Soybean Protein Isolate Group Research Articles

Homogenization pressure and soybean protein concentration impact the stability of perilla oil nanoemulsions

Perilla oil (PO) nanoemulsions (PON) were prepared using different concentrations (2, 3, and 4%) of soybean protein isolate (SPI) at different homogenization pressures (80, 100, 120, and 140 MPa). The stability of the PON and the interaction between interfacial protein structure and stability were investigated. The results showed that SPI concentration changed the particle size, ζ-potential, and interfacial protein concentration of the PON, but the SPI concentration did not change the interfacial protein structure. The PON from the 3% SPI group had the smallest particle size, the highest absolute ζ-potential, and the highest interfacial protein concentration. Physical stability and oxidant stability of the PON were best with 3% SPI. However, homogenization pressure not only changed the stability but also changed the structure of the interfacial proteins. Taken together, the PON at 120 MPa of pressure were the most stable. As homogenization pressure increased, the α-helix and β-sheet contents of the interfacial protein decreased, and random coil content increased. The SPI unfolded on the surface of the oil droplets, increasing the flexibility of the SPI, so that the protein was more easily adsorbed on the surface of the oil droplets, thereby increasing the stability of the PON.

Mechanical Properties and Fire Resistance of Magnesium-Cemented Poplar Particleboard.

Magnesium-cemented poplar particleboard (MCPB) is a new environmental inorganic magnesium cementitious composite without formaldehyde release. In this study, soybean flour (SM), silane coupling agent (KH560), soybean protein isolate (SPI), polyethylene glycol (PEG-400), maleic anhydride (MAH), and polyacrylic acid (PAA) were added to MCPB to improve the mechanical properties, waterproofing properties, and flame retardancy. The results show that the SPI group had the best mechanical performance; the modulus of elasticity (MOE) was up to 5192 MPa and exceeded the Chinese national standard GBT 4897-2015 (GBT) by 67.4%, the modulus of rupture (MOR) reached 17.72 MPa and exceeded GBT by 18%. Thickness swelling (TS) after 24-hour immersion was 0.29% and reached the standard of GBT (≤16%). The fire resistance test of MCPB indicated that the KH560 group improved the flame retardancy, the heat release rate (HRR) was 18kW/m2, the total smoke produced (TSP) was 0.192 m2, the total heat release (THR) was 29.71 MJ/kg, which reached the Chinese national standard GBT 8624-2012.

Elevation of Glucose 6-Phosphate Dehydrogenase Activity Induced by Amplified Insulin Response in Low Glutathione Levels in Rat Liver.

Weanling male Wistar rats were fed on a 10% soybean protein isolate (SPI) diet for 3 weeks with or without supplementing 0.3% sulfur-containing amino acids (SAA; methionine or cystine) to examine relationship between glutathione (GSH) levels and activities of NADPH-producing enzymes, glucose 6-phosphate dehydrogenase (G6PD) and malic enzyme (ME), in the liver. Of rats on the 10% SPI diet, GSH levels were lower and the enzyme activities were higher than of those fed on an SAA-supplemented diet. Despite the lower GSH level, γ-glutamylcysteine synthetase (γ-GCS) activity was higher in the 10% SPI group than other groups. Examination of mRNAs of G6PD and ME suggested that the GSH-suppressing effect on enzyme induction occurred prior to and/or at transcriptional levels. Gel electrophoresis of G6PD indicated that low GSH status caused a decrease in reduced form and an increase in oxidized form of the enzyme, suggesting an accelerated turnover rate of the enzyme. In primary cultured hepatocytes, insulin response to induce G6PD activity was augmented in low GSH levels manipulated in the presence of buthionine sulfoximine. These findings indicated that elevation of the G6PD activity in low GSH levels was caused by amplified insulin response for expression of the enzyme and accelerated turnover rate of the enzyme molecule.

