Abstract
This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X − 305.3)0.104, with R2 = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.
Highlights
Accepted: 26 February 2021Emulsion-based systems for the delivery of lipophilic bioactive compounds, such as capsaicin, β-carotene and curcumin, by incorporating the bioactive compounds in the emulsion droplets, have been widely studied for the purposes of improving water solubility, stability and bioaccessibility [1,2,3,4,5]
The trends of the pH profiles during gastric digestion were similar for both gels, indicating that the structure of the protein matrix did not have a significant effect on the buffering capacity of the emulsion gel
This work demonstrated the effect of gel characteristics on the in vitro gastric digestion behaviour of whey protein emulsion gels containing CAP using a human gastric simulator, and the effect of the structure of the gastric digesta on its in vitro intestinal digestion and the bioaccessibility of CAP
Summary
Accepted: 26 February 2021Emulsion-based systems for the delivery of lipophilic bioactive compounds, such as capsaicin, β-carotene and curcumin, by incorporating the bioactive compounds in the emulsion droplets, have been widely studied for the purposes of improving water solubility, stability and bioaccessibility [1,2,3,4,5]. Lu et al [4] investigated the use of nanoemulsions for the delivery of capsaicin and reported that the bioaccessibility of capsaicin increased from about 10% in the unformulated form to about 80% in the capsaicinloaded nanoemulsion after in vitro lipid digestion. The behaviour of liquid emulsions during in vitro gastrointestinal digestion has been widely investigated in recent decades, one of the common behaviours investigated is flocculation/coalescence of oil droplets in the gastrointestinal tract [6,7,8]. Different from liquids, solid/semi-solid foods undergo more complicated processes during digestion, because they require mastication during oral processing, trituration and disintegration of the solid particles in the stomach to form particles that are small enough to pass through the pyloric sphincter. Solid/semi-solid foods usually take a longer time to digest
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