In vitro digestion of interfacial protein structures

Abstract

It is important to understand how interfacial composition influences the digestion of coated interfaces in order to rationally design emulsion based food products with specific digestion profiles. This study has been designed to investigate the effects of gastrointestinal digestion on protein covered interfaces. In this work, we have used a new apparatus fully designed and assembled at the University of Granada: the OCTOPUS. This new device enables the design of a customised static sequential in vitro digestion process in a single droplet. Physiological conditions of each compartment/step of the digestion process are met through subphase exchange of artificial digestive media, hence mimicking the transit through the gastrointestinal tract. We can measure in situ the evolution of the interfacial tension throughout the whole simulated gastrointestinal transit and the mechanical properties of the interfacial layer (interfacial dilatational modulus) after each digestion stage (mouth, stomach, small intestines). The in vitro digestion model used here focuses on pepsinolysis and lipolysis of two dairy proteins: b-lactoglobulin (BLG) and b-casein (BCS) adsorbed at the olive oil-water interface. The results show different susceptibilities of interfacial layers of BLG and BCS to pepsinolysis; while pepsinolysis of adsorbed BLG weakens the interfacial network, pepsinolysis of adsorbed BCS strengthens it as measured by the dilatational moduli. These numbers provide an interfacial scenario for previous findings on emulsification of these proteins, which was found to improve BLG pepsinolysis but somehow protected BCS from pepsinolysis in the stomach. The desorption profiles provide quantification of the extent of lipid digestion in subsequent simulated intestinal fluid containing lipase. The extent of lipid hydrolysis was found to be similar in BLG and BCS covered interfaces and comparable to that in the absence of coverage (pure oil-water interface) indicating that proteins do not comprise a barrier to lipolysis. This similar susceptibility is attributed to the similar interfacial properties of the interfaces reaching the duodenum despite the structural differences between native BCS and BLG, thus demonstrating the impact of the transit through the gut on lipolysis. This research allows identification of the interfacial mechanisms affecting enzymatic hydrolysis of proteins and lipolysis. The results can be exploited in tailoring novel food matrices with improved functional properties such as decreased digestibility, controlled energy intake and low allergenicity.

Potential bioavailability enhancement of bioactive compounds using food-grade engineered nanomaterials: a review of the existing evidence

“…114 Different peptide patterns arising from enzymatic digestion, in turn, might play a role with respect to the allergenicity of the protein. 173 To our knowledge, the only studies investigating the effect of purely protein-based delivery systems for food applications concerned the delivery of vitamin D. The encapsulation of vitamin D in rCM resulted in a protection of vitamin D from degradation superior to a commercial Tween 80-based supplement while the bioavailability of vitamin D from both preparations was similar. Conclusions about possible differences with respect to the fate of the preparations in the GIT and their impact on the absorption of vitamin D cannot be drawn from that study, because the test systems were comprised of very different constituents and of different complexities (the rCM were added to 1% fat milk while the Tween-80 micelles were given in the form of an aqueous suspension).…”

Subphase exchange experiments with the pendant drop technique

“…Still, NaGDC displayed a clearly faster desorption rate than NaTC hence suggesting different surface interactions [31]. Subsequent work including dilatational rheology, studied the desorption profile from the oil-water interface for a physiologically relevant mixture of the same BS, NaTC and NaGDC [32]. This mixture also turned out to be reversibly adsorbed at the oil-water interface under more realistic conditions of ionic strength and temperature.…”

“…The different gastrointestinal media are injected into the pendant drop by subphase exchange of physiological solutions. The multiexchange device allows applying sequential digestive media and measuring synergisms and cumulative effects at the interface, which have proven to be determinant in the fate of interfaces along the gastrointestinal tract [32]. Owing to the presence of enzymes in the digestive media, the reactions at interfaces now include enzymatic hydrolysis and can be more complex than the processes reviewed in previous sections (desorption, penetration, displacement and complexation).…”

“…Macierzanka and co-workers importantly conclude that emulsification affects proteolysis of BCS and BLG, hence opening up a whole new research to look into the proteolysis of interfacial layers. A similar experiment was later reproduced with The OCTOPUS, which allowed a more realistic subphase multi-exchange approach [32]. Therein we apply a customised in vitro digestion model by sequentially simulating the different compartments of the gastrointestinal tract in a single droplet [32].…”

Monitoring experiments using mobile devices

“…Hence, some kinds of experiments need several hours to finish without the interaction of users and sometimes experiments are carried out in special laboratories where researchers have to stay long periods of time in order to check the successful of these experiments [6] [7]. In the latter case, in addition, the researcher usually has to supervise the experiment by inspection on a screen.…”