Plant Proteins Differently Affect Body Fat Reduction in High-fat Fed Rats

This study examined the effects of corn gluten (CG), wheat gluten (WG), and soybean protein isolate (SPI), as well as their hydrolysates, on weight reduction in rats fed a high-fat diet. Eight-month-old male Sprague–Dawley rats (n=70) were fed a high-fat diet (40% of the calories were fat) for 4 weeks. Rats were then randomly divided into seven groups and were fed isocaloric diets with different protein sources for 8 weeks. The protein sources were casein (control group), intact CG (CG group), CG hydrolysate (CGH group), intact WG (WG group), WG hydrolysate (WGH group), intact SPI (SPI group), and SPI hydrolysate (SPIH group). Body weight gain, adipose tissue weights, lipid profiles in plasma and liver; and hepatic activities of carnitine palmitoyl transferase, fatty acid synthase (FAS), malic enzyme, and glucose-6-phosphate dehydrogenase were assessed. The CGH group showed significant weight reduction compared with the other groups. Epididymal fat pad and plasma triglycerides in the CGH group were the lowest and were significantly different than those in the control group. FAS activity in the CGH group was significantly lower than that in the other groups. In conclusion, the CGH diet of these experimental animals demonstrated a weight-reducing effect by lowering the adipose tissue weight and by affecting the activities of hepatic lipogenic enzymes.

Effects of Dietary Soybean Peptides on Hepatic Production of Ketone Bodies and Secretion of Triglyceride by Perfused Rat Liver

Soybean protein isolate (SPI) was digested with protease to produce a peptides containing the low-molecular fraction (LD3) or a mixture of high- and low-molecular fractions (HD1). Rats were fed a diets containing SPI, LD3, or HD1 at a protein level equivalent to the 20% casein diet for 4 weeks. The serum triglyceride concentration was lower in rats fed SPI, LD3, and HD1 diets than in rats fed the casein diet, and the differences were significant for the cholesterol-enriched diet. The value for the LD3 group was the lowest among all groups for both the cholesterol-free and -enriched diets. The level of triglyceride in the post-perfused liver was significantly lower in the LD3 and HD1 groups and the SPI group than in the casein group irrespective of the presence of cholesterol in the diet. In the cholesterol-free diet, LD3 feeding as compared to casein feeding caused a reduction in triglyceride secretion from the liver to perfusate and an increment of hepatic ketone body production. The addition of cholesterol to the diets somewhat attenuated these effects of LD3. These results suggest that the low-molecular fraction in soybean peptides causes triglyceride-lowering activity through a reduction in triglyceride secretion from the liver to the blood circulation and the stimulation of fatty acid oxidation in the liver. There is a possibility that soybean peptides modulate triglyceride metabolism by changes in the hepatic contribution.

Site-Specific Induction of Metallothionein in N-Nitrosodimethylamine-Treated Rat Liver.

The effects of dietary protein and sulfur-containing amino acids on oxidative responses against N-nitrosodimethylamine (NDMA) treatment were investigated in rat liver, focusing on the mechanism of metallothionein (MT) induction. Rats were fed a 10% soybean protein isolate (SPI) diet or SPI supplemented with 0.3% L-methionine (SPI-Met) for 3 weeks after weaning. Rats fed on SPI showed lower glutathione (GSH) levels and higher MT levels in the liver than those fed on SPI-Met. After treatment with NDMA (20 mg/kg, i.p.), MT levels were elevated significantly in both groups, whereas GSH levels were only elevated in the SPI group. Pathologically, necrosis and hemorrhage were seen in the livers of NDMA-treated rats of both dietary groups, suggesting oxidative damage caused by NDMA treatment. Immunological histochemistry using anti-MT antibody showed that most of the MT was distributed in the cytosol region of all the rat groups. The ratios of the MT-positive cells were correlated to MT levels that were chemically analyzed. It was notable that the localization of MT staining in the hepatic lobules was altered after NDMA injection. The MT staining was principally observed around the central vein before injection, whereas it was more markedly observed at the peripheral region after NDMA treatment. These results indicate that the synthesis of hepatic MT basically occurs around the central vein with oxygen stress caused by insufficient oxygen supplement and/or stimulated oxygen consumption. NDMA could be oxidatively metabolized at the peripheral region with sufficient supplemental oxygen from the artery, resulting in oxidative stress and stimulation of MT synthesis there. Thus, distribution of tissue MT might vary depending on the site of oxidative stress.

Differential effects of dietary casein and soybean protein isolate on lipopolysaccharide-induced hepatitis in D-galactosamine-sensitized rats.

Effects of dietary protein type on lipopolysaccharide (LPS)-induced hepatitis, as assessed by plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, were investigated in D-galactosamine (GalN)-sensitized rats. The plasma ALT and AST activities in rats fed on 25% soybean protein isolate (SPI) diet were significantly suppressed to about 1/4 and 1/5 of the values in rats fed on 25% casein diet, respectively, 8 h after the injection of LPS + GalN. Although hepatic ALT and AST activities of normal rats were also lower in the SPI group than in the casein group, this could not explain the differences in plasma enzyme activities between the two groups. The hepatic glutathione concentration of normal rats was lower in the SPI group than in the casein group, but it was reversed in rats injected with drugs. The results suggest that SPI can protect animals from LPS + GalN-induced hepatitis, and that the hepatic glutathione level may participate in the effects of SPI.

