Sensory pyrazines

Several sensory modalities can be involved in complex interactions involving at least three cues rats learnt better to associate the bitter taste of quinine in water with a context such as a black or white box if a pyrazine was also present (the specific compound used was 2-methoxy-3-isobutyl pyrazine) (Kaye etal, 1989). It is said the odor potentiates learning the connection between taste cue and context. ... 

Pyrazines (4, 6, 10, 11). The pyrazines constitute a very important class among flavor compounds. They have been identified in various food systems, and they are associated with pleasant and desirable food flavor properties. As a rule, the alkyl derivatives produce roasted--nutlike sensory impressions. The acetylpyrazines also have an essential place among flavoring agents. They have a characteristic roasted note, reminiscent of popcorn. 

As the final pH of meat increases above the normal range of 5.6-5.8, there is a decrease in meat flavour.101102 The reaction between norfuraneol and cysteine, which plays a crucial role in meat flavour, is very sensitive to pH.103 At pH 4.5, the major volatile products are mercaptoketones, furan- and thiophenethiols, 2-methyltetra-hydrothiophenone, and 3,5-dimethyl-l,2-dithiolan-4-one, whereas, at pH 6.5, these compounds were detected, if at all, only in traces, except for the thiophenone however, pyrroles, pyrazines, thiazoles, and oxazoles had achieved prominence. The sensory observations are a clear reflection of such differences. Similar effects of pH had been found for the ribose-cysteine and other systems.104... 

Pyrazines. In the thirties, the attention on pyrazines was focused on its industrial role in dyes, photographic emulsions and chemotherapy. Its importance in life processes was indicated in its derivative, vitamin B2 (riboflavin, 6,7-dimethyl-9-(l -D-ribityl isoalloxazine). Later,in the midsixties, it was identified in foods and its contributions to the unique flavor and aroma of raw and processed foods attracted the attention of flavor chemists Pyrazine derivatives contribute to the roasting, toasting, nutty, chocolaty, coffee, earthy, caramel, maple-like, bread-like, and bell pepper notes in foods. The reader is referred to the reviews on Krems and Spoerri (88) on the chemistry of pyrazines, and the review of pyrazines in foods by Maga and Sizer (89, 90) Table XVI summaries sensory description and threshold of selected pyrazines. 

Pyrazine Sensory Description Water Mineral Oil Vegetable Oil... 

Pyrazines, Sensory Description and Odor Threshold (Cont.)... 

For analysis of free compounds, the headspace analysis with a multiphase fiber is even more interesting and less time-consuming. This approach can replace the majority of the quantification of free compounds measured by SPE techniques, considering also the possibility of the sampling automation using a GC-MS system which can be coupled to a statistical treatment of fragments abundance (Kinton et al., 2003 Cozzolino et al., 2006). Moreover, HS-SPME/GC-MS is a very effective and efficient method to analyze specific compounds present in trace levels at about ppt level, because they can be better and selectively enriched in the headspace. This method is employed nowadays to quantify some important and peculiar sensory compounds such as ethyl and vinylphenols, pyrazines, cork off-flavour substances (TCA, etc.) and other contaminants such as geosmine (Riu et al., 2002 Chatonnet et al., 2006) and, as shown below, sulphur volatiles. 

Group 24 represents the world of pyrazines. The sensory profile of the listed compounds ranges from toast to coffee and cocoa notes reminiscent of the wonderful aroma of many culinary pleasures. 

Peak 24 was identified as 2-ethyl-6-methyl pyrazine. This was a typical pyrazine which had been identified in peanuts. Organoleptically this compound represented roasted, nutty, earthy notes. The positive correlation of +0.98129 (C.D.) showed that sensory preference increased with concentration. These plots indicated that a decrease in carbonyls with a subsequent increase in pyrazines were important to good quality peanut flavor. This supported the work of Mason et al (13, and Johnson 2, 6). 

Correlation of instrumental and sensory data showed that a decrease in carbonyls with a subsequent increase in pyrazines is important for good quality peanut flavor. 

