The author describes how his interest in the nutritional value of soybeans led to a trail of research that had many ramifications. In an attempt to account for the poor nutritional value of raw soybeans and the beneficial effect of heat treatment, a protein displaying hemagglutinating activity and capable of inhibiting the growth of rats was isolated and characterized. This protein subsequently proved to be an example of a class of proteins that were later referred to as "lectins". Lectins were also isolated from kidney beans and shown to be even more toxic than the soybean lectin. Concurrent studies with the soybean trypsin inhibitors revealed that these proteins inhibited growth by stimulating the secretory activity of the pancreas and could in the long term cause acinar cell adenoma of the pancreas. Acute experiments with human subjects showed that the human pancreas also responded to the stimulatory effects of the so-called Bowman-Birk soybean inhibitor. The studies on soybean trypsin inhibitors were expanded to include a protease inhibitor present in blood, alpha-1-antitrypsin, a deficiency of which leads to emphysema in humans. The mechanism whereby this protein inhibits leucocyte elastase was investigated. On the basis of these results the intratracheal administration of a synthetic peptide inhibitor of elastase attached to albumin microspheres was found to prevent elastase-induced emphysema in hamsters.

Milk may serve as a vector for the transmission of substances of extrinsic origin which can be potentially toxic to the consumer. These toxins may originate in cow's milk from the ingestion of plants known to contain toxic substances or feeds contaminated with mycotoxins, or residues of pesticides or herbicides. Harm to the consumer of cow's milk may also result from the use of antibiotics used for the treatment of disease in cows or for their growth enhancement. In the case of human breast milk, the routes of exposure can be quite diverse. These include milk derived from nursing mothers who have received medication in the form of drugs or antibiotics. Non-medical contaminants may originate from the mother's excessive use of alcohol, coffee, or tobacco. Other routes of contamination include the diagnostic use of radioisotopes, the transmission of allergens such as peanuts, mercury poisoning from dental fillings or fish, and contamination of the mother's diet with pesticide residues.

For soybeans to serve as a good source of protein for feeding animals as well as humans, a certain amount of heat treatment or some other form of processing must be applied. This is because there are present in soybeans certain heat-labile factors that exert an adverse effect on the nutritional value of the protein. The so-called protease inhibitors have received the most attention in this regard and have been shown to exert their antinutritional effect in the short term by causing pancreatic hypertrophy and hyperplasia in the rat, the underlying cause for an inhibition of growth in these animals. The prolonged feeding of raw soy flour or an enriched trypsin inhibitor fraction from soybeans to rats results in the development of hyperplastic and neoplastic nodules of the pancreas, including carcinomas. It should be emphasized that all of these adverse effects are seen when protease inhibitors are present in relatively high concentrations in the diet and may be completely unrelated to the anticarcinogenic effects seen at low concentrations of the Bowman-Birk inhibitor. Brief mention is also made of any possible adverse effects that may result from the presence of phytic acid and saponins in soybeans.

There are a number of components present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are the protease inhibitors and lectins. Protease inhibitors exert their antinutritional effect by causing pancreatic hypertrophy/ hyperplasia, which ultimately results in an inhibition of growth. The lectin, by virtue of its ability to bind to glycoprotein receptors on the epithelial cells lining the intestinal mucosa, inhibits growth by interfering with the absorption of nutrients. Of lesser significance are the antinutritional effects produced by relatively heat stable factors, such as goitrogens, tannins, phytoestrogens, flatus-producing oligosaccharides, phytate, and saponins. Other diverse but ill-defined factors appear to increase the requirements for vitamins A, B-12, D, and E. The processing of soybeans under severe alkaline conditions leads to the formation of lysinoalanine, which has been shown to damage the kidneys of rats. This is not generally true, however, for edible soy protein that has been produced under milder alkaline conditions. Also meriting consideration is the allergenic response that may sometimes occur in humans, as well as calves and piglets, on dietary exposure to soybeans.

