Chromatographic determination of soluble fraction of carbohydrates in legumes from Algeria

Abstract

Legumes are an essential source of energy and nutrients for humans and their cultivation has facilitated the settlement of people in different regions of the world. In countries from the north of Africa, such as Argelia, these foods can be consumed as cooked seed or as flour in the preparation of some foodstuffs. According to FAO (2012) the consumption of legumes in Algeria is 17 g/person/day. Considering the water soluble fraction, a-galactosides, galactosyl derivatives from sucrose are one of the most important compounds. These carbohydrates act as antinutritional factors or beneficial compounds (prebiotics, immunomodulators, antihipertensives...), depending on the dose at which they are consumed. Thus, it has been found that 3 g/day is the effective daily dose of a-galactosides to obtain health benefits, whereas higher intake can cause negative effects. It is also known that the processing can exert a certain protection against these components. Therefore it is of paramount importance the knowledge of the occurrence of these compounds in legumes in order to select the most adequate processing to preserve their quality and bioactivity. In this work, chromatographic determination of soluble fraction of carbohydrates in five samples of legumes (chick peas, lentils, beans, peas, faba) from Argelia has been carried out. Two different methods HPLC-RID and GC-FID were used for their characterization. In the former, the extraction of carbohydrates was carried out with water at 60°C and glucose, sucrose, raffinose, stachyose and verbascose were detected in all samples. The highest recovery was obtained for the carbohydrates with the highest polymerization degree (DP), with values close to 99% in the case of verbascose. For GC analysis, apart from those carbohydrates previously detected, ajugose and different cyclitols, as myoinositol, were found. In these analyses, Carrez solution was used for sample preparation and the highest recovery values (³83%) were obtained for compounds with DP ³2, verbascose presenting a value close to 98%. In general, the most abundant carbohydrates were stachyose and verbascose and the quantified levels were variable depending on the analysed specie and within the range showed for legumes from other countries. Similar total amounts of agalactosides were obtained by both chromatographic methods, although GC allowed the detection of higher number of compounds, including galactosyl cyclitols.