Different tastants and low-caloric sweeteners induce differential effects on the release of satiety hormones

Recent studies have found different types of taste receptors located along the intestine. However, the effect of tastants, and in particular sweet tastants, on satiety hormone release is still unknown.     

Direct induction of CCK and GLP-1 release from murine endocrine cells by intact dietary proteins

Scope: Consumption of high‐protein diets cause elevated levels of CCK and GLP‐1. Although unknown, this might be due to protein breakdown by various proteases that originate from the gastrointestinal tract. This study investigated which dietary proteins, hydrolysates, or synthetic‐peptides are most potent to affect secretion of CCK and GLP‐1 in STC‐1 cells known for satiety hormone release. Methods and results: Addition of intact proteins to STC‐1 cells exerted strong effects on secretion of satiety hormones. Casein, whey, and pea showed strongest effects on CCK release, whereas casein, codfish, egg, and wheat showed most pronounced effects on GLP‐1 release. Egg‐hydrolysate stimulated release of CCK and GLP‐1, whereas all other tested hydrolysates and synthetic‐peptides showed no significant effects on hormone release. Addition of a combination of trypsin and casein‐hydrolysate, codfish, egg, egg‐hydrolysate, sodium‐casein, wheat‐hydrolysate, or wheat resulted in additional stimulation of CCK release, compared to only the protein. Addition of a combination of DPP‐IV and egg‐hydrolysate, ovomucoid, or sodium‐casein decreased GLP‐1 levels. Conclusion: This study showed that specific intact, or partially digested proteins, in contrast to protein‐hydrolysates and synthetic‐peptides, stimulated hormone release. We conclude that intact proteins exert strong effects on satiety hormone release, and may therefore provide potent dietary supplements for prevention or treatment of obesity.     

Possible abilities of dietary factors to prevent and treat diabetes via the stimulation of glucagon‐like peptide‐1 secretion

There is a pressing need for countermeasures against diabetes, which has increased in incidence, becoming a global issue. Glucagon‐like peptide‐1 (GLP‐1), a molecule secreted in enteroendocrine L cells in the lower small and large intestines, is thought to be one of the most important molecular targets for the prevention and treatment of diabetes. There has been increasing interest in the possible ability of dietary factors to treat diabetes via modulating GLP‐1 secretion. There is thought to be a close relationship between incretin and diet, and the purported best approach for using dietary factors to increase GLP‐1 activity is promotion of secretion of endogenous GLP‐1. It have been reported that nutrients as well as various non‐nutrient dietary factors can function as GLP‐1 secretogogues. Here, we present our findings on the GLP‐1 secretion‐stimulating functions of two dietary factors, curcumin and extract of edible sweet potato leaves, which contain caffeoylquinic acid derivatives. However, it is necessary to reveal in greater detail the stimulation of GLP‐1 secretion by dietary factors for preventing and treating diabetes. It is desirable to clarify the exact GLP‐1 secretory pathway, the effect of metabolites derived from dietary factors in gut lumen, and the relationship between incretin and meal.     

A nondigestible saccharide,fructooligosaccharide, increases the promotive effect of a flavonoid, α‐glucosyl‐isoquercitrin,on glucagon‐like peptide 1 (GLP‐1) secretion in rat intestine and enteroendocrine cells

This study conducted in vivo and in situ experiments with rats to investigate the glucagon‐like peptide‐1 (GLP‐1) secretion in response to oral or ileal administration of α‐glucosyl‐isoquercitrin (20–40 mmol in 2 mL; Q3G), fructooligosaccharides (200 mmol in 2 mL; FOS) and Q3G + FOS. Direct effects on GLP‐1‐producing l ‐cells were also examined by an in vitro study using a murine enteroendocrine cell line, GLUTag. To evaluate the plasma GLP‐1 level, blood samples from jugular cannula for in vivo and portal cannula for in situ experiments were obtained before and after administration of Q3G, FOS, or Q3G + FOS. We found tendencies for increases but transient stimulation of GLP‐1 secretion by Q3G in in vivo and in situ experiments. Although FOS alone did not have any effects, Q3G + FOS enhanced and prolonged high plasma GLP‐1 level in both experiments. In addition, application of Q3G on GLUTag cells stimulated GLP‐1 secretion while FOS enhanced the effect of Q3G. Our results suggest that Q3G + FOS possess the potential for the management or prevention of Type 2 diabetes mellitus (T2DM) by enhancing and prolonging the GLP‐1 secretion via direct stimulation of GLP‐1 producing l ‐cell.     

