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Comparison of the Maillard-Derived Aroma Volatiles of Cooked Milled and Brown Rice
14
CHAPTER
Comparison of the MaillardDerived Aroma Volatiles of Cooked Milled and Brown Rice Dody D. Handoko, Lisa Methven, J. Stephen Elmore and Donald S. Mottram Department of Food and Nutritional Sciences, University of Reading, Whiteknights, Reading, Berkshire, UK
14.1 INTRODUCTION Flavor is the key driver and main measure of quality, and the main discriminator between rice varieties. Postharvest processes (harvesting, drying, milling, and storage) and cooking processes (boiling, puffing, or extrusion) have a profound effect on the flavor of cooked rice. Rice bran contains amino acids, minerals, and antioxidants. In brown rice, the bran and germ is still present, but it is partly or totally removed in milled rice, also known as white rice. Basmati, Jasmine or Sintanur are examples of fragrant rice varieties, which have a flavor similar to that of popcorn. This desirable flavor is associated with the presence of 2-acetyl-1-pyrroline [1]. Electric rice cookers are often used in Asian countries to cook rice by boiling. Raw rice is usually washed with water prior to cooking. The objective of this research was to compare the Maillard reaction volatiles of cooked milled and brown rice. In addition, the levels of free amino acids and sugars in the rice varieties were measured in order to explain the volatile formation pathways.
14.2 MATERIALS AND METHODS Two milled fragrant rice cultivars (Basmati – Pure Basmati, Tilda, and Jasmine – Thai Jasmine Rice, Tilda), one milled non-fragrant rice (long grain, retailer brand), and one brown non-fragrant rice (long grain, retailer brand) were purchased from a UK supermarket. Rice was washed, and then cooked using an electric rice cooker (Sanken SJ-100, 1.0 L Active Jar, Indonesia). In order to be cooked properly, milled rice requires 30 minutes of cooking, while brown rice requires 40 minutes V. Ferreira and R. Lopez (Eds): Flavour Science. DOI: http://dx.doi.org/10.1016/B978-0-12-398549-1.00014-3
© 2014 2013 Elsevier Inc. All rights reserved.
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of cooking. The volatile compounds of cooked rice were collected on a Tenax trap (Supelco, UK) and analyzed using an Agilent 7890A/5975C GC/MS (Agilent, UK) coupled with an Automated Thermal Desorption unit (Turbomatrix ATD Perkin Elmer, UK). For flavor precursor analysis, cooked rice was freeze-dried and then ground, whereas the raw rice was ground only. Free amino acids were analyzed by an Agilent 6890/5975 GC/ MS following the EZ-Faast derivatization method (Phenomenex, UK), while sugars were analyzed by ion chromatography (Dionex 8220i, UK).
14.3 RESULTS Results are shown in Tables 14.1 and 14.2. Table 14.1 Major Volatile Aroma Compounds in Cooked Milled and Brown Ricea Milled Brown NonNonVolatile Compounds Identificationb Basmati Jasmine Fragrant Fragrant Maillard Reaction Products
Methanethiol 3-Methylbutanal 2-Methylbutanal Methyl pyrazine Furfural 2,5 and 2,6-Dimethylpyrazine 5-Methylfurfural Trimethylpyrazine Phenylacetaldehyde
ms MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI
n.d. 4 (17) n.d. n.d. n.d. n.d.
n.d. 4 (22) n.d. n.d. n.d. n.d.
n.d. 7 (50) n.d. n.d. n.d. n.d.
5 (87) 33 (39) 59 (40) 16 (18) 7 (36) 12 (28)
MS + LRI MS + LRI MS + LRI
n.d. n.d. n.d.
n.d. n.d. n.d.
n.d. n.d. n.d.
