Chapter 9
Production of Natural Flavors Using a Cold Extrusion Process 1,3
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M. H. Cho , X. Zheng , S. S. Wang , Y. Kim , and Chi-Tang Ho 1
Department of Chemical and Biochemical Engineering, Rutgers University, P.O. Box 909, Piscataway, NJ 08855-0909 Department of Food Science, Cook College, Rutgers University P.O. Box 231, New Brunswick, NJ 08903
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Cold extrusion of moistened waxy corn starch mixed with methionine or with cysteine produced methional (potato chipflavorcomponent) or hydrogen sulfide (meatflavorcomponent) as keyflavorsamong several other compounds. Cold extrusion process produced thoseflavorsmore efficiently than thermal cooking in a heating bomb or hot extrusion process. Shear energy intensity was a critical factor for flavor generation in the cold extrusion process. Naturalflavorsfromcold extrudates were more pleasant than those generated from thermal treatment for these reaction systems. Conventional extrusion processes are usually operated at high temperature to supply heat energy into the material, even though there is also shear energy input in the extruder. If the operating temperature of the extrusion process is decreased below 60°C, which was called "cold extrusion" by Wang et al. (7), the thermal effect might be significantly diminished comparing to the shear effect. The viscosity of rheological material in the extruder can be increased tremendously at low temperature, which creates a high shear energy environment in the extruder. Wang et al. (7,2) demonstrated that shear energy alone can cause starch conversion without thermal energy input by using both a capillary rheometer and a single screw extruder. Wang (2,5) also suggested that shear energy is more efficient than thermal energy in the conversion of starch material based on activation energy calculations. Recentiy, Yam et al. (4) showed that the conversion of com meal was achieved by reverse screw elements during twinscrew extrusion below 60°C, in which they also reported that the conversion was due to shear alone, since thermal effects were negligible at these low temperatures. 3
Current address: Department of Chemical Engineering, Yeungnam University, Gyongsan 712-749, Korea Corresponding author
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0097-6156/95/0610-0120$12.00/0 © 1995 American Chemical Society
9. CHO ET AL.
Production of Natural Flavors Using Cold Extrusion Process 121
The objectives of this study are to produce natural flavorsfromamino acid-starch mixtures by using cold extrusion processes, and to compare characteristics of flavor generations between thermal treatment and cold extrusion processes. As case 1, the methional formationfromL-methionine-starch mixture was performed. Methional has aflavorsimilar to potato chips, which was already produced by cold extrusion process below 40°C (7). But, Lee et al. (5) reported that potato chip-like aroma was noticed only when methionine was treated under deep-fat frying conditions above 180°C. And, as case 2, the hydrogen sulfide formation from L-cysteine-starch mixture was performed. Hydrogen sulfide is a basic compound that has been identified repeatedly in meatflavor(
