13.05.96, Josef Kerler: (Prof. Dr. W. Grosch):
"Evaluation of warmed-over flavour (WOF) in cooked chicken and beef"
11.07.96, Michael Rychlik: (Prof. Dr. W. Grosch):
"Aroma compounds of toasted wheat bread in relationship to recipe and manufacturing process"
Summaries
"Evaluation of warmed-over flavour (WOF) in cooked chicken and beef"
by Josef Kerler
The aroma of cooked chicken can be characterized as meaty/chicken-like, fatty, sweet/caramel-like, and sulfury/cabbage-like. When cooked chicken is stored in a refrigerator for two days and subsequent warmed up, these descriptors are becoming weaker and an off-flavour is perceivable. This off-flavour, which can be characterized as cardboard and green-metallic, is described in the literature as warmed-over flavour (WOF).
To evaluate the character impact compounds of both freshly cooked chicken (sample I) and stored chicken showing WOF (sample II), two screening methods were used: aroma extract dilution analysis (AEDA) and static headspace gc/olfactometry (GC/O-H). Each method was carried out in parallel with both samples I and II. Based on high flavour dilution (FD) factors, the key aroma compounds of the in total 50 detectable odourants of freshly cooked chicken were found to be: (E,E)- and (E,Z)-2,4-decadienal, 4-hydroxy-2,5-dimethyl-3(2H)furanone (furaneol), butyric acid, 3-hydroxy-4,5-dimethyl-2(5H)furanone (sotolon), 2-furfurylthiol, 2-acetyl-2-thiazoline, acetic acid, hexanal, 1-octene-3-one, methional, (E)-2-nonenal, 2/3-methylbutyric acid, (E,E)-2,4-nonadienal, methanethiol, dimethyl trisulfide, acetaldehyde and methylpropanal.
The formation of WOF was characterized by an increase of hexanal, 1-octene-3-one, trans-4,5-epoxy-(E)-2-decenal, and acetaldehyde as well as by a decrease of (E,E)- and (E,Z)-2,4-decadienal, 4-hydroxy-2,5-dimethyl-3(2H)furanone, 3-hydroxy-4,5-dimethyl-2(5H)furanone, 2-furfurylthiol, and dimethyl trisulfide.
To evaluate which compounds contribute to WOF, the concentrations of 22 aroma compounds were determined in samples I and II by means of stable isotope dilution analysis. The evaluation of the (off-)flavour was completed by calculating the aroma values (ratio of concentration to odour threshold) as well as by aroma reconstitution's.
Based on high aroma values, the flavour of freshly cooked chicken is characterized by methanethiol, (E,E)- and (E,Z)-2,4-decadienal, (E,E)-2,4-nonadienal, 2-furfurylthiol, (E)-2-nonenal, acetaldehyde, dimethyl trisulfide, 4-hydroxy-2,5-dimethyl-3(2H)furanone, methional, 2-acetyl-2-thiazoline and 3-hydroxy-4,5-dimethyl-2(5H)furanone. The contribution of these compounds to the aroma of cooked chicken was confirmed by organoleptical tests. A seven membered panel scored similar intensities for the descriptors of both the reconstituted chicken aroma and the aroma of cooked chicken.
WOF of stored and reheated chicken was due to an increase of the lipidoxidation products hexanal, 1-octene-3-one, and trans-4,5-epoxy-(E)-2-decenal as well as of methional and acetaldehyde. In addition, the off-flavour was reinforced by the decrease of desired aroma compounds, such as (E,E)-2,4-decadienal, 2-furfurylthiol, 4-hydroxy-2,5-dimethyl-3(2H)furanone, 3-hydroxy-4,5-dimethyl-2(5H)furanone, dimethyltrisulfide, and (E,E)-2,4-nonadienal. A reconstituted aroma which was based on the quantitative data of the key odourants could simulate WOF as compared to reheated chicken.
