Oligosaccharide Content and Composition of Legumes and Their Reduction by Soaking,Cooking, Ultrasound,and High Hydrostatic Pressure

Oligosaccharides, including raffinose, stachyose, ciceritol, and verbascose, are commonly found in legumes and often result in flatulence in humans. Effects of soaking, soaking with ultrasound (47 MHz), soaking with high hydrostatic pressure (HHP, 621 MPa), and subsequent cooking on the oligosaccharide content of lentils, chickpeas, peas, and soybeans were investigated. Legumes were soaked for 3 or 12 hr in water, soaked for 1.5 or 3 hr with ultrasound, or soaked for 0.5 or 1 hr with HHP. Oligosaccharides of lentils and chickpeas were mainly composed of raffinose, ciceritol, and stachyose, while those of peas and soybeans were raffinose and stachyose. Verbascose was the minor oligosaccharide in lentils and peas and was absent in chickpeas and soybeans. Ciceritol was not detected in peas and soybeans. Total oligosaccharide content of raw legumes ranged from 70.7 mg/g in yellow peas to 144.9 mg/g in chickpeas. Soaking was effective for the reduction of oligosaccharides in the tested legumes. Compared with soaking for 3 hr, soaking legumes with ultrasound for 3 hr in all tested legumes or soaking legumes with HHP for 1 hr, with exception of soybeans, appeared to be more effective for the reduction of oligosaccharides. The effect of cooking on the reduction of oligosaccharide content of presoaked legumes was evident in lentils, while oligosaccharide content of chickpeas, peas, and soybeans was either unchanged or even increased by cooking after presoaking, with or without ultrasound, probably due to the leaching of other soluble components and the release of bound oligosaccharides during cooking. During soaking or cooking of legumes, raffinose leached out faster than other oligosaccharides.