Source of flavor

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

The Maillard reaction has received much attention since the 1950 s as the source of flavor chemicals in cooked foods. Numerous compounds produced by this reaction have been reported in the last two decades. The major flavor chemicals are nitrogen- and sulfur-containing heterocyclic compounds. For example, nitrogen-containing pyrazines contribute a characteristic roasted or toasted flavor to cooked foods. Sulfur-containing thiophenes and thiazoles give a characteristic cooked meat flavor. A striking property of these compounds is their extremely low odor thresholds. 

The oxidation products of lipids include volatile aldehydes and acids. Therefore, lipids are one of the major sources of flavors in foods. For example, much of the desirable flavors of vegetables such as tomatoes, cucumbers, mushrooms, and peas (Ho and Chen, 1994) fresh fish (Hsieh and Kinsella, 1989), fish oil (Hu and Pan, 2000) and cooked shrimp (Kuo and Pan, 1991 Kuo et al., 1994), as well as many deep-fat fried foods such as French-fried potatoes (Salinas et al., 1994) and fried chicken (Shi and Ho, 1994), are contributed by lipid oxidation. LOX-catalyzed lipid oxidation produces secondary derivatives, e.g., tetradecatrienone, which is a key compound of shrimp (Kuo and Pan, 1991). The major difference between the flavors of chicken broth and beef broth is the abundance of 2,4-decadienal and y-dodeca-lactone in chicken broth (Shi and Ho, 1994). Both compounds are well-known lipid oxidation products. A total of 193 compounds has been reported in the flavor of chicken. Forty-one of them are lipid-derived aldehydes. 

There are many reports of Pseudomonas cultures producing musty, earthy, and potato-like odors ( l-6). The work of Morgan et al. (T) established 2-methoxy-3-isopropyl pyrazine to be partially responsible for these odors. Subsequently, 2-methyoxy-3-isopropyl pyrazine was found in bell peppers (8), a similar compound 2-methoxy-3-secbutyl pyrazine was identified in galbanum oil (9), and several 2-methoxy-3-alkyl pyrazines were identified in various raw botanicals (10). The odor threshold exhibited by 2-methoxy-3-isobutyl pyrazine (1 part in 10 indicates flavor significance for these compounds even at the exceptionally low concentrations in which they occur in foods and other natural products Producing these compounds from microbial fermentations could be an economical source of flavor for the food industry. 

Many of these chemicals are based on cresols. By the end of the year 2003, many more will be added to this list. It is important to note that 80% of these aroma chemicals are exported to various countries in the world. There is little doubt therefore that India is emerging as a major source of flavor and fragrance chemicals. (Source Flavors and Fragrances Association of India or FAFAI, 2000). 

Vanilla became known in Europe following Cotters conquest of the Aztec kingdom in 1519. Many centuries earlier, vanilla was a source of flavoring and used... 

Figure I continued. Sources of flavor and fragrance chemicals...

Cheese. Low-fat cheeses such as part-skim mozzarella or string cheese are also mostly protein with very little fat. Hard cheeses have protein, too, and are great sources of flavor, though they do include more fat. 

Yeast extracts represent an important source of volatile sulfur compounds, many of which possess low odor threshold values. They are used as sources of flavor for a range of savory foods, especially when a meaty note is required. In spite of the usefulness of yeast extracts, there are very few reports of their volatile flavor components. The production of yeast extracts is briefly reviewed, and the volatile sulfur compounds which have been identified are discussed. A recent study is presented in which the aroma components of some yeast extracts were analyzed. A total of 268 compounds were identified, including 67 sulfur compounds. The 34 sulfur compounds reported for the first time comprised 3 aliphatic sulfur compounds, one sulfur-substituted benzene derivative, 10 thiophenes, 18 thiazoles and 2 alicyclic sulfur compounds. Their importance as components of flavors and routes to their formation are considered. 

Apart from the fact that the current Directive 88/388/EC will turn into a Regulation, there are many changes that will have an impact on how essential oils and extracts will be used as source of flavors. The most important issue is how the so-called biologically active substances are addressed. 

The most important natural sources of flavors are the essential oils derived from spices, fruits, and flowers as well as extractives and exudates (resins) from certain plant sources and animal secretions, e.g., musk. Essential oils are aromatic substances which are widely used in several industries such as perfume, pharmaceutical, food, and nutrition. These are mixtures of more than 200 compounds [14,16]. It contains monoterpenes, sesquiterpene hydrocarbons, and their oxygenated derivatives, along with aliphatic and aromatic aldehydes, alcohols, esters, and nonvolatile residues. Generally, terpenes are unsaturated com-... 

Hopefully, the discussion offered above on sources of flavor information will help readers use the literature and Internet more effectively in their job whether it is in industry, government, or academia. The Internet is rapidly replacing reference books and radically transforming how industry and academia relate internally, and with the rest of the world. 

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