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Pyrazine composition as influenced by the smoking conditions of hickory sawdust
G. Charalambous (Ed.), Food Flavors: Generation, Analysis and Process Influence © 1995 Elsevier Science B.V. All rights reserved
1025
Pyrazine composition as influenced by the smoking conditions of hickory sawdust Z. Chen and J.A. Maga Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
Abstract The role of smoke generation temperature (250 versus 350'C), air supply (presence or absence) and sawdust moisture content (12, 20, 30%) on resulting pyrazine composition was investigated. The major pyrazines identified with all variables were pyrazine, 2-methoxy-3-methylpyrazine, 2-ethoxy-3ethylpyrazine, 2-propyl-3,6-dimethylpyrazine, 2-butyl-3,5-dimethylpyrazine, 2-acetyl-3-methylpyrazine, and 2-acetyl-3,6-dimethylpyrazine. The presence or absence of air had little if any influence on resulting pyrazine composition. In contrast, the initial moisture content of the sawdust did influence final pyrazine ratios. As moisture content increased, the relative amount of 2-butyl-3,5-dimethylpyrazine increased primarily as the result of decreased amounts of 2-methoxy-3-methylpyrazine. As would be expected, the temperature of smoke generation had a dramatic influence on pyrazine composition, with higher amounts of 2-ethoxy-3-ethylpyrazine and 2propyl-3,6-dimethylpyrazine present at the lower temperature, and higher levels of 2-butyl-3,5-dimethylpyrazine and 2-acetyl-3-methylpyrazine present at the higher smoking temperature. Thus it is apparent that the level and intensity of smoke aroma associated with the pyrazine fraction can be altered as influenced by smoke generation conditions.
1.
INTRODUCTION
The smoke processing of food is an age old tradition that is still quite popular today, primarily due to the unique aroma that can result from the process. As a result, many investigators have attempted to characterize the volatile composition of wood smoke, and to date, over 400 compounds have been identified. Phenols have been thought to be the major contributors to wood smoke aroma [1-13], but other classes of compounds have also been implicated [14-24]. Among these are pyrazines which are thermally produced and have been characterized as possessing a smoky aroma [25], although few pyrazines have been actually identified in wood smoke [15,26]. Reports have also appeared in the literature demonstrating the fact that smoke generation variables such as temperature [23, 27-31], air supply [28], and wood moisture content [32] can also significantly influence the volatile composition of wood smoke. Therefore, the objective of this study was to specifically investigate the formation of pyrazines from hickory wood sawdust as influenced by wood moisture, air and smoke generation temperature.
1026
2.
MATERIALS AND METHODS
2.1. Sawdust source A commercial sample of hickory wood sawdust used for smoking foods was obtained and passed through a series of sieves to minimize particle size distribution. The 60-80 mesh fraction was used in this study. 2.2. Smoke generation A small all glass laboratory smoke generator consisting of a 3-holed 500 ml round bottom flask and a water cooled condenser was constructed. One port was fitted with a thermometer that was positioned in the center of the sawdust; the condenser was fitted to another; and the third permitted or prohibited the introduction of air. In the studies with air, compressed air was metered in the chamber at a rate of 20 cc per minute. When air was not desired, the air port was stoppered. The flask was placed in a rheostatcontrolled heating mantle. A 150 g charge of sawdust was placed in the flask and the wood temperature raised to 250 or 350'C in the presence or absence of air. The resulting smoke was condensed in 100 ml of water. The resulting liquid smoke was permitted to rest at room temperature to permit insoluble tars to settle. Smoke was generated from three separate batches of wood with the resulting liquid smokes being combined for subsequent analysis. 2.3. Moisture content The initial moisture content of the sawdust was determined to be 12%, and based on this, tap water was added to representative samples of sawdust to have final moisture contents of 12, 20 or 30%. The sawdust plus appropriate water addition were mixed for one hour in a stoppered flask and permitted to equilibrate for 4 hours at room temperature before smoke generation. 2.4
Pyrazine extraction and analysis 50 ml of each liquid smoke were transferred to a separatory funnel and 100 mg of internal standard (trimethylpyrazine) added. The use of the internal standard permitted the relative quantitation of pyrazines based on gas chromatographic peak area data. The system was then extracted three times with 30 ml portions of ether. The ether extracts were combined and extracted three times with 30 ml portions of pH 1.0 water. The aqueous extracts were combined, adjusted to pH 8.5, and extracted three times with 30 ml portions of dichloromethane. The dichloromethane extracts were combined and concentrated over anhydrous calcium sulfate. A Perkin-Elmer Model Sigma 2B gas chromatograph equipped with a 1.9 M stainless steel column packed with 10% Carbowax 20M on 200-120 mesh Gas-Chrom Q was utilized. Initial column temperature was 60'C for 5 minutes, followed by a 2Vminute rise to 150" and a lOVminute rise to 275*C. Injector and flame ionization detector temperatures were 275" and 320"C, respectively. The unit was coupled to a Micromass Model 16F mass spectrometer operating at an ion beam setting of 70^Y with an accelerating voltage of 4KV. This unit in turn was coupled to a V.G. Datasystem Model 2000 storage system where spectra were evaluated for most probable match against standard published spectra data.
