Mechanical characterization and pH response of fibril-reinforced microcapsules prepared by layer-by-layer adsorption

Despite the fair number of microencapsulation principles that have been developed, the actual protection and targeted delivery of sensitive ingredients remains a challenge in the food industry. A suitable technique should use food-grade and inexpensive materials, and ensure tight control over the capsule size and release trigger mechanism. For example, encapsulates may need to survive the low pH of the stomach to release their contents in the neutral environment of the small intestine. In this work we present layer-by-layer (LbL) microcapsules assembled from whey protein isolate (WPI), high-methoxyl pectin (HMP) and WPI-fibrils. The narrow size distribution of these capsules is determined by the oil-in-water droplets used as templates, and their mechanical properties and pH response can be tuned by the number of layers adsorbed. Capsules with more than eight layers have a mechanical strength comparable to chemically cross-linked polymer capsules, because of the reinforcement by the WPI-fibrils in combination with the shell completion. Typically, capsules with five layers survive pH 2 for more than 2 h, but dissolve within 30 min at pH 7. At higher number of layers, the capsules are even more stable. Contrary to other encapsulates, these capsules can be dried and are suitable for application in dry products.