Microencapsulation of Fermented Noni Juice with Blend of Maltodextrin and Gum Acacia Using Microfluidic Jet Spray Dryer

Abstract

Morinda citrifolia L. (Noni) fruit products, such as noni juice is well known for their potential therapeutic properties including antioxidant activity, anti-inflammatory, and anti-bacterial. However, only limited consumer can accept its unpleasant aroma and taste. Furthermore, its stability in processing and storage can affect its biological properties. This study aimed to microencapsulate noni juice by spray drying using a microfluidic jet spray dryer (MFJSD) to improve its stability and application in food systems. Noni juice consists of low molecular sugars and organic acids which result in sticky behavior due to its low glass transition temperature. Thus, spray drying noni juice alone without any wall material is almost impossible. Carbohydrates such as maltodextrins (MD) are commonly used as wall material due to its low viscosity and good solubility. On the other hand, gum acacia (GA) is well known for its film-forming ability and emulsification properties. Therefore, maltodextrin and gum acacia were used as wall material in the present study. Maltodextrin and gum acacia were blended with noni juice into different ratios (5:5, 7:3 and 9:1) to investigate the optimum ratio for better powder stability. The feed solutions were prepared with core to wall ratio of 1:2 and spray drying at inlet temperature of 170°C. The characteristics of spray dried noni juice powder were determined including moisture content, water activity, density, flowability, dissolution rate, hygroscopicity, glass transition temperature, morphology, particle size distribution and retention of bioactive compounds. In addition, the interaction between wall materials was studied using Fourier Transform Infrared Spectroscopy (FTIR), and crystalline-amorphous state of spray dried powder was confirmed by using X-ray diffractometer (XRD). Storage stability of spray dried noni juice powder was assessed by evaluating the retention of bioactive compounds after storage of 84 days at 4°C and 22 °C. In vitro digestion study was carried to investigate the digestibility of spray dried noni juice powder. Moreover, core to wall ratio of 1:3 and different inlet temperatures (160° and 180°) were also applied in the present study to determine their effect on physicochemical properties of powder produced. Spray dried noni juice powder with MD to GA ratio of 5:5 has the lowest moisture content and water activity. Results also indicate that moisture content can be reduced by decreasing core to wall ratio or increasing inlet temperature. Bulk density and tapped density were the highest in spray dried noni juice powder with MD to GA ratio of 9:1. However, all of the spray dried noni juice powder exhibited good flowability and intermediate cohesiveness. High dissolution rate was determined in all of the spray dried noni juice powder (< 1 minute). The findings showed that glass transition temperature and particle size could be increased by increasing the concentration of gum acacia used in the blend of wall material, inlet temperature and core to wall ratio. FTIR analysis showed that the ingredients of wall materials were retained in all of the spray dried noni juice powder, while XRD pattern showed the amorphous characteristic of the spray dried noni juice powder. Images from the optical microscope and scanning electron microscopy revealed that all the spray dried noni juice powder exhibited irregular but spherical shape with uniform size and narrow distribution. Different degree of wrinkles can be observed with noni juice spray drying with different MD to GA ratio. The highest retention of antioxidant activity and iridoids content was found in spray dried noni juice powder with MD to GA ratio of 5:5 suggesting better protection was provided. However, higher total phenolic content was observed in spray dried noni juice powder with MD to GA ratio of 9:1.The storage test was conducted at 4° C and 22° C for a period of 84 days. Overall, total phenolic content and antioxidant activity in spray dried noni juice powders was highly retained (>90%) during the storage period at both storage temperatures except for the spray dried powder with MD to GA ratio of 9:1. These results may be related to the particle size of the spray dried noni juice powder. The retention of deacetylasperulosidicacid (DAA) was highly (>95%) retained in all of the spray dried noni juice powder while asperulosidic acid (AA) content was slightly dropped to 86-88% after storage of 84 days. The in vitro digestion results suggested that spray dried noni juice powder with MD to GA ratio of 5:5 would provide better protection of bioactive compounds as the retention of bioactive compounds was higher. The presence of protein in gum acacia might contribute to the protection of bioactive compounds and allow them to pass through mouth, stomach and intestinal phase. In summary, this research has shown that microencapsulation of noni juice with a blend of maltodextrin and gum acacia could be achieved by spray drying using MFJSD to enhance their stability and bioaccessibility.