Polyphenols (espiacelly tanins) - bind proteins (form hydrophilic or hydrophobic

complexes) and inhibit absorption of mineral elements, eg. iron.

Ensyme inhibitors - trypsine and alfa-amylase inhibitors. Trypsin inhibitors inhibit activity of trypsine and chemotripsine and inhibit absorpcion and digestion of proteins. Alfa-amylase inhibitors (e.g. citric acid, oxalic acid, heavy metals) - inhibit activity of alfa-amylase (influence digestion of starch negativelly).

Many polyphenolic compounds also inhibit iron absorption. An important example are the polyphenols that people consume in beverages such as tea and coffee, such as tannic acid. In addition, the consumption of 2+ minerals such as calcium can inhibit the absorption of iron. These anti-nutrient compounds only inhibit non-heme iron; heme iron is not affected by anti-nutrients. This free full text article from Hallberg and Hulthen describes the main iron inhibitors: http://www.ncbi.nlm.nih.gov/pubmed/10799377

Polyphenolic compounds, Trypsin inhibitor, Phytate, saponins, Lectins

In addition to compounds mentioned above, dietary fibre in cereals also interact with absorption of nutrients. For example, barley beta-glucans are proven for cholosterol lowering. Lowering absorption of cholesterol is considered as one of mechanisms for such an effect.

http://www.efsa.europa.eu/en/efsajournal/doc/2471.pdf

thanks to everybody for providing such insightful answers

There is a way to minimize the negative effect of these anti-nutrients through germination, increases the enzyme activity 5-6 times due to proteolytic release of enzymes by the inactivation of enzyme inhibitors- soaking grains , seeds and legumes to begin the germination for 24 hours and wash carefully before cooking. Sprouting is another way and neutralizes phytic acid. Saponins can be removed from grains like quinoa by washing them well. Unfortunately modern farming techniques prevent grains from germinating.

Dear Ashish,these are common antinutrient factors found in grains:- Lectins, Phytate, Goitrogens, Trypsin inhibitor, Alpha-amylase inhibitor, Raffinose Oligosaccharides, Polyphenolics, Saponins.