*2.4.3 Oligosaccharides*

Oligosaccharides, found in legumes, such as raffinose, stachyose, ciceritol, and verbascose (**Figure 7**), frequently cause flatulence in humans consuming legume seeds. They also induced discomfort and diarrhea. Nonetheless, oligosaccharides have recently been reported to have bioactive activities, particularly in small amounts. Raffinose was found in all parts of the legume plants, but it is built up in the seeds and roots during development. There were detectable amounts of these oligosaccharides in chickpeas, lentils, lupins, beans, peas, and faba beans (from 0.4 to 16.1% dry matter), with significant differences between the pulses studied [38]. In another study, Fan et al. [21] discovered that raffinose, stachyose, and verbascose were more concentrated in the seed kernels than in the seed coats (ratio of content in kernel/coat >1); the same was true for adzuki bean, pea, and broad bean, which showed the distribution ratio of oligosaccharides between 1 and 2

**Figure 7.** *Chemical structure of oligosaccharides: Raffinose (a), stachyose (b), ciceritol (c), verbascose (d).*

*Nutraceutical Properties of Legume Seeds: Phytochemical Compounds DOI: http://dx.doi.org/10.5772/intechopen.100171*

in kernel and coat. Green soybean and mung bean, however, had higher levels of stachyose and raffinose in their seed coats than kernels (ratio of content in kernel/ coat <1). Legumes generally have a decrease in total oligosaccharide content after soaking, which is most likely due to oligosaccharides leaching into the soaking water [43]. In chickpeas, lentils, yellow peas, green peas, and soybeans, it is observed that the oligosaccharide content is reduced after soaking in water with different factors (ultrasound and high hydrostatic pressure).

#### **2.5 Antinutritional factors**

Besides the nutritional compounds, legume seeds also contain some antinutritional factors (ANFs) that have been identified as bioactive constituents, which are lectins, phytic acid, alkaloids, amines, cyanogens, and other factors (**Figure 8**). Some of the ANFs that have unfavorable, undigested, or toxicological properties can be eliminated through plant genotype selection, postharvest, or thermal processing such as dehulling, soaking, germination, extraction, boiling, leaching, and/or fermentation [47].

Phytic acid is known widely as myo-inositol hexaphosphate (IP6), which is majorly stored in plants along with the salts (called phytates) [16, 38]. It is mostly considered an antinutrient due to its strong mineral, protein, and starch binding properties, which reduces bioavailability. Therefore, phytates affect enzyme activity, such as pepsin and trypsin; they also change the solubility, as well as digestibility. It has, however, been recognized for its antioxidant activity due to its ability to inhibit the formation of hydroxyl iron radicals. Another phytochemical of interest in legume seeds are lectins. Lectins are proteins or glycoproteins that are widely present in pulse and have the unique property of binding to carbohydrate-containing molecules. Lectins are hardly protein that does not degrade easily, and they can withstand stomach acid and digestive enzymes. Legumes have a wide range of lectin concentrations. They have been reported to contribute between 2.4 and 5% of total protein (17–23%) in kidney bean seeds, 0.8% of total protein in soybean and lime bean (34% and 21%, respectively), and approximately 0.6% of total protein (24–25%) in pea seeds [16].

Some of alkaloids are neurotoxins or neuromodulators. Quinolizidine alkaloids (QAs) are neurotoxin-secondary metabolites found in some Fabaceae, particularly in the genus Lupinus, including *Lupinus albus, L. mutabilis, L. angustifolius***,** and others. QAs protect plants from insect pests; however, QA levels in food must be less than 0.02% when lupin is used as an ingredient. Pyrrolizidine alkaloids have the potential to cause mutations and even cancer in both animals and humans.

**Figure 8.** *Chemical structure of some ANFs: Phytic acid (a), quinolizidine alkaloids (b), pyrrolizidine alkaloids (c).* Furthermore, some toxins have long-term consequences by affecting species survival and reproductive fitness. The toxicity of alkaloids varies with concentration and is nontoxic at lower levels. Lupanine is the most toxic and higher in *L. albus* (700 mg/g total alkaloids), while sparteine (300 mg/g total alkaloids in *L. luteus*) and lupinine are the least toxic. After enzymatic hydrolysis, cyanogenic glucosides release HCN after wounding. HCN is a respiratory poison because it inhibits the mitochondrial respiratory chain and is lethal to most animals [48].

The endophytic fungus *Phomopsis leptostromiformi*s is frequently found in *L. angustifolius*, an Australian forage plant used to feed sheep. Because of its antimitotic activity, this microorganism produces fomopsins and hepatocarcinogenic toxins that affect sheep [49].

Aside from lectins, protease inhibitors isolated from legume are divided into two main categories: the Kunitz inhibitor, which has a specificity aimed primarily against trypsin, and the Bowman-Birk inhibitor, which has the ability to inhibit chymotrypsin and trypsin at separate binding sites. They are found in common beans, lima beans, cowpeas, and lentils [16]. These hydrolyzed or modified proteins will become bioactive peptides (BPs), be commercialized as a nutraceutical product, and be involved in several body functions. BPs can be liberated from food proteins and exhibit bioactivity in both the small and large bowels [50].
