2 ± 0.7 bc 0.96 ± 0.07 d

5.8 ± 0.0 de 19.1 ± 0.8 f

1.8 ± 0.0 a

2.5 ± 0.2 ab

1.0 ± 0.1 bc

50.0 ± 1.9 a

diacetyl 0.91 ± 0.00 d

7.4 ± 0.1 ghi 10.3 ± 0.0 bc 0.96 ± 0.10 d

R7

10.4 ± 0.2 bc

MG

6.7 ± 0.2 efg 15.1 ± 0.2 d

glyoxal

mg/kg cookie

R8

82.8 ± 8.2 d

8.9 ± 0.2 ab

22.4 ± 3.5 h

1.5 ± 0.1 de

1.0 ± 0.2 bc

R3

R4

51.7 ± 2.9 a

6.7 ± 0.2 a

1.4 ± 0.0 de

3-DG

R2

1-DG

51.6 ± 1.7 a

G

1.7 ± 0.1 efg 11.3 ± 0.3 bc

a

R1

a

Table 2. α-Dicarbonyl Compounds, Furfurals, and Sugar Contents of Cookies Prepared from Different Recipes

Journal of Agricultural and Food Chemistry Article


Article

Journal of Agricultural and Food Chemistry

However, in the recipe containing only NaHCO3 (R8, dough pH of 7.38 ± 0.06) as leavening agent the concentration of HMF decreased to the level of control (R1, dough pH of 7.90 ± 0.08). It is clear that the formation of HMF depends on the pH of the final product, which was the same in R1 and R8, rather than the initial pH of dough. This was consistent because HMF is formed in the later stages of heating and NH4HCO3 is activated at the beginning of the baking process and leaves a product with lower pH at the later stages of baking in the absence of NaHCO3. Besides, in both R8 (NH4HCO3 omitted) and R6 (NaHCO3 omitted) the concentrations of 1-deoxyglucosone and 3-deoxyglucosone remarkably decreased with respect to R5 (free of both leavening agents), as they are kinetically formed earlier than HMF.40 Therefore, their formation rates should depend more on the initial pH value of the product, which was higher in R6 and R8 than in R5. Effect of CaCl2 on α-Dicarbonyls and Furfurals in Cookies. Addition of CaCl2 (R9, 0.5%, and R10, 1%, on flour basis) to the control formulation (R1) resulted in a significant increase in the concentration of glucose and fructose and a significant decrease in sucrose (Table 2). In R9, no significant changes were observed in the amount of α-dicarbonyl compounds, except a decrement in methylglyoxal and diacetyl concentrations. Slight increases were observed (p < 0.05) when the CaCl2 was increased to 1% (R10), which were not significant for 3-deoxyglucosone and methylglyoxal (p > 0.05), and also diacetyl remained lower. The concentrations of 3-deoxyglucosone in R9 and R10 per total amount of reducing sugars in their cookies were lower than in the control sample. The same profile of α-dicarbonyl compounds was also obtained in R11 and R12, where NaCl was omitted from CaCl2 added cookies. On the other hand, HMF formation was more than doubled in cookies containing 1% CaCl2 (R10 and R12). The increase in the concentration of 1-deoxyglucosone was due to the higher fructose resulting from sucrose hydrolysis, because the amounts of 1-deoxyglucosone per amount of fructose in the cookies were slightly lower or the same when CaCl2 was added. In the absence of NaCl and NaHCO3, the addition of CaCl2 (R7−R13) triggered sucrose hydrolysis in a higher rate with respect to the change observed from R2 to R12. Therefore, the concentrations of 1-deoxyglucosone, 3-deoxyglucosone, HMF, and furfural increased. These increments were more dramatic when also NH4HCO3 was omitted together with NaHCO3. It should be mentioned that the increments in α-dicarbonyl compounds were from the effect of calcium on sucrose hydrolysis, and they were not related to further enhancement of the degradation of glucose or fructose. The amounts formed per the total amount of reducing sugars did not change or even slightly decreased. On the other hand, increases in the amount of HMF were not just the results of sucrose hydrolysis. There was obviously a catalyzing effect of calcium because more HMF was formed per the amount of reducing sugars. There are generally two pathways considered for the formation of HMF from glucose: (i) ring opening and consecutive dehydration via open-chain intermediates (mainly 3-deoxyglucosone and 3,4-dideoxyglucosone) and (ii) ring opening and isomerization to fructose and consecutive dehydration via fructofuranose ring intact.11 In addition to these, cleavage of sucrose glycosidic bond directly yields a cyclic fructofuranosyl cation, which dehydrates to HMF.41 It has been shown that 90% of the HMF formed from sucrose results from the fructose moiety under pyrolysis condition.12 The increases in the formation of HMF should be related to the catalysis of

