Grassy flavor

Two other types of oxidative changes occur during heating of lipids which result in undesirable flavor of meat. These are referred to as "warmed-over flavor" (WOF) and "grassy" flavor. 

Prominent volatiles related to "grassy" flavor of lamb according to Suzuki (34) were hexanal, heptanal, 2,3-octanedione, 2,4-hepta-dienal, 3-hydroxy-2-octanone, 2-nonenal, 2-decenal, 2,4-decadienal,... 

The development of a characteristic, objectionable, beany, grassy, and hay-like flavor in soybean oil, commonly known as reversion flavor, is a classic problem of the food industry. Soybean oil tends to develop this objectionable flavor when its peroxide value is still as low as a few meq/kg, whereas other vegetable oils, such as cottonseed, com, and sunflower, do not (15, 51). Smouse and Chang (52) identified 71 compounds in the volatiles of a typical reverted-but-not-rancid soybean oil. They reported that 2-pentylfuran formed from the autoxidation of linoleic acid, which is the major fatty acid of soybean oil, and contributes significantly to the beany and grassy flavor of soybean oil. Other compounds identified in the reverted soybean oil also have fatty acids as their precursors. For example, the green bean flavor is caused by c/i-3-hexenal, which is formed by the autoxidation of linolenic acid that usually constitutes 2-11% in soybean oil. Linoleic acid oxidized to l-octen-3-ol, which is characterized by its mushroom-like flavor (53). 

Fig. 11.11. Enzymatic formation mechanism of aldehydes and Ce alcohols, responsible for grassy flavors (Crouzet, 1986). (1) [Acyl]hydrolase (2) lipoxygenase in the presence of oxygen (3) peroxide cleavage enz3me (4) alcohol dehydrogenase...

Polyunsaturated fatty acids in vegetable oils, particularly finolenic esters in soybean oil, are especially sensitive to oxidation. Even a slight degree of oxidation, commonly referred to as flavor reversion, results in undesirable flavors, eg, beany, grassy, painty, or fishy. Oxidation is controlled by the exclusion of metal contaminants, eg, iron and copper addition of metal inactivators such as citric acid minimum exposure to air, protection from light, and selective hydrogenation to decrease the finolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

Use of some oilseed proteins in foods is limited by flavor, color, and flatus effects. Raw soybeans, for example, taste grassy, beany, and bitter. Even after processing, residues of these flavors may limit the amounts of soybean proteins that can be added to a given food (87). The use of cottonseed and sunflower seed flours is restricted by the color imparted by gossypol and phenoHc acids, respectively. Flatus production by defatted soy flours has been attributed to raffinose and stachyose, which are removed by processing the flours into concentrates and isolates (88). 

Soybeans. Soybeans are not eaten raw because they are too hard and have an unpalatable grassy—beany flavor. Small amounts are roasted and salted for snacks. Nut substitutes for baked products and confections are also manufactured from soybeans. Larger amounts are used in Oriental foods, some of which are increasingly popular in the United States. 

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. 

Hhong et ah (2009) described the sensory attributes of morama oil as fresh, thick, creamy, and smooth with a grassy and earthy aroma and raw nutty flavor and aftertaste. Compared to both sunflower and olive oils, potato chips fried in morama oil were rated as more acceptable by consumers (Tlhong et ah, 2009). Therefore, as a cooking oil, morama oil has great potential in terms of consumer acceptability. However, its acceptability as a salad oil remains imexplored. 

The overwhelming consideration in regard to lipid deterioration is the resulting off-flavors. Aldehydes, both saturated and unsaturated, impart characteristic off-flavors in minute concentrations. Terms such as painty, nutty, melon-like, grassy, tallowy, oily, cardboard, fishy, cucumber, and others have been used to characterize the flavors imparted by individual saturated and unsaturated aldehydes, as well as by mixtures of these compounds. Moreover, the concentration necessary to impart off-flavors is so low that oxidative deterioration need not progress substantially before the off-flavors are detectable. For example, Patton et al (1959) reported that 2,4-decadienal, which imparts a deep-fried fat or oily flavor, is detectable in aqueous solution at levels approaching 0.5 ppb. 

