Roasted aroma

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. 

The heat processing of tea leads to many complex chemical changes in tea. Tea s taste and aroma is affected by heat in at least three ways by reducing the content of bitter soluble catechins, by the development of roast aromas and by the thermal degradation of 0-carotene. Studies pertaining to the heat-induced changes in tea and appropriate model systems are reviewed. 

Green tea is usually made from Camellia sinensis var. sinensis (small leaf type). In China, jasmine tea is made from common kamairi-cha (from var. sinensis) while var. assamica (large leaf type) is used for Indonesian jasmine tea. The Indonesian jasmine tea has a stronger roast aroma than Chinese jasmine tea (3). The var. assamica tea leaf also contains a much higher level of polyphenolic catechins than var. sinensis. 

The aroma concentrate from hoji-cha has a strong characteristic roast aroma. Hoji-cha produced about 3 times the aroma concentrate than the original ban-cha. From the basic fraction which comprised 29% of the aroma concentrate, 19 different pyrazines were identified. The neutral fraction which was 47% of the aroma concentrate contained furans and pyrroles along with the original tea aroma. In addition, ionone related compounds such as theaspirone, dihydroactinidiolide and a large amount of B-ionone were found in the neutral fraction. Table III shows the increase of furan and pyrrole content due to roasting of the ban-cha (4). 

It has been shown that the aroma of tea is affected by the heat treatment received. Tea aroma and flavor are greatly influenced by catechins and proceeds by more than one pathway. The catechins influence tea aroma and flavor in three ways. First, catechins have a bitter, astringent taste. Second in order to reduce the level of soluble catechins (i.e. in var. assamica), a second heat treatment is required. This refiring produces a stronger roast aroma. Third catechins strongly influence the pyrolysis of B-carotene and L-theanine. 

Raw shrimp has little odor, but develops a pleasant characteristic roast aroma upon cooking. Antarctic krill is becoming important protein source because of its abundance. Although taxo-nomically different, krill is much like shrimp in appearance and will be treated as small shrimp in this report. Cooked krill, however, possesses a less acceptable aroma compared to shrimp. 

FINAL Red-brown Dark brown Aldol condens. Polymerization Strecker degrad. COj evolution Sulfites do not decolorize Acidic fluorescence Reducing pvr. in acids Caramel, roasted aromas Colloids, melanins form... 

More than 600 components have been isolated [8] from natural beef aroma. We have estimated that only 94 of these volatiles find their origin in the MaiUard reaction and of these 50% are pyrazine derivatives which contribute more to a roasted aroma than to a meat aroma. ... 

W. Baltes and G. Bochmann, Model reactions on roast aroma formation. IV. Mass spec-trometric identification of pyrazines from the reaction of serine and threonine with... 

Baltes W. (1990) Roast aroma formation. The role of amino acids during the Maillard reaction. 4th Int Symp. Maillard React., Lausanne, Switzerland, Sept. 1989, Finot et at. Eds, Birkhauser Verlag (1990), 43-61. 

Baltes W. and Bochmann G. (1986a) Model reactions on roast aroma formation—The reaction of serine and threonine with sucrose. 3rd Int. Symp. MaiUard React., Tokyo, Japan, July 1985, Fujimaki et al. Eds, Kodansha Ltd and Elsevier (1986), 245-55. 

Bohnenstengel C. and Baltes W. (1992) Model reactions on roast aroma formation. XII. Reaction of glucose with aspartic acid or asparagine at three different remperatures. Z. Lebensm. Unters. Forsch. 194, 366-71. 

Volatile components of natural and roasted hazelnuts have been investigated by several researchers [7,88,90-98]. Among several volatile aroma-active compounds detected in roasted hazelnut, 5-methyl-( )-2-hepten-4-one (fllbertone) has been reported as the primary odorant (nutty-roasty and hazelnutlike) [88,93,94,96]. Alasalvar et al. [98] studied the comparison of natural and roasted Turkish Tombul hazelnuts and found a total of 39 compounds in natural hazelnut and 79 compounds in roasted hazelnut. These included ketones, aldehydes, alcohols, aromatic hydrocarbons, terpenes, furans, pyrroles, pyrazines, and acids. Pyrazines, pyrroles, terpenes, and acids are detected in roasted hazelnut only. The combination of several volatile aroma-active components that increases upon roasting may contribute to the distinctive and unique flavor of roasted hazelnut. Pyrazines together with ketones, aldehydes, furans, and pyrroles may contribute to the characteristic roasted aroma of hazelnut. Detail information about flavor and volatile compounds in major tree nuts are detailed in Chapter 7. 

Table 5.23. Pyrrole and pyridine derivatives with a roasted aroma...

The aroma of fried chicken is primarily caused by the Strecker aldehydes methyl propanal, 2-and 3-methyl butanal as well as the roast aroma substances 2-acetyl-2- thiazoline, 2-acetyl-1-pyrrohne and the two alkyl pyrazines. The thiazoline and the p3trroline are also formed in lower concentrations during the boiling of meat. 2-Acetyl- 2-thiazoline is the most important roast aroma substance in meat fried for only a few min-... 

Few researchers have examined the effects of different cooking methods on the aroma of cooked meat. MacLeod and Coppock [14] compared the aromas of boiled and roasted beef using SDE. They suggested that carbonyl compounds, sulfides, pyrroles, and pyridines were associated with roasted aroma, whereas benzenoids and furans may be associated with the desirable qualities of well-cooked boiled beef In the experiment we describe here, headspace adsorption on Tenax TA was used to compare the aroma profiles of pressure-cooked and grilled lamb muscle. 

G MacLeod, BM Coppock. A comparison of the chemical composition of boiled and roast aromas of heated beef. J Agric Food Chem 25 113-117, 1977. 

---