Raw Soy Research Articles

Short-term effects of feeding raw soya flour on pancreatic cell turnover in the rat.

Pancreatic acinar cell turnover was studied after a 48-h fast and in rats fed raw soya flour (RSF) for up to 28 days. Feeding RSF for 2 days resulted in a significant increase in pancreatic weight and RNA content while protein was increased by the 4th day compared with rats fasted for 48 h. RSF also resulted in a significant increase in RNA by the 4th day and weight and protein by the 7th day compared with rats fed heated soya flour (HSF). This pancreatic hypertrophy was maintained for the rest of the study period. Two days after starting RSF, pancreatic DNA synthesis, measured by the rate of incorporation of [3H]thymidine into pancreatic DNA, had increased sixfold compared with that in animals fed HSF but returned to control values again by the 4th day on the diet. Autoradiography showed that this increase in DNA synthesis occurred in both acinar and duct cells, with turnover in acinar cells preceding that in duct cells. A second more gradual rise in DNA synthesis was seen from the 7th to 28th day. This peak in DNA synthesis was associated with an increased total pancreatic DNA content and occurred predominately in duct cells with a smaller contribution from acinar cells. Histological studies of the pancreas during the 1st wk showed cell damage and tissue necrosis, possibly due to exposure to high levels of cholecystokinin released by RSF. The first peak in DNA synthesis may be a regenerative response to this damage. The second more delayed peak appears to be hyperplasia in response to a trophic stimulus, again possibly mediated by cholecystokinin.

Pancreatic blood flow in the rat during enlargement, involution, and cholecystokinin treatment.

We studied the effect of raw soya flour (RSF) given as a single gavage or for long-term periods on pancreatic blood flow. These effects were compared with the response to treatment with cholecystokinin (CCK) since it has been suggested that RSF feeding releases CCK. In acute experiments total pancreatic blood flow was significantly increased after infusion of CCK (60 Ivy dog units X kg-1 X h-1) and after gavage with preparations of RSF or heated soya flour (HSF). When expressed as flow per 100 g pancreatic weight, the greatest increase was seen after gavage with RSF. In separate chronic studies, total pancreatic blood flow was significantly increased in rats fed RSF for 4 wk compared with rats fed HSF, but because of pancreatic enlargement in rats fed RSF flow per 100 g pancreatic weight was similar in the two groups. When rats fed RSF for 4 wk were changed to standard rat cubes for 48 h before study, pancreatic blood flow (ml/min and ml X min-1 X 100 g pancreas-1) and total pancreatic DNA decreased significantly compared with rats fed RSF continuously. However, when CCK was infused intravenously during the 48-h period on cubes, pancreatic blood flow and DNA remained significantly increased and were not significantly different from values in rats fed RSF continuously. These results show that the effects of RSF feeding and CCK treatment on pancreatic growth and blood flow are similar and are consistent with the postulated role of CCK as the trophic hormone released by RSF feeding.

Processed Protein Foods Characterized by In Vitro Digestion Rates

ABSTRACTIn vitro tryptic digestion assays and determination of relative digestion rates of food proteins described previously were used to evaluate changes in the rate of digestion following processing technologies. If pH drop measurements are used, a simple mode for the determination of relative digestion rates is suggested based on the comparison with a single reference of the same protein source. The effect of processing technologies could be tested in vitro. Significant increase in the velocity of digestion was found on microwave treatment of lentil and raw soy bean as well as on acid treatment of commercial defatted soy meals. Increase in the in vitro digestion rates was reflected in decreased feed consumption per weight gain in pig feeding experiments.

Effects of soybean flour on the pancreas of rats.

