Mechanisms of riboflavin sensitivity under light storage

초록

Riboflavin is easily destroyed under light. The mechanism for light sensitivity and how to reduce the destruction of riboflavin under light were not reported. The objectives are to determine the mechanisms of light sensitivity and how to reduce the destruction of riboflavin under light. Riboflavin was prepared in H2O and D2O at 12.5, 25, 50 and 100 mM. Ascorbic acid or NaN3 at 0, 40, 80 and 160 mM were prepared in riboflavin samples. Samples in duplicate were stored in a light box at 1000 lux. and 30°C and in dark. The degradation of riboflavin during storage was determined at 447 nm. Singlet oxygen was trapped by 2,2,6,7-tetramethyl-4-piperidone and determined by ESR Spectrometer. ESR showed that riboflavin produced singlet oxygen under light. Destruction of riboflavin after 24 h with light, and without light was 90 and 22%, respectively. As the ascorbic acid content added to riboflavin increased, the destruction of riboflavin under light decreased. The ascorbic acid protected the riboflavin under light, but did not protect it without light. The riboflavin destructions with 0 mM and 160 mM ascorbic acid under light were 95% and 28% after 96 hrs, respectively. Similarly, as the concentration of NaN3 added to riboflavin increased, riboflavin destruction under light decreased. Ascorbic acid and NaN3, the singlet oxygen quenchers, protected riboflavin destruction under light, not in dark. The destructions of riboflavin in D2O and H2O under light storage were 66 and 40% respectively, but were the same in the dark. The lifetime of singlet oxygen in D2O is longer than that in H2O. Results indicated that riboflavin produces singlet oxygen from triplet under light. The electrophilic singlet oxygen thus formed reacts with riboflavin with many double bonds and destroys it. Ascorbic acid and sodium azide, single oxygen quenchers, can reduce the destruction of riboflavin in foods by quenching singlet oxygen.