Effect of Ambient Temperature, Cold Fluorescent Light and Oxidative Oil Quality on the Stability of Retinyl Palmitate and Its Antioxidant Activity in Soybean Oil

Abstract

Objectives: Fortification of soybean oil with retinyl palmitate is known to be an effective strategy to counteract vitamin A deficiency. However, stability of vitamin A in vegetable oils strongly depends on environmental factors, e.g. temperature, light, oxygen availability, oxidative oil quality, and storage time. The current study investigated the stability of retinyl palmitate and its effect on the oxidative status of soybean oil stored under household conditions. Methods: Soybean oil was fortified with retinyl palmitate (31.6 IU/g) and filled in transparent 0.5 L PET bottles. The closed bottles were either stored in the dark or exposed to cold fluorescent light at 22ºC or 32ºC for 56 days. By intermittent opening for sampling, the headspace volume increased, thereby mimicking consumer handling. Results: After 56 days of storage, the concentration of retinyl palmitate was significantly reduced by 84.8±5.76%, independent of temperature and light exposure. When retinyl palmitate was added to already oxidized soybean oil, characterized by a peroxide value of 17.3 meq O2/kg, a retinyl palmitate reduction by 80.3±13.6% was determined already after 28 days of storage. Addition of retinyl palmitate to soybean oil also increased its antioxidant capacity by exhibiting a tocopherol-saving effect. Conclusions: In conclusion, fortification of soybean oil with retinyl palmitate increased its oxidative stability, although a significant loss of retinyl palmitate during household storage and handling was demonstrated over time. When retinyl palmitate was added to highly oxidized soybean oil, this storage-associated loss was accelerated.