Influence of Different Genotypes on Trypsin Inhibitor Levels and Activity in Soybeans

Enzymatic and Algebraic Methodology to Determine the Contents of Kunitz and Bowman-Birk Inhibitors and Their Contributions to Total Trypsin or Chymotrypsin Inhibition in Soybeans

Soybeans are the number one source of plant proteins for food and feed, but the natural presence of protein protease inhibitors (PIs), namely, the Kunitz trypsin inhibitor (KTI) and the Bowman-Birk inhibitor (BBI), exerts antinutritional effects. This communication describes a new methodology for simultaneously quantitating all parameters of PIs in soybeans. It consists of seven steps and featured enzymatically measuring trypsin and chymotrypsin inhibitory activities, respectively, and subsequently determining the contents of reactive KTI and BBI and the contributions of each toward total PI mass and total trypsin or chymotrypsin inhibition by solving a proposed system of linear equations with two variables (C = dB + eK and T = xB + yK). This enzymatic and algebraic (EA) methodology was based on differential inhibitions of KTI and BBI toward trypsin and chymotrypsin and validated by applications to a series of mixtures of purified KTI and BBI, two KTI-null and two conventional soybeans, and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The EA methodology allowed calculations of PI composition and the contributions of individual inhibitors toward total inhibition with ease. It was first found that although BBI constituted only about 30% of the total PI mass in conventional raw soybeans, it contributed about 80% toward total chymotrypsin inhibitor activity and about 45% toward trypsin inhibitor activity. Therefore, BBI caused more total protease inhibitions than those of KTI. Furthermore, the so-called KTI-null soybean mutants still contained measurable KTI content and thus should be named KTI-low soybeans.

The effect of radiofrequency heat treatment on trypsin inhibitor activity and in vitro digestibility of soybean varieties (Glycine max. (L.) Merr.)

Kunitz (KTI) and Bowman-Birk (BBI) trypsin inhibitors were characterized in soybean seeds. Cultivars having KTI/BBI (Pannónia Kincse, PK) or lacking KTI (Aries; Hilario; Bahia) were assessed with well-characterized soybean varieties having Ti-a or ti types of KTI mobility. The TIA values of Pannónia Kincse (9.8 ± 0.48 mg/g) were not significantly different (p ≤ 0.05) from Ti-a samples (10.07 ± 1.86 mg/g), while of Aires, Bahia, Hilario (6.19 ± 1.89) were identical (p ≤ 0.05) with ti samples (6.63 ± 1.99). Radiofrequency heat treatment (RF) decreased TIA values (p ≤ 0.05) at ≥ 100 °C. However, in the traditional soybean variety, the RF at 110 °C was more effective in eliminating the residual KTI activity. The remaining or the disapperaing bioactive form of trypsin inhibitors were succesfully characterized by the means of a standardized in vitro digestion model. It showed that residual BBI-originated trypsin inhibitor activity was in the stomach even after RF at 110 °C, whereas its chymotrypsin inhibitor activity was not detectable at all. Although PK and KTI null types of soybean seeds still required an energy-saving, gentle heat treatment to inactive the trypsin inhibitors before using them as food or feed, the physicochemical properties and processing quality of soybean products were protected, improved.

Determination of protease inhibitors, glycinin, and beta-conglycinin in soybeans and their relationships

In order to search for suitable soybean varieties for different applications, the protein contents of Kunitz trypsin inhibitor (KTI), Bowman-Birk trypsin inhibitor (BBI), glycinin (11S), and β-conglycinin (7S) of 93 soybean samples from different sources and harvest years were quantified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Meanwhile, the protease inhibitory activities against trypsin and chymotrypsin were determined. Results showed that the individual protein contents and trypsin inhibitor activities differed significantly (p < 0.05) among soybean samples. KTI contents ranged from 5.25 to 14.60 mg·g-1 ; BBI contents ranged from 1.81 to 5.74 mg·g-1 ; 11S varied from 13.65% to 48.55% and 7S varied from 15.68% to 42.15% of total soluble protein; trypsin and chymotrypsin inhibitory activities were 8.93-20.95 mg TI·g-1 and 4.18 -12.79 mg CI·g-1 , respectively. Excellent linear relationships existed between trypsin inhibitor contents and their activities. The regression equations offer a rapid method for estimating the activity of KTI or BBI in raw soybeans. PRACTICAL APPLICATION: The regression equations established based on a large number of soybean varieties offered a rapid method to estimate the activity of trypsin inhibitors. The data presented here provided useful information for the food industry or breeders to select soybean varieties with different inhibitory activities or protein contents for different food processing applications.

