Nutritional evaluation of protein, phosphorus, calcium and magnesium bioavailability from lupin (Lupinus albus var. multolupa)-based diets in growing rats:: effect of α-galactoside oligosaccharide extraction and phytase supplementation

The nutritional composition of the legume Lupinus albus var. multolupa, raw or after alpha-galactoside extraction, and its effect on the bioavailability of protein, P, Ca, and Mg by growing rats was evaluated using a balance technique. The protein and dietary fibre content of the lupin flours studied was high, and 89-94 % of the dietary fibre was present as insoluble dietary fibre. The alpha-galactoside extraction process did not disrupt the nutritional quality of protein, and the digestive and metabolic utilisation of this nutrient was high and comparable with that obtained from a casein-cystine control diet (pair-fed to the average daily food intake of the experimental groups fed the different lupin diets). Bioavailability of P, Ca, and Mg from the lupin diets tested was high, and supplementation of an exogenous microbial phytase (750 phytase units/kg) did not cause any further improvement. Mineral content in the bone tissue (femur and sternum) did not correlate to mineral balance, which, on the other hand, was related to the mineral content of other tissues such as blood, plasma, liver and kidney. Due to its ability to grow under adverse edaphic and climatic conditions and to its good nutritional quality, alpha-galactoside-free lupin flour supplemented with the required amounts of minerals and vitamins to meet nutrient requirements can be used as an excellent dietary source for the preparation of dietetic products.