Effect of Oxygen on Thermal Degradation of 5‐Methyl‐5,6,7,8‐Tetrahydrofolic Acid

Abstract

Previous studies of thermal degradation of folic acid have not given consistent rate expressions or activation energies. The present study employed a model system which eliminated oxygen mass transfer limitations to examine degradation as a result of heating. A pseudo first-order reaction rate constant (k ah& and an activation energy (E,) for thermal degradation due to an oxidative mechanism were estimated to be 0.154 f 0.044 min-' and 16.3 kcal/mol, respectively.In the presence of Nz, these parameters were estimated to be 0.094 ? 0.009 min-' and 23.3 kcal/mol, respectively. While elimination of oxygen will not ensure folic acid retention, the overall degradation rate will be reduced significantly.

Folates in Fruits and Vegetables: Contents, Processing, and Stability

“…Influence of pH on activation energy for 5‐CH 3 ‐H 4 folate degradation appears limited (Mnkeni and Beveridge ; Indrawati and others ), though lower activation energies are found in food media (Mnkeni and Beveridge ) or in the presence of ascorbic acid (Indrawati and others ). Under air (or with an initial oxygen concentration of 8 mg/L, corresponding to saturation of water by oxygen in ambient conditions), similar activation energies have been reported for 5‐CH 3 ‐H 4 folate degradation by Mnkeni and Beveridge (), Barrett and Lund (), Viberg and others () and Indrawati and others (), while much lower activation energies were reported by Chen and Cooper () and Ruddick and others (). This was attributed by Barrett and Lund () and by Viberg and others () to a limitation by oxygen diffusion in some of the experimental systems.…”

“…Under air (or with an initial oxygen concentration of 8 mg/L, corresponding to saturation of water by oxygen in ambient conditions), similar activation energies have been reported for 5‐CH 3 ‐H 4 folate degradation by Mnkeni and Beveridge (), Barrett and Lund (), Viberg and others () and Indrawati and others (), while much lower activation energies were reported by Chen and Cooper () and Ruddick and others (). This was attributed by Barrett and Lund () and by Viberg and others () to a limitation by oxygen diffusion in some of the experimental systems. Data on impact of oxygen itself are contradictory: slightly higher activation energies are reported for 5‐CH 3 ‐H 4 folate degradation after degassing by Barrett and Lund () and Mnkeki and Beveridge () in apple juice, but lower ones at 5.3 mg/L than at 8 mg/L initial oxygen in citrate buffer by Mnkeni and Beveridge (), while Viberg and others () determined activation energies as 107 kJ/mol for the aerobic degradation, and 62 kJ/mol for anaerobic degradation.…”

“…This was attributed by Barrett and Lund () and by Viberg and others () to a limitation by oxygen diffusion in some of the experimental systems. Data on impact of oxygen itself are contradictory: slightly higher activation energies are reported for 5‐CH 3 ‐H 4 folate degradation after degassing by Barrett and Lund () and Mnkeki and Beveridge () in apple juice, but lower ones at 5.3 mg/L than at 8 mg/L initial oxygen in citrate buffer by Mnkeni and Beveridge (), while Viberg and others () determined activation energies as 107 kJ/mol for the aerobic degradation, and 62 kJ/mol for anaerobic degradation. Activation energies for folate degradation are higher than those reported for vitamin C losses (about 30 to 40 kJ/mol) and lower than those for carotenoid degradation (>100 kJ/mol) (Renard and Maingonnat ).…”

“…Mnkeni and Beveridge () also observed a decrease in 5‐CH 3 ‐H 4 folate degradation when the initial oxygen concentration was decreased from 8 to 5.3 mg/L (by nitrogen‐flushing), between 100 and 140 °C. Barrett and Lund () also found a faster degradation of 5‐CH 3 ‐H 4 folate in the presence of oxygen between 40 and 92 °C when comparing the data obtained under oxygen saturation or in an oxygen‐free system. Reaction rates and activation energies are reported in the reaction was only slightly faster in the presence of oxygen at 92 °C ( t 1/2 of 4.5 min compared with 7.4 min without oxygen), but much faster at 40 °C ( t 1/2 about 150 min compared with 1200 min) in connection to a higher activation energy.…”

Who Would Have Thought? The Story of a Food Engineer

“…We studied kinetics of vitamin degradation (Hamm & Lund 1978, Navankassatusus & Lund 1982, Arabshahi & Lund 1988, Barrett & Lund 1989), enzymes (Ling & Lund 1978a,b;Hyslop et al 1979;Park & Lund 1984;Chang et al 1988), texture (Lund 1982aRao & Lund 1986;Stoneham et al 2000;Sandu & Lund 1985a), and mutagen formation (Pariza et al 1979). Our research included papers on experimental protocol to determine kinetic parameters of constituents in foods (Lenz & Lund 1980).…”