In the spring of 1942 I was inducted into the U.S. Army after having received a BS degree in Food Technology from the Massachusetts Institute of Technology, a degree which, in the eyes of the army, preeminently qualified me for an assignment as an instructor in the Cooks and Bakers School of the Quartermaster Carp at Fort Knox Kentucky. Most of the rest of my career in the army was spent as a mess officer in European Theater of Operations. Following my discharge from the army in 1946, I entered the Ph.D. program in Biochemistry and Nutrition at the University of Southern California. After devoting one year to intensive course work to get back on track with respect to chemistry, which by this time had become but a very hazy memory, I was afforded the opportunity of returning to active duty, the carrot on the stick being that I would be free to complete the research I needed for my Ph.D. degree. To this end, I was assigned to the Quartermaster Food and Container Institute, then located in Chicago. One of the projects the army was interested in at that time was the increased utilization of soybeans as a possible substitute for meat protein in the army ration program. Thus began my involvement with soybeans. Based on the early observation by Osborne and Mendel’, it was well known that the nutritive value of soybean protein did not support the growth of rats unless it had been subjected to heat treatment. It was generally believed at that time that the beneficial effect of heat was due to the inactivation of a trypsin inhibitor which had been previously isolated by Kunitzr from raw soybeans. The main objective of my thesis research was to elucidate the mechanism whereby the trypsin inhibitor exerted its deleterious effect on animal growth. Based on experiments in which the purified Kunitz inhibitor had been added to the diets fed to rats, it became apparent that the trypsin inhibitor did not fully account for the poor growth seen with raw soybeans3. Adding the trypsin inhibitor to heated soybeans failed to lower the growth rate of rats to the same extent as a diet containing unheated soybeans. Thus began my search for the presence of some other component in soybeans which might be responsible, at least in part, for its poor nutritive value. After receiving my Ph.D. degree and my release from the Army in 1949, I joined the staff of the Department of Biochemistry at the University of Minnesota. As is the case with most fresh Ph.D.s who assume a new academic position and are pressured into showing some evidence of productivity as rapidly as possible, I chose an area of research

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHeat inactivation of the Kunitz and Bowman-Birk soybean protease inhibitorsChristina M. DiPietro and Irvin E. LienerCite this: J. Agric. Food Chem. 1989, 37, 1, 39–44Publication Date (Print):January 1, 1989Publication History Published online1 May 2002Published inissue 1 January 1989https://doi.org/10.1021/jf00085a010RIGHTS & PERMISSIONSArticle Views600Altmetric-Citations75LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (767 KB) Get e-Alerts Get e-Alerts

This study was undertaken to clarify the issue of whether feedback regulation of pancreatic enzyme secretion occurs in humans. A naturally occurring inhibitor of trypsin and chymotrypsin, the Bowman-Birk inhibitor of soybeans, was used to reduce the activities of these enzymes normally secreted by the pancreas into the duodenum. Pure pancreatic juice was collected by endoscopic retrograde cannulation of the pancreatic duct in a protocol consisting of three periods: period 1 (15 min), collections of juice without return to the duodenum ("washout phase"); period 2 (35 min), intraduodenal infusion of juice to which buffered saline or heat-inactivated Bowman-Birk inhibitor had been added; and period 3 (55 min), intraduodenal infusion of juice in which greater than 90% of the trypsin and chymotrypsin activities had been abolished by treatment with the active inhibitor. Control experiments were included in which untreated juice was infused in period 3 as well as period 2. Enzyme analyses (trypsin, chymotrypsin, elastase, and amylase) of samples of juice collected at 5-min intervals revealed a twofold to threefold increase in the output and concentration of all four enzymes in period 3 compared with period 2. These results thus confirm the existence of feedback control in humans.

Brown beans and kidney beans were subjected to two modes of cooking in a household slow cooker: (A), a fixed low setting for 10 h, and (B), a high setting for 2.5 h and a low setting for 7.5 h. Temperature changes in the beans were recorded. With treatment A over 90% of the hemagglutinating and trypsin inhibitor activities occurred after 6 h at which time the temperature had reached 80°C. With treatment B inactivation of these activities was almost complete at the end of 2 h when a maximum temperature of 100°C had been attained. The in vitro digestibility of the bean protein was considerably increased by either treatment. By way of contrast, only 20 min of heating was required to destroy these activities when the beans were brought to a boil in an open vessel.

1.1. The dissociation constants (Ki) of the interaction of 10 naturally occurring inhibitors with rat anionic and bovine trypsins were determined employing three independent methods.2.2. Both enzymes bound very tightly (Ki < 10−9) to bovine pancreatic, lima bean, and the Kunitz soybean inhibitors.3.3. With the exception of ovomucoid, rat trypsin bound more tightly than bovine trypsin to inhibitors derived from navy bean, lima bean, soybean (Bowman-Birk) and potato and to ovoinhibitor, leupeptin and antipain.4.4. These findings emphasize the caution that must be exercised in the interpretation of experiments involving the inhibition of trypsins from heterologous species of animals by naturally occurring inhibitors.