1 (44) 7 (28) 5 (30)
MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI
16 (4) 12 (12) 141 (3) 11 (14) 53 (14) 2 (41)
34 (4) 31 (2) 362 (8) 22 (36) 68 (8) 2 (7)
27 (49) 17 (35) 476 (40) 12 (34) 158 (31) 3 (26)
33 (38) 5 (17) 263 (30) 3 (40) 167 (21) 3 (33)
MS + LRI
20 (8)
23 (32)
n.d.
n.d.
Lipid Oxidation Reaction Products
Pentanal Pentanol Hexanal 1-Octen-3-ol Nonanal (E,E)-2,4-decadienal Others
2-Acetyl-1-pyrroline
Peak area values relative to that of 1,2-dichlorobenzene (peak area = 100); average values of triplicate analysis are given with coefficient of variation (%) in parenthesis; n.d., not determined. b MS + LRI , mass spectrum and LRI match to those of authentic compounds; ms, mass spectrum match that in NIST/EPA/NIH database. a
Comparison of the Maillard-Derived Aroma Volatiles of Cooked Milled and Brown Rice
85
Table 14.2 Concentration of Sugars in Raw and Cooked (Freeze-Dried) Milled and Brown Ricea Cooked Remaining Effect of Rice Sugars Raw Rice Rice (%)b Cookingc
Basmati
Jasmine
Milled Non-fragrant Brown Non-fragrant
Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose
8.2 (19) 2.2 (29) 51.0 (28) n.d. 6.0 (12) 2.0 (10) 32.7 (7) 0.3 (9) 3.6 (18) 1.0 (22) 31.2 (19) n.d. 4.4 (2) 2.0 (6) 173.8 (2) n.d.
7.2 (8) 1.3 (9) 16.4 (9) n.d. 6.0 (3) 1.0 (5) 11.2 (3) 0.2 (11) 4.3 (8) 0.6 (10) 5.5 (9) n.d. 3.8 (3) 1.8 (4) 176.8 (2) n.d.
89 59 32
n.s. n.s. *
100 49 34 76 121 66 18
n.s. ** ** * n.s. n.s. **
86 94 102
** n.s. n.s.
a
Average values of triplicate analysis (mg/0.1 g weight) are given with coefficient of variation (%) in parenthesis; n.d., not determined. b Percent remaining after cooking. c Probability that there is a significant effect of cooking on concentration; n.s., no significant difference between means (P > 0.05); * significant at 0.05 > P > 0.01; ** significant at P < 0.01.
14.4 DISCUSSION AND CONCLUSION The cooked brown non-fragrant rice contained more Maillard-derived volatiles (such as Maillard furans, Strecker aldehydes, and pyrazines) and lipid-derived volatiles than cooked milled rice (Table 14.1). This may be because brown rice contained more free amino acids [2] and lipids than the milled rice [3]. The Maillard-derived volatiles and lipid-derived volatiles may result both from cooking and postharvest processing. Lam and Proctor [4] reported that lipid oxidation products, particularly aldehydes, are important contributors to the aroma of raw rice. 2-Acetyl-1-pyrroline (2AP) was only found in the cooked milled fragrant rice; it may already be present in the raw fragrant rice. During the cooking of milled rice, sucrose, the most abundant sugar, underwent the highest and most significant loss, while the glucose level remained constant (Table 14.2). Cao et al. [5] found this phenomenon in
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ageing of milled rice, and Lamberts et al. [6] in parboiling of brown rice. However, sucrose and fructose levels in brown rice remained constant during cooking, while the glucose underwent significant losses. Changes in free amino acids on cooking were smaller than those observed for sugars (results not shown). Levels of proline and ornithine, which are considered as main precursors of 2AP, were low and remained constant on rice cooking. In the milled rice, asparagine, glutamic acid, and aspartic acid, the most abundant free amino acids, underwent the highest loss on cooking. The reaction of amino acids with reducing sugars may contribute to formation of pyrazine, pyridine, pyrrole, and oxazole [7,8]. However, levels of asparagine and aspartic acid in brown non-fragrant rice remained constant on cooking, whereas glutamic acid underwent significant loss.