Role of Gastric Digestion in the Absorption of Slowly Digestible Peptide, Oligo-L-Methionine, in Rats

Absorption of a slowly digestible peptide, oligo-L-methionine (OM), added to a low casein diet was faster than absorption of OM added to a low soybean protein isolate diet in early stages of feeding in chronic portal-cannulated rats. In the present study, the gastric digestion of 14C-labeled OM in rats fed a casein-based diet was higher than that in rats fed an soybean protein isolate-based diet 30 min and 3 hr after feeding. In rats with chronic bile-pancreatic juice diversion from the proximal small intestine, the higher gastric solubilization of OM in the stomach of the casein group was also observed, but the contents of soluble digest of OM in the stomach were lower than those in the normal rats. The portal absorption of OM in the casein group was higher than in the soybean protein isolate group both 30 min and 4 hr after feeding in the bile-pancreatic juice-diverted rats, and the difference of the portal absorption between the diet groups corresponded to the difference of the amount of solubilized OM in the upper small intestine; this, in turn, depends on pepsin digestion in the stomach. These findings suggest that the difference between the two diet groups in the ability to digest OM in the stomach can at least partly explain the higher portal absorption of OM in the casein group in the early stages of feeding.

Absorption of oligo-L-[35S]methionine after feeding of a low casein or a low soybean protein isolate diet in rats.

We studied the absorptive properties of oligo-L-methionine (OM), which is an enzymatically synthesized and slowly digestible peptide. Previously, we demonstrated that when OM was added to a low casein diet, the improvement of the body weight gain was higher than when OM was added to a low soybean protein isolate (SPI) diet and we suggested that the difference in the supplementary effect of OM depends on its absorptive rate. In the present study, the OM absorption estimated by the portovenous difference in radioactivity derived from 35S-labeled OM was higher in the casein diet than in the SPI diet in early stages of feeding after fasting. Absorbed OM was quantified by subtracting the radioactivity of [35S]OM remaining in the whole gut from the ingested [35S]OM, 90 and 180 min after feeding casein and SPI diets containing 3% [35S]OM. We also estimated the absorptive efficiencies by subtracting the amount of radioactivity remaining in the intestines from the amount of [35S]OM emptied from the stomach as percentages of the emptied OM. Both the amount of absorbed OM and absorptive efficiencies of OM were higher in the casein group than in the SPI group, and the higher absorptive efficiency in the casein group indicates a higher digestibility for OM when rats are fed a 3% OM diet after fasting. The digestibility of [35S]OM measured by fecal excretion of radioactivity of OM during normal feedings for diets containing 0.3% [35S] OM for 7 days was about 80% in the casein group and 60% in the SPI group. We conclude that the different supplementary effects of OM in the low casein and SPI diets depend on the difference in OM digestibility. The difference in the digestibility of OM may partly depend on the faster absorption rate of OM in the early stages of feeding.

Pancreatic protease secretion profiles after spontaneous feeding of casein or soybean protein diet in unrestrained conscious rats

Under unrestrained physiologic conditions, the exocrine pancreatic secretion of digestive enzymes were observed with chronic bile-pancreatic duct cannulated rats. Bile-pancreatic juice (BPJ) was intermittently collected after spontaneous feeding of an 8% casein or an 8% soybean protein isolate (SPI) diet under recirculation of BPJ to the duodenum. The operative damage of cannula implantation was recovered for 5 days on a 25% casein diet, which was examined by food consumption and the basal secretion (pancreatic secretion during fasting) of total protein and trypsin. After feeding of both the test diets, the secretions of total protein, trypsin, chymotrypsin, and carboxypeptidase A were increased rapidly and about two-fold from the basal secretion. There were peak values at 15 min in the SPI group and at 30 min in the casein group. In the casein-fed rats, the protein and protease secretions maintained high levels for the initial 150 min, but in the SPI fed rats those secretions were decreased from 15 min after feeding. The protein and protease secretions tended to be higher in the casein group than in the SPI group after 30 min, and effect of ‘diet’ was significant in analysis of variance. The secretion profiles of protein and three proteases were similar, and specific activities of three proteases were not increased significantly in both the groups. We conclude that these low-protein diets are potent stimulators of the exocrine pancreatic secretion after spontaneous feeding in unrestrained rats.

