Effects Of Different Preprocessing Methods On Nutrition Qualities Of Four Common Vegetables

Effects of fresh-cutting, boiling and stir-frying three different preprocessing methods were studied on vitamin C, total phenolics content and the ability of DPPH radical scavenging, based on four vegetables lettuce, purple cabbage, cucumber and carrot as materials. Vitamin C, total phenolics and DPPH radical scavenging rate were determined respectively by 2,6-dechloro-indophenol titration method, Folin-Ciocalteu method and spectrophotometry. The results showed that:Fresh-cutting is the best preprocessing way for four vegetables, which had no significant influence on the nutrients(p > 0.05). After cooking, the content of vitamin C, phenolics, DPPH radical scavenging rate and chlorophyll in lettuce, carotene in carrot decreased significantly(p < 0.05) except that DPPH radical scavenging rate in stir-fried lettuce remained unchanged.Preprocessing had different effects on the nutrients in different kinds of vegetables. The retention of vitamin C and phenolics was highest in stir-fried purple cabbage, while DPPH radical scavenging rate decreased highest. Nutrients were better remained in stir-fried lettuce than boiled. Stir-fried cucumber and carrot samples had a better retention of VC, but worse in phenolics and DPPH radical scavenging ability.It shows that there was a positive correlation between total phenolics content and DPPH radical scavenging ability in raw and cooked vegetables. The correlation coefficient respectively: lettuce showed R2 = 0.538, purple cabbage R2=0.422, cucumber R2=0.796, carrot R2=0.945. The correlation showed significant differences in various vegetables, which was highest in carrot and lowest in purple cabbage.