ACKNOWLEDGEMENT This research project was supported by the Indonesian Agency for Agricultural Research and Development and GIRACT (www.giract.com).
REFERENCES [1] R.G. Buttery, L.C. Ling, B.O. Juliano, J.G. Turnbaugh, Cooked rice aroma and 2acetyl-1-pyrroline, J. Agric. Food Chem. 31 (1983) 823–826. [2] T. Saikusa, T. Horino, Y. Mori, Free amino acids in the rice kernel and kernel fractions and the effect of water soaking on the distribution, J. Agric. Food Chem. 42 (1994) 1122–1125. [3] B.O. Juliano, Polysaccharides, protein, and lipids of rice, in: B.O. Juliano (Ed.), Rice; Chemistry and Technology, second ed., AACC, Brooklyn Park, MN, 1985, pp. 59–174. [4] H.S. Lam, A. Proctor, Milled rice oxidation volatiles and odor development, J. Food Sci. 68 (2003) 2676–2681. [5] Y.H. Cao, Y. Wang, X.L. Chen, J.N. Ye, Study on sugar profile of rice during ageing by capillary electrophoresis with electrochemical detection, Food Chem. 86 (2004) 131–136. [6] L. Lamberts, I. Rombouts, K. Brijs, K. Gebruers, J.A. Delcour, Impact of parboiling conditions on Maillard precursors and indicators in long-grain rice cultivars, Food Chem. 110 (2008) 916–922. [7] H.-I. Hwang, T.G. Hartman, C.-T. Ho, Relative reactivities of amino acids in pyrazine formation, J. Agric. Food Chem. 43 (1995) 179–184. [8] H.-I. Hwang,T.G. Hartman, C.-T. Ho, Relative reactivities of amino acids in the formation of pyridines, pyrroles, and oxazoles, J. Agric. Food Chem. 43 (1995) 2917–2921.
CHAPTER
Comparison of the MaillardDerived Aroma Volatiles of Cooked Milled and Brown Rice Dody D. Handoko, Lisa Methven, J. Stephen Elmore and Donald S. Mottram Department of Food and Nutritional Sciences, University of Reading, Whiteknights, Reading, Berkshire, UK
14.1 INTRODUCTION Flavor is the key driver and main measure of quality, and the main discriminator between rice varieties. Postharvest processes (harvesting, drying, milling, and storage) and cooking processes (boiling, puffing, or extrusion) have a profound effect on the flavor of cooked rice. Rice bran contains amino acids, minerals, and antioxidants. In brown rice, the bran and germ is still present, but it is partly or totally removed in milled rice, also known as white rice. Basmati, Jasmine or Sintanur are examples of fragrant rice varieties, which have a flavor similar to that of popcorn. This desirable flavor is associated with the presence of 2-acetyl-1-pyrroline [1]. Electric rice cookers are often used in Asian countries to cook rice by boiling. Raw rice is usually washed with water prior to cooking. The objective of this research was to compare the Maillard reaction volatiles of cooked milled and brown rice. In addition, the levels of free amino acids and sugars in the rice varieties were measured in order to explain the volatile formation pathways.
14.2 MATERIALS AND METHODS Two milled fragrant rice cultivars (Basmati – Pure Basmati, Tilda, and Jasmine – Thai Jasmine Rice, Tilda), one milled non-fragrant rice (long grain, retailer brand), and one brown non-fragrant rice (long grain, retailer brand) were purchased from a UK supermarket. Rice was washed, and then cooked using an electric rice cooker (Sanken SJ-100, 1.0 L Active Jar, Indonesia). In order to be cooked properly, milled rice requires 30 minutes of cooking, while brown rice requires 40 minutes V. Ferreira and R. Lopez (Eds): Flavour Science. DOI: http://dx.doi.org/10.1016/B978-0-12-398549-1.00014-3
© 2014 2013 Elsevier Inc. All rights reserved.
