Thermally Generated Flavors - American Chemical Society

Chapter 40

Flavor Formation during Frying and Subsequent Losses during Storage and Microwave Reheating in Pancakes Downloaded by CALIFORNIA INST OF TECHNOLOGY on April 3, 2017 | http://pubs.acs.org Publication Date: November 30, 1993 | doi: 10.1021/bk-1994-0543.ch040

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H.-C. Li , S. J. Risch , and G. A. Reineccius 1

Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108 Golden Valley Microwave Foods Inc., 6866 Washington Avenue, Minneapolis, MN 55344 2

Based on aromagram data, the key aroma compounds contributing to pancake flavor were found to be the 2,4decadienals (in batter and formed during frying), methionine (Maillard product), 2-acetyl pyrazine (Maillard product) and linalool (in batter). While a relatively large amount of furans and a pyranone were formed during frying, these components are considered to make little contribution to flavor due to their high sensory thresholds. The losses of individual flavor compounds during microwave reheating of fried pancakes were considerable ranging from 10 to 56%. The losses of flavor compounds (blueberry) added to batter are also considerable during frying (086%), frozen storage (10-30% during 7 weeks) and microwave reheating (1-17%). The losses during microwave reheating would likely have been greater if most of the highly volatile flavor components were not already lost by the time the pancakes were reheated. The Maillard reaction is well known for its contribution to the flavor of a variety of foods during cooking or baking. Certain classes of compounds are generally known to be formed via the Maillard reaction. The specific flavor impact compounds vary with different types of food and the reactants available. A detailed review of nonenzymatic browning will not be presented as part of this chapter as it is covered in other chapters of the book. The products investigated in this research were microwave pancakes. While there has been substantial research on flavor development in flour-based food systems during heating (e.g. cake 1, sponge cake 2, bread 3-6, and crackers 7), little information is available on the flavor of fried flour-based foods. The first part of this study focussed on determining the flavor compounds present in uncooked pancake batter and which compounds formed during frying. The fate of volatile compounds contributing to pancake flavor was determined 0097-6156/94/0543-0466$06.00/0 © 1994 American Chemical Society Parliment et al.; Thermally Generated Flavors ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

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as a function of frozen storage and microwave reheating. The final part of this research examined the retention of a blueberry flavor added to the batter before cooking.

Downloaded by CALIFORNIA INST OF TECHNOLOGY on April 3, 2017 | http://pubs.acs.org Publication Date: November 30, 1993 | doi: 10.1021/bk-1994-0543.ch040

Experimental Sample Preparation. Flavor compounds were determined in raw pancake batter (unfiled), fried pancakes, frozen stored pancakes and blueberry flavored (model blueberry flavor) pancakes. The pancake batter was prepared from a commercial mix (flour, vegetable oil, eggs, sugar, buttermilk, salt and leavening) by simply combining the mix with equal weights of water and blending by hand until lump free. The batter was fried on a Teflon coated griddle (no additional fat) at 190C until golden brown in color. A sample of the fried pancakes was analyzed immediately for volatile compounds while the remainder of the pancakes were placed in Z i p Lock bags and frozen (-20C) overnight prior to microwave reheating. The microwave reheated pancakes were also analyzed for volatiles. The blueberry flavored pancakes were prepared by combining 600 g pancake mix, 600 g water and 20 m L blueberry model flavor solution. The blueberry model flavor consisted of ethyl-2-methyl butyrate, ethyl valerate, maltol, γ-decalactone, cis-3-hexenol, linalool, anethole and α-terpineol. This model system was made up in acetone with each compound at a concentration of 0.6 mg/mL. The compounds chosen are typical of what might be found in an artificial blueberry flavor. A 60 g sample of batter was saved for analysis and the remainder was fried at 200C. A portion of these pancakes was analyzed immediately for volatiles while the remainder were placed in Z i p Lock bags and frozen (-20C). The frozen pancakes were analyzed weekly over a seven week period for volatiles and the remaining samples (after seven weeks frozen storage) were reheated in a microwave oven and again analyzed for volatiles. Both flavored and unflavored pancakes were reheated in a home microwave oven (Litton II, 650 watts). The pancakes were reheated individually for 1.5 min to reach serving temperature. Flavor Isolation. Flavor isolation was done by distillation/solvent extraction under vacuum to obtain qualitative and quantitative data on the unflavored pancakes. Losses of added blueberry flavor were quantified using direct solvent extraction. Distillation/Solvent Extraction. For the raw batter, 200 g dry pancake mix was combined with 1300 g distilled water and mixed well. This dilute batter was added to a rotary evaporator and then distilled (47C water bath under 640 mm H g vacuum) until 300 m L of distillate was collected. The distillate was extracted twice with 100 m L methylene chloride in a separatory funnel. The extract was dried with anhydrous magnesium sulfate, filtered and concentrated to a volume of approximately 100 u L under a stream of nitrogen. The fried pancakes were treated similarly, except for quantitative