1027
3.
RESULTS AND DISCUSSION
Commercial food smoking is normally done in the presence of air without adjusting the moisture content of the sawdust. However, one variable that can be controlled in a commercial operation is the actual smoke generation temperature. Data typifying these conditions are summarized in Table 1. Table 1 Role of smoke generation temperature on resulting pvrazine composition Smoking temp. (^C) (12% moisture) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl *:
250 4.96* 24.55 33.18 14.97 3.17 16.93 2.24
350 6.87 28.56 17.70 4.00 12.19 25.70 4.98
Relative percent
From the above, it can be seen that increasing the smoke generation temperature from 250* to 350*C clearly modified the proportion of resulting pyrazines. The major differences were the drops in the relative amounts of 2-ethoxy-3-ethylpyrazine and 2-propyl-3,6-dimethylpyrazine along with increases in the amounts of acetylpyrazine derivatives. These data would indicate that pyrazines have optimum thermal ranges for their formation or one could also postulate that thermal degradation and or rearrangements could have occurred thereby influencing the relative amounts of pyrazines present. Relative to the presence of air during smoke generation, it can be seen from Table 2, that significant changes in pyrazine composition did not occur, and thus at least under the conditions evaluate in this study, air was not a significant factor. One could postulate that the presence of air could result in an increase in oxidative reactions, but in this study with the types of pyrazines identified , air was not an influential factor. Table 2 Role of air during smoke generation on resulting pvrazine composition Conditions (350^C, 12% moisture) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl *:
Relative percent
Air 6.87* 28.56 17.70 4.00 12.19 25.70 4.98
No air 8.06 24.07 21.07 6.23 7.74 28.85 3.98
1028 The last variable evaluated was the moisture content of the sawdust just prior to smoke generation, which could be an important factor since compound formation rates can be influenced by moisture content. Table 3 Role of sawdust moisture content (%) on resulting pvrazine composition Conditions (350'C, Air) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl
12 6.87* 28.56 17.70 4.00 12.19 25.70 4.98
20 5.35 26.53 17.14 6.75 15.74 22.93 5.56
30 6.44 22.72 17.09 7.14 19.70 21.18 5.73
*: Relative percent As can be seen from the above, moisture content did influence pyrazine composition. For example, the relative proportion of 2-butyl-3,5-dimethylpyrazine increased as moisture content increased, while the amount of 2methoxy-3-methylpyrazine decreased. Therefore, these data clearly demonstrate that smoke generation variables such as sawdust moisture content and the actual smoke generation temperature can influence the relative amounts of resulting pyrazines produced. This in turn could impact on the overall aroma properties of the resulting smoke.
4.