83
84
Dody D. Handoko et al.
of cooking. The volatile compounds of cooked rice were collected on a Tenax trap (Supelco, UK) and analyzed using an Agilent 7890A/5975C GC/MS (Agilent, UK) coupled with an Automated Thermal Desorption unit (Turbomatrix ATD Perkin Elmer, UK). For flavor precursor analysis, cooked rice was freeze-dried and then ground, whereas the raw rice was ground only. Free amino acids were analyzed by an Agilent 6890/5975 GC/ MS following the EZ-Faast derivatization method (Phenomenex, UK), while sugars were analyzed by ion chromatography (Dionex 8220i, UK).
14.3 RESULTS Results are shown in Tables 14.1 and 14.2. Table 14.1 Major Volatile Aroma Compounds in Cooked Milled and Brown Ricea Milled Brown NonNonVolatile Compounds Identificationb Basmati Jasmine Fragrant Fragrant Maillard Reaction Products
Methanethiol 3-Methylbutanal 2-Methylbutanal Methyl pyrazine Furfural 2,5 and 2,6-Dimethylpyrazine 5-Methylfurfural Trimethylpyrazine Phenylacetaldehyde
ms MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI
n.d. 4 (17) n.d. n.d. n.d. n.d.
n.d. 4 (22) n.d. n.d. n.d. n.d.
n.d. 7 (50) n.d. n.d. n.d. n.d.
5 (87) 33 (39) 59 (40) 16 (18) 7 (36) 12 (28)
MS + LRI MS + LRI MS + LRI
n.d. n.d. n.d.
n.d. n.d. n.d.
n.d. n.d. n.d.
1 (44) 7 (28) 5 (30)
MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI MS + LRI
16 (4) 12 (12) 141 (3) 11 (14) 53 (14) 2 (41)
34 (4) 31 (2) 362 (8) 22 (36) 68 (8) 2 (7)
27 (49) 17 (35) 476 (40) 12 (34) 158 (31) 3 (26)
33 (38) 5 (17) 263 (30) 3 (40) 167 (21) 3 (33)
MS + LRI
20 (8)
23 (32)
n.d.
n.d.
Lipid Oxidation Reaction Products
Pentanal Pentanol Hexanal 1-Octen-3-ol Nonanal (E,E)-2,4-decadienal Others
2-Acetyl-1-pyrroline
Peak area values relative to that of 1,2-dichlorobenzene (peak area = 100); average values of triplicate analysis are given with coefficient of variation (%) in parenthesis; n.d., not determined. b MS + LRI , mass spectrum and LRI match to those of authentic compounds; ms, mass spectrum match that in NIST/EPA/NIH database. a
Comparison of the Maillard-Derived Aroma Volatiles of Cooked Milled and Brown Rice
85
Table 14.2 Concentration of Sugars in Raw and Cooked (Freeze-Dried) Milled and Brown Ricea Cooked Remaining Effect of Rice Sugars Raw Rice Rice (%)b Cookingc
Basmati
Jasmine
Milled Non-fragrant Brown Non-fragrant
Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose Glucose Fructose Sucrose Maltose
8.2 (19) 2.2 (29) 51.0 (28) n.d. 6.0 (12) 2.0 (10) 32.7 (7) 0.3 (9) 3.6 (18) 1.0 (22) 31.2 (19) n.d. 4.4 (2) 2.0 (6) 173.8 (2) n.d.
7.2 (8) 1.3 (9) 16.4 (9) n.d. 6.0 (3) 1.0 (5) 11.2 (3) 0.2 (11) 4.3 (8) 0.6 (10) 5.5 (9) n.d. 3.8 (3) 1.8 (4) 176.8 (2) n.d.