Parliment et al.; Thermally Generated Flavors ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


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THERMALLY GENERATED FLAVORS

purposes an adjustment had to be made for moisture loss during the frying operation. Thus 400 g pancake batter (1:1 mix:water) was fried as noted earlier and the resultant pancakes were weighed and moisture loss determined. After cooling, the pancakes were blended well with 1100 g (plus the amount of water lost during frying) distilled water in a Waring blender. This mixture was distilled in the rotary evaporator as described for the pancake batter. Quantitative data were obtained by adding known amounts of pure reference standards to the batter or pancakes. Thus recoveries as well as losses during concentration etc. could be accurately determined. A l l analyses were replicated four times and averaged. Direct Solvent Extraction. Pancake batter was analyzed for added blueberry flavor compounds by slowly adding 35 m L acetone (containing ethyl hexanoate as an internal standard) to 15 g of the batter while mixing on a magnetic stirplate. The resultant mixture was then filtered and the filtrate frozen at -70C for 90 min to solidify the fat. The liquid portion was recovered by filtering, dried with anhydrous magnesium sulfate and filtered again. This extract was concentrated to approximately 1 m L under nitrogen and analyzed by gas chromatography. The cooked pancakes were analyzed immediately after frying, frozen storage (over night) and microwave reheating. The water loss was calculated during cooking, storage and microwave reheating. Samples were taken to represent 7.5 g dry pancake mix and water added to reach a total sample weight of 15 g. The amount of water added was dependent on the water lost during heating and storage. The sample was mixed with 35 g acetone solution containing internal standard and prepared as described for the batter. The samples were analyzed by G C and the percent retention relative to the initial batter were calculated. Flavor Analysis. Flavor isolates were analyzed by gas chromatography (GC), mass spectrometry (MS) and odor analysis (aromagram). Gas Chromatography/Mass Spectrometry. Flavor isolates were analyzed (1 uL) by G C / M S using a Hewlett Packard model 5890 G C coupled to a model 5970 Mass Selective Detector. A 30 m χ 0.32 mm i.d. (1 um phase thickness) DB-5 column (5% phenyl substituted methyl silicone, from J & W Scientific, Folsom, C A ) was used. The G C temperature program was started at 40C (0.5 min post injection hold) and then programmed at 3C/min to a final temperature of 170C (final time 10 min). The compounds were tentatively identified by comparison to either our in-house or National Bureau of Standards libraries. Identity was confirmed by co-chromatography with reference compounds. Aromagram Analysis. Following identification of the volatile compounds in the pancakes, the extracts were used to produce aromagrams. The G C effluent was sniffed directly from the end of the capillary column (passed


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Table I. Compounds Identified In Pancake Batter and/or Fried Pancakes Compound a

l,2-Propanediol 1-Pentanol Hexanal Furfural Furfuryl Alcohol Hexanol 2H-Pyran-2-one ' Methional 2-Acetyl Pyrazine ' 2-Acetyl Furan t-2-Heptenal 5-Methyl Furfural Benzaldehyde Heptanol l-Octen-3-ol 1,3,7-Octatriene t-2-Octenal 2-Octen-l-ol 2,3-Pentanediol 6-Me-5-Methylene Heptanone Linalool 2-Undecene 2-Undecenal 2,4-Decadienal (Isomer) 2,4-Decadienal (Isomer)

Fried

X X X

Sweet Faint stale Grassy, green Bready Candy Faint sweet c Potato Popcorn Coffee Oily

