Aroma Defects

Several authors have reported a wide range of concentrations for this compound in wines (Dittrich and Staudenmayer 1970 Wenzel et al. 1980 Lavigne 1996). In wines with reduction aroma defects, it is present in concentrations between 0.8 and over 80 p.g/L. 

Riesen, R. In Undesirable fermentation aromas Henick-Kling, T., Ed. NYSAES Wine Aroma Defects Workshop Geneva, NY 1992 pp. 1-43. 

Omission of furaneol (no. 1 in Table 6.41) led to a very significant aroma defect which was perceived by all six members of the panel. The model smelt green and fruity. When (Z)-3-hexenal (no. 2) was missing, the caramel-like/sweetish note of furaneol predominated ]75]. In contrast, a lack of odorants nos. 9-12 was only detected by one or two panellists, respectively, indicating a lower aroma impact of these substances. 

Wines with a 2-aminoacetophenone content close to the perception threshold are always described by tasters as prematurely aged . However, some wines with this aroma defect do not contain any 2-aminoacetophenone, so this is not the only molecule responsible for white wines with prematurely aged aromas. 

Henick-Kling, T. 1992. Wine aroma defects. Proceedings of the ASEV/ES Workshop, p. 39. 

Riesen, R. 1992. Undesirable fermentation aromas. Proc. of the ASEV/ES Workshop Wine Aroma Defects. T. Henick-Kling (ed.). Corning, NY American Society ofEnology Viticulture pp. 1-43. 

During soya processing, volatile degradation compounds (hexanal, etc.) with a bean-like aroma defect are formed because of the enzymatic oxidation of unsaturated fatty acids. These defects can be eliminated by the enzymatic oxidation of the resultant aldehydes to carboxylic acids. Since the flavor threshold values of these acids are high, the acids generated do not interfere with the aroma improvement process. 

Heme (Fe +) and hemin (Fe +) proteins are widely distributed in food. Lipid peroxidation in animal tissue is accelerated by hemoglobin, myoglobin and cytochrome C. These reactions are often responsible for rancidity or aroma defects occurring during storage of fish, poultry and cooked meat. In plant food the most important heme(in) proteins are peroxidase and catalase. Cytochrome P450 is a particularly powerful catalyst for lipid peroxidation, although it is not yet clear to what extent the compound affects food shelf life in situ . 

Pentylpyridine contributes to the smell of roasting lamb fat (greasy, suety odor threshold 0.12 pg/kg water) it produces an aroma defect in soybean products (cf. 16.3.1.1). The precursors identified were ammonia from the pyrolysis of asparagine and glutamine and 2,4-decadienal ... 

Some terpenes are readily oxidized during food storage. Examples of aroma defects resulting from oxidation are provided in Table 5.5 and Section 22.1.1.1. 

The odor thresholds of skatole have been determined in sunflower oil (15.6pg/kg) and on starch (0.23 pg/kg). This compound plays a role in the aroma of Emmental cheese (cf. 10.3.5) and causes an aroma defect in white pepper (cf. 22.1.1.2.1). It can probably also be formed nonenzymatically from tryptophan by the... 

Strecker degradation, oxidation to indolylacetic acid and decarboxylation. The oxidative cleavage of skatole yields o-aminoacetophenone (cf. Formula 5.36), which has an animal odor and is the key aroma substance of tortillas and taco shells made of com treated with lime (Masa corn). In the case of milk dry products, o-aminoacetophenone causes an aroma defect (cf. 10.3.2). Its odor threshold of 0.2pg/kg (water) is very low. On the other hand, p-amino-acetophenone has an extremely high odor threshold of 100 mg/kg (water). 

During the concentration and drying of milk, reactions that are similar to those described for heat-treated milk (cf. 10.1.3.5 and 10.3.1) occur, but to a greater extent. Thwefore, like the aroma of UHT milk (cf. 10.3.1 and Table 10.38), the aroma of condensed milk is also caused by Maillard reaction products. The stale flavor that appears when condensed milk is stored for longer periods is due especially to the presence of the degradation product of tryptophan, o-aminoacetophenone, which is aroma active in concentrations >lpg/kg. A mbbery aroma defect results from higher concentrations of benzothiazole. 

The content of free but)tric and caprylic acid as well as (Z)-3-hexenal rises when cream is whipped (Table 10.39). Pasteurization results in the formation of 2-acetyl-2-thiazoline in whipped cream and the content of (E,Z)-2,6-nonadienal is greatly increased. A model corresponding to Table 10.39 (without No. 12, 14, 17 and 20) approaches the aroma of whipped pasteurized cream and reproduces especially the "creamy" note. Maillard reaction products are also characteristic of the aroma of milk powder. The development of aroma defects during the storage of whole milk powder is due to products of lipid peroxidation, e. g., (Z)- and (E)-2-nonenal. 

Rancid, soapy aroma defects, which occur in butter samples with very low concentrations of free fatty acids, can be due to contamination with anionic detergents (sodium dodecyl sulfate, sodium dodecyl benzosulfonate). Detergents of this type are used to disinfect the udder and the milking machine. 

