The stability of retinol, alpha-tocopherol, trans-lycopene, and trans-beta-carotene in liquid-frozen and lyophilized serum.

The concentrations of retinol, alpha-tocopherol, and trans-beta-carotene in lyophilized serum stored at -25 degrees C and -80 degrees C have been monitored for 10 years. There was no evidence of degradation of any of these compounds over the 10-year period. Retinol, alpha-tocopherol, and trans-beta-carotene were less stable at -25 degrees C in liquid-frozen serum than they were in lyophilized serum. At -80 degrees C, trans-beta-carotene levels were stable for up to 3 years of storage in liquid-frozen serum. Both retinol and alpha-tocopherol appeared stable in liquid-frozen serum for at least 5 years at -80 degrees C. The effect of repeated freeze/thaw cycles on retinol, alpha-tocopherol, trans-lycopene, and trans-beta-carotene in liquid-frozen and reconstituted lyophilized serum both stored at -20 degrees C was also studied. Retinol, alpha-tocopherol, trans-lycopene, and trans-beta-carotene in reconstituted lyophilized serum stored at -20 degrees C were stable for at least 3 days with minimal (< 5) freeze/thaw cycles.