X X X X X X X

X X X X X X X X X X X X X X X X X X X

X X X X X X

X X X X X X

Cucumber Floral

5


5

X

a b

b

a b

b

X

5

a

3

a

a

Sensory Properties

Batter

Cherry Mushroom Mushroom, fishy Metallic, sour

Fatty Fatty, tallowy Fatty, tallowy

a

Compound identity was not confirmed by co-chromatography with a pure reference compound. Compounds found only in the fried pancakes. N o odor associated with this peak at concentration found in product.

b

c

through a heated exit port) and the character of each eluting compound was recorded. Successive dilutions were made to determine the compounds having the greatest flavor and aroma impact (8,9). Results and Discussion Fried Pancakes vs. Batter. The volatile compounds identified in pancake batter and fried pancakes as well as their sensory properties are listed i n Table I. Eighteen of the twenty five volatile compounds identified in the fried pancakes



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were originally present in the raw pancake mix. The majority of the volatiles in raw pancake mix are known to be products of lipid oxidation e.g. 1-pentanol, hexanal, hexanol, l-octen-3-ol, t-2-heptenal, heptanol, 1,3,7-octatriene, t-2octenal, 2-undecene, 2-undecenal and the 2,4-decadienals (10-13). While lipid oxidation products may be enhanced by heating, it is obvious that many are present prior to any heating of the product. Compounds such as benzaldehyde and linalool probably were present as natural components of the flour. Frying resulted in the formation of seven compounds which are assumed to be produced via the Maillard reaction. The majority of these are oxygenated heterocyclic compounds associated with sugar degradation under mild heating. These ftorans and pyranones have been found in other flour-based foods (e.g. bread, 10). Methional and 2-acetyl pyrazine likely arose from the Strecker degradation and condensation of Maillard products, respectively. Quantitative changes in some of these volatiles are presented in Table II. It should be noted that the quantitative data on fried pancakes represents the amounts of these compounds in the batter plus any additional amounts formed during frying less any losses that may have occurred via volatilization.

Table II. Concentration of Flavor Compounds in Batter and Fried Pancakes Compound

Batter

Fried

Change (%)

•ppb1- Pentanol Hexanal Furfural Furfuryl Alcohol Hexanol 2-Acetyl Furan t-2-Heptenal 5-Methyl Furfural Heptanol l-Octen-3-ol Linalool 2,4-Decadienal (Total)

454 689 0 0 32 0 61 0 6 64 94 12,249

109 310 5,844 5,824 16 495 27 514 4 16 59 11,147

76 55

49 56 28 75 27 9


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For compounds such as 1-pentanol and l-octen-3-ol, approximately 75% of the amount present in the batter was lost during frying. The 2,4-decadienals changed little in concentration during frying since they are formed during heating which would offset losses due to volatilization. The significance of the Maillard reaction is obvious in the case of the furans. Furfural and furfuryl alcohol went from undetected in the batter to be major volatiles in the fried pancakes. Frying and Microwaving Pancakes. The data presented in Table III give an overall comparison of flavor loss in pancakes due to frying and their subsequent reheating from the frozen state in a microwave oven. More compounds are included in this Table than in Table I since these data are based on normalized G C peak areas rather than absolute quantities (i.e. pure standards were not required to obtain these data). Losses for compounds which were not present in the raw batter but formed during frying are based on the amount in the fried pancakes. The main observation that can be made from these data is that there is significant loss of flavor compounds not only during frying but also during the brief microwave reheating. The aroma profile that is obtained i n fried pancakes represents the true character of pancakes - the combination of flavor losses and formation during frying yields an aroma that is pancake. The changes induced by microwave reheating may result in an imbalanced aroma profile and less than ideal product. Flavor losses from only microwaving ranged from 10 to 56%. Aromagram Results. Aromagrams were generated to determine which volatile compounds had the most significant impact on the aroma/flavor of pancakes. A t the highest aroma extract dilution, five compounds could still be detected by effluent sniffing. These were two isomers of 2,4-decadienal, methional, 2-acetyl pyrazine and linalool. As noted earlier, the decadienals are from the thermal degradation of fat while methional (a Strecker aldehyde) and 2-acetyl pyrazine are from the Maillard reaction. The source of the linalool is not known with certainty but likely comes from the flour. Based on aromagram theory, these data indicate that the compounds most important for the flavor of pancakes are a combination of those from thermal fat degradation and the Maillard reaction. The group of compounds which were evident in the aromagram in the next to final dilution were phenyl ethyl alcohol (based on its retention time and odor character), 2-undecenal, t-2-octenal and two oily/fatty compounds which were not identified. The phenyl ethyl alcohol is likely formed from another Strecker aldehyde, phenyl acetaldehyde, and the other compounds are from fat degradation, reinforcing the two significant contributors to the flavor of pancakes. Blueberry Flavored Pancakes. Blueberry is the most common flavor added to pancakes. This flavor must be added prior to frying of the batter, and thus must withstand the frying and microwave reheating processes. The last section of this research investigated the losses of model blueberry flavor compounds added to


