Compendium of the most significant studies with reference to properties, intake, effects.

Feng, Z., Chen, X., Li, J. J., & Ren, D. (2013). An alkaline protease from Kocuria kristinae F7: properties and characterization of its hydrolysates from soy protein. European Food Research and Technology, 236(2), 293-301.

Abstract. An alkaline serine protease (SF1) from Kocuria kristinae F7 was purified. The molecular mass of the SF1 protease was estimated to be 57 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). The N-terminal amino acid sequence of the first 14 amino acids of the SF1 protease showed low homology with bacterial proteases, suggesting that the enzyme had not been described previously. The SF1 protease exhibited maximal activity at pH 9.0 and 60 °C. The activity of the SF1 protease was enhanced by the presence of Ca2+ and Mg2+ ions. It showed high stability in the presence of NaCl and ethanol. Reverse-phase high-performance liquid chromatography (RP-HPLC) analyses indicated that soybean protein isolates treated with the SF1 protease generated four principal new hydrophilic peptides. Mass spectrometry analyses indicate that the distribution of molecular weight of these peptides was from 0.705 to 1.305 kDa. Hydrolysis of soybean protein isolates with the SF1 protease increased the level of total free amino acids, essential amino acids and flavor amino acids. The SF1 protease may decrease the bitterness of soy protein hydrolysates. The results showed that the SF1 protease of Kocuria kristinae F7 appears to be good candidate enzyme for potential application in acceleration of fermented soybean food ripening.

Kovalenko, Igor, Rippke, Glen, Hurburgh, Charles, Hurburgh, Charles Determination of Amino Acid Composition of Soybeans (Glycine max) by Near-Infrared Spectroscopy Journal of Agricultural and Food Chemistry 54 (2006): 3485–3491, doi:10.1021/jf052570u. Copyright 2006 American Chemical Society.

Abstract. Calibration equations for the estimation of amino acid composition in whole soybeans were developed using partial least squares (PLS), artificial neural networks (ANN), and support vector machines (SVM) regression methods for five models of near-infrared (NIR) spectrometers. The effects of amino acid/ protein correlation, calibration method, and type of spectrometer on predictive ability of the equations were analyzed. Validation of prediction models resulted in r 2 values from 0.04 (tryptophan) to 0.91 (leucine and lysine). Most of the models were usable for research purposes and sample screening. Concentrations of cysteine and tryptophan had no useful correlation with spectral information. Predictive ability of calibrations was dependent on the respective amino acid correlations to reference protein. Calibration samples with nontypical amino acid profiles relative to protein would be needed to overcome this limitation. The performance of PLS and SVM was significantly better than that of ANN. Choice of preferred modeling method was spectrometer-dependent

Ghahri, S., & Pizzi, A. (2018). Improving soy-based adhesives for wood particleboard by tannins addition. Wood science and technology, 52(1), 261-279.

Abstract. Two different types of commercial tannins, namely chestnut (a hydrolysable tannin) and mimosa (a condensed flavonoid tannin), were used with two different types of hardener, namely hexamine and glyoxal, to upgrade soy-based adhesives for bonding of wood particleboard. Different soy-based adhesive formulations were tested by differential scanning calorimetry (DSC) and by thermomechanical analysis (TMA). The physical properties of different adhesive formulations such as viscosity, solid contents, acidity and density were also measured. One-layer laboratory particleboards bonded with the experimental adhesive formulations were prepared and tested. Based on the results obtained, tannins appear to decrease effectively soy-based adhesives’ viscosity. The TMA analysis showed that chestnut tannin extract appeared to react well with soy flour and to improve the soy flour adhesion properties. The TMA results also showed that both tannin types shorten the adhesives gel time and gel temperature. The DSC analysis also showed that tannin changes the thermal properties of soy-based adhesive and decreases both its glass transition temperature (Tg) and its denaturation temperature (Td). Moreover, particleboard bonded with tannin-modified adhesives showed internal bond strength results higher than particleboard bonded with unmodified soy adhesive. Thickness swelling and water absorption of the boards decreased when using tannins in soy-based adhesive formulations....… of chemical bonding between tannins and soy amino acids was studied by matrix-assisted …Based on the results obtained, covalent and ionic bonds can form between soy amino acids …

Luiking, Y. C., Deutz, N. E., Jakel, M., & Soeters, P. B. (2005). Casein and soy protein meals differentially affect whole-body and splanchnic protein metabolism in healthy humans. The Journal of nutrition, 135(5), 1080-1087.