control recipe (R1), as expected. The effect of NaCl on sucrose degradation was apparently more pronounced at lower pH, that is, in the absence of leavening agents. Effect of KCl on α-Dicarbonyls and Furfurals in Cookies. Sodium reduction is mostly achieved by replacing sodium with potassium. Replacing NaCl (R1) with KCl (R15) provided almost the same α-dicarbonyl compound and furfural profile, except for a decrement in glucosone (Table 2). These observations were the same when cookies were formulated without leavening agents and KCl was added (R16 with respect to R5). Effect of NaHCO3 on α-Dicarbonyls and Furfurals in Cookies. Omitting NaHCO3 (R1−R6) resulted in a pH drop of about 0.6, and thereby the α-dicarbonyl compound profile and furfurals significantly changed, consistent with the expected pH dependence (Table 2), except for methylglyoxal (see effect of NH4HCO3 discussed in the next subsection). The concentrations of 1-deoxyglucosone, 3-deoxyglucosone, glucosone, methylglyoxal, HMF, and furfural increased in the recipes R6 (NaHCO3 omitted) and R7 (both NaHCO3 and NaCl omitted) with respect to control R1. Although sucrose and glucose in these recipes were not significantly different from one another (p > 0.05), the amount of fructose was significantly higher in R6 (NaHCO3 omitted) than in control R1 (p < 0.05). Effect of NH4HCO3 on α-Dicarbonyls and Furfurals in Cookies. When only NH4HCO3 was eliminated from the recipe (R1−R8) the pH of the dough decreased from 7.90 ± 0.08 (R1) to 7.38 ± 0.06 (R8), but the pH of the cookies was not significantly different (Table 2). The concentration of 3-deoxyglucosone increased from 51.6 ± 1.7 to 62.5 ± 2.3 mg/kg. The concentrations of glucosone, glyoxal, methylglyoxal, and diacetyl significantly reduced (p < 0.05). The amount of HMF slightly increased (from 7.4 ± 0.7 to 8.3 ± 1.1 mg/kg), but it was not statistically significant (p > 0.05). The effect of NH4HCO3 on α-dicarbonyl compound formation, especially methylglyoxal, was just not related to pH. Even though individual presence of NH4HCO3 (R6) and NaHCO3 (R8) produced similar pH values in dough (7.31 ± 0.18 and 7.38 ± 0.06, respectively), their effects on α-dicarbonyl compound formation were different (Table 2). During baking, ammonia is released from NH4HCO3 and moves away from the cookie, and thereby a lower pH is obtained in the final stages of heating. On the other hand, NaHCO3 is degraded to Na2CO3, and the final pH of the product remains higher. Taking recipe R5 as a control product, which was free of both leavening agents, the concentration of methylglyoxal increased from (R5) 7.5 ± 0.3 to 19.1 ± 0.8 mg/ kg by the addition of NH4HCO3 (R6) and to 8.2 ± 0.1 mg/kg by addition of NaHCO3 (R8). This clearly indicated that ammonia is involved in the degradation of reducing sugars to form methylglyoxal rather than a pH effect. On the other hand, increments in the levels of glyoxal and diacetyl were similar, and that could be related to pH dependency. These observations are in line with the previous findings that NH4HCO3 leads to higher amounts of glyoxal, methylglyoxal, and diacetyl as compared to NaHCO3 from glucose and fructose in pH 7 buffer.39 In addition, it has been reported that commercial cookies formulated with NH4HCO3 contain higher amounts of methylglyoxal.25 The concentrations of HMF were interestingly similar in the recipes from which both leavening agents were absent (R5, dough pH of 6.40 ± 0.06) and in which NH4HCO3 was present (R6, dough pH of 7.31 ± 0.18) (p < 0.05) (Table 2). E


