(417g) Cereal Fiber Based Encapsulation of Selected Polyphenols and Their Solid State Characterization

Polyphenols are naturally occurring potent antioxidants which have been shown to have anti-inflammatory and cardiovascular protective effects but have processing and formulation challenges since they are sensitive acidic pH and are bitter in taste. In order to overcome these challenges, they are often encapsulated, mainly using technologies such as spray drying. Although spray drying is an extensively used process in the food industry, the materials used to encapsulate an active ingredient are limited to gum Arabic, maltodextrins and modified starches. The overall goal of this research work is to evaluate potential of a novel prebiotic water soluble cereal fiber to encapsulate the polyphenols Quercetin (Qn) and Naringin (Nn) using spray drying. The cereal fiber chosen for these experiments shows faster and higher solubility in cold water and is more economical compared to Gum Arabic, which is the most widely used encapsulation material.

The cereal fiber was found to show extremely high solubility with a maximum of 62% (w/v) dissolving in water. The solutions were found to Newtonian in nature and a 20% solution was only found to be twice as viscous as water, whereas a 10% Gum Arabic solution was found to be almost five times as viscous as water. These low viscosities enable higher fiber loading for spray drying. The moisture sorption behavior of the cereal fiber was studied using dynamic vapor sorption between relative humidities of 0-95% using two cycles of adsorption-desorption. The fiber was found to be highly hygroscopic beyond RH of 60% with a maximum adsorption of 50% moisture (w/w) at a RH of 95% while forming an irreversible gel-like structure.

The influence of polyphenol type, cereal fiber viscosity and spray dryer inlet temperature on the morphology and size distribution of spray dried particles was studied. Suspensions were prepared with 3% Qn/Nn in either a 20% or 40% cereal fiber solution. Inlet temperatures of 155 and 180 ° C were evaluated for spray drying at a constant pump flow rate of 4 mL/min. For Naringin encapsulation, most of the resulting particles were found to be smooth, spherical and fully amorphous, indicating conversion of crystalline Naringin to amorphous form as a result of spray drying. However, for the encapsulation of Quercetin particles, X-Ray Diffraction spectrum consistently showed small proportion of crystalline peaks indicating incomplete transformation of crystalline Quercetin to amorphous form. The peaks were found to not overlap with those of pure Qn, suggesting formation of a different crystalline form upon spray drying.  This could possibly be due to incomplete solubilization of Qn prior to spray drying, owing to its poor water solubility, leaving a proportion of particles in crystalline state, which transformed during spray drying. SEM data showed that a mix of particles with spherical and ellipsoidal morphology, but with a smooth surface, indicating their encapsulation by CFG. SEM results showed larger and smooth particles compared to the original needle shaped Qn/Nn crystals, indicating effective encapsulation of polyphenols by the cereal fiber.

The particle size determined by Laser diffraction was found to vary from 0.15-30 µm with a median particle size of 5-7 µm for encapsulated Qn and Nn particles with an exception: Nn spray dried in a 20% of the cereal fiber solution at 155 ° C, with a median particle size of 11 µm. The spray dryer inlet temperature and %CFG variations were found to have no significant effect on the median particle size(p<0.05). Measurement of Hausner and compressibility ratios indicated poor to very, very poor flow behavior for all particles according to USP classification.  The encapsulated Naringin particles showed a maximum moisture sorption of 21% (w/w) which was a significant reduction compared to the pure fiber (50% w/w).

Hence, in conclusion, it was qualitatively shown that the cereal fiber under study effectively encapsulated both Naringin and Quercetin. The encapsulated Naringin particles showed a decreased hygroscopic tendency compared to the cereal fiber, decreasing its hygroscopicity. However, traces of crystallinity were found for encapsulated quercetin particles which pose the risk of re-conversion to crystalline form during storage/processing. This risk needs to be mitigated by changing the solvent for spray drying or reducing the content of Qn in the slurry. Encapsulation also resulted in poor particle flow behavior which needs to be improved depending on the final product of intended use.  Future work will be dedicated to quantify the amount of polyphenols encapsulated, understand the dissolution kinetics of spray dried powders in simulated gastric and intestinal fluids and sensory evaluation to evaluate taste masking potential of the cereal fiber compared to gum arabic.