REFERENCES
1 M.E. Knowles, J. Gilbert and D.J. McWeeny, J. Sci. Food Agric. 26 (1975) 189. 2 M.R. Kornreich and P. Issenberg, J. Agric. Food Chem., 20 (1972) 1109. 3 A.O. Lustre and P. Issenberg, J. Agric. Food Chem., 18 (1970) 1056. 4 A. Radecki, H. Lamparczyk, J. Grzybowski, J. Halkiewicz, P. Bednarek, J. Bolfrukiewicz and W. Radecki, Brom. Chem. Tokskol., 1 (1976) 327. 5 A. Radecki, P. Bednarek, J. Boltrukiewicz, R. Cacha, W. Rapicki, J. Grzybowski, J. Hackiewicz and H. Lamparczyk, Brom. Chem. Tokskol., 8 (1975) 179. 6 A. Radecki, J. Halkiewicz, H. Lamparczyk, J. Grzybowski, P. Bednarek, J. Boltrukiewicz, R. Cacha and W. Rapicki, Brom. Chem. Tokskol., 8 (1975) 185. 7 A. Radecki, J. Grzybowski, J. Halkiewicz and H. Lamparczyk, Acta Aliment. Pol., 3 (1977) 203. 8 J.B. Luten, J.M. Ritskes and J.M. Weseman, Z. Lebensm. Unters. Forsch., 168 (1979) 289. 9 W. Fiddler, R.C. Doerr, A.E. Wasserman and J.M. Salay, J. Agric. Food Chem., 14 (1966) 659. 10 M. Fujimaki, K. Kim and T. Kurata, Agric. Biol. Chem., 38 (1974) 45. 11 K. Kasahara and K. Nishbori, Bui. Jap. Soc. Sci. Fish., 45 (1979) 1543.
1029 12 W. Baltes and I. Sochtig, A., Z. Lebensm. Unters. Forsch., 169 (1979) 17. 13 C.Z. Olsen, Proc. Eur. Meat Res. Workers, 22 (1976) F7:l. 18 (1970) 14 W. Fiddler, A.E. Wasserman and R.C. Doerr, J. Agric. Food Chem 934. 15 K. Kim, T Kurata and M. Fujimaki, Agric. Biol. Chem., 38 (1974) 53. 16 A. Radecki, J. Grzybowski, J. Halkiewicz H. Lamparczyk, P. Bednarek, J. Boltrukiewicz and W. Rapicki, Brom. Chem Tolksyk., 9 (1976) 461. 17 A. Radecki and J. Grzybowski, Brom Chem. Tolksyk., 14 (1981) 129. 18 H. Ishiwata, H. Watanabe, M. Watanabe, T. Hayashi, Y Hara, S Kato and A. Tanimura, Bull. Nat. Inst. Hyg. Sci., 94 (1976) 112. 19 J.E. Hoff and A J. Kapsalopoulou, J. Gas Chromatog., 1 (1964) 296. 20 R.C. Doetur, A.E. Wasserman and W. Fiddler, J. Agric Food Chem., 14 (1966) 662. 21 S. Love and L.J Bratzler, J. Food Sci., 31 (1966) 218. 22 H.A. Hamid and R.L. Saffle, J. Food Sci., 30 (1965) 697. 23 R.W. Porter, L.J. Bratzler and A.M. Pearson, J. Food Sci, 30 (1965) 615. 24 D.E. Hruza, M. Van Praag and H. Heinsonn, J. Agric. Food Chem., 22 (1974) 123. 25 J.A. Maga, Crit. Rev. Food Sci. Nutr., 19 (1982) 1. 26 J.A. Maga, Progress on Flavor Research, J. Adda, Ed., Elsevier, Amsterdam, (1984) 409. 27 J.A. Maga and Z. Chen, Flavor Frag. J., 1 (1985) 37. 28 S. Jordan, J. Food Sci. Technol., 15 (1968) 335. 29 W. Baltes, R. Wittkowski, J. Sochtig, H. Block and L. Toth, The Quality of Foods and Beverages, Vol.2: Chemistry and Technology, G. Charalambous, Ed., Academic Press, New York, (1989) 1. 30 H. Daun, Lebensm. Wiss. Technol., 5 (1972) 102. 31 S. Simon, A.A. Rypinski and I.W. Tauber, Food Technol. 20 (1966) 1494. 32 V.M. Gorbatov, N.N. Krylova, W.P. Volovinskava, Y.N. Lyaskovskaya, K.I. Bazatova, R.I. Khalamova and G.Y. Yakouleva, Food Technol., 25 (1971) 71.
