In the small intestine the nature of the environment leads to a highly heterogeneous mucus layer primarily composed of the MUC2 mucin. We set out to investigate whether the soluble dietary fibre sodium alginate could alter the permeability of the mucus layer. The alginate was shown to freely diffuse into the mucus and to have minimal effect on the bulk rheology when added at concentrations below 0.1%. Despite this lack of interaction between the mucin and alginate, the addition of alginate had a marked effect on the diffusion of 500 nm probe particles, which decreased as a function of increasing alginate concentration. Finally, we passed a protein stabilised emulsion through a simulation of oral, gastric and small intestinal digestion. We subsequently showed that the addition of 0.1% alginate to porcine intestinal mucus decreased the diffusion of fluorescently labelled lipid present in the emulsion digesta. This reduction may be sufficient to reduce problems associated with high rates of lipid absorption such as hyperlipidaemia.

In the present study, we hypothesised whether in vitro digestion of salmon oil would release different amounts of PUFA depending on the origin of the lipolytic enzymes used. For this purpose, in vitro digestion of salmon oil (SO) was performed using human duodenal juice (HDJ) or a commercial enzyme preparation consisting of porcine pancreatin and bile (PB). The lipolytic effect was determined by measuring the release of fatty acids (FA) using solid-phase extraction and GC -flame ionisation detection, withdrawing samples every 20 min during digestion. The amount of FA released indicated that a plateau was reached after 80 min with approximately similar amounts of FA detected using both HDJ and PB (379 (SD 18) and 352 (SD 23) mg/g SO, respectively). However, the release of 18 : 2, EPA (20 : 5) and DHA (22 : 6) was significantly different during in vitro digestion. At 80 min, HDJ and PB released 43 and 33 % of 18 : 2, 14 and 9 % of EPA and 11 and 9 % of DHA, respectively. Both enzyme preparations released approximately the same amounts of the other FA analysed. The effect of the addition of bile salts (BS) was significantly different in the two enzyme systems, where porcine pancreatin highly responded to the increase in BS concentration, in contrast to HDJ.

We hypothesize that the rate of release of lipids from salmon muscle during in vitro digestion is altered by additional meal components. In vitro digestion of salmon was performed using a mixture of porcine gastrointestinal enzymes and bile salts. Broccoli and barley were also added to the digestion simulating a meal. The extent of lipolysis was determined by measuring the release of fatty acids (FAs) during sampling at the simulated gastric phase endpoint (60 minutes) and 20, 40, 60, 80, 110 and 140 minutes simulated small intestinal phase, using solid phase extraction and GC-FID. Adding barley resulted in a lower overall release of FA from salmon, whereas broccoli caused an initial delay followed by increased release from 80-140 min when lipid digestion of salmon alone plateaued. The impact of broccoli and barley on the release of peptides and digesta viscosity were also measured. The effect of different components in the meal shown by this in vitro study suggests that it would be possible to make dietary changes affecting the lipolysis, further triggering specific responses in the gastrointestinal tract. However, these observations need to be validated in vivo, and the mechanisms need to be further examined.