Article


Effect of NaCl, KCl, and CaCl2 on Browning Development in Cookies. As can be seen in Table 3, addition of NaCl (R2 to R1 (1%) and R3 (1.5%)) remarkably increased the browning ratio and a* values and decreased L*. Because the addition of NaCl did not considerably affect the amounts of α-dicarbonyl compounds, browning provided by NaCl in cookies cannot be directly associated with α-dicarbonyl compounds, but furfurals. Removal of leavening agents resulted in lower surface browning due to the decrease in pH, as expected. Addition of NaCl in the absence of both leavening agents, that is, lower pH (R4 to R5), had no effect on browning ratio. This was consistent with the levels of HMF (R4 to R5), which were not statistically different (p < 0.05). This indicated that the reduction in browning due to the pH drop of about 1 unit could not be compensated by NaCl addition because nonenzymatic browning is restricted to a certain extent at lower pH.

the pathways of either direct dehydration of fructofuranose over cyclic intermediates or degradation of sucrose to form fructofuranosyl cation. Cations have no effect on the formation of 3-deoxyglucosone, or the amounts even decreased per amount of reducing sugars, as in the presence of calcium. The results were also supported by the findings of Mayes et al., who indicated that HMF formation from glucose through isomerization to fructose and dehydration over cyclic intermediates has lower energy barriers than other pathways investigated by computational methods.42 In a subsequent study, Mayes et al. showed that Na+ modifies rate constants by the interaction, especially with the transition states in a particular stereochemistry, and the rate constants become higher for dehydration of the intact fructofuranose ring.35 This observation was also supported by multiresponse kinetic modeling of elementary reaction steps in glucose and glucose−NaCl model systems under caramelization conditions.36

Table 3. CIE L*a*b* Values and Browning Ratios of Cookies Prepared from Different Recipesa

a

Different letters in the columns of L*,a*,b* and browning ratio indicate statistically significant difference (p < 0.05). F


Article


study of Maillard reaction kinetics.49 To clarify the positive effect of NaCl, KCl, and CaCl2 on browning development in cookies in relation with α-dicarbonyl compounds and furfurals, model reaction systems of glucose (caramelization) and glucose−glycine (1:1; Maillard reaction) were also investigated. Effect of NaCl, KCl, and CaCl2 on Browning Development and Reaction Products in Glucose Model System. In a glucose model system (caramelization) the addition of equimolar NaCl, KCl, and CaCl2 decreased the amounts of glucosone, 1-deoxyglucosone, and 3-deoxyglucosone and substantially increased the amounts of HMF and furfural under dry heating conditions (Table 4). The results were in accordance with our previous findings.36 The browning intensities remarkably increased by the addition of NaCl, KCl, and CaCl2 to glucose (Table 5). When the amounts of α-dicarbonyl compounds and furfurals were considered in relation with browning development, it was obvious that the degradation reaction of glucose became predominant to form furfurals and an increase in the browning intensity was observed. By addition of CaCl2, degradation of glucose became very intense after heating at 180 °C for 15 min, and dark brown insoluble components formed. After limiting the reaction time to 5 min in glucose−CaCl2, the browning intensity considerably increased, and lower amounts of insoluble components formed. It was shown that in the presence of NaCl the rate constants of glucose−fructose interconversion increased 2.5-fold at 180 °C and dehydration of fructose to HMF became 4 times faster.36 As the formation rate constants of certain α-dicarbonyl compounds were found to be decreasing or unchanged,36 browning development provided by cations should be related to furfurals under caramelization conditions. The results are in agreement with those for cookies because they are formulated with high amounts of sugars and free amino acids are found in limited amounts in all-purpose wheat flour. Effect of NaCl, KCl, and CaCl2 on Browning Development and Reaction Products in Glucose−Glycine Model System. To observe the effects of NaCl, KCl, and CaCl2 in the Maillard reaction, glucose−glycine model systems were also investigated under dry heating conditions. Because degradation of sugars proceeds at a higher rate in the presence of amino acids, the reaction time was limited to 3 min at 180 °C. Under these conditions the amounts of glucosone and 3-deoxyglucosone decreased (p < 0.05), and other α-dicarbonyl compounds changed to various degrees by the addition of NaCl, KCl, and CaCl2 to a glucose−glycine model system. The amounts of HMF did not change in the presence of NaCl and KCl (p > 0.05); on the other hand, in the presence of CaCl2 the amount of HMF increased 4-fold. Furfural was not quantitated in glucose−glycine model systems because of a coeluting compound. In these model systems heated at 180 °C for 3 min, color intensity decreased by the addition of NaCl and KCl, and it increased by the addition of CaCl2. Because the reaction rates were probably very high at 180 °C and insoluble melanoidins were formed together with substantially lower amounts of determined reaction products, it was decided that the changes could be misleading. Therefore, the reactions of a glucose− glycine model system were also heated at 140 °C for 2 min, and relatively higher amounts of reaction products were observed (Table 4) together with no insoluble fractions, except in the presence of CaCl2. Despite the decrement in 3-deoxyglucosone in the presence of salts when heated at 180 °C, the amounts of 1-deoxyglucosone and 3-deoxyglucosone significantly increased

