Cracker-like aromas

Maltol and isomaltol (1 and 2 in Figure 1) enhanced the fresh bread character of yeast rolls (6) when added at a level of 0.1 %. Other workers (7.) showed that 2-acetyl-l,4,5,6-tetrahydropyridine (3 in Figure 1) restores a cracker-like aroma to bread when added at a level of 6 mg/kg. In the pure state this chemical displays a cracker-like aroma and an odor threshold of 1.6 jig/kg (8). 

Crackers are generally subdivided into three basic categories saltines or soda crackers (also known as cream crackers in the United Kingdom), sprayed crackers, and savory crackers (Hoseney, R.C. Wade, P. Findley, J.W. 1988 Soft wheat products in press). They are a class of baked product with a unique flavor and texture. Crackers are usually made of wheat flower, water, fat, yeast and salt by a process that combines fermentation, baking and dehydration to yield a thin low moisture product. Saltines are the simplest cracker with a typical "cracker-like aroma. This paper reviews the basic flavor chemistry of saltine crackers and presents preliminary data on the extraction of volatile compounds from these crackers. 

While several reviews on the role of ingredients are available, none of these describe the flavor chemistry of cracker sponge and dough (2, 3, 4, 5). However, some insight into the chemistry of cracker aroma can be obtained from examination of products that have a "cracker-like aroma" such as white bread crust. 

Both fractions obtained from crackers extracted less than one week after baking had strong cracker-like aromas. The Freon 113 fraction had a cracker, roasted grain, cooked rice aroma while the ethyl acetate fractions had a cracker, sweet baked good, burnt butter aroma. A preliminary analysis of the two fractions by gas chromatography-mass spectrometry on a 25 m by. 22 mm methyl silicone column between 700 and 1800 retention indices showed the compounds listed in Table 2. 

The reaction of rhamnose and proline produces many pleasant aromas which are important to the food industry among them are bready, cracker-like and roasted aromas. These aromas are greatly influenced by changes in reaction conditions such as temperature, pH and the relative concentration of reactants (l.,2). The effects of changes in reaction conditions may be additive or synergistic. Research was undertaken to determine the prevalence and importance of synergies (variable interactions) between common reaction condition parameters for the reaction of rhamnose and proline. 

Since in particular the cracker-like crust odor note was lacking in the synthetic mixture, it was concluded that the character impact compound for this odor note occurs in a concentration in the bread too low to be detected by headspace analysis. Later on the basis of its aroma quality and its very low odor threshold of 0.04 ppb (water), Mulders et al. (19) proposed 2-[(methyldithio)methyl] furan (4 in Figure 1) as the compound which should be responsible for the "golden brown" crust aroma of white bread. 

Brettanomyces yeast species and two Lactobacillus bacteria species were responsible for the mousiness in wines. The taint was produced by each class of microorganisms only in the presence of lysine and ethanol. The two 2-acetyltetrahydopyridine (ACTPY) isomers produced a "mousiness" described by Heresztyn as possessing an extremely unpleasant taste and odor the odor was described as bready, cracker-like, and popcom-like. Others have described the aroma as "a most disgusting smell reminiscent of mouse urine or acetamide"(82). 

The flavor is weak, chemical (Chemisis, 1963). It has a cracker-popcorn like aroma character according to Buttery (1999) who gave a threshold in water of 37 ppb, ca 4500 times lower than that of 2-acetylpyrrole (K.50). 

Watanabe and Sato (1972) observed that this product adds a slightly caramel-like character to the flavor of cooked beef, but Peterson et al. (1975), on the contrary, considered that it confered to canned beef stew an unpleasant antiseptic-like aroma, reminiscent of plastic. Buttery (1999) compared several 2-acyl nitrogen-containing heterocycles with a cracker, popcorn-like aroma character 2-acetylpyrrole is the less potent with a threshold of 170ppm in water (the 3,4-dihydro-2//-pyrrolyl derivative has a threshold of 0.1 ppb and the pyridyl derivative, N.22, of 19ppb). 

A -heterocyclic compounds other than pyrazines such as pyrrolines, pyrrrolidines, piperidines and pyrroles are also very important flavor compounds. The formation of pyrrolines and pyrrolidines are reported to be generated from the reaction of proline with glucose (Shigematsu et aL, 1975 Tressl et aL, 1985a). The pyrrolidines possess smoky and roasty aromas while 2-acetyl-1-pyrroline was reported by Tressl et al. (1985b) to have a cracker-like odor. The pyrrole rings from proline and hydroxyproline are present in many of their reaction products. N-acetylpyrrole exhibits a cookie-like and mushroom-like odor (Tressl et ai, 1986). 

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