Compounds of Browned Flavor Derived from Sugar-Amine Reactionsl

products of specillc Amadori compounds, such as l-deoxy-l-piperidino-D-fructose and 1-deoxy-l-prolino-D-fructose (3,6). Fractionation of the less volatile, vacuum-distilled products by cold fmger, with subsequent gas-liquid chromatography (GLC) accompanied by sniffmg of the effluent vapors at successive recorder peaks, has separated the components into a series of compounds that were classilled broadly as amine· or amide·like; popcorny, nutty, or bready; and caramel-like. Also, aromas generally emerged from the GLC columns in this order. Two groupings of compounds that give characteristic browned aromas are indicated in Fig. 1. Compounds of fragrant caramel aroma are cyclic enolones that have planar, or nearly planar, alicyclic or a·heterocyclic structures. They contain contiguous carbonyl, enolic hydroxyl, and C·alkyl (methyl or ethyl) groups. Within a set of differently substituted 3.hydroxy4H-pyran-4-ones, loss of the C-alkyl. group, or displacement of it to a position not adjacent to the enolone, resulted in loss of caramel aroma (1). Since substitution or removal of the enol group also caused loss of caramel aroma, all three groups are needed. The ring BROWNED FLAVORS ARE those that generate from nonenzymatic browning reactions. They are essential for the recognition and acceptance by taste of many processed foods, especially cereal-derived foods. Browned flavors include caramelized sugar aromas (1); food aromas that have been described variously as toasted, baked, nutty, or roasted (2); corny and amine-like aromas from cooked grains and meals; and both the desirable and undesirable burnt aromas and bitterish tastes of roasted malt, nuts, coffee, chicory, cocoa, meats, fruits, and vegetables (2). The objectionable burnt and bitter flavors of overheated or long-stored dehydrated foods also fall within this class. Recent characterizations of flavor compounds isolated from browning reactions allow us to correlate the aromas, structures, molecular shapes, and routes of formation of these compounds. The fIrst correlation was presented for six compounds with caramel-like aromas in a 1965 symposium (1). Since then, additional compounds of .particular interest to cereal chemists have been isolated from model sugar-amine reactions and from processed foods. The new group contains not only compounds of caramel aroma, but also nitrogenous compounds of nutty, bready, and popcorny aromas. Structural relationships are apparent within each of these two groups of compounds. Although the caramel-aroma compounds contain no nitrogen, they are formed through sugar-amine condensation and the Amadori rearrangement-and at lower temperatures and in higher yields than would occur by non-amino thermal degradation of the sugars (1,36). Arnadori compounds (1-amino-l-deoxy-2-ketoses) are important nonvolatile precursors in the formation of browned flavor compounds from Maillard reactions (35). Therefore, our recent research has involved isolation and structure determination of the low-temperature pyrolysis