1025
Pyrazine composition as influenced by the smoking conditions of hickory sawdust Z. Chen and J.A. Maga Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
Abstract The role of smoke generation temperature (250 versus 350'C), air supply (presence or absence) and sawdust moisture content (12, 20, 30%) on resulting pyrazine composition was investigated. The major pyrazines identified with all variables were pyrazine, 2-methoxy-3-methylpyrazine, 2-ethoxy-3ethylpyrazine, 2-propyl-3,6-dimethylpyrazine, 2-butyl-3,5-dimethylpyrazine, 2-acetyl-3-methylpyrazine, and 2-acetyl-3,6-dimethylpyrazine. The presence or absence of air had little if any influence on resulting pyrazine composition. In contrast, the initial moisture content of the sawdust did influence final pyrazine ratios. As moisture content increased, the relative amount of 2-butyl-3,5-dimethylpyrazine increased primarily as the result of decreased amounts of 2-methoxy-3-methylpyrazine. As would be expected, the temperature of smoke generation had a dramatic influence on pyrazine composition, with higher amounts of 2-ethoxy-3-ethylpyrazine and 2propyl-3,6-dimethylpyrazine present at the lower temperature, and higher levels of 2-butyl-3,5-dimethylpyrazine and 2-acetyl-3-methylpyrazine present at the higher smoking temperature. Thus it is apparent that the level and intensity of smoke aroma associated with the pyrazine fraction can be altered as influenced by smoke generation conditions.
1.
INTRODUCTION
The smoke processing of food is an age old tradition that is still quite popular today, primarily due to the unique aroma that can result from the process. As a result, many investigators have attempted to characterize the volatile composition of wood smoke, and to date, over 400 compounds have been identified. Phenols have been thought to be the major contributors to wood smoke aroma [1-13], but other classes of compounds have also been implicated [14-24]. Among these are pyrazines which are thermally produced and have been characterized as possessing a smoky aroma [25], although few pyrazines have been actually identified in wood smoke [15,26]. Reports have also appeared in the literature demonstrating the fact that smoke generation variables such as temperature [23, 27-31], air supply [28], and wood moisture content [32] can also significantly influence the volatile composition of wood smoke. Therefore, the objective of this study was to specifically investigate the formation of pyrazines from hickory wood sawdust as influenced by wood moisture, air and smoke generation temperature.
1026
2.
MATERIALS AND METHODS
2.1. Sawdust source A commercial sample of hickory wood sawdust used for smoking foods was obtained and passed through a series of sieves to minimize particle size distribution. The 60-80 mesh fraction was used in this study. 2.2. Smoke generation A small all glass laboratory smoke generator consisting of a 3-holed 500 ml round bottom flask and a water cooled condenser was constructed. One port was fitted with a thermometer that was positioned in the center of the sawdust; the condenser was fitted to another; and the third permitted or prohibited the introduction of air. In the studies with air, compressed air was metered in the chamber at a rate of 20 cc per minute. When air was not desired, the air port was stoppered. The flask was placed in a rheostatcontrolled heating mantle. A 150 g charge of sawdust was placed in the flask and the wood temperature raised to 250 or 350'C in the presence or absence of air. The resulting smoke was condensed in 100 ml of water. The resulting liquid smoke was permitted to rest at room temperature to permit insoluble tars to settle. Smoke was generated from three separate batches of wood with the resulting liquid smokes being combined for subsequent analysis. 2.3. Moisture content The initial moisture content of the sawdust was determined to be 12%, and based on this, tap water was added to representative samples of sawdust to have final moisture contents of 12, 20 or 30%. The sawdust plus appropriate water addition were mixed for one hour in a stoppered flask and permitted to equilibrate for 4 hours at room temperature before smoke generation. 2.4
Pyrazine extraction and analysis 50 ml of each liquid smoke were transferred to a separatory funnel and 100 mg of internal standard (trimethylpyrazine) added. The use of the internal standard permitted the relative quantitation of pyrazines based on gas chromatographic peak area data. The system was then extracted three times with 30 ml portions of ether. The ether extracts were combined and extracted three times with 30 ml portions of pH 1.0 water. The aqueous extracts were combined, adjusted to pH 8.5, and extracted three times with 30 ml portions of dichloromethane. The dichloromethane extracts were combined and concentrated over anhydrous calcium sulfate. A Perkin-Elmer Model Sigma 2B gas chromatograph equipped with a 1.9 M stainless steel column packed with 10% Carbowax 20M on 200-120 mesh Gas-Chrom Q was utilized. Initial column temperature was 60'C for 5 minutes, followed by a 2Vminute rise to 150" and a lOVminute rise to 275*C. Injector and flame ionization detector temperatures were 275" and 320"C, respectively. The unit was coupled to a Micromass Model 16F mass spectrometer operating at an ion beam setting of 70^Y with an accelerating voltage of 4KV. This unit in turn was coupled to a V.G. Datasystem Model 2000 storage system where spectra were evaluated for most probable match against standard published spectra data.
