Color-protected Agents Formulation Optimization and Influence on Quality of Microwave Vacuum-Dried Lemon Slices

In order to maintain the color of microwave vacuum-dried (MVD) lemon slices, the composition and its concentration of color protection liquid for lemon slices were optimized, and its effects on the quality changes of treated lemon slices were also investigated. In this work, the distilled water treatment group was used as the blank control group, the formulation of color-protected agents without sulfite was decided through the single factor and response surface tests, which included 0.60% EDTA-2Na, 0.38% L-cysteine and 0.82% citric acid, respectively. Moreover, both L^* value and the color difference value of slices treated with this composite color protection liquid were the best among all the samples. Furthermore, the verification test showed that the average values of L^* and color difference value of treated lemon slices were 78.52 and 11.61, respectively. And the agreement between the predicted value and the test value was 98.44% and 97.33%, respectively. On the other hand, the quality changes between lemon slices treated by the color protection liquid and control slices were analyzed. The compared results of the quality changes between treated lemon slices and control samples indicated that the amino nitrogen, ascorbic acid contents and reducing sugar of lemon slices treated with the color protection liquid were 38.61, 81.79 mg/100 g, and 14.75 g/100 g, respectively, which were all higher than that in the control samples. More importantly, 58 and 56 kinds of volatile components were detected in the color protection group and the control group, respectively. The main characteristic aroma components including α-pinene, β-pinene, myrcene, γ-terpinene and citral in the treated lemon were higher than that in the control slices. However, the content of citral was lower than that in the control simple. These results indicated that the color protection treatment could effectively inhibit the nonenzymic browning of the microwave vacuum-dried lemon slices and also retained its original nutrients and aroma components at a greater extent.