Browning ratio considerably decreased in R6 (NaHCO3 omitted) and R7 (both NaHCO3 and NaCl omitted) with respect to R1, due to the pH drop (p < 0.05; Table 3). In contrast to the case of both leavening agents being omitted (R4 and R5; pH drop of about 1 unit), in the absence of only NaHCO3 (R7; pH drop of 0.5), the addition of NaCl (R6; pH drop of 0.6) increased the browning ratio from 52.7 ± 3.3 to 58.9 ± 5.2, but the difference was not statistically different (p > 0.05). This also partially supported the above-mentioned relationship of browning development by NaCl being related to HMF rather than α-dicarbonyl compounds, which were not changed. Replacing NaCl (R1) with KCl (R15) provided a similar browning ratio and color values (Table 3). Therefore, similar aspects of nonenzymatic browning reactions can also be obtained by KCl. The similarity in the browning achievement by NaCl and KCl was also reported in the model systems.43,44 In the presence of NaCl, the addition of CaCl2 (R9 and R10) did not provide further improvement in the browning of cookies with respect to control R1 (Table 3). On the other hand, in the absence of NaCl, the addition of CaCl2 (R9 and R10) restored the browning to the level of control cookies (R1), as it decreased in cookies without NaCl (R2). In the absence of leavening agents, no further improvement was achieved on browning by the addition of CaCl2 (R7 to R13 and R4 to R14). It should be again mentioned that at lower pH values nonenzymatic browning is restricted to a certain extent, and obviously this cannot be compensated in cookies by the effect of cations. The effect of metal cations on the browning provided by the Maillard reaction seems to be quite complex because there are contradictory findings in the literature. It has been shown that the color intensity increased with higher salt (NaCl and KCl) concentration in cereal model systems and in breakfast cereals.43,45 Moreau et al. also clearly demonstrated that the browning provided by NaCl is linked neither to the hygroscopic behavior of NaCl nor to the physical state of the cereal model systems (mimicking breakfast cereals) by comparing their glass transition temperatures.43 Rizzi investigated the effects of cationic species on Maillard browning in aqueous pH 7.2 buffered (bis/tris) solutions of amino acids and pentose sugars after heating at 100 °C for 80 min.44 His findings showed that the presence of NaCl increased browning, which was also similar in the presence of KCl, and CaCl2 was reported to increase more. The results of the present paper are in line with the findings of Moreau et al. and Rizzi.43−45 On the other hand, Kwak and Lim observed that either 1% or especially 10% NaCl greatly inhibited browning in aqueous binary mixtures of glucose and different amino acids in pH 6.5 citrate−phosphate buffer heated at 100 °C for 6 h.46 Similarly, Yamaguchi et al. observed that with increasing NaCl concentration in aqueous mixtures of glucose−lysine (pH 6 and 7.5 phosphate buffers, 100 °C for 120 min) and glucose− β-lactoglobulin (pH 6 phosphate buffer, 70 °C up to 24 h), browning significantly decreased.47 Cerny et al. investigated the Maillard reaction in aqueous mixtures of glucose and methionine in phosphate buffer over pH 7 and observed a decrement in browning in the presence NaCl during incubation at 40 °C for up to 15 days.48 These counterarguments might be related to the use of phosphate buffer, which is known to greatly enhance the Maillard reaction, and also to different reaction conditions applied. Rizzi discussed how complications may arise from the popular use of phosphate buffers in the G


