Influence of DL methionine and sodium metabisulphite on the photostability of vitamin k1.

On exposure to UV light at 254 nm in a borosilicate glass actinometer, vitamin k1 decomposed rapidly with a degradation rate constant of 7.63 day-1. Under UV irradiation, DL methionine and sodium metabisulphite were found to have some photostabilizing effect for vitamin k1 formulations. The degradation rates were reduced by 43.4% and 60.4% in the presence of 0.1% w/v of DL methionine and 0.2% w/v of sodium metabisuphite, respectively. When vitamin k1 formulations were stored at room temperature in clear glass bottles and exposed to the weaker light source of both room fluorescent light and natural daylight, vitamin k1 decomposed at a much slower degradation rate constant of 0.31 day-1. Despite the slower degradation rate, DL methionine and sodium metabisuphite failed to protect vitamin k1 from degradation on exposure to this weaker light source. When vitamin k1 was stored in white plastic bottles under the same testing conditions, the photo-protective effect of these photostabilizers reappeared. The protection provided extended the shelf-life from one day to 2.5 days. When amber glass bottles replaced white plastic bottles as storage containers, vitamin k1 was found stable on an open bench for at least 30 days. Such stability was also observed when vitamin k1 was stored in a refrigerator in either white plastic bottles or amber bottles. Findings in this study showed that package and storage conditions that shield the products from light are still the most efficient ways to maintain the photostability of vitamin k1. However, photostabilizers such as DL methionine and sodium metabisulphite may provide additional protection to vitamin k1 when it is stored in less effective light-resistant containers.