The roasting process subjects peanuts to internal temperatures of 130 -150 C during which the typical roast peanut flavor is produced. The most important constituents of peanuts responsible for flavor formation are the amino acids, sugars, protein and lipids. There are close to 300 flavor compounds identified in roasted peanuts. Pyrazines contribute roasted nutty aroma and aldehydes are responsible for harsh green aroma. Recent development in the research include application of an absorption polymer Tenax GC to collect volatiles, quantitation of flavor components and computer aided correlation of instrmental and sensory data. 

Maga JA (1982) Pyrazines in foods an update. CRC Grit Rev Food Sci Nutr 16 1-48 Maga JA (1989) Sensory and stability properties of added methoxypyrazines to model and authentic wines. In Charalambous G (ed) Flavors and off-flavors, proceedings of the 6th international flavour conference, Rethymnon, Crete, Greece, 5-7 Jiily 1989. Elsevier, Amsterdam, pp 61-70... 

Lee et al (1993) have examined the quality of sesame seed oil roasted for 30, 60, 90 and 120 min at 100, 200 and 300°C. Seeds roasted at 200°C for 90 min gave the highest yield of oil as well as overall aroma and taste quality. The oil contained low amounts of a brown-black precipitate and exhibited most favored sensory quality as evidenced by subjective analysis. Similarly, the oil obtained from seeds roasted at 200°C contained the highest number of volatile flavor compounds with relatively high concentrations of fur-furals (sweet candy like) and pyrazines (roasted like) that are known to contribute to the... 

More than 100 different pyrazines have been identified in various food products. The sensory properties of the pyrazines are quite diverse. The alkyl pyrazines (Figure 5.5a) generally possess roasted, nut-like notes while methoxypyrazines (Figure 5.5b) often possess earthy, vegetable notes [47]. The 2-isobutyl-3-methoxy pyrazine has a freshly cut green pepper flavor with a sensory threshold of 0.002 ppb in water. The acetyl pyrazines typically have a popcorn character, and 2-acetonyl pyrazine has a... 

Thiazoles and pyrazines have somewhat similar sensory properties. Pittet and Hniza [54] and Ho and Jim [63] have reported that the alkylthiazoles give green, nutty, roasted, vegetable, or meaty notes. Trimethyl thiazole is reported to have a cocoa, nutty character. 2-isobutyl thiazole is one of the best known thiazoles and has a strong, green odor of tomato leaf This compound is considered to be important to tomato flavor. 2,4-dimethyl-5-vinyl thiazole has a nut-like odor. 2-acetyl thiazole is characterized as having a nutty, cereal, and popcorn flavor [47],... 

In terms of key aroma components, Czerny et al. [59] conducted sensory studies using volatiles identified in previous studies as potential contributors to coffee aroma [60] to determine the odorants truly characterizing freshly brewed Colombian coffee. They found 2-furfurylthiol, 4-vinylguaiacol, several alkyl pyrazines, furanones, acetaldehyde, propanal, methylpropanal, and 2- and 3-methylbutanal had the greatest impact on the coffee flavor. 

As can be seen in Table 9.5, nutrient source had a strong influence on the production of the methoxy pyrazines by a selected mutant of Pseudomonas perolens. The end result is that an organism that initially produced a few ppb of the methoxy alkyl pyrazines was converted into an organism that produced ppm levels of the target compounds. While one may not think that ppm levels of an aroma compound is significant, these pyrazines have sensory thresholds in the pptr levels. 

A fast and efficient method based on the use of SFE and GC MS for the analysis of flavor compounds from roasted peanuts has been recently developed [14]. A group of substances known to be related to roasted flavor were identified and quantified using the full scan mode. Total ion chromatograms of extracts of two peanut samples roasted under different conditions are shown in Figure 1. The GC MS analysis confirmed the presence of pyrazine compounds and other flavor substances, such as methyl pyrrole, that are associated with the roasting conditions and sensory perceptions of a taste panel. 

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