+ + + +

NaCl KCl CaCl2 CaCl2 1.8 ± 0.1 b 1.3 ± 0.0 a 1.4 ± 0.0 a nd

9.0 ± 0.2 b 9.7 ± 1.0 b

10.4 ± 1.1 b 4.8 ± 1.7 a

180 °C × 3 min 180 °C × 3 min

180 °C × 3 min 180 °C × 3 min

140 °C × 2 min 140 °C × 2 min

140 °C × 2 min 140 °C × 2 min

G 4.1 ± 0.7 b 0.2 ± 0.1 a 0.8 ± 0.2a nd nd

× × × × ×

T×t

°C °C °C °C °C

15 min 15 min 15 min 15 min 5 min

180 180 180 180 180

4.7 0.4 3.7 4.0 1.3

b a a b c

105 ± 0.8 b 461 ± 8.1 d

85.3 ± 0.6 a 117 ± 1.2 c

2.8 ± 0.1 a 91.5 ± 6.2 b

4.5 ± 0.7 a 5.9 ± 0.7 a

± ± ± ± ±

1-DG 17.3 3.8 4.2 21.6 39.4

b

7.2 9.0 1.4 0.3 0.8

c b b a bc

674 ± 3.0 b 1101 ± 4.8 d

598 ± 4.8 a 731 ± 22.6 c

13.2 ± 1.0 b 9.5 ± 0.4 a

19.2 ± 1.4 c 12.6 ± 0.5 b

± ± ± ± ±

3-DG 48.3 28.2 31.0 7.2 35.0

± ± ± ± ± 2.4 0.0 0.3 2.1 0.4

GO bc a a c ab

8.6 ± 1.1 ab 7.1 ± 2.2 a

12.6 ± 0.4 b 8.1 ± 2.4 ab

8.2 ± 1.7 a 10.7 ± 0.4 b

8.5 ± 0.2 ab 7.3 ± 0.1 a

11.0 6.2 6.0 12.1 7.3

12.0 ab 18.2 a 6.1 a 16.9 c 3.8 bc

MG ± ± ± ± ±

13.4 ± 1.5 a 12.4 ± 1.4 a

15.6 ± 0.5 a 12.5 ± 1.1 a

27.4 ± 0.6 a 45.8 ± 0.7 b

28.0 ± 0.7 a 28.0 ± 1.4 a

55.7 33.3 46.6 109 85.9

nmol of product ± ± ± ± ± 0.1 0.1 0.2 4.3 0.8

DA a a a b b

2.2 ± 0.1 a 3.0 ± 0.5 b

2.3 ± 0.1 a 1.9 ± 0.0 a

9.4 ± 0.4 a 51.7 ± 1.0 c

7.6 ± 0.6 a 11.4 ± 0.6 b

0.5 1.1 1.5 15.7 10.9

55.5 d 374 c 89.2 b 27.1 b 80.1 a

180 ± 4.6 a 1335 ± 43.8 c

254 ± 6.0 b 236 ± 3.5 ab

97 ± 0.6 a 479 ± 8.2 b

109 ± 0.7 a 98 ± 4.3 a

± ± ± ± ±

HMF 328 1299 1871 1774 3493

nq nq

nq nq

nq nq

nq nq

± ± ± ± ± 5.0 a 12.0 a 0.8 a 57.3 c 15.8 b

FUR 28.1 79.9 86.6 845.6 568.8

± ± ± ± ± 0.05 0.02 0.03 0.01 0.01

initial c b a d d

5.36 ± 0.03 b 6.01 ± 0.01 d

4.85 ± 0.06 a 5.67 ± 0.03 c

5.36 ± 0.03 b 6.01 ± 0.01 d

4.85 ± 0.06 a 5.67 ± 0.03 c

6.03 5.52 5.36 6.13 6.13

pH ± ± ± ± ±

0.30 0.04 0.06 0.04 0.04

heated c b b a a

3.24 ± 0.01 a 3.84 ± 0.03 b

3.19 ± 0.04 a 3.26 ± 0.02 a

3.25 ± 0.00 ab 3.42 ± 0.01 c

3.32 ± 0.04 b 3.23 ± 0.03 a

4.49 4.00 4.02 3.30 3.51

a Letters in each column, within a group, indicate statistically significant difference (p < 0.05). Glc, glucose; Gly, glycine; G, glucosone; 1-DG, 1-deoxyglucosone; 3-DG, 3-deoxyglucosone; GO, glyoxal; MG, methylglyoxal; DA, diacetyl; HMF, 5-hydroxymethyl-2- furfural; T, temperature; t, time; nq, not quantitated. bSemiquantitated according to 3-deoxyglucosone calibration curve.

Glc + Gly Glc + Gly + NaCl Glc + Gly + KCl Glc + Gly + CaCl2

Glc + Gly Glc + Gly + NaCl Glc + Gly + KCl Glc + Gly + CaCl2

Glc Glc Glc Glc Glc

b

Table 4. Amount of α-Dicarbonyl Compounds and Furfurals Formed from 100 μmol of Glucose in the Presence or Absence of Glycine, NaCl, KCl, and CaCl2a

Journal of Agricultural and Food Chemistry Article

