Optimization of the production process and quality evaluation of mulberry-purple potato compound freeze-dried fruit blocks

Lyophilized products have been limited to the formula options of a single product. It is also lacking in diversity in nutrition and taste. Alternatively, both mulberry and purple potato have been renowned for their sweet taste and rich content of anthocyanins and bioactive compounds. Specifically, the high starch content of purple potatoes can contribute significantly to the texture, color, nutrition, flavor, and overall quality of food products. In this study, the mulberry and purple potato were combined to increase the diversity of compound freeze-dried fruit and vegetable products on the market. The taste and nutritional value of freeze-dried products were also improved under the unique combination. Firstly, the mulberry and purple potato were mixed at a ratio of 3:7. The compound freeze-dried fruit block was prepared by vacuum freeze-drying. Furthermore, an initial single-factor test was conducted to determine the optimal quantities of five additives: pectin, maltodextrin, gum arabic, fructose syrup, and citric acid, in order to ensure the high quality, excellent taste, and robust nutrition of the mulberry and purple potato compound freeze-dried fruit block. A composite scoring system was established with the influencing factors, such as color difference, hardness, brittleness, and hygroscopic property. The composite score was optimized to enhance the quality of the compound freeze-dried fruit block. Consequently, the experimental factors were narrowed down to the specific ranges: pectin supplementation (0.15%, 0.20%, and 0.25%), maltodextrin supplementation (7.00%, 8.00%, and 9.00%), fructose syrup supplementation (3.00%, 4.00%, and 5.00%), and citric acid supplementation (0.15%, 0.20%, and 0.25%). Subsequently, a response surface optimization test was conducted with the composite score as the key response value. The results indicated that the optimal combination of parameters was obtained to prepare the compound freeze-dried fruit block: 0.20% pectin, 8.00% maltodextrin, 4.00% fructose syrup, 0.24% citric acid, and 0.20% gum arabic. This optimal formula was achieved in a composite score of 0.87. The sensory evaluation demonstrated that the overall sensory acceptability of products scored 8.90 points, which was 25.35% higher than that of the control group. The finished product also shared a significantly higher level of market appeal and consumer acceptance. In addition, the optimal products then exhibited remarkable improvements in the various qualities. Specifically, the fracturability was enhanced by 80.53%. The microstructure of the product was much smoother, denser, and more organized. In the contents of bioactive ingredients, the ascorbic acid, total phenol, total flavone, and total anthocyanin increased by 2.91%, 3.53%, 23.10%, and 11.36%, respectively. The antioxidant capacities were measured using DPPH, ABTS, and FRAP tests, which were elevated by 26.92%, 11.27%, and 39.95%, respectively. A higher quality was obtained than before. In summary, supplementary materials were added to effectively enhance the product quality of the compound freeze-dried fruit block. The findings enriched the taste and nutritional value of these products, particularly in the diversity of compound freeze-dried fruit and vegetable products on the market. The novel insights were then offered to develop the freeze-dried products.