Most of the previous studies on the preservative effect of ascorbic acid derivatives have been done in the buffered systems (Chen & Cooper, 1979; O’Broin et al., 1975; Paine-Wilson & Chen, 1979). O’Broin et al. (1975) reported that the activity of tetrahydrofolate became zero when 5 ng/ml solution without ascorbic acid was autoclaved (121C for 12–15 min) but under similar conditions, 67% folate activity was retained if 1% ascorbic acid was used in the solution. Chen and Cooper (1979) reported that an aqueous solution of 5-methyl-tetrahydrofolate containing 0.1% ascorbic acid lost 20% of its activity when heated for 3 h at 100C. However, under the same conditions without ascorbic, it lost 90% of its activity in 65 min of heating