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Table III. Changes in Concentration of Flavor Compounds Due to Frying and Reheating Compound

Batter

1,2-Propanediol 1-Pentanol Hexanal Furfural Furfuryl Alcohol Hexanol 2H-Pyran-2-one 2-Acetyl Furan t-2-Heptenal 5-Methyl Furfural Benzaldehyde Heptanol l-Octen-3-ol 1,3,7-Octatriene t-2-Octenal 2-Octen-l-ol 2,3-Pentanediol 6-Me-5-Methylene Heptanone Linalool 2-Undecene 2-Undecenal 2,4-Decadienal

100 100 100 ND ND 100 ND ND 100 ND 100 100 100 100 100 100 100 100 100 100 100 100

a

b

b

Cooked % change64 76 55 100 100 49 100 100 56 100 19 28 75 28 48 28 30 26 37 13 43 9

Microwaved

a

NQ 91 80 70 49 89 NQ 68 84 80 NQ 72 85 NQ 78 84 NQ NQ 49 NQ NQ 47

N Q - Not quantified in microwaved product. N D - Not detected in this product.



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pancakes in order to gain some insight into the loss of flavor compounds characteristic of blueberry. Since it is unlikely that the flavor compounds used in blueberry flavoring would be present in significant quantities in either the batter or produced during frying, it was felt that we could evaluate flavor losses due to volatilization during both frying and microwave reheating. The losses of eight different compounds typically used in artificial blueberry flavor are presented in Table I v . The data show that there are substantial losses of these compounds during frying, storage and reheating of pancakes. It is interesting to note that for ethyl-2-methyl butyrate and ethyl valerate, 69% and 86% respectively, were lost during the original frying step. Of the small amount left in the pancakes, there were additional losses during frozen storage and microwaving, resulting in essentially complete loss of the compounds in the microwaved pancakes. Very little α-terpineol, maltol and anethole were lost during initial frying while ca. 25% was lost during extended frozen storage. This is expected considering that these types of products have minimal packaging. There were additional losses of these compounds during microwave reheating but these losses were minor.

Table Iv. Loss of Added Blueberry Flavor compounds Frozen Compound

Et-2-Me-Butyrate cis-3-Hexenol Et Valerate Linalool a-Terpineol Maltol Anethole γ-Decalactone

Fried

1-Week

69 51 86 21 2 0 8 11

% loss*90 65 93 26 3 10 16 14

7-Weeks Microwaved

97 74 96 49 28 30 27 35

98 91 99 65 32 32 38 33

* Average values of four replicates.

The magnitude of losses during microwave reheating are reasonable considering previous research (14-16). Compounds such as α-terpineol, maltol, anethol and γ-decalactone are fat soluble and of low vapor pressure. There would not be significant losses of these compounds during microwave reheating. We would have expected greater losses of the very volatile compounds (ethyl butyrate, cis-3-hexenol and ethyl valerate) however, most of these volatiles were lost prior to microwaving and thus, their loss had already occurred.


