59D-36 |
Reaction kinetics and mechanism for the formation of intrinsic chemical markers |
C. J. DOONA, E. W. Ross, and I. A. Taub. Office of Senior Scientist, US Army-Natick SBCCOM, 1 Kansas St, Bldg 36, Rm E-108, Natick, MA 01760 Intrinsic chemical markers are time-temperature integrators that accurately reflect the cumulative thermal effect on foods subjected to sterilization temperatures. Exploiting marker production to ensure bacterial destruction requires determining the kinetics of marker formation. Determine the kinetics rate law and Arrhenius parameters for the formation of M-1 and M-2 by evaluating rate constants over a systematically varied range of parameters. Activation energies are incorporated into a mathematical model that calculates bacterial destruction based on measuring marker production. Whey protein gel containing various amounts of ribose, glucose, and whey were heated in sealed glass tubes at constant temperatures over the range of 116-133 °C. Marker yields were analyzed at appropriate time increments using HPLC/UV-Vis. Similar samples were heated in pressurized vessels using microwave energy to compare the kinetics data obtained from different thermal processing methods. Time-domain NMR was used to evaluate T1 times of whey gel, and MALDI-TOF mass spectrometry was used to identify the reactive protein constituents of whey. Evaluating marker concentration versus time data generated pseudo-first-order rate constants that exhibited first-order dependences on each constituent: whey, glucose, and ribose. In samples with whey protein in excess, the rate of marker formation increased with temperature, yielding activation energies of 32.6 and 21.3 kcal/mol for M-1 and M-2, respectively. Lysine significantly increased the rate of marker formation. T1 times for the whey gel were relatively constant (» 0.7 msec) despite heating at 121 °C for periods up to 2 h, and mass spectral data verified the presence of the proteins a-lactalbumin and b-lactoglobulin in whey. Determining the kinetics rate law for the formation of intrinsic chemical markers of sterilization validates the approach for evaluating the activation energies. These values can be used directly in the mathematical model that quantitatively predicts bacterial destruction in thermally processed foods from measurements of marker yields.
Session 59D, Food Chemistry: Proteins and Physicochemical Properties
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