Chloroplast thylakoid membrane-stabilised emulsions.

BACKGROUND: Thylakoid-stabilised emulsions have been reported to possess satiety-promoting effects and inhibit pancreatic lipase-colipase activity in vitro, which prompted the investigation of their interfacial properties. RESULTS: Thylakoid membranes isolated from spinach were used as an emulsifier/stabiliser in oil (triglyceride)-in-water emulsions. Emulsions were characterised with respect to droplet size, interfacial tension, creaming, surface load and electron microscopy. The effects of pH and thylakoid concentration were also considered. Droplet size decreased with increasing thylakoid concentration, reaching a plateau around 15 microm beyond concentrations of 2 mg protein mL(-1) oil. The resulting emulsions were stable against coalescence but were subject to creaming. The surface pressure (air/water interface) of the thylakoid isolate was 44 mN m(-1) and the surface load 13 mg m(-2) at 10 mg protein mL(-1) oil. Electron micrographs showed thylakoids adsorbed as bunched vesicles on the drop surfaces. The stabilisation mechanism can be described as a combined effect of surface-active molecules, mainly membrane proteins but also membrane lipids, exposed on surfaces of thylakoid membrane vesicles adsorbed as particles. CONCLUSION: Thylakoid membranes effectively stabilise oil-in-water emulsions, which should facilitate their incorporation in food with satiety-promoting effects. To the authors' knowledge, this is the first study on the emulsifying properties of an isolated biological membrane as a functional ingredient.

A large scale method for preparation of plant thylakoids for use in body weight regulation.

A method for preparation of thylakoids from plant leaves on a large scale is described. The method involves: 1) disruption of the cells with a blender followed by filtration to remove large cell debris and non disrupted cells. 2) precipitation of the thylakoids by adjusting the pH to the isoelectric point, pH 4.7. 3) a washing step by dilution of the precipitate in water followed by precipitation at the same pH. 4) concentration of the precipitate by freeze- thawing or freeze -drying to get the final product. The product is characterized, with respect to protein composition, by SDS-PAGE and mass-spectroscopy, the content of carotenoids, particularly the xanthophylls violaxanthin, antheraxanthin, and zeaxanthin. The thylakoid preparation has about the same capacity to inhibit pancreatic lipase/colipase activity as thylakoids prepared by standard laboratory methods using sucrose in the medium and centrifugation. In a study with mice, it was found that, when the thylakoids were added to the food over 32 days, they significantly reduced the body weight gain and the percentage body fat. The large scale method described here allows studies on the effect of thylakoids in appetite regulation on experimental animals in a longer lasting time and also on humans.

Thylakoids promote release of the satiety hormone cholecystokinin while reducing insulin in healthy humans.

OBJECTIVE: The effects of a promising new appetite suppressor named "thylakoids" (membrane proteins derived from spinach leaves) were examined in a single meal in man. Thylakoids inhibit the lipase/colipase hydrolysis of triacylglycerols in vitro and suppress food intake, decrease body-weight gain and raise the satiety hormone cholecystokinin (CCK) in rats, but their effects in man remain unclear. The aim of this study was to investigate whether thylakoids, when added to a test meal, affect appetite regulation and blood parameters in healthy individuals. MATERIAL AND METHODS: In an intervention crossover study, healthy individuals of normal weight (n=11) were offered a high-fat meal with and without the addition of thylakoids. Blood samples were taken 0 (prior to meal), 30, 60, 120, 180, 240, 300 and 360 min after the start of the meal. Blood samples were analysed for satiety and hunger hormones (CCK, leptin and ghrelin), insulin and blood metabolites (glucose and free fatty acids). RESULTS: The CCK level increased, in particular between the 120 min time-point and onwards, the ghrelin level was reduced at 120 min and leptin level increased at 360 min after intake of the thylakoid-enriched meal. The insulin level was reduced, whereas glucose concentrations were unchanged. Free fatty acids were reduced between time-point 120 min and onwards after the thylakoid meal. CONCLUSIONS: The addition of thylakoids to energy-dense food promotes satiety signals and reduces insulin response during a single meal in man.

Thylakoids suppress appetite by increasing cholecystokinin resulting in lower food intake and body weight in high-fat fed mice.

Thylakoids are membranes isolated from plant chloroplasts which have previously been shown to inhibit pancreatic lipase/colipase catalysed hydrolysis of fat in vitro and induce short-term satiety in vivo. The purpose of the present study was to examine if dietary supplementation of thylakoids could affect food intake and body weight during long-term feeding in mice. Female apolipoprotein E-deficient mice were fed a high-fat diet containing 41% of fat by energy with and without thylakoids for 100 days. Mice fed the thylakoid-enriched diet had suppressed food intake, body weight gain and body fat compared with the high-fat fed control mice. Reduced serum glucose, serum triglyceride and serum free fatty acid levels were found in the thylakoid-treated animals. The satiety hormone cholecystokinin was elevated, suggesting this hormone mediates satiety. Leptin levels were reduced, reflecting a decreased fat mass. There was no sign of desensitization in the animals treated with thylakoids. The results suggest that thylakoids are useful to suppress appetite and body weight gain when supplemented to a high-fat food during long-term feeding.

Chloroplast membranes retard fat digestion and induce satiety: effect of biological membranes on pancreatic lipase/co-lipase.

Human obesity is a global epidemic, which causes a rapidly increased frequency of diabetes and cardiovascular disease. One reason for obesity is the ready availability of refined food products with high caloric density, an evolutionarily new event, which makes over-consumption of food inevitable. Fat is a food product with high caloric density. The mechanism for regulation of fat intake has therefore been studied to a great extent. Such studies have shown that, as long as fat stays in the intestine, satiety is promoted. This occurs through the fat-released peptide hormones, the best known being CCK (cholecystokinin), which is released by fatty acids. Hence, retarded fat digestion with prolonged time for delivery of fatty acids promotes satiety. Pancreatic lipase, together with its protein cofactor, co-lipase, is the main enzymatic system responsible for intestinal fat digestion. We found that biological membranes, isolated from plants, animals or bacteria, inhibit the lipase/co-lipase-catalysed hydrolysis of triacylglycerols even in the presence of bile salt. We propose that the inhibition is due to binding of lipase/co-lipase to the membranes and adsorption of the membranes to the aqueous/triacylglycerol interface, thereby hindering lipase/co-lipase from acting on its lipid substrate. We also found that chloroplast membranes (thylakoids), when added to refined food, suppressed food intake in rats, lowered blood lipids and raised the satiety hormones, CCK and enterostatin. Consequently, the mechanism for satiety seems to be retardation of fat digestion allowing the fat products to stay longer in the intestine.