Introduction: Natural substances with plant sources are rich in bioactive and useful compounds that promote health and improve the physicochemical properties of food products. Compounds such as antioxidants, polyphenols, pigments, flavors and etc. are among the most important bioactive plant-based compounds. Red beetroot is one of the unique plants that are rich in antioxidants, anthocyanins, and red pigmentation. The red pigment of the red beetroot is known as betacyanin, and betanin is the major betacyanin compound in red beetroot. Therefore, due to the red beetroot rich in natural pigments, especially betalains, this plant product has a high potential for use as a natural colorant in food, pharmaceutical, and cosmetic products. However, the restrictions on the use of natural and edible pigments are unstable during processing and preservation. The encapsulation process is one of the effective strategies in the food industry to resolve this problem and to protect bioactive compounds during production and storage. Different methods have been used for encapsulation of bioactive compounds, among which the most prominent ones are freeze-drying, emulsion, spray drying, liposomal, niosome, coacervation, and so on. Freeze drying and spray drying are two of the most widely used and industrial methods for the encapsulation of bioactive compounds, pigments, extracts, pharmaceuticals, and microorganisms. So, the aim of this study was to produce red beetroot pulp powder as a source of bioactive and colorant compounds using spray and freeze-drying processes.
Materials and methods: Whey protein isolate (WPI) and maltodextrin with a DE 18-20 in different ratios (100: 0, 75:25, 50:50, 25:70 and 0: 100) as wall materials were used to the beetroot extract encapsulation. The spray drying process of the extracts was carried out at an inlet air temperature of 140 °C and outlet air temperature of 65-70 °C with a pump power of 75%, a compressed air flow of 3.5 m3/h, and a feed flow rate of 5 mL/min. To dry the freeze-dried extracts, each sample was first kept at a temperature of -18°C for 3 h, and then the drying operation was performed in a freeze dryer for 24 h. In all treatments, the Brix feed solution was kept constant at 10%. The produced powders were evaluated in terms of encapsulation efficiency, moisture content, water solubility, and total phenol content.
Results & discussion: The results showed that by increasing the amount of WPI to 50% (50:50 ratio), encapsulation efficiency significantly increased (p<0.05). In the spray and freeze-dried samples, the lowest moisture content was observed in the sample treated with 100% maltodextrin. Increasing the maltodextrin ratio significantly (p<0.05) increased the solubility of the powders in water. The evaluation of total phenol content showed that the red beetroot extract powders prepared with freeze dryer had the total phenol content. Also, the powder samples obtained from the ratio of 50:50 maltodextrin to WPI had the highest total phenolic content. Based on the results obtained in this study, it was found that the use of the 50:50 ratio for maltodextrin and WPI resulted in desirable physicochemical properties in the powders obtained by both drying methods. Therefore, due to the high costs of freeze-drying and the results of the present study, it can be concluded that the spray drying method with the conditions applied during this study can be used as an effective and promising method for the production of natural pigments based on red beetroot extract for use in food, pharmaceutical, and cosmetic industries. Hence, using a 50:50 ratio for maltodextrin and WPI as wall materials and drying aid is recommended for the production of red beetroot pulp powder.