We have reviewed the growth-promoting and carcinogenic effects of feeding raw soya flour to rats. If the raw soya flour-containing diets are fed for more than a year, about 10% of the animals develop pancreatic cancer. In addition, feeding raw soya flour markedly potentiates the action of even subthreshold amounts of pancreatic carcinogens. The raw soya flour therefore acts as a potent promoter, as well as a weak carcinogen. In view of this promotion, the rat fed raw soya flour is a sensitive model for screening pancreatic carcinogens. It is not known whether the human pancreas responds to dietary trypsin inhibitors in a manner similar to the rat. However, in view of the use of soya-based products in human nutrition--especially in infant foods--we urge that the effect of all soya-based products intended for human use be tested on the rat pancreas in long-term feeding studies, combined with subthreshold doses of azaserine to highlight any promoting activity of the product. It seems probable that if a product exerts no effect on the rat pancreas, the human pancreas will also be spared from noxious effects.

Comparative Inhibition of Trypsins from Several Species by Soybean Trypsin Inhibitors

Inhibition by soybean trypsin inhibitor (SBTI) preparations of trypsins and of total proteolytic activity from several species was compared. Rat, monkey, human, bovine, porcine and mink trypsins were all inhibited 90–100% by SBTI, although there were species differences at low SBTI concentrations. Extent of inhibition of trypsin from the various species did not correlate with SBTI-induced pancreatic enlargement. Total proteolytic activity was inhibited up to 40% in rat, monkey, and human preparations by SBTI, and inhibition curves were similar. SBTIs extracted from unheated soy protein isolate (USPI) or raw soy flour (RSF) were approximately equal in their ability to inhibit human trypsin. SBTI extracted from heated soy protein isolate (SPI) was slightly less effective in inhibiting human trypsin than SBTI from either RSF or USPI.

Potentiation of pancreatic carcinogenesis in the rat by DL-ethionine-induced pancreatitis.

We have assessed the influence of an attack of acute pancreatitis on the incidence of experimentally induced pancreatic cancer in rats. A low-protein diet plus repeated injections of DL-ethionine produced acute pancreatitis in rats. The animals were then fed either a diet of raw soya flour or a non-soya-containing diet and given repeated injections of azaserine, a weak pancreatic carcinogen. The rats that had recovered from acute pancreatitis developed pancreatic cancer, whereas those without previous pancreatitis did not. We conclude that the interaction of recovery from acute pancreatitis with a pancreatic carcinogen predisposes to pancreatic cancer in rats.

Growth, Digestibility and Enzymatic Activities in the Pancreas and Intestines of Hamsters Fed Raw and Heated Soy Flour

The nutritional effects of feeding raw and heated soy flour to young golden Syrian hamsters were investigated over a period of 32 days. Those animals fed raw soy flour grew much more poorly than those fed heated soy flour, an effect which was reflected in a lower food efficiency as well. Growth retardation of hamsters fed raw soy flour was accompanied by a lower apparent digestibility of the protein (54%) compared to heated soy flour (76%). The pancreases of animals fed raw soy flour were increased in size and had elevated levels of trypsin, chymotrypsin, amylase, and lipase. With the exception of trypsin activity in the small intestine, similar differences in enzyme activities between the raw and heated soy groups were generally found in the small intestine, cecum, large intestine, and feces. There was, however, a progressive decrease in these activities in the lower regions of the intestinal tract and feces. It is concluded that the hamster, in common with several other species of animals, is sensitive to the effects of the trypsin inhibitors in raw soy flour, and may provide a useful model for studying the long-term effects of trypsin inhibitors on the pancreas.

Effects on the Monkey, Pig and Rat Pancreas of Soy Products with Varying Levels of Trypsin Inhibitor and Comparison with the Administration of Cholecystokinin

Raw and heated soy flour and casein diets were compared in rats, pigs, and monkeys with respect to growth, pancreatic changes, fecal trypsin, and nitrogen digestibility. Cholecystokinin injection was compared to feeding raw soy flour and casein in rats and casein in pigs. Several soy protein preparations were fed to rats and monkeys. Neither raw soy flour nor any other soy product produced pancreatic enlargement in pigs or monkeys. Casein and heated soy flour performed similarly. By comparison, other effects of raw soy flour were as follows. Growth was depressed 60% in rats and 84% in pigs, but not at all in monkeys. Nitrogen digestibility was depressed 5, 45, and 9% in rats, pigs, and monkeys, respectively. Pancreatic DNA, RNA, and protein levels were unchanged in monkeys fed raw soy flour. In rats, RNA per milligram pancreas was increased 40%, in pigs 20%. Pancreatic protein was decreased 7% in pigs and increased 47% in rats. Changes in pancreatic trypsin, chymotrypsin, lipase, and amylase were dissimilar in the three species. Fecal trypsin was elevated 300–400% in rats, and decreased approximately 50% in pigs and monkeys. Cholecystokinin injections in pigs and rats produced changes both quantitatively and qualitatively different from those seen with raw soy flour. Feeding of heated soy flour or soy protein isolates was comparable to feeding casein in all three species, and produced no deleterious effects.

