Composition & Nutritive Value

Irwin Valley lupin products are sourced solely from Australian Sweet Lupin. 

There is very little starch in the grain of the Australian Sweet Lupin which is in marked contrast to crops such as rice, wheat and other legumes such as field peas and lentils.

 

Carbohydrates
The seed coats (hulls) and cotyledons contain different types of carbohydrate.  Lupin hulls contain little protein and lipid and are predominantly composed of structural polysaccharides; cellulose, hemicelluloses and pectins.  One hundred grams of lupin hull contains 95g fibre. Furthermore, xylose is present in large quantities, followed by uronic acid.  Thus the composition of the lupin hull much resembles that of the soy hull.

The main carbohydrate reserves of the cotyledons are the non-structural polysaccharides of the cell walls, with the main components being galactose, arabinose and uronic acid.  These complex compounds are referred to as non-starch polysaccharides (NSP).  Their structure is based on a backbone of rhamno-galacturonans.  The water-soluble portion, about 20% of the NSP, is considered to have bio-active (as well as textural) properties due to its viscous nature and effect on intestinal transit time.  As with soy, arabino-galactanes are important components of the cell wall material of the cotyledon. In fermentation tests on lupin fibres with micro organisms of the human intestine, it was shown than extensive biodegradation occurs. An important attribute of the cotyledon NSP is their ability to hold large quantities of water, about 8-fold by weight for lupins, and maintains normal gut motility. 

Lupin oligosaccharides are higher α-galactosides of sucrose.  The oligosaccharide-fraction (5-12%) contains raffinose, stachyose, verbascose and ajugose.  Raffinose has one galactose moiety linked to sucrose through an a 1,4 bond, while stachyose has two, verbascose three and ajugose four.  These compounds cannot be metabolised by humans and are a rich source of nutrients for bifidobacteria in the colon.

Protein 
The protein content of the kernel is very high and can constitute more than half the total weight.  The bullk of the proteins consists of the globulin type storage proteins (called conglutins); they comprise about 85% of the total protein and have similar size and physical properties to the storage proteins of other grain legume species.  The remaining 15% of proteins are albumins, which are soluble at pH 5 and vary in size from about 6,000 to 117,000 daltons.

The digestibility and bioavailability of the protein are comparable to soy protein. In both legumes the sulphur containing amino acids are the limiting amino acids, however the amino acid lysine is present in large quantities (Table 2).  A combination of lupin with cereal proteins results in a high supplemental effect, which increases the nutritional value of this combination and brings it almost in line with animal protein (Uauy et al, 1995; Yanez et al 1985).

Lipids
The lipid content of Australian Sweet Lupin comprises of triglycerides (71%), phospholipids (15%), free sterols (5%), glycolipids (3.5%) sterol and wax esters (0.5%), free alcohols (0.4%) and unidentified waxy material (4%).  The sterols present in the non-saponifiable fraction of the oil are sitosterol and campesterol as the main components, and stigmasterol and avenasterol as secondary. 

The oils have high antioxidant capacities due in part to Vitamin E. The total tocopherol content (Vit E) content of is around 2.3-4.6 mg/kg of which 87% is. During germination, the concentration of gamma-tocopherol decreases as alpha-tocopherol is formed. 

 

Minerals and trace elements
The mineral (ash) content of different Australian Sweet Lupin varieties fluctuates between 3.2 and 4.6g/100g dry matter.  Typical results follow (in mg/g): calcium between 15 and 29, magnesium 11 - 20, sodium 3 - 11 and potassium 66 - 90. Results of trace elements (in mg/kg): iron 31 - 150, zinc 24 - 45, and copper 2.5 – 6.8.  Legumes are considered to be a good source of minerals and trace elements, and Australian Sweet Lupin feature a higher calcium and phosphate content than cereals.  The content of trace elements varies dependent on the mineral content of the soil. 

Anti-nutritional or bio-actives?
Legume grains contain a range of compounds, traditionally known as anti-nutritional factors (ANF) or anti-nutrients, with apparent untoward effects on species ingesting them.    While some ANF have a negative effect on feed utilisation by farmed livestock, they can also have beneficial effects in humans, such as preventing the development of some forms of cancer and of osteoporosis.    

Unlike most legume grains, lupins do not need to be heated to denature the proteinaceous ANF and make them safe for consumption by humans or animals.  The content of proteinaceous ANF in domesticated Australian Sweet Lupin is very low.  Typically, trypsin inhibitor activity is < 0.1 mg/kg, and chymotrypsin inhibitor activity < 0.1 mg/kg.  Lectin activity is virtually non-existent in Australian Sweet Lupin.   

Phytate (inositol hexaphosphate and lower substituted homologues and their salts) contributes about one-half of the total phosphorus content in Australian Sweet Lupin.  Phytate can form insoluble complexes with divalent cations, particularly Ca++ and Zn++, thus making them less available for absorption and utilisation.  Human studies have shown similar rates of absorption of phosphorus from Australian Sweet Lupin-based foods comparable to soy products.  

Saponins are present in Australian Sweet Lupin ranging from 55 to 730 mg/kg.  Saponins are plant glycosides in which the non-sugar moiety is a steroid or a triterpenoid compound.  Saponins are generally harmless to humans: some are claimed to be beneficial in lowering blood cholesterol levels and protecting against coronary heart disease.  The concentrations in lupin are lower than in many other legume species.

Isoflavones had generally been regarded as ANF because of their negative effects on fertility in ruminants grazing pasture medics and subterranean clovers. However, they are now recognised as preventative agents against some forms of cancer and osteoporosis in women.  Isoflavones are present in lupin in the green leaf material and in the hypocotyls of germinating seeds (sprouts).  

The lupin alkaloids are usually bicyclic, tricyclic or tetracyclic derivatives of quinolizidine.  Grain of modern domesticated Australian Sweet Lupin cultivars typically contains less than 200 mg/kg alkaloids.  In contrast, grain from ‘bitter’ wild types that still exist in many countries may contain from 5,000 to 40,000 mg/kg alkaloids. The quinolizidine alkaloids are mild toxins and have a short half-life in humans.  They are excreted largely unchanged in the urine of >90% of humans. 

The mycotoxins associated with lupins are from the family of phomopsins, a group of linear hexapeptides with an anti-microtubule effect which is most pronounced in the liver and kidney.  The most recent varieties of Australian Sweet Lupin are resistant to invasion by the responsible fungus (Diaporthe toxica), coupled with the dry Western Australian climate the risk of phomopsin contamination is extremely low, and likely to be even less in the future.

However grain that contain phomopsins can be easily removed from the rest of the harvested grain by grading, using screens, gravity tables and aspirators.  A rapid enzyme-linked immunosorbent assay for the phomopsins is readily available to the food industry. 

 

References:
Uauy, R., Gattas, V & Yanez, E. (1995) “Sweet lupins in human nutrition” In: World Review of Nutrition and Dietetics 77: 75-88 Ed. A.M. Simopoulos.
Yáñez, E., Ballester, D. and Ivanovic, D. (1985).  Wheat and oat fortification with sweet lupin flour (L. albus cv. Maleolupa).  Nutrition Reports International 31:  493-499.