The content of raffinose oligosaccharides in legumes and their importance for animals

Abstract

In recent years, there has been a growing interest in the use of legume seeds for human and animal nutrition for various reasons. Independence from the import of genetically modified soybean products, feed quality and price play an important role in animal nutrition (Święcicki et al., 2020). Legume seeds are a rich source of nutrients for humans, thus their consumption prevents various diseases of civilization, such as hypertension, type 2 diabetes, hyperlipidaemia, and overweight (Conti et al., 2021). Legumes can fix atmospheric nitrogen, improve soil physical condition, require lower energy input (Rubiales and Mikic, 2015) and perfectly complement crop rotation. It is well known that legumes also contain antinutrients (Gulewicz et al., 2014), such as trypsin inhibitors, lectins, phytic acid, tannins, quinolizidine alkaloids, saponins, and raffinose family oligosaccharides (RFOs). They have a diverse structure, and their activity and concentration in seeds are species-specific. Chemically, these compounds are sucrose homologues with (1→6) glycosidic linkages of galactose molecules. RFOs perform critical physiological functions. They increase drought and low temperature resistance, are responsible for respiration during germination, and extend the shelf life of legumes (Gu et al., 2018). Although RFOs are considered antinutrients for animals (Banti, 2021), recently these compounds have been recognized as functional substances with ABSTRACT. The interest of consumers, as well as the food and feed industry in legumes is constantly increasing. However, the use of legume seeds is limited by the fact that they contain various non-nutritive compounds such as raffinose family oligosaccharides (RFOs). On the other hand, RFO compounds are considered prebiotic substances improving health and growth of organisms. Our study consisted in the long-term monitoring of RFO contents in seeds of several legumes cultivated in Poland. The seeds of pea (25 cultivars), faba bean (5 cultivars), and lupins (41 cultivars) were harvested between 2013 and 2019, whereas soybean seeds (27 cultivars) were harvested between 2015 and 2019. The analysis showed that the content of RFOs in soybean seeds ranged from 33.75 to 69.30 mg per g dry matter (DM), 57.23 to 130.38 mg/g DM in lupin seeds – 52.03 to 80.60 mg/g DM in pea seeds, and from 32.15 to 65.17 mg/g DM in faba bean seeds. Yellow lupin seeds had the highest total RFO contents in DM, whereas faba bean and soybean seeds showed the lowest RFO contents. Stachyose was the dominant oligosaccharide in all soybean and lupin seeds, while verbascose was the dominant oligosaccharide in most pea and faba bean seeds. Some pea cultivars contained more stachyose than verbascose. Crop species, cultivar, growing environment, and processing methods determine the suitability of individual seeds for the feed and food industry. Received: 24 February 2022 Revised: 19 April 2022 Accepted: 2 May 2022