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Journal of Agricultural and Food Chemistry Table 5. Browning Development and Color Intensity as Aborbance (λ= 420 nm) in Model Reaction Systemsa

a

Letters in the rows of absorbance indicate statistically significant difference (p < 0.05). Glc, glucose; Gly, glycine; T, temperature; t, time.

at 140 °C by the addition of NaCl, KCl, and CaCl2 (Table 4). The changes in other α-dicarbonyl compounds were minor and statistically not different (p < 0.05), except in the presence of CaCl2 glucosone and glyoxal decreased and diacetyl increased. The amount of HMF was found to be not statistically significant different between glucose−glycine and glucose−glycine− NaCl (p > 0.05). On the other hand, in the presence of KCl, HMF decreased, and in the presence of CaCl2, it increased 5-fold. With increasing amounts of 1-deoxyglucosone and 3-deoxyglucosone, the color intensity decreased in the presence of NaCl, KCl, and CaCl2 (Table 5). It should be mentioned that the color intensity obtained by the Maillard reaction was higher, to a large extent, than caramelization, as expected. The decreases of the color intensity in the Maillard reaction by the presence of salts obviously did not simulate the cookies rich in sugars because caramelization reactions predominate. Many spectroscopic studies and theoretical calculations indicated that the zwitterionic structures of amino acids are stabilized by interaction with metal cations.50−52 Therefore, the decrease in the nucleophilic strength of the amino groups should result in a decrease in the rate of Maillard reaction, as was observed in the mitigation of acrylamide formation in the presence of cations.27,30 The decrease in the browning intensity in glucose−glycine systems in the presence of salts therefore should be related to less participation of zwitterionic glycine, which is stabilized with cations, in carbonyl−amine reactions. Accumulation of higher amounts of 1-deoxyglucosone and 3-deoxyglucosone in a glucose−glycine model system heated at 140 °C in the presence of salts was also related to the lower reactivity of zwitterionic glycine. This observation was in line with the computed stabilities of the ionic complexes of glycine with alkali metals and alkaline-earth metals, which are in the order Mg2+ > Ca2+ > Li+ > Na+ > K+.51 Higher accumulations of 1-deoxyglucosone and 3-deoxyglucosone followed the order CaCl2 > NaCl > KCl. Shorter chain α-dicarbonyl compounds glyoxal, methylglyoxal, and diacetyl are highly volatile, and their reactions with amino compounds are often not very conclusive because they leave the reaction medium, and move to

