Nanostructured Lipid Carriers Based on Rice Wax and Stearic Acid Combined with Spray Drying for Xanthohumol Encapsulation

Nanostructured lipid carriers (NLCs) are effective delivery systems due to high loading capacity, physicochemical stability, protection against environmental degradation, and controlled release of bioactives. However, NLCs often present limited long-term physical stability, and combining drying methods is a promising strategy to overcome this limitation. In this context, spray drying enhances shelf life by reducing water content and slowing chemical, physical, and biological degradation. This study aimed to develop an ingredient containing hop-derived polyphenol (xanthohumol) utilizing NLCs stabilized with plant-based proteins. NLCs were first produced as carriers and subsequently dried by spray drying using soy, rice, and pea proteins as wall-materials. Lipidic mixtures (10% w/w) consisted of high-melting solid fat (3% w/w stearic-acid or rice-wax) and 7% (w/w) oleic acid. NLCs were produced via a two-step hot process (80 °C) to prevent early lipid solidification, including high-shear homogenization (15,000 rpm, 5 min) and microfluidization (~52 MPa, single-cycle). The spray-drying step was performed using a 0.7 mm two-fluid nozzle with a drying airflow of 35 m³/h, a feed rate of 6 mL/min, and inlet/outlet temperatures of 140.0±1.0 °C and ~65.0±1.0 °C, respectively. Lipid mixtures were evaluated by oscillatory rheology (frequency and temperature sweeps). NLCs were characterized by particle-size, polydispersity-index, X-ray diffraction, and atomic force microscopy, while spray-dried particles were analyzed for particle size. The rice-wax-based lipid mixture showed higher crystallization rates than stearic-acid, as indicated by temperature sweeps, and stronger solid-like behavior with a higher storage modulus (G'). These properties were reflected in NLC characteristics. The rice-wax NLCs exhibited a smaller particle-size (~179 nm) and lower polydispersity-index (~0.450) than stearic-acid NLCs, suggesting faster interfacial solidification and reduced coalescence. This behavior is associated with a more ordered crystalline structure in rice-wax NLCs, as evidenced by more intense X-ray diffraction peaks at 4.1, 3.7, and 2.5 Å. Whereas, stearic-acid showed peaks at 4.1 and 3.7 Å with a broader amorphous halo, indicating a less ordered structure. Morphological analysis also indicated smoother surfaces in rice-wax NLCs, whereas stearic-acid NLCs showed slight irregularities. After spray-drying, NLCs size remained largely unchanged, indicating that polymorphic stability was key to structural preservation.