Nitrogen-protected microwave-assisted extraction of ascorbic acid from fruit and vegetables.

In this study, nitrogen-protected microwave-assisted extraction (NPMAE), in which microwave-assisted extraction was performed under nitrogen protection, was initially developed and combined with HPLC separation for the determination of ascorbic acid (AA), an oxidizable component, from fruit and vegetables. The extraction conditions of NPMAE were investigated by extraction of AA from guava, and the chosen conditions were as follows: extraction solvent of 0.25% metaphosphoric acid solution, solid/liquid ratio of 1:10 g/mL, microwave power of 400 W and irradiation time of 10 min. Subsequently, this novel NPMAE method was evaluated by extraction of AA from different fruit and vegetables, such as guava, yellow pepper, green pepper and cayenne pepper. Compared with conventional MAE and solvent extraction methods, the oxidation of AA was significantly reduced or prevented in the process of NPMAE, providing higher extraction yield of AA. These results suggested the potential of NPMAE method for the extraction of oxidizable compounds from different spices of matrices.