WOF in pan-fried beef patties was also described as cardboard and metallic. WOF in beef patties was evaluated by determining the concentrations of 11 aroma compounds in samples of both freshly fried and fried, stored and reheated patties. These compounds were previously selected using AEDA and GC/O-H. The quantitative data were established by comparing organoleptically the aroma profiles of the reconstitution with that of the beef patties. This study revealed that both a decrease of the desirable odourants 4-hydroxy-2,5-dimethyl-3(2H)furanone, 3-hydroxy-4,5-dimethyl-2(5H)furanone and an increase of hexanal and trans-4,5-epoxy-(E)-2-decenal were responsible for WOF formation in beef. In both chicken and beef, the concentrations of the four above mentioned odourants showed comparable changes during the storage of the meat.
The formation of WOF in pan-fried beef patties could be inhibited by adding propyleneglycol and ethylenediaminetetraacetic acid to the meat before pan-frying. These additives could retard the increase of hexanal and trans-4,5-epoxy-(E)-2-decenal and, thus, the lipidoxidation rate. However, both samples the freshly fried and the stored/reheated beef showed another off-flavour, which was characterized as metallic and cured meat-like.
Furthermore, the aroma's of chicken broth and cooked chicken were compared by evaluating the concentrations of 14 character impact compounds. Higher aroma values for (E,E)- and (E,Z)-2,4-decadienal as well as for 4-hydroxy-2,5-dimethyl-3(2H)furanone were determined in the chicken broth as compared to the chicken meat. This was in good agreement with the stronger fatty and sweet/caramel-like odour of the broth. On the other hand, the lower intensity of the sulfury/cabbage-like as well as the roasty odour note in the broth was due to lower aroma values of methanethiol, 2-furfurylthiol, dimethyl trisulfide, and 2-acetyl-2-thiazoline.
Concerning WOF in chicken and beef, it can be concluded that the aroma quality of stored and reheated meat can only be increased by retarding lipidoxidation. It is therefore recommended (I) to use suitable (natural) antioxidants (e.g. nor-furaneol) in combination with chelators, and (ii) to store the meat in vacuum and/or at low temperatures.
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"Aroma compounds of toasted wheat bread in relationship to recipe and manufacturing process"
by Michael Rychlik
The aroma of toasted wheat bread is similar to that of the wheat bread crust and is described as roasty, malty and buttery. Aroma extract dilution analysis showed 36 neutral/ basic and 15 acidic compounds to be potent odorants, among which 2-acetyl-1-pyrroline, (E,E)-2,4-decadienal, methional, guajacol, (E)-2-nonenal, 3-methylbutanal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 2- and 3-methylbutanoic acid were those with the highest flavor dilution (FD) factors. Besides these, methylpropanal, 2,3-butanedione und dimethyl trisulfide were detected by gaschromatography-olfaktometry of static headspace samples as important flavor compounds.
For calculation of the more reliable aroma activity values (OAV, ratio of concentration to odour threshold) 23 of compounds with high FD-factors were quantified and odour thresholds were determined. 2-Acetyl-1-pyrroline, (E)-2-nonenal, 3-methylbutanoic acid, 4-hydroxy-2,5-dimethyl-3(2H)furanone, methional, δ-decalactone and 2,3-butanedione showed the highest OAV.
As aroma of toasted bread changes with browning of the slices, the concentration of important odorants was followed depending on the browning. To evaluate the colour visually browning standards were used.
It was shown that the concentrations of 2-acetyl-1-pyrroline, methylpropanal und (E,E)-2,4-decadienal increased continuously with stronger browning, whereas the formation of 4-hydroxy-2,5-dimethyl-3(2H)furanone and 2,3-butanedione was strongly enhanced in the medium browning range. Amounts of methional and 3-methylbutanal reached a maximum at medium browning, whereas that of (E)-2-nonenal stayed nearly constant.
Changes in the recipe of a standard wheat bread resulted in different aromas which were also examined. The use of wholemeal flour, different fats, amount of yeast and addition of wheat bran revealed characteristic aroma differences.
Increasing yeast amounts resulted in higher concentrations of 2-acetyl-1-pyrroline and 2-furfurylthiol, which caused a roasty-burnt flavor.
In roasted wholemeal toast fat oxidation products increased and caused a sweet, fatty flavor. High amounts of isomeric methylbutanoic acids led to the sweaty flavor of a wheat bran toast. Mainly responsible for the buttery flavor of a toasted bread, baked with margarine or butter, was δ-decalactone.
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