Long-term high animal protein diet reduces body weight gain and insulin secretion in diet-induced obese rats

BACKGROUND: The effects of a high protein diet on insulin secretion and glucose metabolism have been quite controversial. The aim of this study was to evaluate the effects of long‐term isocaloric high animal protein intake on insulin secretion in diet‐induced obese rats. RESULTS: After the experimental period (24 weeks), the high‐fat diet‐induced obese rats that were fed isocaloric high‐protein diets (HP) had lower body weight gain (P < 0.01) and lower visceral fat (P < 0.05) than normal protein (NP) rats. Fasting plasma glucagon‐like peptide‐1 (GLP‐1) was also reduced significantly (P < 0.05), as well as serum insulin levels at 5 min and 10 min by intravenous insulin releasing test. In addition, insulin mRNA and pancreatic duodenal homeodomain‐1 (PDX‐1), GLP‐1 protein expression were both markedly lower in HP rats (P < 0.05), while PDX‐1 mRNA in HP rats had no difference from NP rats. CONCLUSION: These results suggest that long‐term isocaloric high animal protein intake reduces the acute insulin response in obese rats and the decrease of insulin is associated with both reduced weight gain and inhibition of PDX‐1 expression. GLP‐1 might be a negative feedback for the balance of energy metabolism secondary to changes of body weight and visceral fat. Copyright © 2012 Society of Chemical Industry     

Dietary-resistant starch improves maternal glycemic control in Goto-Kakizaki rat

Scope: Dietary prebiotics show potential in anti‐diabetes. Dietary resistant starch (RS) has a favorable impact on gut hormone profiles, including glucagon‐like peptide‐1 (GLP‐1) consistently released, a potent anti‐diabetic incretin. Also RS reduced body fat and improved glucose tolerance in rats and mice. In the current project, we hypothesize that dietary‐resistant starch can improve insulin sensitivity and pancreatic β cell mass in a type 2 diabetic rat model. Altered gut fermentation and microbiota are the initial mechanisms, and enhancement in serum GLP‐1 is the secondary mechanism. Methods and results: In this study, GK rats were fed an RS diet with 30% RS and an energy control diet. After 10 wk, these rats were mated and went through pregnancy and lactation. At the end of the study, pancreatic β cell mass, insulin sensitivity, pancreatic insulin content, total GLP‐1 levels, cecal short‐chain fatty acid concentrations and butyrate producing bacteria in cecal contents were greatly improved by RS feeding. The offspring of RS‐fed dams showed improved fasting glucose levels and normal growth curves. Conclusion: Dietary RS is potentially of great therapeutic importance in the treatment of diabetes and improvement in outcomes of pregnancy complicated by diabetes.     

Effect of quantifying peptide release on ruminal protein degradation determined using the inhibitor in vitro system