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Conclusions The key aroma compounds contributing to pancakeflavorwere found to be both indigenous to the batter and formed during frying. The batter contributed fatty/fried notes (2,4-decadienals and other unsaturated aldehydes) and a floral note (linalool). Quantitatively, the major compounds formed during frying were furans and a pyranone. However, based on the aromagram data, these compounds made little or no contribution to pancake flavor. The most important flavor compounds formed during frying were Strecker aldehydes (methional and indirectly, phenyl acetaldehyde) and 2-acetyl pyrazine. While frying likely resulted in the formation of additional unsaturated aldehydes, we could not distinguish their formation from that which was initially present in the batter (loss during frying vs formation from heat). Flavor losses during microwave reheating of fried pancakes were considerable and ranged from 10 to 56%. One would expect these losses to influence sensory perception of the product. The losses offlavorcompounds (blueberry) added to batter are also considerable during frying (0-86%), frozen storage (10-30% during 7 weeks) and microwave reheating (1-17%). The losses during microwave reheating would likely have been greater if most of the highly volatileflavorcomponents were not already lost by the time the pancakes were reheated. Literature Cited 1. Whorton, C.B.,; Reineccius, G.A. In Thermal Generation of Aromas; Parliment, T.H.; McGorrin, R.J.; Ho, C.T., Eds. ACS Symposium Series 409; Amer. Chem. Soc.:Washington D.C., 1989; pp 526-532. 2. Yoko, T. Agric.Biol.Chem. 1977, 41, 2361-2368. 3. Schieberle, P. In Thermal Generation of Aromas; Parliment, T.H.; McGorrin, R.J.; Ho, C.T., Eds. ACS Symposium Series 409; Amer. Chem. Soc.:Washington D.C., 1989; pp 268-275. 4. Schieberle, P.; Grosch, W. In Thermal Generation ofAromas; Parliment, T.H.; McGorrin, R.J.; Ho, C.T., Eds. ACS Symposium Series 409; Amer. Chem. Soc.:Washington D.C., 1989; pp 259-267. 5. Luning, P.A.; Roozen, J.P.; Moest, R.A.; Posthumus, M.A. Food Chem. 1991, 41, 81-91. 6. Hunter, I.R.; Walden, M.K.; Scherer, J.H.; Lundin, R.E. Cereal Chem. 1969, 46, 189-195. 7. Yong, L.F.M.; Acree, T.E.; Lavin, E.H.;Butts, R.M. In Thermal Generation of Aromas; Parliment, T.H.; McGorrin, R.J.; Ho, C.T., Eds. ACS Symposium Series 409; Amer. Chem. Soc.:Washington D.C., 1989; pp 276-284. 8. Acree, T.E.; Barnard, J.; Cunningham, D.G. In Analysis of Volatiles; Schreier, P., Ed. W. de Gruyter: Berlin, 1984, pp 251-268. 9. Schieberle, P.; Grosch, W. Z. Lebensm. Unters. Forsch. 1987, 185, 111-113. 10. Schieberle, P.; Grosch, W. In Topics in Flavour Research; Berger, R.G., Nitz, S.; Schreier, P.; Eds.; H. Eichhorn: Marzling-Hangenham, 1985, pp 161-171.



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Flavor Formation during Frying and Losses during Storage 4

11. Nawar, W.W. In Flavor Chemistry of Fats and Oils; Min, D.B.; Smouse, T.H.; Eds. Amer. Oil Chem. Soc.:Champaign, IL, 1985, pp 39-60. 12. Grosch, W. In Food Flavours, Part A: Introduction. Morton, I.D.; MacLeod, A.J., Eds. Elsevier: New York, NY, 1982, pp 325-337. 13. Flavors in Lipid Foods; Min, D.B.; Smouse, T., Eds.; American Oil Chemists Society, Champaign, IL, 1989. 14. Heinze, R.F. Cereal Foods World. 1989, 34, 334-339. 15. Steinke, J.A.; Frick, C.M.; Strassburger, K.J.; Gallagher, J.A. Cereal Foods World. 1989, 34, 330-333. 16. Steinke, J.A.; Frick, C.M.; Gallagher, J.A.; Strassburger, K.J. In Thermal Generation of Aromas; Parliment, T.H.; McGorrin, R.J.; Ho, C.T., Eds. ACS Symposium Series 409; Amer. Chem. Soc.:Washington D.C., 1989; pp 519-525. RECEIVED February

9, 1993


Thermally Generated Flavors - American Chemical Society

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