Functional Properties of Raw and Heat Processed Winged Bean (Psophocarpus tetragonolobus) Flour

ABSTRACTNitrogen solubility, emulsification capacity, foam capacity, fat and water absorption capacity of raw and heat‐processed winged bean flour were compared with those of raw soy flour, both as a function of pH and NaCl concentration. Nitrogen solubility vs pH profile showed only one minimum, at pH 4.5. Heat processing of winged bean flour lowered nitrogen solubility. Water and fat absorption capacity of winged bean flour were 2.1 g/g and 1.4 g/g, respectively; those of raw soy flour were 3.1 g/g and 1.2 g/g. Heat processing increased water and fat absorption capacity of winged bean flour by 38% and 57%, respectively. Emulsification capacity of raw winged bean flour was higher than that of raw soy flour by about 30–60% depending on the pH. Heat processing diminished emulsification and foam capacity of winged bean flour by about 35% and 18%, respectively. Incorporation of NaCl up to 0.4M improved emulsification capacity of winged bean flour and foam capacity up to 0.2 M.

Further studies of the effects of raw soya flour on the rat pancreas.

Rats were fed partial diets of raw soya flour. The full pancreatic effects of soya flour, including the development of pancreatic cancer, were observed with diets containing only 25% raw soya flour or when soya flour was restricted to 2 days per week. Soya flour appears to promote pancreatic cancer induced by an exogenous carcinogen.

Significance of soya trypsin inhibitors in nutrition

AbstractAlthough recent evidence clearly indicates that trypsin inhibitors (TI) and low protein digestibility are the major factors responsible for the pancreatic hypertrophic and growth inhibitory effects of raw soybeans, there was uncertainty regarding the biological threshold level of TI at which these biological effects occur. To obtain such data, dehulled defatted flakes (10% dietary protein) containing graded levels of TI were fed to weanling rats for 4 weeks in two feeding trials. Normal pancreas weights were obtained in rats fed samples in which only 54 to 68% of the original TI of raw soya flour was inactivated. In partially toasted flakes with a nitrogen digestibility value of 77%, the average tolerance level of dietary TI activity that did not cause pancreatic hypertrophy was calculated to be 385 mg TI/100 g diet. TI tolerance level at maximum nitrogen digestibility of 85%, which did not significantly lower weight gain and reduce protein efficiencey ratios, was 260 mg TI/100 g diet. Continuous ingestion of high levels of TI (459 mg TI/100 g diet) in a 20% protein diet for 215 days did not inhibit growth nor cause pancreatic hypertrophy when compared to rats fed toasted soya flour diets. Pancreatic hypertrophy that occurs in rats fed raw soya diets containing up to about 1300 mg TI/100 g diet for 35 days was reversed by switching the rats to control diets or to 30% toasted flour. In long‐term feeding studies, no pancreatic hypertrophy occurred in rats fed commercial edible‐grade soya flour, concentrate, or isolate from time of weaning to adulthood (ca. 300 to 330 days). TI content of the diets ranged from 178 to 310 mg/100 g diet. Microscopic examination of the pancreas revealed no abnormalities. Gross appearances of heart, kidney, spleen and liver were normal. In long‐term feeding, vitamin B‐12 supplements were needed to provide optimum growth and to maintain body weight. Results of numerous chemical analyses, relatively short‐term human tests and long‐term animal feeding studies indicate that with proper control of manufacturing processes, soya protein products can be produced that, in mixed diets, have protein nutritional value approaching that of animal protein.