The aim of this work was to compare use of an o-phthaldialdehyde (OPA) colorimetric assay (OPA-C), which responds to both free AA and peptides, with an OPA fluorimetric assay (OPA-F), which is insensitive to peptides, to quantify rates of ruminal protein degradation in the inhibitor in vitro system using Michaelis-Menten saturation kinetics. Four protein concentrates (expeller-extracted soybean meal, ESBM; 2 solvent-extracted soybean meals, SSBM1 and SSBM2; and casein) were incubated in a ruminal in vitro system treated with hydrazine and chloramphenicol to inhibit microbial uptake of protein degradation products. Proteins were weighed to give a range of N concentrations (from 0.15 to 3 mg of N/mL of inoculum) and incubated with 10 mL of ruminal inoculum and 5 mL of buffer; fermentations were stopped after 2 h by adding trichloroacetic acid (TCA). Proteins were analyzed for buffer-soluble N and buffer extracts were treated with TCA to determine N degraded at t = 0 (FD0). The TCA supernatants were analyzed for ammonia (phenol-hypochlorite assay), total AA (TAA; OPA-F), and TAA plus oligopeptides (OPA-C) by flow injection analysis. Velocity of protein degradation was computed from extent of release of 1) ammonia plus free TAA or 2) ammonia plus free TAA and peptides. Rate of degradation (k_d) was quantified using nonlinear regression of the integrated Michaelis-Menten equation. The parameters K_m (Michaelis constant) and k_d (Vmax/K_m), where Vmax = maximum velocity, were estimated directly; k_d values were adjusted (Ak_d) for the fraction FD0 using the equation Ak_d = k_d − FD0/2. The OPA-C assay yielded faster degradation rates due to the contribution of peptides to the fraction degraded (overall mean = 0.280/h by OPA-C and 0.219/h by OPA-F). Degradation rates for SSBM samples (0.231/h and 0.181/h) and ESBM (0.086/h) obtained by the OPA-C assay were more rapid than rates reported by the National Research Council (NRC). Both assays indicated that the 2 SSBM differed in rumen-undegradable protein (RUP) content; the more slowly degraded SSBM had RUP content (35% by OPA-C) similar to that reported by the NRC. The RUP content of ESBM (42% by OPA-C) was lower than the NRC value. Preliminary studies with 4 additional protein concentrates confirmed that accounting for peptide formation increased degradation rate; however, a trend for an interaction between assay and protein source suggested that peptide release made a smaller contribution to rate for more slowly degraded proteins. The OPA-C assay is a simple and reliable method to quantify formation of small peptides.     

Molecular forces involved in heat-induced pea protein gelation: Effects of various reagents on the rheological properties of salt-extracted pea protein gels

The molecular forces involved in the gelation of heat-induced pea protein gel were studied by monitoring changes in gelation properties in the presence of different chemicals. At 0.3 M concentration, sodium thiocyanate (NaSCN) and sodium chloride (NaCl) showed more chaotropic characteristic and enhanced the gel stiffness, whereas sodium sulfate (Na₂SO₄) and sodium acetate (CH₃COONa) stabilized protein structure as noted by increasing denaturation temperatures (T_d) resulting in reduced storage moduli (G′). To determine the involvement of non-covalent bonds in pea protein gelation, guanidine hydrochloride (GuHCl), propylene glycol (PG), and urea were employed. The significant decrease in G′ of pea protein gels with the addition of 3 M GuHCl and 5 M urea indicated that hydrophobic interactions and hydrogen bonds are probably involved in pea protein gel formation. The increase in G′ with increasing PG concentration (5–20%), demonstrated hydrogen bonds and electrostatic interaction involvement. No significant influence was observed on G′ with addition of different concentrations of β-mercaptoethanol (2-ME), low levels of dithiothreitol (DTT), and up to 25 mM N-ethylmaleimide (NEM), which indicated that disulfide bonds are not required for gel formation, but data at higher DTT and NEM concentrations and slow cooling rates showed a minor contribution by disulfide bonds. Reheating and recooling demonstrated that gel strengthening during the cooling phase was thermally reversible but not all the hydrogen bonds disrupted in the reheating stage were recovered when recooled.     