A modified amnion chemotaxis assay is described for measurement of polymorphonuclear leukocyte(s) (PMNL) migration (random and directed) into a viable membrane. The primary modifications are the use of 111In-oxide-labelled PMNL and replacement of the nitrocellulose ‘trap’ filter with a type I collagen sponge. The modifications resulted in four important benefits: (1) the quantification of PMNL migration was simplified; (2) reader subjectivity was eliminated; (3) the information gained of the migration process was enhanced; and (4) the assay time was decreased. The amnion chemotaxis assay with the modifications reported should provide the means of evaluating several aspects of the inflammatory response of PMNL.

The effects of feeding mice raw or heated soy flours or casein in the presence and absence of injected azaserine were investigated over a period of 18 months. Although the feeding of raw soy flour (compared with heated soy flour or casein) caused a significant inhibition of growth and an enlargement of the pancreas, there was no macroscopic evidence of pancreatic nodules in any of the six experimental groups. Microscopic examination of the pancreas revealed a somewhat higher (not significant) incidence of atypical acinar cell nodules in all animals injected with azaserine, but this difference was little influenced by the diets themselves. We concluded that raw soy flour itself has no carcinogenic effect on the mouse pancreas and does not enhance the sensitivity of the mouse pancreas to azaserine. Thus, it cannot be assumed that the appearance of pancreatic nodules constitutes an obligatory sequela of pancreatic hypertrophy and/or hyperplasia in all species of animals.

Brown beans and kidney beans were subjected to two modes of cooking in a household slow cooker: (A), a fixed low setting for 10 h, and (B), a high setting for 2.5 h and a low setting for 7.5 h. Temperature changes in the beans were recorded. With treatment A over 90% of the hemagglutinating and trypsin inhibitor activities occurred after 6 h at which time the temperature had reached 80°C. With treatment B inactivation of these activities was almost complete at the end of 2 h when a maximum temperature of 100°C had been attained. The in vitro digestibility of the bean protein was considerably increased by either treatment. By way of contrast, only 20 min of heating was required to destroy these activities when the beans were brought to a boil in an open vessel.

A survey of 59 species of tropical legume seeds revealed high interspecific variation in proteinaceous capacity to inhibit bovine trypsin (a digestive enzyme) and to agglutinate human (type B, Rh positive) and laboratory rabbit red blood cells. The legume subfamily Mimosoideae was conspicuous for the absence of seeds with very weak trypsin inhibition. Congenerics sometimes differed strongly from each other with respect to both trypsin inhibition and phytohemagglutination. Half the species of seeds displayed no hemagglutinating capacity with one or the other kinds of red blood cells, and in only 27% of the 30 cases where there was some activity did the same species of seed actively agglutinate both species of red blood cells. A species of seed that had hemagglutinating capacity was almost invariably associated with moderate to high levels of trypsin inactivation. While it has been long known that a great diversity of small toxic and potentially defensive molecules occur in legume seeds and that one species of seed often contains several of them, we now feel that it is reasonable to consider legume seeds as also containing a high diversity of potentially toxic protein molecules. A single seed is likely to contain, at the least, three to four classes of defensive compounds, any or all of which, or some in combination, may be the cause of a seed being rejected by a potential seed predator.

To test the feasibility of using liposomes to deliver therapeutic agents to the lungs, the effect of liposome-encapsulated superoxide dismutase (SOD) or catalase on pulmonary oxygen toxicity was studied in rats. The SOD or catalase was encapsulated in negatively changed multilamellar liposomes and administered directly into the trachea of adult rats, which were subsequently exposed to hyperoxia (greater than 95% O2). Response to hyperoxia was examined by studying lung SOD and catalase activities, survival rates, and lung morphology. Rats receiving liposome-encapsulated SOD or catalase showed increased levels of enzyme activities in the lung homogenates compared with those in the control groups after 24 to 72 h of hyperoxic exposure. Elevated enzyme levels in the lungs of rats treated with liposome-encapsulated SOD or catalase were accompanied by a significant improvement in survival rates after 72 h of hyperoxic exposure and less lung injury than in the other control groups.