Effect of diet on pancreas damage induced by excess lysine

To clarify the effects of different protein levels in the diet on the severity of lysine-induced pancreatitis, macroscopic and electron microscopic observations of the pancreas, and analysis of the enzymes in pancreaticobile juice and blood serum were performed. A large injection of lysine induced necrosis of pancreatic acinar cells in a wider area in 5%-casein diet group, than in 20%-casein diet group or 20%-soybean protein isolate (SPI) diet group. On the other hand, as a complication of pancreatitis, necrotic figures of the fatty tissues in the retroperitoneum and mesenterium were macroscopically observed more in 20%-casein group and 20%-SPI group, but were not found in 5%-casein group. In 24 hours after injection, secretion of pancreaticobile juice decreased in 5%-casein group, but was not changed in 20%-casein group and 20%-SPI group. The trypsin activity in pancreaticobile juice was extremely lowered on one and three days in 5%-casein group, but was significantly elevated on one day in 20%-casein and 20%-SPI groups. It is thus known that the pancreatitis caused in the low protein nutritional state is seirous in the degree of damage of the pancreas itself, but is low in the incidence of complications, while the pancreatitis occurring in the sufficient protein uptake state, regardless of the type of protein, is relatively light in the severity of damage of the pancreas itself, but is likely to induce complications.

In vivo evaluation of free chymotrypsin activity in the lumen using benzoyl- L-tyrosyl-p-aminobenzoic acid in portal cannulated rats

In vivo chymotrypsin activity in lumen was estimated by portal absorption of p-aminobenzoic acid (PABA) in the portal cannulated rats after feeding of diets containing benzoyl- L-tyrosyl-PABA (BT-PABA), to predict protease activities regarding the negative feedback regulation of exocrine pancreatic secretion. The PABA concentrations of portal plasma depending on hydrolysis of BT-PABA in the lumen was maximum at 20 min after feeding of both an 8% casein and an 8% soybean protein isolate (SPI) diet containing 3% BT-PABA. The concentrations of the casein group were decreased more rapidly, and were significantly lower at 80 and 100 min than that of the SPI group. The concentrations were minimum at 120 min in both the groups, and then increased rapidly in the casein group. Casein, SPI, and their peptic hydrolysates inhibit in vitro chymotrypsin-catalyzed hydrolysis of BT-PABA more than 50%. Thus, the rapid decrease in the portal concentration of PABA may depend on the competition with the dietary proteins or their hydrolysates in the lumen. The inhibition of in vitro hydrolysis by SPI and its hydrolysate were a little stronger than that by casein and its hydrolysate, respectively. The discrepancy between in vivo and in vitro BT-PABA hydrolysis suggests that factors other than the competition also affect the in vivo hydrolysis of BT-PABA. High activities of chymotrypsin in the lumen at 20 min after feeding may be able to inhibit the exocrine pancreatic secretion, and low level of the protease activity in the casein group at 120 min may be able to enhance the secretion by removal of the negative feedback mechanism.

Effects of Dietary Proteins on Absorption and Gastrointestinal Movement of p-Aminobenzoic Acid in Conscious Rats.

We monitored the absorption and movement of dietary soluble components along the gastrointestinal tract of rats by using p-aminobenzoic acid (PABA) as a marker after feeding 8 and 16% casein or soybean protein isolate (SPI) diets containing 1% PABA. The portal concentration of PABA, as an index of absorption, increased rapidly and reached the same high level 10 min after the feeding of all four diets, and the increased level of portal PABA was maintained for 30-80 min in each group. The increased levels of the SPI-fed groups continued longer than those of the casein-fed groups. In contrast, the gastric emptying rate slowed after 20 min in all the groups, and the gastric emptying of PABA for the initial 60 min in the 8% casein group was significantly faster than that in the 8% SPI group. The PABA content of the first small intestinal segment, which may be influenced by small intestinal transit, was higher in the casein group. These results indicate that the absorptive rate of PABA is determined not only by gastric emptying but also by small intestinal transit. The gastric emptying and the content of PABA in the first segment of the small intestine was not correlated in 8% protein groups. This suggests that the effect of SPI on gastrointestinal movement is different from that of casein.