Improved gelation functionalities of myofibrillar protein from pale,soft and exudative chicken breast meat by nonenzymatic glycation with glucosamine

The potential of nonenzymatic glycation of myofibrillar proteins (MPs) to improve the gelation functionalities of pale, soft and exudative (PSE‐like) chicken breast meat was investigated. MP suspensions (4 mg mL^?1) obtained from both normal and PSE‐like chicken breast meat were mixed with glucosamine at a ratio of 1:6 (protein : glucosamine) in phosphate‐buffered saline (0.6 m KCl, 20 mm K₂HPO₄/KH₂PO₄, 0.02% NaN₃ and pH 7.5) and incubated at 37 °C for 12 h. Untreated normal and PSE‐like MP suspensions maintained at 4 °C were used as positive and negative controls, respectively. The glycation treatment increased the surface hydrophobicity but decreased the reactive sulfhydryl contents compared to those of the control (P < 0.05), indicating that the tertiary conformation of the protein changed. Correspondingly, these glycated samples also exhibited significant improvements in gel strength and the water‐holding capacity (P < 0.05). Conclusively, nonenzymatic glycation is a potential technique to improve the properties and offer a means for effective use of PSE‐like meat.     

Fractionation of angiotensin I converting enzyme inhibitory activity from pea and whey protein in vitro gastrointestinal digests

In vitro gastrointestinal digestion of pea and whey protein produced high angiotensin I converting enzyme (ACE) inhibitory activity with IC₅₀ values of 0.070 and 0.041 mg protein ml^?1 respectively. Ultrafiltration/centrifugation using a membrane with a molecular weight cut‐off of 3000 Da decreased the IC₅₀ value to 0.055 mg protein ml^?1 for pea permeate and 0.014 mg protein ml^?1 for whey permeate. Further fractionation by reverse phase HPLC gave IC₅₀ values as low as 0.016 mg protein ml^?1 for pea and 0.003 mg protein ml^?1 for whey. Consequently, these purification steps enriched the ACE inhibitory activity of the pea digest more than four times and that of the whey digest more than 13 times. HPLC profiles after digestion and ultrafiltration indicate that high ACE inhibitory activity is due to short and more hydrophobic peptides. The results also suggest that potent ACE inhibitory peptides were present alongside low active peptides in whey hydrolysate, while all peptides had more or less the same ACE inhibitory activity in pea hydrolysate. In addition, the hydrolysates and enriched fractions will resist in vivo gastrointestinal digestion after oral administration. Hence these ACE inhibitory peptides, as part of functional foods, can play significant roles in the prevention and treatment of hypertension. Copyright © 2004 Society of Chemical Industry     

Effects of gastrointestinal digestion and heating on the allergenicity of the kiwi allergens Act d 1, actinidin, and Act d 2, a thaumatin-like protein

Kiwifruit is a significant elicitor of allergy both in children and adults. Digestibility of two kiwifruit allergens, actinidin (Act d 1) and thaumatin-like protein (Act d 2), was assessed using an in vitro digestion system that approximates physiological conditions with respect to the passage of food through the stomach into the duodenum. Act d 1 precipitated in simulated gastric fluid at pH 2 and digestion of the aggregated protein proceeded slowly. The residual precipitate redissolved completely in simulated duodenal fluid at pH 6.5 and was partially digested. Forty percent of Act d 2 remained intact during gastric digestion and were cleaved by duodenal proteases into large fragments covalently linked by disulfide bonds. Both digested allergen samples displayed nearly unchanged IgE binding abilities. Circular dichroism spectra were used to analyze heat and acid-induced unfolding. Thermal stability of both allergens was strongly pH dependent. While Act d 1 was irreversibly destabilized in acidic solutions, heat-induced denaturation of Act d 2 at pH 2 was fully reversible. IgE binding to Act d 2 but not Act d 1 was detected in processed food products. The stability of Act d 1 and Act d 2 provides one explanation for the allergenic potency of kiwifruit.     