Bioactive peptides in cereals and legumes: agronomical, biochemical and clinical aspects

Cereals and legumes are key components of a healthy and balanced diet. Accordingly, many national nutritional guidelines emphasize their health promoting properties by placing them at the base of nutritional food pyramids. This concept is further validated by the observed correlation between a lower risk and occurrence of chronic diseases and the adherence to dietary patterns, like the Mediterranean diet, in which cereal grains, legumes and derived products represent a staple food. In the search for a dietary approach to control/prevent chronic degenerative diseases, protein derived bioactive peptides may represent one such source of health-enhancing components. These peptides may already be present in foods as natural components or may derive from hydrolysis by chemical or enzymatic treatments (digestion, hydrolysis or fermentation). Many reports are present in the literature regarding the bioactivity of peptides in vitro and a wide range of activities has been described, including antimicrobial properties, blood pressure-lowering (ACE inhibitory) effects, cholesterol-lowering ability, antithrombotic and antioxidant activities, enhancement of mineral absorption/bioavailability, cyto- or immunomodulatory effects, and opioid-like activities. However it is difficult to translate these observed effects to human. In fact, the active peptide may be degraded during digestion, or may not be absorbed or reach the target tissues at a concentration necessary to exert its function. This review will focus on bioactive peptides identified in cereals and legumes, from an agronomical and biochemical point of view, including considerations about requirements for the design of appropriate clinical trials necessary for the assessment of their nutraceutical effect in vivo.

Bioactive proteins and energy value of okara as a byproduct in hydrothermal processing of soy milk

The nutritional properties of raw okara obtained as a byproduct from six soybean varieties during hydrothermal cooking (HTC) of soy milk were assessed. The composition and residual activity (rTIA) of trypsin inhibitors (TIs), contents of lectin, proteins, fats, and carbohydrates, and energy values (EV) were correlated with the respective physicochemical properties of soybean and okara. Kunitz (KTI) and Bowman-Birk (BBI) TIs both comprised okara rTIA. TIs content was higher in okara (5.19-14.40%) than in soybean (3.10-12.17%), which additionally enriched okara by cysteine. Contents of KTI (r = 1.00;p < 0.05) and BBI (r = 0.89;p < 0.05) as well as BBI monomeric (r = 0.89;p < 0.05) and polymeric forms (r = 0.95;p < 0.05) in okara and in soybean were strongly correlated. Low urease index activity indicated that okara was heated adequately to inactivate antinutritional factors. The proximate composition of raw okara, advantageous rTIA, and a very low EV (2.74-3.78 kJ/g) qualify this byproduct for potential application in food preparation as a functional ingredient in dietary products.

Characterization of proteins from kernel of different soybean varieties

BACKGROUND

Total soybean proteins, storage proteins, glycinin (11S) and β-conglycinin (7S) fractions and their respective subunits in seven soybean varieties were analyzed. In this work we also present the correlation between concentration and activity of bioactive proteins, lipoxygenase and proteinase inhibitors.

RESULTS

Glycinin and β-conglycinin comprise about 750 g kg(-1) of the bean storage protein and as such account for both quantity and quality of the kernel protein. The 11S concentration of the varieties studied ranged from 503.4 to 602.9 g kg(-1) and those of 7S varied from 178.2 to 230.6 g kg(-1) of total extractable proteins. The ratio of 11S/7S proteins varied from 2.43 to 3.29 among the varieties. A very strong positive correlation was found between the concentration of Kunitz trypsin inhibitor and activity of total trypsin inhibitor (r = 0.96). However, lipoxygenase concentration did not show a strong correlation with lipoxygenase activity.

CONCLUSION

It appears that among the seven ZP soybean genotypes there are genotypes with different amounts of subunits that should be bred in the future for a desired level of protein components.

Soybean-based biomaterials: preparation, properties and tissue regeneration potential

Future successes in regenerative medicine will depend on the development of new biodegradable biomaterials able to control tissue regeneration in vitro and in vivo. None of the products currently available to surgeons can combine all the essential characteristics for biodegradable biomaterials, which are tunable degradation rate, controlled inflammatory reaction, no toxicity and stimulation of tissue regeneration. These clinical features should be provided, together with ease of handling during surgery and cost-effective production. Here, an overview is presented of a novel class of soybean-based biomaterials, which can be manufactured as different hydrogel formulations, all tailored for specific clinical applications. ln vitro and in vivo studies have ascertained their activity on various biochemical and cellular components of regenerating tissues. Beyond their use, the ascertained bioactivity of some of the soybean components may open new investigations and commercial routes in regenerative medicine.