ANTIMICROBIAL ACTIVITY OF FATTY ACIDS AND THEIR ESTERS AGAINST A FILM-FORMING YEAST IN SOY SAUCE

Antimicrobial activity of fatty acids and their glycerol and sugar esters against a film-forming yeast isolated from raw soy sauce was determined in diluted soy sauce. In a series of fatty acids (alkyl chain length of 7, 9, 11 and 13) and their monglycerides, capric acid and monolaurin had the highest inhibitory activity. Two selected sugar esters (sucrose monocaprate and sucrose monolaurate) could not completely inhibit the growth of test organism throughout 3 weeks.

THYROID ACTIVE FACTOR IN HEATED SOYBEAN FRACTIONS

ABSTRACTExtracts obtained from defatted soybean flour by water extraction and acetone fractionation caused a decrease in radioiodine uptake by rat thyroid “in viva” up to 24 hr after administration of the extract by stomach tubing. The inhibitory effect was evident at 24 hr only when either the extract or the flour had been previously autoclaved. Similar results were recorded when extracts from commercial products such as soybean milk, protein concentrate, and toasted flour were used. However, using extracts from unheated raw soy flour, the inhibitory effect was only present 6 hr after ingestion and it subsequently disappeared. The active factor is not precipitated by 90% ethanol. Isolated soybean isoflavones either autoclaved or nonautoclaved did not show any inhibitory activity.

The effects of long-term feeding of soya flour on the rat pancreas.

Rats were fed raw and heated soya flour for up to 2 years. The rats fed raw soya flour all developed pancreatic hypertrophy and hyperplastic and adenomatous nodules. Four of 26 rats fed raw soya flour continuously and 1 of 5 rats fed raw soya flour for 2 days each week developed pancreatic cancer. Preheating the soya flour seemed to protect against the pancreatic hyperplastic and neoplastic changes.

Raw soya flour and nitrosamines-a potent mixture for rats: Levison, D. A., Morgan, R. G. H., Brimacombe, J. S., Hopwood, D., Coghill, G. & Wormsley, K. G. (1979). Carcinogenic effects of di(2-hydroxypropyl)nitrosamine (DHPN) in male Wistar rats: promotion of pancreatic cancer by a raw soya flour diet. Scand. J. Gastroent.14, 217

Raw soya flour and nitrosamines-a potent mixture for rats: Levison, D. A., Morgan, R. G. H., Brimacombe, J. S., Hopwood, D., Coghill, G. & Wormsley, K. G. (1979). Carcinogenic effects of di(2-hydroxypropyl)nitrosamine (DHPN) in male Wistar rats: promotion of pancreatic cancer by a raw soya flour diet. Scand. J. Gastroent.14, 217

Carcinogenic effects of Di(2-hydroxypropyl)nitrosamine (DHPN) in male Wistar rats: promotion of pancreatic cancer by a raw soya flour diet.

Di(2-hydroxypropyl)nitrosamine was administered to rats fed raw or heated (control) soya flour diets. The group fed raw soya flour developed hyperplastic and adenomatous pancreatic nodules and pancreatic adenocarcinomata. We conclude that a diet of raw soya flour augments the carcinogenicity of pancreatic carcinogens in the rat.

Effects of soy proteins containing trypsin inhibitors in long term feeding studies in rats.