the headspace of the tube.36,40 At this point, it should be mentioned that the elementary reaction steps of the Maillard reaction could be affected differently to various degrees in the presence of these salts. Therefore, the elementary reaction rate constants need to be calculated to get insights on the effects of salts in the Maillard reaction as has been successfully demonstrated for glucose degradation by multiresponse kinetic modeling and also by computational chemistry methods.35,36,42 The pH of the 0.1 M glucose−glycine equimolar aqueous solution was found to be increased by the addition of equimolar NaCl, KCl, and CaCl2. Because these cations increase and stabilize the zwitterionic form of glycine, more protonation of amino groups should be supplemented from the environment, thereby producing a medium with a higher pH value. Contrary to that, Rahn and Yaylayan demonstrated that a 4.8 M glycine− NaCl solution became acidic during incubation at room temperature for 20 min by using 2,6-dichloroindophenol redox dye as a pH indicator in spectrophotometric measurement.38 Their results indicated that HCl is released in the concentrated glycine−NaCl, clearly similar to the behavior of the glycine hydrochloride solution.38 In conclusion, in the presence of salts, dehydration of reducing sugars is catalyzed to form more furfurals but not more α-dicarbonyl compounds in cookies. The increase in the concentration of α-dicarbonyl compounds at lower pH values stems from higher sucrose hydrolysis due to the formation of glucose and fructose as precursors. Cations have no direct effect on reducing sugar dehydration to yield formation of 1-deoxyglucosone and 3-deoxyglucosone because the amounts do not increase per amount of reducing sugars under caramelization conditions. Higher amounts of HMF formation in cookies do not relate to 3-deoxglucosone formation. Therefore, the catalyzing effect of cations should occur on the pathways comprising cyclic intermediates either from sucrose degradation or from fructose dehydration. Model reaction systems showed that effects of NaCl, KCl, and CaCl2 on browning enhancement in cookies proceed through caramelization reactions, by increasing the formation of furfurals. On the one hand, cations I


