Influence of alkaloids and oligosaccharides from white lupin seeds on utilization of diets by rats and absorption of nutrients in the small intestine

Abstract

The influence of quinolizidine alkaloids and oligosaccharides from white lupin seeds was studied on the absorption of nutrients in the small intestine and utilization of diets by rats. The source of oligosaccharides and alkaloids was the ethanol extract from high- and low-alkaloid seeds. The respective content of alkaloids in the extracts was 118.7 and 7.9 g kg −1 d.m., and of oligosaccharides 546.5 and 867.9 g kg −1 d.m. The alkaloid fraction obtained from the ethanol extract of high-alkaloid seeds by fractionation with organic solvents and ion exchange chromatography was also used. A distinct reduction of true protein digestibility (from 95.7% to 90.5%) was found in the experiment in which oligosaccharides were added to the casein diet in the amount of 17.09 g kg −1 (the amount contained in the diets with 150 g kg −1 low-alkaloid white lupin seeds). An adverse influence of alkaloids on casein digestibility was found only for the highest addition of alkaloids (0.32 g kg −1), corresponding to their level in the diet with 500 g kg −1 low-alkaloid lupin seeds. Using the perfusion technique, it was found that oligosaccharides decreased the absorption rates of glucose and methionine in the rat small intestine. Application of 203.53 mg of oligosaccharides during 1-h perfusion, i.e., the amount present in the 24-h diet with 100 g kg −1 lupin seeds decreased the absorption of glucose (from 88.42 to 66.21 mg h −1) and methionine (from 0.332 to 0.116 mg h −1) from the perfusion fluid compared to the control fluid. Glucose and methionine absorption did not correlate with alkaloid content in the perfusion fluid, whereas it correlated with oligosaccharide content in this fluid: r=−0.561 ** and r=−0.645 **, respectively. Extraction of alkaloids and oligosaccharides resulted in an increase of the utilization of protein from lupin seeds. The highest PER (2.40) was noted for the diet with extracted low-alkaloid seeds, which contained low levels of alkaloids and oligosaccharides: 0.09 and 1.13 g kg −1, respectively. Significantly lower PER was noted for the diet containing crude seeds of low-alkaloid lupin variety (alkaloid level 0.16 g kg −1) and the highest amount of oligosaccharides (29.2 g kg −1).