Lipid Digestion of Protein Stabilized Emulsions Investigated in a Dynamic In Vitro Gastro-Intestinal Model System
Helbig, A. ; Silletti, E. ; Aken, G.A. van; Oosterveld, A. ; Minekus, M. ; Hamer, R.J. ; Gruppen, H. - \ 2013
Food Digestion 4 (2013)2-3. - ISSN 1869-1978 - p. 58 - 68.
This study investigated the effect of gastric passage of protein stabilized emulsions, i.e., whey protein isolate (WPI) and lysozyme, under dynamic in vitro conditions on both the gastric and intestinal lipolysis. Emulsions were prepared at neutral pH to enable an opposite surface charge. Experiments were performed in a multi-compartmental digestion model (TNO Gastro-Intestinal Model) including a gastric compartment simulating in vivo conditions, i.e., gradual acidification, mixing, lipolysis and proteolysis. Under gastric conditions, lysozyme-stabilized emulsions remained macroscopically homogenous, whereas WPI-stabilized emulsions separated into a cream and serum layer. Microscopy revealed flocculation of both emulsions, but larger particles were found for the initial negatively charged WPI-stabilized emulsions compared to the positively charged lysozyme-stabilized emulsions. This suggested that creaming was due to larger flocs formation caused by a change from net negative to net neutral charge as an effect of the gradual decreasing pH. Analysis of lipid composition, i.e., free fatty acids (FFA), monoglycerides, diglycerides (DG) and triglycerides revealed mainly FFA and DG in the gastric compartment. As a result of creaming, the entry of lipids into the small intestinal part was delayed for WPI-stabilized emulsions. However, the total amount of FFA released at the end of the experiment was similar for both emulsions. Our results show, that the charge differences affected the creaming behavior, but not the lipase activity, on the two studied emulsions.
Digestion of dietary fat : gastrointestinal behaviour of emulsions and human physiological responses
Helbig, A. - \ 2013
Wageningen University. Promotor(en): Harry Gruppen; Rob Hamer, co-promotor(en): Erika Silletti. - S.l. : s.n. - ISBN 9789461735607 - 166
voedingsvet - spijsvertering - vetemulsies - spijsverteringskanaal - darmfysiologie - verzadigdheid - dietary fat - digestion - fat emulsions - digestive tract - intestinal physiology - satiety
Two in vitromodels were used to understand emulsion behavior and the subsequent formation of free fatty acids (FFA), monoglycerides (MG) and diglycerides (DG). Emulsions stabilized by whey protein isolate (WPI) or gum arabic (GA), varying in droplet size, were digested under intestinal conditions. Concentrations of FFA, MG and DG, assessed by gas chromatography, decreased with increasing droplet size. FFA release from gum arabic-stabilized emulsions was higher compared to WPI-stabilized emulsions showing an influence of the interface. Next, lipolysis of protein stabilized emulsions (i.e. WPI or lysozyme) and the influence of flocculation at the isoelectric point (pI) were investigated in a dynamic gastrointestinal model. The stomach properties including gradual acidification caused WPI-stabilized emulsions to cream during transition through the pI of the protein. This resulted in delayed intestinal lipolysis compared to the lysozyme-stabilized emulsion. Thus, since gastric passage affects emulsion behavior and intestinal lipolysis, the gastric passage should be part of digestion models. Next, in a human study emulsion behavior and resulting lipolytic products were related to the release of satiety hormones, satiety perception and ad libitumintake. Also, gallbladder volume and oral processing were studied. A delayed entry into the duodenum and lipolysis for the un-homogenized sample resulted in lower CCK, delayed GLP-1/PYY responses and barely gallbladder contraction compared to the homogenized emulsion. No difference was found between treatments on ghrelin, only the perception 'desire to eat´ was elevated for homogenized emulsions. Oral processing induced prolonged gallbladder contraction, but had no additive effect on other measures. A homogenous system as such is possibly not effective to induce pronounced satiety perceptions compared to phase separated or creamed systems using the same emulsifier. Moreover, the release of gastrointestinal hormones cannot directly be related to the satiating effect of food.
Emulsion properties of algae soluble protein isolate from Tetraselmis sp.
Schwenzfeier, A. ; Helbig, A. ; Wierenga, P.A. ; Gruppen, H. - \ 2013
Food Hydrocolloids 30 (2013)1. - ISSN 0268-005X - p. 258 - 263.
in-water emulsions - diffusing wave spectroscopy - whey-protein - physicochemical properties - stabilized emulsions - flocculation - emulsifiers - adsorption - microalgae - pectin
To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl2 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d32 = 1 µm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ¿-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ¿-potential remained negative over the whole pH range investigated. An increase in ionic strength (=100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.
In vitro study of intestinal lipolysis using pH-stat and gas chromatography
Helbig, A. ; Silletti, E. ; Timmerman, E. ; Hamer, R.J. ; Gruppen, H. - \ 2012
Food Hydrocolloids 28 (2012)1. - ISSN 0268-005X - p. 10 - 19.
pancreatic lipase activity - human gastric lipase - fat digestion - bile-salt - stereoselective hydrolysis - emulsion flocculation - droplet sizes - digestibility - triglycerides - absorption
Developing healthy products requires in-depth knowledge of digestion. This study focuses on lipid digestion in relation to emulsion properties typically followed by pH-stat. Although this is a fast and easy method to follow the overall digestion, it provides no details on lipid digestion products. Thus, the aims of the present study were to use gas chromatography (GC) to determine all products present during lipolysis, i.e. monoglycerides (MG), diglycerides (DG) and triglycerides (TG), and to compare this method with the pH-stat method for free fatty acids (FFA). Fine, medium and coarse emulsions stabilized with two different emulsifiers (whey protein isolate (WPI) or gum arabic) were digested under in vitro intestinal conditions. Although the amount of FFA increased for both methods for WPI stabilized emulsions, the amount of FFA was 2–3 times higher when determined by GC compared with pH-stat. GC analysis showed decreasing amounts of MG and DG with increasing droplet size for both emulsions. Molar ratios of FFA/DG and MG/DG were twofold higher for WPI than for gum arabic stabilized emulsions. This indicates that the total production of lipolytic products (i.e. FFA + MG + DG) depends on the droplet size and the emulsifier but their proportions only depend on the emulsifier. Although pH-stat provides a fast measure of FFA release, it is influenced by the emulsifier type at the oil–water interface and therefore care should be taken when interpreting pH-stat results. We suggest combining this method with GC for accurate FFA determination and further evaluation of all lipolytic products.
|Influence of droplet size and surfactants on the breakdown kinetics of emulsions in an in vitro digestion model
Helbig, Anne - \ 2009