Phytol is a precursor for several other diterpenoids (phyt-l-ene, phyt-2-ene, phytane, neophytadiene, phytadiene and dihydrophy-tol) that produce a "grassy" odor when heated at 150°C or higher and heating may contribute directly to this undesirable flavor. 

The most detailed smdies on the flavor of fish oil in recent years were probably those of Hsieh et al. (78, 79), Lin et al. (80), and Lin (81). In their studies, a series of alkanals, alkenals, alkadienals, and alkatrienals were determined by dynamic headspace gas chromatography-mass spectrometry in cmde menhaden oils (Table 11). Most of these aldehydes contributed to the characteristic oxidized oily odors, such as green grassy, waxy, and rancid in the crude oils. Alkatrienals, i.e., nonatrienal and decatrienals, were also found at ppb levels in the dynamic headspace of the crude oils. 2-fraM5,4-frflMi,7-cA-Decatrienal, 2-fra 5,4-d5,7-di-decatrienal,... 

Deodorization/Physical Refining Quality control is especially concerned with flavor, free fatty acid concentration, color, stability, and trace contaminants. With respect to routine flavor testing, two-three trained panelists test the flavor of small sample of the oil. The oil must be essentially bland, but very slight beany or grassy notes are tolerated. Free fatty acids, color, and stability testing is done by the AOCS official methods (76). 

At low levels of oxidation, the degree and type of change known as flavor reversion is characteristic for each oil. For example, soybean oil develops a flavor that is described as beany or grassy. This flavor has been attributed to the formation of 2-pentylfuran (18) and 3-c -hexenal (19). Canola oil (LEAR) develops flavors similar to those of soybean oU. The flavor reversion of sunflower seed and safflower seed oils are described as seedy. Similarly, com and pahn oils develop flavors of distinct type. These reversion flavors are observed long before other objectionable oxidative off-flavors are formed. With many of these oils, the cause of the reversion flavors is not well understood. In the case of most well-processed oils, the reversion flavor is not a frequent problem. 

Canola oil is stable and should be stored in an airtight, light-resistant container in a cool, dry place. During storage, grassy, paintlike, or rancid off-flavors can develop. 

The prior art section in the patent explains that conventional hexane exuaction of soy beans leaves constituents in the extracted meal that give raw, grassy, and bitter flavors that are detrimental to the meal s organoleplic quality. Emphasis has been directed to replace the hexane used in the tfaditional process with work focused on the development of a supercritical CO2 extraction process. Most of the research effort has been directed to achieving a high quality of oil. When soy bean flakes are extracted with CO2, the color, quality, metals content etc., of the oil are excellent, but the residual flake still retains some of the grassy and bitter off flavors. 

Sensory evaluation provides information most closely associated with the quality of food lipids. Flavor or odor defects may be detected by panelists before they are recognised by chemical or instrumental methods. For example, the fishy and grassy taste produced in linolenic acid-containing oils such as soybean oil occurs at very low levels of oxidation only detected by sensory analyses. The limitations of this method are poor reproducibility and high cost of panelists and the necessary facilities. The recommended approach is to use more reproducible chemical or instrumental methods to complement or support the sensory analyses (Frankel 1998). 

The odor is described as fresh, lemon-like, grassy-herbaceous, with a sweet-floral undertone. The overall lift is primarily fruity-green (Arctander, 1967), The flavor is green, fatty, nutty, sweet (Chemisis, 1995). 

In unseasoned stewed tomatoes, 2% sucrose reduced seed flavor and grassiness, augmenting sweetness and cooked flavor. An even more interesting effect was the increase of flavor amplitude. Sugar was found complementary to salt, pepper, and butter in the stewed tomatoes. Again, it was noted that sugar reduced saltiness. 

---