Isomerization of retinyl palmitate using conventional lipid extraction solvents

Area of Science:

• Food Chemistry
• Analytical Chemistry
• Nutritional Science

Background:

• Previous studies found chloroform-ethanol-water unsuitable for retinyl palmitate extraction due to significant isomerization.
• Retinyl palmitate, a form of vitamin A, exists in various isomeric forms, with all-trans-retinyl palmitate being the most common.

Purpose of the Study:

• To investigate the extent of retinyl palmitate isomerization in different solvents under gold fluorescent laboratory light.
• To determine the impact of light exposure on retinyl palmitate isomer stability in common extraction solvents.

Main Methods:

• Purified all-trans-retinyl palmitate solutions in hexane were diluted with methyl t-butyl ether, hexane, methylene chloride, and stabilized chloroform.
• Solutions were exposed to gold fluorescent laboratory light for varying durations (2, 4, 6.5 hours) or kept in the dark.
• High-performance liquid chromatography (HPLC) with fluorometric detection was used to quantify all-trans-, 9-cis-, and 13-cis-retinyl palmitate isomers.

Main Results:

• Significant isomerization of all-trans-retinyl palmitate to 9-cis-retinyl palmitate was observed in chloroform and methylene chloride under light.
• Isomerization increased with exposure time in chlorinated solvents.
• Hexane and methyl t-butyl ether showed minimal isomerization, and chlorinated solvents did not promote isomerization in the absence of light.

Conclusions:

• Chlorinated solvents (chloroform, methylene chloride) promote retinyl palmitate isomerization when exposed to light, including standard laboratory fluorescent light.
• To maintain the integrity of vitamin A esters during extraction, chlorinated solvents should be avoided.
• Alternative solvents like hexane or methyl t-butyl ether are preferable for retinyl palmitate extraction to prevent light-induced isomerization.