Effect of whey and pea protein blends on the rheological and sensory properties of protein-based systems flavoured with cocoa

Whey and pea protein combined in different proportions (100W:0P, 75W:25P, 50W:50P, 25W:75P, 0W:100P) were used to prepare protein-based systems flavoured with cocoa and containing κ-carrageenan or κ-carrageenan/xanthan gum as thickeners. Steady and dynamic shear rheological properties of samples were measured at 10 °C and sensory differences were evaluated. Protein-based systems exhibited a shear-thinning flow behaviour that was fitted to the simplified Carreau model. Samples showed different viscoelastic properties, ranging from fluid-like to weak gel behaviour. For both types of system (with and without xanthan gum) viscosity, pseudoplasticity and elasticity rose on increasing the pea protein proportion in the blend. The sample with only whey protein obeyed the Cox-Merz rule, while in the rest of the samples complex viscosity was higher than apparent viscosity. Regarding sensory properties, the protein blend ratio mainly affected sample thickness, which rose as pea protein proportion increased. However, at the same time, the chocolate flavour and sweetness decreased and the off-flavour increased.     

One-step multiplex PCR method for the determination of pecan and Brazil nut allergens in food products

BACKGROUND: A one‐step polymerase chain reaction (PCR) method for the simultaneous detection of the major allergens of pecan and Brazil nuts was developed. Primer pairs for the amplification of partial sequences of genes encoding the allergens were designed and tested for their specificity on a range of food components. RESULTS: The targeted amplicon size was 173 bp of Ber e 1 gene of Brazil nuts and 72 bp of vicilin‐like seed storage protein gene in pecan nuts. The primer pair detecting the noncoding region of the chloroplast DNA was used as the internal control of amplification. The intrinsic detection limit of the PCR method was 100 pg mL^?1 pecan or Brazil nuts DNA. The practical detection limit was 0.1% w/w (1 g kg^?1). The method was applied for the investigation of 63 samples with the declaration of pecans, Brazil nuts, other different nut species or nuts generally. In 15 food samples pecans and Brazil nuts allergens were identified in the conformity with the food declaration. CONCLUSION: The presented multiplex PCR method is specific enough and can be used as a fast approach for the detection of major allergens of pecan or Brazil nuts in food. Copyright © 2011 Society of Chemical Industry     

Heat shock transiently enhances the synthesis rate of Sis1p,a ribosome-associated DnaJ protein in the oleagenous yeast Apiotrichum curvatum

DnaJ proteins have been localized in different intracellular compartments of eukaryotes. In Apiotrichum curvatum, a fat-storing yeast, we found a DnaJ homolog associated with ribosomes and large cytosolic complexes as well. Using a plant DnaJ probe and a cDNA library constructed from poly(A)⁺ -RNA of A. curvatum grown on oleate we isolated a SIS1 cDNA coding for a 39·5 kDa protein. The putative protein contains neither a zinc finger motif nor a CAAX motif but is characterized by a J-domain at the N-terminal region and a large G-rich region in the middle part of the molecule. Heat shock applied for 1 h resulted in a pronounced but transient increase of the SIS1 mRNA. An antiserum was raised against the bacterially expressed protein. Cell fractions from A. curvatum were further separated by sedimentation centrifugation on sucrose gradients. Analysing the sub-fractions, we detected Sis1p mainly associated with ribosomes, and with particles sedimenting at approximately 200S. Hsp70 was found to be associated with the 200S fraction. The respective cytosolic A. curvatum Hsp70 cDNA was cloned and sequenced. High salt conditions caused the removal of Hsp70 and Sis1p from the 200S complexes. Mild RNase treatment of the 200S fraction afforded monosomes and 200S complexes unaffected by RNase. Heat shock led to a pronounced increase in the rate of de novo synthesis. However, due to the large pools of Sis1p on ribosomes and large cytosolic complexes, the increase in gene activation did not lead to a significant change of the total amount of Sis1p. Accession numbers are: Y12079 for ACHSP70 and Y12080 for ACSIS1. © 1998 John Wiley & Sons, Ltd.