1027
3.
RESULTS AND DISCUSSION
Commercial food smoking is normally done in the presence of air without adjusting the moisture content of the sawdust. However, one variable that can be controlled in a commercial operation is the actual smoke generation temperature. Data typifying these conditions are summarized in Table 1. Table 1 Role of smoke generation temperature on resulting pvrazine composition Smoking temp. (^C) (12% moisture) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl *:
250 4.96* 24.55 33.18 14.97 3.17 16.93 2.24
350 6.87 28.56 17.70 4.00 12.19 25.70 4.98
Relative percent
From the above, it can be seen that increasing the smoke generation temperature from 250* to 350*C clearly modified the proportion of resulting pyrazines. The major differences were the drops in the relative amounts of 2-ethoxy-3-ethylpyrazine and 2-propyl-3,6-dimethylpyrazine along with increases in the amounts of acetylpyrazine derivatives. These data would indicate that pyrazines have optimum thermal ranges for their formation or one could also postulate that thermal degradation and or rearrangements could have occurred thereby influencing the relative amounts of pyrazines present. Relative to the presence of air during smoke generation, it can be seen from Table 2, that significant changes in pyrazine composition did not occur, and thus at least under the conditions evaluate in this study, air was not a significant factor. One could postulate that the presence of air could result in an increase in oxidative reactions, but in this study with the types of pyrazines identified , air was not an influential factor. Table 2 Role of air during smoke generation on resulting pvrazine composition Conditions (350^C, 12% moisture) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl *:
Relative percent
Air 6.87* 28.56 17.70 4.00 12.19 25.70 4.98
No air 8.06 24.07 21.07 6.23 7.74 28.85 3.98
1028 The last variable evaluated was the moisture content of the sawdust just prior to smoke generation, which could be an important factor since compound formation rates can be influenced by moisture content. Table 3 Role of sawdust moisture content (%) on resulting pvrazine composition Conditions (350'C, Air) Pvrazine Pyrazine 2-Methoxy-3-methyl 2-Ethoxy-3-ethyl 2-Propyl-3,6-dimethyl 2-Butyl-3,5-dimethyl 2-Acetyl-3-methyl 2-Acetyl-3,5-dimethyl
12 6.87* 28.56 17.70 4.00 12.19 25.70 4.98
20 5.35 26.53 17.14 6.75 15.74 22.93 5.56
30 6.44 22.72 17.09 7.14 19.70 21.18 5.73
*: Relative percent As can be seen from the above, moisture content did influence pyrazine composition. For example, the relative proportion of 2-butyl-3,5-dimethylpyrazine increased as moisture content increased, while the amount of 2methoxy-3-methylpyrazine decreased. Therefore, these data clearly demonstrate that smoke generation variables such as sawdust moisture content and the actual smoke generation temperature can influence the relative amounts of resulting pyrazines produced. This in turn could impact on the overall aroma properties of the resulting smoke.
4.
