Flavor compounds yeasts

In addition, the influence of baker s yeast on the composition of other crust flavor compounds was followed by an aroma extract dilution analysis. 

Comparison of Crust Flavor Compounds from Yeast and Chemically Leavened Wheat Flour Doughs... 

The flavor compounds of the crust from the chemically leavened model bread were then compared to those recently identified (6) in the crust of a standard wheat bread which was leavened by addition of yeast (Table I). One striking difference was that Acp (No. 16), which showed the highest FD-factor in the yeast-leavened bread showed a very low FD-factor in the chemically leavened bread. This indicated, that the flour contained only minor amounts of the precursor (s) for the formation of Acp. On the other hand, 2(E),4(E)-decadienal, 2(E),4(E)-nonadienal, l-octen-3-one and 2(Z)-nonenal, which are undoubtedly formed by a heat-induced oxidative degradation of the flour lipids, became predominant odorants in the chemically leavened compared to the yeast-leavened bread. 

Table I. Comparison of the Important Neutral/Basic Volatile Crust Flavor Compounds of a Chemically Leavened Wheat Bread (CL—WB)a With Those of a Yeast-leavened Wheat Bread (YL-WB)b ...

The results reveal that baker s yeast is a potent source for precursors of 2-acetyl-l-pyrroline. It appears likely that the flavor compound is formed in the yeast cells from proline and dihydroxyacetone phosphate via 1-pyrroline and pyruvaldehyde. This is corroborated by the results of c-labeling experiments which showed that the acetyl group in the Acp stems from a sugar degradation product and that the pyrroline ring was derived from proline. 

Traditional fermentation using microbial activity is commonly used for the production of nonvolatile flavor compounds such as acidulants, amino acids, and nucleotides. The formation of volatile flavor compounds via microbial fermentation on an industrial scale is still in its infancy. Although more than 100 aroma compounds may be generated microbially, only a few of them are produced on an industrial scale. The reason is probably due to the transformation efficiency, cost of the processes used, and our ignorance to their biosynthetic pathways. Nevertheless, the exploitation of microbial production of food flavors has proved to be successful in some cases. For example, the production of y-decalactone by microbial biosynthetic pathways lead to a price decrease from 20,000/kg to l,200/kg U.S. Generally, the production of lactone could be performed from a precursor of hydroxy fatty acids, followed by p-oxidation from yeast bioconversion (Benedetti et al., 2001). Most of the hydroxy fatty acids are found in very small amounts in natural sources, and the only inexpensive natural precursor is ricinoleic acid, the major fatty acid of castor oil. Due to the few natural sources of these fatty acid precursors, the most common processes have been developed from fatty acids by microbial biotransformation (Hou, 1995). Another way to obtain hydroxy fatty acid is from the action of LOX. However, there has been only limited research on using LOX to produce lactone (Gill and Valivety, 1997). 

Mold-ripened cheeses are inoculated with mold spores which germinate and, via metabolic transformation, produce additional characteristic flavor compounds. Blue-vein cheeses are good examples. In these cheeses, surface molds, yeasts, and bacteria (micrococci) become dominant as the cheese pH drops due to the lactic flora early in maturation. The main... 

Lactobacillus and Leuconostoc sp. are involved in the conversion of malic acid to lactic acid and CO which improves flavor and mellowness of wines(16). Important wine flavor compounds derived from yeast metabolism during fermentation ares Alcohols... 

D. of the types 1 and 2 are highly active secondary flavor compounds which are formed from aldehydes, hydrogen sulfide, and ammonia (1) or 1-pyrroline (2) when food is heated, i.e., from degradation products of lipids, amino acids and thiamin. D. occur especially in yeast extracts and meat flavor as well as in aromas of peanuts, cocoa, and seafoodsWidely distributed is thialdine (1 R, R R =CH3), CsH.jNSj, Mr 163.30, cryst. rusty and meat-like odor, mp. 46 °C. (C2-C4)-Alkyldimethyl- and dialkylmethyl-D. - exhibit interesting odor notes such as peanut, egg, cocoa, or fried onions, as does compound 2 (CgH NS2, Mr 189.33, mp. 40.5 °C), which occurs in yeast extracts, pork, and seafood aromas. 

Nurgel, C. Erten, H. Canbas, A. Cabaroglu, T. Selli, S. (2003). Fermentative aroma in wines from Vitis vinifera cv. Kalecik karasi in relation with inoculation with selected dry yeasts. Journal International des Sciences de la Vigne et du Vin 37,155-161 Nykanen, L. (1986). Formation and occurrence of flavor compounds in wine and distilled alcoholic beverages. American Journal of Enology and Viticulture 37 (1), 84-96 Oliveira, J.M. Araujo, I.M. Pereira, O.M. Maia, J.S. Amaral, A.J. Maia, M.O. (2004). 

Yeast extracts (YEs) are sources of natural flavor compounds, and their exact composition varies according to the type of yeast and the conditions used for its propagation and the production of the final YE. This chapter is devoted to a review of the volatile sulfur compounds of YEs (many of which play a crucial role in determining the overall flavor) and to a report of some sulfor compounds which have recently been identified as components of selected YEs. 

Some non-Saccharomyces yeasts can spoil wine through synthesis of various volatile odor and flavor compounds. Yet, another concern regarding these yeasts involves nutrient depletion. Like Saccharomyces, non-Saccharomyces yeasts require various nutrients such as nitrogen, vitamins, and minerals which may be depleted before Saccharomyces initiates fermentation. This could potentially adversely affect alcoholic fermentation. 

Wang, C.L., et al. (1996) Changes of fatty acids and fatty acid-derived flavor compounds by expressing the yeast 6-9 desatu-rase gene in tomato. J. Agric. Food Chem. 44, 3399-3402... 

Klingenberg, A. and Hanssen, H.-P. (1988) Enhanced production of volatile flavor compounds from yeasts by adsorber techniques. I. Model investigations. Chem. Biochem. Eng., 2, 222-224. 

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