Microencapsulation of Bifidobacterium adolescentis with legume protein isolates crosslinked with genipin

Abstract

The overall goal of this research was to design a crosslinked legume protein microcapsule capable of increasing viability of Bifidobacterium adolescentis when exposed to acidic conditions in order to maintain sufficient probiotic numbers for a host to experience a positive health benefit. Legume protein isolates derived from chickpea (CPI), faba bean (FPI), lentil (LPI) and soy (SPI) were used as wall materials to test the effect of protein-type on the protective nature of the capsule. The research was designed into two phases: first, the characterization of select physicochemical properties of legume proteins and their emulsifying properties; and second, the design of a genipin crosslinked capsule for carrying probiotics. In study 1, the physicochemical properties of legume protein isolates were investigated for their ability to stabilize an oil-in-water emulsion in the presence and absence of genipin. Solubility, surface (charge and hydrophobicity), and interfacial (interfacial tension) characteristics of all protein isolates were determined along with their crosslinking ability with genipin. Solubility was found to be highest in CPI (~94%), followed by LPI (~90%), FPI (~85%) and SPI (~50%). Surface characteristics of the protein isolates revealed similar zeta potentials (~ -47 mV) for CPI, LPI and FPI, while that of SPI was lower (~ -44 mV). In contrast, surface hydrophobicity was greatest for CPI (~137 arbitrary units, AU), followed by SPI/LPI (~70 AU) and FPI (~24 AU). A significant reduction in interfacial tension (from 16.73 to ~8.42 mN/m) was observed in canola oil-water mixtures in the presence of legume proteins. Genipin crosslinking affinity was found to be similar for each protein isolate as indicated by similar UV spectroscopic values. Overall, emulsion stability as determined by creaming in canola oil-water mixtures increased in the presence of genipin regardless of the legume protein present. Maximum stability in the presence of genipin was highest for SPI (65%), followed by FPI (61%), LPI (56%) and finally, CPI (50%). Based on this knowledge, all legume proteins were used as wall materials to encapsulate a probiotic core material. Encapsulation was performed using an emulsification technique where canola oil was used to form the continuous phase, and a mixture of legume protein isolate solutions, genipin and Bifidobacterium adolescentis was used to form the aqueous discontinuous phase. Although various capsules formulation (with and without biopolymer coatings/prebiotics) and preparation methods (stir rates, crosslinking times) were tested, the micron sized capsules produced were not adequate for protecting Bifidobacterium adolescentis during acid challenge.