AbstractPancreatic hypertrophy that occurs in rats fed raw soy flour containing about 1200 mg tripsin inhibitor (TI)/100 g diet was reversed by switching the rats to control diets or to diets containing 30% toasted defatted soy flour. No pancreatic hypertrophy occurs in rats fed commercial, edible grade soy flours, concentrate or isolate from time of weaning to adulthood (ca. 300 days). TI content of the soy diets ranged from 178–420 mg/100 g. Except for pancreas enlargement in rats fed raw soy flour, gross and microscopic examination of pancreata revealed no abnormalities. The gross appearance of heart, kidney, spleen, and liver was normal. Soy flour, protein concentrate, and protein isolate in a formulated corn‐soy diet provided optimum growth and maintained body weight only if supplemented with vitamin B‐12 in long term feeding studies with rats. In the absence of such supplementation, rats fed soy diets initially grew at a rate equal to or greater than those fed a comparable corn‐casein control diet; but, with continued feeding for ca. 300 days, body weight of rats fed the casein control was significantly greater than that of the soy flour‐fed rats. Those fed soy isolate ceased to grow; and rats fed soy concentrate lost weight. No significant differences were found in organ weights between groups fed soy products and casein, except for increased kidney, liver, and testes weights relative to body weight with the group fed soy concentrate. Supplementation of the soy diets with vitamin B12 stimulated growth to the greatest extent, calcium pantothenate or riboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the soy diets with vitamin B12 stimulated growth to the greatest extent, calcium pantothenate or roboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the control diet was without effect. The dietary protein level in these diets was 20%, with casein or soy protein representing 75% of total protein. When fed continuously to rats from weaning to adulthood, properly processed soy protein products, when balanced with essential nutrients, can provide growth comparable to corn‐casein diets.

Potentiation of the action of azaserine on the rat pancreas by raw soya bean flour

Rats were treated with raw soya flour to produce pancreatic hypertrophy and also received azaserine, a pancreatic carcinogen. The combined treatment resulted in the development of large numbers of hyperplastic nodules in the acinar tissue of the rat pancreas. We conclude that the pancreas of the rat stimulated to proliferate by raw soya flour provides a sensitive model for detecting and studying pancreatic carcinogens.

Sterol composition of Bulgarian soya and corn oils.

The free sterols, the sterol esters and the sterol glycosides of the raw soya and corn oils as well as those of the technical lecithin and the deodorizer distillated of the latter oils were isolated by preparative TLC. The composition of each of the isolated sterol derivatives was determined by GLC and MS. Sitosterol, campesterol, stigmasterol and an unknown sterol with a molecular weight of 428 are contained in almost all of the examined fractions of the soya oil and its refinement byproducts. Dehydrocampesterol is present in the free sterols of the raw soya oil and the soya lecithin. Stigmasterol is contained in the soya deodorizer distillate in high amounts. It was established that cholesterol was present in the sterol esters of the raw soya oil high amounts. Delta7-stigmastenol occurs only in the sterol esters of the latter oil. Sitosterol, campesterol and stimgasterol are the main components of all sterol fractions of the corn oil and its refinement products. Dehydrocampesterol and unknown sterols with molecular weights of 428 are present in the free sterols of the raw corn oil. Some sterol glycosides of the soya and corn lecithin are esterified with the same major fatty acid components of the glycerides, palmitic acid being the main one. The fatty acid compositon of sterol esters of the raw soya and corn oil roughly corresponds to the fatty acid composition of oils.

Enzymic Activities in the Pancreas, Digestive Tract and Feces of Rats Fed Raw or Heated Soy Flour

Trypsin, chymotrypsin and amylase levels were determined in the pancreas, all along the intestinal tract, and in the feces of rats fed raw or heated soy flour diets. The levels of all enzymes measured in the pancreas in the non-fasted state were lower in the raw than in the heated soy flour-fed rats. Fasting equalized these levels. Trypsin and amylase tended to be lower, and chymotrypsin was significantly higher in the intestinal tracts of raw soy flour-fed rats than in the group fed heated soy flour; the greatest differences were found in the ileum. Trypsin and chymotrypsin levels in the feces were higher in the group fed raw soy flour than in the group fed heated soy flour. Amylase in the feces of the raw soy flour-fed rats was higher at the beginning of the experiment and dropped sharply to be even lower than in the heated soy flour-fed rats at days 13 to 14 of the experiment. It was concluded that measuring the enzymic levels in the feces is a very sensitive method for determining whether a test diet induces hypersecretion of digestive enzymes in rats. This method can be used from the start of feeding the experimental diet. As the animal need not be killed, the effect of the test diet upon enzymic secretion can be studied as a function of time, and it might be suitable to studies with large animals.