125 mg trypsin inhibitors. De Toledo et al. (2007) found it ranging between 42.6 and
71.6 UTI/mg; Carvalho et al. (2002) reported much higher concentration, i.e.,
122–206 UTI/mg; and Gu et al. (2010) observed that trypsin inhibitors range from
3000 to 6000 mg/100 g of raw soybean grain samples.
1.3.6.3 Lectins
Lectins (hemagglutinin or agglutinin) are the carbohydrate-binding proteins which
are resistant to digestion and are often considered one of the most toxic constituents
of the pulses/beans. Lectins possess high affinity to cellular and intracellular
membrane-associated carbohydrates (glycoprotein and glycolipids) [especially
N-acetyl-D-galactosamine] and thus, by binding, not only reduce their absorption
but can even lead to agglutination of red blood cells, leading to hemolytic anemia
(Liener 1994), impairment of the key enzymes of metabolism, and growth retardation, and if administered orally or intraperitoneally can even lead to death (Grant
et al. 1988). Numerous studies suggest that lectin consumption can also cause the
atrophy of microvilli, intestinal epithelial injury, diarrhea, increased intestinal permeability, and increased proliferation of pathogenic bacteria in the gut (Grant et al.
1995; Pusztai et al. 1991; Pusztai et al. 1995; Machado et al. 2008).
However, recent research suggests that lectins have potent in vivo biological
activities and exhibit anticarcinogenic and antitumor activity by either reduction of
cell proliferation, induction of tumor-specific cytotoxicity of macrophages, or by
having a strong effect on the immune system by production of various interleukins
(de Mejia et al. 2003; de lumen 2005). Soybean seeds contain 300–600 mg/100 g
lectin (Gu et al. 2010), and approximately 6.5 g lectin/kg is reported in defatted soy
meal (Vasconcelos et al. 2001) and approx. 0.2–2% of the soybean protein mass
(de Mejia et al. 2003; Rizzi et al. 2003; Anta et al. 2010). Treatments like soaking
(Hernandez-Infante et al. 1998), heat treatment, and fractionation during food
processing have been reported to be efficient in eliminating lectins and abolishing
its hemagglutinating activity, thus improving the nutritional quality of soybeans
(Vasconcelos et al. 1997).
1.3.6.4 Oxalate
Oxalate, the simplest dicarboxylic acid is synthesized by the body or absorbed from
the gut. It cannot be further metabolized by human beings and must be excreted in
the urine (Massey et al. 1993). Oxalate inhibits calcium absorption in the kidneys
and increases the risk of developing kidney stones, renal edema, and calcification
along with mineral deficiency (Al-Wahsh et al. 2005; Horner et al. 2005). American
Dietetic Association categorizes foods containing more than 10 mg oxalate per
serving as high-oxalate foods (Al-Wahsh et al. 2005). Soybeans contain moderate
amount ranging between 0.67 and 3.5 g oxalate per 100 g (dry weight) (Massey et al.
2001; Horner et al. 2005), which is much lower than the classic high-oxalate foods
1 Soybean (Glycine max)
9
71.6 UTI/mg; Carvalho et al. (2002) reported much higher concentration, i.e.,
122–206 UTI/mg; and Gu et al. (2010) observed that trypsin inhibitors range from
3000 to 6000 mg/100 g of raw soybean grain samples.
1.3.6.3 Lectins
Lectins (hemagglutinin or agglutinin) are the carbohydrate-binding proteins which
are resistant to digestion and are often considered one of the most toxic constituents
of the pulses/beans. Lectins possess high affinity to cellular and intracellular
membrane-associated carbohydrates (glycoprotein and glycolipids) [especially
N-acetyl-D-galactosamine] and thus, by binding, not only reduce their absorption
but can even lead to agglutination of red blood cells, leading to hemolytic anemia
(Liener 1994), impairment of the key enzymes of metabolism, and growth retardation, and if administered orally or intraperitoneally can even lead to death (Grant
et al. 1988). Numerous studies suggest that lectin consumption can also cause the
atrophy of microvilli, intestinal epithelial injury, diarrhea, increased intestinal permeability, and increased proliferation of pathogenic bacteria in the gut (Grant et al.
1995; Pusztai et al. 1991; Pusztai et al. 1995; Machado et al. 2008).
However, recent research suggests that lectins have potent in vivo biological
activities and exhibit anticarcinogenic and antitumor activity by either reduction of
cell proliferation, induction of tumor-specific cytotoxicity of macrophages, or by
having a strong effect on the immune system by production of various interleukins
(de Mejia et al. 2003; de lumen 2005). Soybean seeds contain 300–600 mg/100 g
lectin (Gu et al. 2010), and approximately 6.5 g lectin/kg is reported in defatted soy
meal (Vasconcelos et al. 2001) and approx. 0.2–2% of the soybean protein mass
(de Mejia et al. 2003; Rizzi et al. 2003; Anta et al. 2010). Treatments like soaking
(Hernandez-Infante et al. 1998), heat treatment, and fractionation during food
processing have been reported to be efficient in eliminating lectins and abolishing
its hemagglutinating activity, thus improving the nutritional quality of soybeans
(Vasconcelos et al. 1997).
1.3.6.4 Oxalate
Oxalate, the simplest dicarboxylic acid is synthesized by the body or absorbed from
the gut. It cannot be further metabolized by human beings and must be excreted in
the urine (Massey et al. 1993). Oxalate inhibits calcium absorption in the kidneys
and increases the risk of developing kidney stones, renal edema, and calcification
along with mineral deficiency (Al-Wahsh et al. 2005; Horner et al. 2005). American
Dietetic Association categorizes foods containing more than 10 mg oxalate per
serving as high-oxalate foods (Al-Wahsh et al. 2005). Soybeans contain moderate
amount ranging between 0.67 and 3.5 g oxalate per 100 g (dry weight) (Massey et al.
2001; Horner et al. 2005), which is much lower than the classic high-oxalate foods
1 Soybean (Glycine max)
9