Starch based systems for the colonic delivery of bioactive peptides

Abstract

Bioactive peptides have numerous health benefits, although if taken orally they may be digested during gastrointestinal (GI) transit. Encapsulation is an established method for oral delivery of bioactives. However, many current approaches arise from pharmaceutical applications and may be unsuitable for food due to the materials used, cost and scale of production. Therefore, in this project we set out to create a simple and clean-label encapsulation system, suitable for use in the food industry, which could deliver bioactive peptides to the colon. One potential clean-label entrapment material is resistant starch, which is the portion of starch that resists digestion in the upper GI tract but can be digested by bacteria in the colon. As a model bioactive peptide, the well characterised antimicrobial peptide nisin was used; this peptide is normally digested during GI transit. To prepare the nisin a simple purification process was developed, which produced a powder containing ∼33% nisin from a nisin producing culture and also enriched a commercial nisin preparation over 30-fold to a purity of ∼58%. The digestion of nisin was characterised (in vitro) and 6 nisin fragments (4 of which are bioactive) were identified in the digestion products; it was also observed that nisin formed a complex with bile salts that effected its digestion. Nisin was entrapped in starch through multiple approaches based on spray coating, co-spray drying and gel entrapment. A simple approach based on gel entrapment was the most successful and it was shown in vitro to be capable of protecting a portion of the entrapped nisin during transit in the upper GI tract. Using a murine model, it was determined in vivo that a nisin entrapped in starch gel diet significantly (p < 0.001, n = 10) affected the relative abundance of 3 times as many genera from the lower GI tract than a control nisin in starch diet, despite the mice consuming 3-fold less nisin than the control diet.