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(16) Abordo, E. A.; Minhas, H. S.; Thornalley, P. J. Accumulation of α-oxoaldehydes during oxidative stress: a role in cytotoxicity. Biochem. Pharmacol. 1999, 58, 641−648. (17) Amoroso, A.; Maga, G.; Daglia, M. Cytotoxicity of α-dicarbonyl compounds submitted to in vitro simulated digestion process. Food Chem. 2013, 140, 654−659. (18) Rabbani, N.; Thornalley, P. J. Dicarbonyl stress in cell and tissue dysfunction contributing to ageing and disease. Biochem. Biophys. Res. Commun. 2015, 458, 221−226. (19) Svendsen, C.; Hoie, A. H.; Alexander, J.; Murkovic, M.; Husoy, T. The food processing contaminant glyoxal promotes tumour growth in the multiple intestinal neoplasia (Min) mouse model. Food Chem. Toxicol. 2016, 94, 197−202. (20) Kocadağlı, T.; Göncüoğlu, N.; Hamzalıoğlu, A.; Gökmen, V. In depth study of acrylamide formation in coffee during roasting: role of sucrose decomposition and lipid oxidation. Food Funct. 2012, 3, 970− 975. (21) Moon, J. K.; Shibamoto, T. Formation of carcinogenic 4(5)methylimidazole in Maillard reaction systems. J. Agric. Food Chem. 2011, 59, 615−618. (22) Perez Locas, C.; Yaylayan, V. A. Origin and mechanistic pathways of formation of the parent furan: a food toxicant. J. Agric. Food Chem. 2004, 52, 6830−6836. (23) Friedman, M. Food browning and its prevention: an overview. J. Agric. Food Chem. 1996, 44, 631−653. (24) Degen, J.; Hellwig, M.; Henle, T. 1,2-Dicarbonyl compounds in commonly consumed foods. J. Agric. Food Chem. 2012, 60, 7071− 7079. (25) Arribas-Lorenzo, G.; Morales, F. J. Analysis, distribution, and dietary exposure of glyoxal and methylglyoxal in cookies and their relationship with other heat-induced contaminants. J. Agric. Food Chem. 2010, 58, 2966−2972. (26) Gökmen, V.; Şenyuva, H. Z. Effects of some cations on the formation of acrylamide and furfurals in glucose-asparagine model system. Eur. Food Res. Technol. 2007, 225, 815−820. (27) Gökmen, V.; Şenyuva, H. Z. Acrylamide formation is prevented by divalent cations during the Maillard reaction. Food Chem. 2007, 103, 196−203. (28) Van der Fels-Klerx, H. J.; Capuano, E.; Nguyen, H. T.; Mogol, B. A.; Kocadağlı, T.; Taş, N. G.; Hamzalıoğlu, A.; Van Boekel, M. A. J. S.; Gökmen, V. Acrylamide and 5-hydroxymethylfurfural formation during baking of biscuits: NaCl and temperature-time profile effects and kinetics. Food Res. Int. 2014, 57, 210−217. (29) Açar, Ö . Ç .; Pollio, M.; Di Monaco, R.; Fogliano, V.; Gökmen, V. Effect of calcium on acrylamide level and sensory properties of cookies. Food Bioprocess Technol. 2012, 5, 519−526. (30) Göncüoğlu Taş, N.; Hamzalıoğlu, A.; Kocadağlı, T.; Gökmen, V. Adding calcium to foods and effect on acrylamide. In Calcium: Chemistry, Analysis, Function and Effects; Predy, V. R., Ed.; The Royal Society of Chemistry: 2015; pp 274−290. (31) American Association of Cereal Chemists (AACC) International. Approved Methods of Analysis, 11th ed.; AACC: St. Paul, MN, USA, 2000; Method 10-54.01. (32) Kocadağlı, T.; Gökmen, V. Investigation of α-dicarbonyl compounds in baby foods by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry. J. Agric. Food Chem. 2014, 62, 7714−7720. (33) Mogol, B. A.; Gökmen, V. Computer vision-based analysis of foods: a non-destructive colour measurement tool to monitor quality and safety. J. Sci. Food Agric. 2014, 94, 1259−1263. (34) Fiore, A.; Troise, A. D.; Mogol, B. A.; Roullier, V.; Gourdon, A.; Jian, S. E.; Hamzalioglu, B. A.; Gokmen, V.; Fogliano, V. Controlling the Maillard reaction by reactant encapsulation: sodium chloride in cookies. J. Agric. Food Chem. 2012, 60, 10808−10814. (35) Mayes, H. B.; Nolte, M. W.; Beckham, G. T.; Shanks, B. H.; Broadbelt, L. J. The alpha−bet(a) of salty glucose pyrolysis: computational investigations reveal carbohydrate pyrolysis catalytic action by sodium ions. ACS Catal. 2015, 5, 192−202.

enhance desired browning in cookies in view of food quality. On the other hand, two aspects should be considered in view of food safety. First, sodium reduction can be obtained by replacement with potassium without sacrificing the desired consequences of caramelization in cookies. Second, they both increase the amount of HMF. The addition of calcium to foods to mitigate acrylamide formation may result in an increment in HMF but not α-dicarbonyl compounds.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.6b03870. Total and extracted ion chromatograms of the quinoxaline derivatives of α-dicarbonyl compounds (PDF)

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AUTHOR INFORMATION

Corresponding Author

*(V.G.) E-mail: [email protected]. Phone: +90 312 2977108. Fax: +90 312 2992123. Notes

The authors declare no competing financial interest.

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REFERENCES

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