Development of extrusion-based legume protein isolate–alginate capsules for the protection and delivery of the acid sensitive probiotic, Bifidobacterium adolescentis

Abstract

Entrapment of an acid-sensitive probiotic, Bifidobacterium adolescentis, within capsules comprised of biopolymer mixtures of chickpea, faba, lentil or pea protein isolates with alginate (AL) was developed and produced employing extrusion technology. Capsule size, colour and microstructure were assessed, along with the survival and release of B. adolescentis cells within synthetic stomach juice (SSJ) and synthetic intestinal fluid (SIF). Survival of free and entrapped B. adolescentis was also assessed in commercial yogurt products over time. Capsules were produced by extruding the biopolymer-probiotic solution through a needle into a calcium chloride cross-linking bath. Capsule size was initially examined as a function of needle gauge (16, 18, 19, 23 and 27G) yielding mean diameters ranging from 2.79 (16G) to 1.23mm (27G). All subsequent capsule designs were based on extrusion through an 18G needle (mean diameter of 2.23mm). Capsule colour and microstructure (internal and external) varied amongst the four different protein–AL formulations. All capsule designs showed improved probiotic survival relative to free cells within SSJ, where entrapped cells (~8.5logCFU/g of capsules) experienced an average 2.25log10CFU/mL reduction in viable cell number after 2h, as opposed to free cells which did not survive (<1.0log10CFU/mL) beyond 1h of SSJ exposure. All capsule designs showed an initial burst-release of ~5.2log10CFU/mL immediately after SIF exposure, followed by a more gradual cell release, releasing 6.2log10CFU/mL after 2h. Shelf life studies using yogurt (plain) as a model product over a 30d incubation period at 4°C demonstrated that entrapped cells underwent a ~3.0log10CFU/mL reduction in viable cell number for all capsule designs, relative to free cells which experienced a reduction of ~8.0log10CFU/mL within the first 7d. These results show that legume protein–AL capsules demonstrate promise for the encapsulation, protection and release of probiotics such as B. adolescentis as a supplement and/or food ingredient.