89 59 32
n.s. n.s. *
100 49 34 76 121 66 18
n.s. ** ** * n.s. n.s. **
86 94 102
** n.s. n.s.
a
Average values of triplicate analysis (mg/0.1 g weight) are given with coefficient of variation (%) in parenthesis; n.d., not determined. b Percent remaining after cooking. c Probability that there is a significant effect of cooking on concentration; n.s., no significant difference between means (P > 0.05); * significant at 0.05 > P > 0.01; ** significant at P < 0.01.
14.4 DISCUSSION AND CONCLUSION The cooked brown non-fragrant rice contained more Maillard-derived volatiles (such as Maillard furans, Strecker aldehydes, and pyrazines) and lipid-derived volatiles than cooked milled rice (Table 14.1). This may be because brown rice contained more free amino acids [2] and lipids than the milled rice [3]. The Maillard-derived volatiles and lipid-derived volatiles may result both from cooking and postharvest processing. Lam and Proctor [4] reported that lipid oxidation products, particularly aldehydes, are important contributors to the aroma of raw rice. 2-Acetyl-1-pyrroline (2AP) was only found in the cooked milled fragrant rice; it may already be present in the raw fragrant rice. During the cooking of milled rice, sucrose, the most abundant sugar, underwent the highest and most significant loss, while the glucose level remained constant (Table 14.2). Cao et al. [5] found this phenomenon in
86
Dody D. Handoko et al.
ageing of milled rice, and Lamberts et al. [6] in parboiling of brown rice. However, sucrose and fructose levels in brown rice remained constant during cooking, while the glucose underwent significant losses. Changes in free amino acids on cooking were smaller than those observed for sugars (results not shown). Levels of proline and ornithine, which are considered as main precursors of 2AP, were low and remained constant on rice cooking. In the milled rice, asparagine, glutamic acid, and aspartic acid, the most abundant free amino acids, underwent the highest loss on cooking. The reaction of amino acids with reducing sugars may contribute to formation of pyrazine, pyridine, pyrrole, and oxazole [7,8]. However, levels of asparagine and aspartic acid in brown non-fragrant rice remained constant on cooking, whereas glutamic acid underwent significant loss.
ACKNOWLEDGEMENT This research project was supported by the Indonesian Agency for Agricultural Research and Development and GIRACT (www.giract.com).
REFERENCES [1] R.G. Buttery, L.C. Ling, B.O. Juliano, J.G. Turnbaugh, Cooked rice aroma and 2acetyl-1-pyrroline, J. Agric. Food Chem. 31 (1983) 823–826. [2] T. Saikusa, T. Horino, Y. Mori, Free amino acids in the rice kernel and kernel fractions and the effect of water soaking on the distribution, J. Agric. Food Chem. 42 (1994) 1122–1125. [3] B.O. Juliano, Polysaccharides, protein, and lipids of rice, in: B.O. Juliano (Ed.), Rice; Chemistry and Technology, second ed., AACC, Brooklyn Park, MN, 1985, pp. 59–174. [4] H.S. Lam, A. Proctor, Milled rice oxidation volatiles and odor development, J. Food Sci. 68 (2003) 2676–2681. [5] Y.H. Cao, Y. Wang, X.L. Chen, J.N. Ye, Study on sugar profile of rice during ageing by capillary electrophoresis with electrochemical detection, Food Chem. 86 (2004) 131–136. [6] L. Lamberts, I. Rombouts, K. Brijs, K. Gebruers, J.A. Delcour, Impact of parboiling conditions on Maillard precursors and indicators in long-grain rice cultivars, Food Chem. 110 (2008) 916–922. [7] H.-I. Hwang, T.G. Hartman, C.-T. Ho, Relative reactivities of amino acids in pyrazine formation, J. Agric. Food Chem. 43 (1995) 179–184. [8] H.-I. Hwang,T.G. Hartman, C.-T. Ho, Relative reactivities of amino acids in the formation of pyridines, pyrroles, and oxazoles, J. Agric. Food Chem. 43 (1995) 2917–2921.