Abstract. Dietary protein quality is considered to be dependent on the degree and velocity with which protein is digested, absorbed as amino acids, and retained in the gut as newly synthesized protein. Metabolic animal studies suggest that the quality of soy protein is inferior to that of casein protein, but confirmatory studies in humans are lacking. The study objective was to assess the quality of casein and soy protein by comparing their metabolic effects in healthy human subjects. Whole-body protein kinetics, splanchnic leucine extraction, and urea production rates were measured in the postabsorptive state and during 8-h enteral intakes of isonitrogenous [0.42 g protein/(kg body weight · 8 h)] protein-based test meals, which contained either casein (CAPM; n = 12) or soy protein (SOPM; n = 10) in 2 separate groups. Stable isotope techniques were used to study metabolic effects. With enteral food intake, protein metabolism changed from net protein breakdown to net protein synthesis. Net protein synthesis was greater in the CAPM group than in the SOPM group [52 ± 14 and 17 ± 14 nmol/(kg fat-free mass (FFM) · min), respectively; P < 0.02]. Urea synthesis rates decreased during consumption of both enteral meals, but the decrease tended to be greater in the subjects that consumed CAPM (P = 0.07). Absolute splanchnic extraction of leucine was higher in the subjects that consumed CAPM [306 ± 31 nmol/(kg FFM · min)] vs. those that consumed SOPM [235 ± 29 nmol/(kg FFM · min); P < 0.01]. In conclusion, a significantly larger portion of soy protein is degraded to urea, whereas casein protein likely contributes to splanchnic utilization (probably protein synthesis) to a greater extent. The biological value of soy protein must be considered inferior to that of casein protein in humans.

Dajanta, K., Apichartsrangkoon, A., Chukeatirote, E., & Frazier, R. A. (2011). Free-amino acid profiles of thua nao, a Thai fermented soybean. Food Chemistry, 125(2), 342-347.

Abstract. Thua nao, a rich source of free-amino acids, is a fermented soybean, usually used as seasoning or flavouring enhancer in northern Thailand. Free-amino acids (FAA) of unfermented/cooked soybeans, thua nao, fermented by pure Bacillus subtilis TN51 (TNB51), and a naturally fermented product (TNMX), were investigated by pre-column derivatisation with 9-fluorenylmethyl chloroformate, followed by reversed-phase HPLC. Total FAA and essential amino acids were found at significantly higher concentrations in TNB51 thua nao than in TNMX thua nao (naturally fermented). Both fermented thua nao had much higher concentrations of FAA than had their unfermented counterparts. With respect to taste-enhancing FAA, typical bitter attributes of thua nao came mainly from hydrophobic and basic FAA, whereas an umami attribute came predominantly from acidic FAA.

Potter, S. M. (1995). Overview of proposed mechanisms for the hypocholesterolemic effect of soy. The Journal of nutrition, 125(suppl_3), 606S-611S.

Abstract. A large body of literature indicates that protein from soybeans reduces blood cholesterol concentrations in experimental animals as well as in humans. The mechanism and component of soy responsible has not been established fully. Some suggest that when soy protein is fed, cholesterol absorption and/or bile acid reabsorption is impaired. This is observed in some animal species, such as rabbits and rats, but not in humans nor when amino acids replace intact soy protein. Others propose that changes in endocrine status, such as alteration in insulin:glucagon ratio and thyroid hormone concentrations, are responsible. The metabolic changes that have been observed on soy protein feeding in a variety of animal models, and in some cases humans, include increased cholesterol synthesis, increased bile acid synthesis (or fecal bile acid excretion), increased apolipoprotein B or E receptor activity and decreased hepatic lipoprotein secretion and cholesterol content, which are associated with an increased clearance of cholesterol from the blood. One hypothesis suggests amino acid composition or proportionality of soy causes changes in cholesterol metabolism (possibly via the endocrine system). Others have proposed that nonprotein components (such as saponins, fiber, phytic acid, minerals and the isoflavones) associated with soy protein affect cholesterol metabolism either directly or indirectly.

Blachier, F., Lancha, A. H., Boutry, C., & Tomé, D. (2010). Alimentary proteins, amino acids and cholesterolemia. Amino Acids, 38(1), 15-22.

Abstract. Numerous data from both epidemiological and experimental origins indicate that some alimentary proteins and amino acids in supplements can modify the blood LDL cholesterol, HDL cholesterol and total cholesterol. After an initial approval of the health claim for soy protein consumption for the prevention of coronary heart disease, more recently it has been concluded from an overall analysis of literature that isolated soy protein with isoflavones only slightly decrease LDL and total cholesterol. Other plant extracts and also some proteins from animal origin have been reported to exert a lowering effect on blood cholesterol when compared with a reference protein (often casein). The underlying mechanisms are still little understood. Individual amino acids and mixture of amino acids have also been tested (mostly in animal studies) for their effects on cholesterol parameters and on cholesterol metabolism. Methionine, lysine, cystine, leucine, aspartate and glutamate have been tested individually and in combination in different models of either normo or hypercholesterolemic animals and found to be able to modify blood cholesterol and/or LDL cholesterol and/or HDL cholesterol. It is however not known if these results are relevant to human nutrition.