REFERENCES
1 M.E. Knowles, J. Gilbert and D.J. McWeeny, J. Sci. Food Agric. 26 (1975) 189. 2 M.R. Kornreich and P. Issenberg, J. Agric. Food Chem., 20 (1972) 1109. 3 A.O. Lustre and P. Issenberg, J. Agric. Food Chem., 18 (1970) 1056. 4 A. Radecki, H. Lamparczyk, J. Grzybowski, J. Halkiewicz, P. Bednarek, J. Bolfrukiewicz and W. Radecki, Brom. Chem. Tokskol., 1 (1976) 327. 5 A. Radecki, P. Bednarek, J. Boltrukiewicz, R. Cacha, W. Rapicki, J. Grzybowski, J. Hackiewicz and H. Lamparczyk, Brom. Chem. Tokskol., 8 (1975) 179. 6 A. Radecki, J. Halkiewicz, H. Lamparczyk, J. Grzybowski, P. Bednarek, J. Boltrukiewicz, R. Cacha and W. Rapicki, Brom. Chem. Tokskol., 8 (1975) 185. 7 A. Radecki, J. Grzybowski, J. Halkiewicz and H. Lamparczyk, Acta Aliment. Pol., 3 (1977) 203. 8 J.B. Luten, J.M. Ritskes and J.M. Weseman, Z. Lebensm. Unters. Forsch., 168 (1979) 289. 9 W. Fiddler, R.C. Doerr, A.E. Wasserman and J.M. Salay, J. Agric. Food Chem., 14 (1966) 659. 10 M. Fujimaki, K. Kim and T. Kurata, Agric. Biol. Chem., 38 (1974) 45. 11 K. Kasahara and K. Nishbori, Bui. Jap. Soc. Sci. Fish., 45 (1979) 1543.
1029 12 W. Baltes and I. Sochtig, A., Z. Lebensm. Unters. Forsch., 169 (1979) 17. 13 C.Z. Olsen, Proc. Eur. Meat Res. Workers, 22 (1976) F7:l. 18 (1970) 14 W. Fiddler, A.E. Wasserman and R.C. Doerr, J. Agric. Food Chem 934. 15 K. Kim, T Kurata and M. Fujimaki, Agric. Biol. Chem., 38 (1974) 53. 16 A. Radecki, J. Grzybowski, J. Halkiewicz H. Lamparczyk, P. Bednarek, J. Boltrukiewicz and W. Rapicki, Brom. Chem Tolksyk., 9 (1976) 461. 17 A. Radecki and J. Grzybowski, Brom Chem. Tolksyk., 14 (1981) 129. 18 H. Ishiwata, H. Watanabe, M. Watanabe, T. Hayashi, Y Hara, S Kato and A. Tanimura, Bull. Nat. Inst. Hyg. Sci., 94 (1976) 112. 19 J.E. Hoff and A J. Kapsalopoulou, J. Gas Chromatog., 1 (1964) 296. 20 R.C. Doetur, A.E. Wasserman and W. Fiddler, J. Agric Food Chem., 14 (1966) 662. 21 S. Love and L.J Bratzler, J. Food Sci., 31 (1966) 218. 22 H.A. Hamid and R.L. Saffle, J. Food Sci., 30 (1965) 697. 23 R.W. Porter, L.J. Bratzler and A.M. Pearson, J. Food Sci, 30 (1965) 615. 24 D.E. Hruza, M. Van Praag and H. Heinsonn, J. Agric. Food Chem., 22 (1974) 123. 25 J.A. Maga, Crit. Rev. Food Sci. Nutr., 19 (1982) 1. 26 J.A. Maga, Progress on Flavor Research, J. Adda, Ed., Elsevier, Amsterdam, (1984) 409. 27 J.A. Maga and Z. Chen, Flavor Frag. J., 1 (1985) 37. 28 S. Jordan, J. Food Sci. Technol., 15 (1968) 335. 29 W. Baltes, R. Wittkowski, J. Sochtig, H. Block and L. Toth, The Quality of Foods and Beverages, Vol.2: Chemistry and Technology, G. Charalambous, Ed., Academic Press, New York, (1989) 1. 30 H. Daun, Lebensm. Wiss. Technol., 5 (1972) 102. 31 S. Simon, A.A. Rypinski and I.W. Tauber, Food Technol. 20 (1966) 1494. 32 V.M. Gorbatov, N.N. Krylova, W.P. Volovinskava, Y.N. Lyaskovskaya, K.I. Bazatova, R.I. Khalamova and G.Y. Yakouleva, Food Technol., 25 (1971) 71.