TRIOSE COMPOUNDS IN MAPLE SIRUP^a

Abstract

The characteristic flavor and color of maple sirup are developed during the concentration of the maple sap by atmospheric boiling. An almost flavorless sirup has been produced by low-temperature vacuum evaporation of sap (9,22). Further, by freeze-drying it is possible t o make a completely colorless and flavorless product (22, 23). Therefore, the color and flavor of the sirup is formed by atmospheric boiling from normal constituents of maple sap.The sap as it comes from the tree contains about 25% solids of which sucrose constitututes more than 98% (15). The remainder of the solids consists of organic acids (22), nitrogenous material (21), salts, and several oligosaccharides (24). Monosaccharides, if the sap remains sterile, are entirely absent. However, fermentation of the sap by contaminating microorganisms will cause inversion of the sucrose to amounts of invert sugar. Work a t this laboratory ( 2 4 ) , as well as that reported by E'dson, Jones, and Carpenter (7), has shown that the growth of microorganisms in sap often results in dark-colored sirup. Hayward and Pederson (10) have added acids and alkalies to maple sap, and reported their effect on the sirup produced. During investigations on the color development in sirup (10, 32), it was discovered that the sap passed through an alkaline stage. With the earlier work as a background, the possibility of alkaline degradation of the hexoses was at once suggested as being part of the mechanism of color and flavor development in maple sirup. The alkaline degradation of sugars has been discussed by several authors. Evans in 1942 reported on the breakdown of glucose by alkalies (8). Reviews of color development (browning) in sugar systems have been published by IIodge (13) and Liggett and Deitz (17). Sattler and Zerban (26,32) have discussed the chemical fragmentation of the unfermentable reducing substances in molasses. The ultraviolet spectra of sugars in alkaline solution have been studied by Berl and Feaze1 (2), who found a close relationship among such 3-carbon carbonyls (trioses) as acetol and reductone and the color chromogen of alkaline glucose solutions. Such compounds have been isolated from milk by steam distillation by Keeney and coworkers (26). Also, other carbonyl compounds related to flavor have been isolated by distillation from such diverse food products as cheese ( 5 ) ) corn oil ( 4 ) , apples, (12, 1 4 ) , strawberries ( 6 ) , and pork ( 3 ) .Therefore it seemed possible that such carbonyl compounds as trioses could be isolated from U. S. grade AA sirup by steam distillation. Fancy grade maple sirup seemed the most likely source of carbonyl precursors

MAPLE SIRUP. X. EFFECT OF CONTROLLED FERMENTATION OF MAPLE SAP ON THE COLOR AND FLAVOR OF MAPLE SIRUPa

“…The sirup made from sap fermented by yeast showed the development of a dark color and a strong caramel flavor accompanied by a large increase in free reducing sugars. This is in agreement with current observations (8) -which indicate that in heated sugar solutions the amount of color developed is related to the amount of reducing sugars present.…”

BROWNING OF SUGAR SOLUTIONS. IV. THE EFFECT OF PH ON THE VOLATILE PRODUCTS OF REDUCING SUGARSa

“…Similarly, Sattler and Zerban (17) have isolated acetol and a relatively lesser amount of methylglyosal through solvent extraction of heated aqueous fructose solution. During our investigation on color development in maple sirup, which is thought to occur through an alkaline degradation of the hexose constituents of the sap, several low molecular weight carbonyl compounds have been isolated as their dinitrophenyl-bis-hydrazones (21). In an attempt to clarify further the nature of these compounds and their role in the mechanism of color and flavor development in the sirup, the authors have for some time 7.<!l compounds are produced, a study was made of the effect of pH on the formation of acetol and methylglyoxal from such reducing sugars as glucose, fructose, and dihydroxyacetone.…”

Food Colorant Identification, Isolation and Characterization of High Molecular Weight Brown Colorant of Maple Sirup

“…The strongly alkaline nature of maple sap during the early stages of its evaporation favors the degradation of the simple sugars to trioses (20). The saturated character of the color isolate indicated that color formation had been halted a t the polymerization stage, at which point the chromophore centers had been formed.…”

“…The oxygen content is loicer than the content typical of most carbohydrates, Lvhich indicates that dehydrated intermediates such as acetol have condensed to form part of the polymer. Acetol, previously identified as an important component of the steam distillate of maple sirup (20), has been postulated as an intermediate in color formation during alkaline glucose degradation ( 2 ) .…”

“…These data indicated that the colorant polymers contain a very small amount of highly unsaturated linkages in the presence of a very large amount of highly saturated ones derived mainly from carbohydrates. The strongly alkaline nature of maple sap during the early stages of its evaporation favors the degradation of the simple sugars to trioses (20). The saturated character of the color isolate indicated that color formation had been halted at the polymerization stage, at which point the chromophore centers had been formed.…”