As already indicated, aroma defects can arise in milk and milk products either by absorption of aroma substances from the surroundings or by formation of aroma substances via thermal and enzymatic reactions. 

Exogenous aroma substances from the feed or cowshed air enter the milk primarily via the respiratory or digestive tract of the cow. Direct absorption apparently plays only a minor role. Metabolic disorders of the cow can cause aroma defects, e. g., the acetone content of milk is increased in ketosis. 

A series of aroma defects are caused by enzymatic reactions. These include ... 

The typical aroma substances of egg white and egg yolk are still unknown. The fishy aroma defect that can occur in eggs is caused by trimethy-lamine TMA, which has an odor threshold that depends on the pH (25 pg/kg, pH 7.9) because only the undissociated form is odor active. TMA is formed by the microbial degradation of choline, e. g., on feeding fish meal or soy meal. Normally, TMA does not interfere because it is enzymatically oxidized to odorless TMA oxide. However, in feed, e. g., soy meal, substances exist which could inhibit this reaction. 

The shelf life of dried egg white is essentially unlimited. Whole egg powder devoid of sugar has a shelf hfe of approx. 1 year at room temperature, while sugarless yolk lasts 8 months at 20-24 °C and more than a year in cold storage. The shelf-life of powders containing egg yolk is limited by aroma defects which develop gradually from oxidation of yolk fat. The compositions of dried egg products are given in Table 11.14. 

If cooked meat is stored for a short time, e. g., 48 h at ca. 4 °C, an aroma defect develops, which becomes unpleasantly noticeable especially after heating and is characterized by the terms metallic, green, musty and pungent. This aroma defect, also called warmed over flavor (WOF), is caused by lipid peroxidation (cf. 12.6.2.1). The indicator of this aroma defect is hexanal, which increases as shown in Table 12.27. 

Other changes which contribute to the aroma defect are the increase in metaUic/musty smelling epoxydecenal, which, like hexanal, is formed in the peroxidiation of linoleic acid (cf. 3.7.2.1.9), and the decrease in HD3F. The latter is probably due to the reaction of its enolic OH group with peroxy radicals. 

It is well known that on cold storage, aroma defects can appear faster in a high-fat fish than in a low-fat fish. This is clearly shown in an experiment in which salmon and cod were stored for 14 weeks at different temperatures and then boiled. While the aroma of the fish stored at —60 °C was perfect, the relatively low temperature of — 13°C had a negative effect on the aroma. The salmon had an intensive fatty/train oil odor and, in comparison, the low-fat cod had only a more intensively malty odor. The aroma defect of the fatty fish, which becomes very unpleasantly noticeable, is based on the peroxidation of polyunsaturated co-3 fatty acids, which results in a 13 fold increase in (Z)-3-hexenal (compare LII with LI in Table 13.10), an 8 fold increase in (Z)-4-heptenaI and a 9 fold increase in (Z,Z)-3,6-nonadienaI. In low-fat cod, these aldehydes increased at most by a factor of 3. 

Peroxide Value, The method for determination of peroxide concentration is based on the reduction of the hydroperoxide group with HI or Fe +. The result of the iodometric titration is expressed as the peroxide value. The Fe " method is more suitable for detemuning a low hydroperoxide concentration since the amount of the resultant Fe +, in the form of the ferrithiocyanate (rhodanide) complex, is determined photometrically with high sensitivity (Fe-test in Table 14.27). The peroxide concentration reveals the extent of oxidative deterioration of the fat, nevertheless, no relationship exists between the peroxide value and aroma defects, e. g. rancidity (already existing or anticipated). This is because hydroperoxide degradation into odorants is influenced by so many factors (cf. 3.7.2.1.9) which mdkc its retention by fat or oil or its further conversion into volatiles unpredictable. 

Carbonyl Compounds. The analysis of the compounds responsible for the rancid aroma defect of a fat or oil is of great value. Volatile carbonyls (cf. 3.7.2.1.9) are among such compounds. 

The gas chromatographic determination of individual carbonyl compounds appears to be a method suitable for conparison with findings of sensory panel tests. Analytical methods for the odorants causing aroma defects is still in the early stages of development because only a few fats or fat-containing foods have been examined in such detail that the aroma substances involved are clearly identified. 

The weU studied warmed-over flavor of cooked meat (cf. 12.6.2.1) is an example. It can be controlled relatively easily because the easy-to-determine hexanal has been identified as the most important off-flavor substance. On the other hand, the easily induced rancid aroma defect of rape-seed oil is primarily caused by the volatile hy-... 

To simplify the analytical procedure, individual aldehydes (e. g., hexanal, 2,4-decadienal), which are formed in larger amounts during lipid peroxidation, have been proposed as indicators. In most of the cases, however, it was not tested whether the indicator increases proportionally to the off-flavor substances which cause the aroma defect. 

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

Small chain fatty acids like propionic acid and butyric acid cause an aroma defect. 

The taste and odor profile of a beer, including possible aroma defects, can be described in detail with the help of 44 terms grouped into 14 general terms, as shown in Fig. 20.3. Apart from a great variety of terms for odor notes, the terms bitter, salty, metallic, and alkaline are used only for taste and the terms sour, sweet, body etc. are applied to both taste as well as odor. 

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