Lupin Protein - Composition and Amino Acids
Lupin seeds are increasingly attracting attention, mainly due to their high protein content, which can reach up to 46.5g per 100g in certain varieties (Lupinus luteus) 1.
White lupin has the highest values of essential amino acids and the best amino acid composition, followed by blue and yellow lupin 2. Sweet lupin seeds are suitable for the production of sweet lupin flour and lupin protein. Even sweet lupin flour is rich in plant proteins, ranging from 39% to 45% plant-based proteins. Only lupin protein concentrates (45% to 80% protein) and lupin protein isolate (90% protein) contain more proteins.
Lupin protein is obtained from the seeds of the legume lupine. To produce lupine protein, the seeds of the sweet lupine are peeled and flaked 3. Subsequently, the so-called flakes are filled into containers and processed into a mash with water. Through repeated decantation, the bitter substances are rinsed out, and numerous other "foreign substances" are removed. Despite the processing, the proteins remain well-preserved 4.
Lupine protein is lactose-free, cholesterol-free, and gluten-free. It is ideal for people with celiac disease (gluten intolerance).
Plant Protein Compounds
The main plant protein fractions are glutelin and albumins 56 7. The glutelin fraction consists essentially of α-conglutin (11S globulin and "legumin-like") and β-conglutin (7S globulin and "vicilin-like") 8 9 10. Fractions with smaller proportions of the total protein content are γ-conglutin and δ-conglutin. Plant protein fractions consist of various proteins, which in turn are composed of different amino acids.
Lupine protein contains sufficient amounts of leucine 11. Leucine is one of the key amino acids associated with muscle maintenance and muscle building 12 13. Additionally, it also contains higher amounts of arginine and lysine.
Percentage distribution of amino acids 14:
Limiting Amino Acids
When considering the nutritional physiology of lupine seed proteins, they lack the sulfur-containing amino acid methionine (first limiting amino acid), as well as tryptophan and valine. 15 16. If the protein powder is enriched with small amounts of methionine, the biological value can be significantly improved 17. Foods high in methionine can be found here. Nevertheless, most of the essential amino acids in lupine protein isolates are at an acceptable level compared to reference values for infants and adults 18.
Protein Quality and PDCAAS
In a 1992 study involving nine healthy men, the protein quality of lupin protein was examined in comparison to egg protein 19. It was found that lupin protein is a good plant-based protein source with high protein quality. However, the net protein utilization was 23% lower compared to egg proteins. Net protein utilization measures the efficiency of converting ingested proteins into body proteins.
The protein quality of a food is determined using the PDCAAS method, which assesses its ability to meet human requirements for essential amino acids. The PDCAAS is derived from the digestibility of amino acids and the amino acid profile. For lupin protein, the PDCAAS value is 0.92, indicating high protein quality 20. The maximum value a food can achieve is 1.0.
Lupin protein no longer contains absorption-inhibiting ingredients 21 22 23. As a result, it is easily digestible overall and offers high bioavailability. Corresponding measurements have shown that between 83 and 91% of the proteins are digested 24 25 26. Lupine protein isolate is thus digested almost as well as soy protein (91.5%). In further comparison of the digestion rate, rice protein performs even better with 96.66% 27.
Are lupine proteins toxic?
Studies have shown that lupine protein is not toxic and therefore suitable for consumption 28. The toxicity of proteins depends on their specific structures. Through certain processing methods such as heating, the toxins are reduced or even completely eliminated.
Allergens in Lupine Protein
A small portion of the population is allergic to lupine 29. Lupine contains allergens (substances that can trigger allergic reactions) such as α-conglutin and β-conglutin. Therefore, all food products that contain even traces of lupine must be labeled 30 31 32 33.
A lupine allergy can occur separately or in cross-reactions with other allergens such as soybeans, peanuts, green beans, and peas. 34 35. Symptoms of a lupine allergy can include: oral allergy syndrome, inflammation of the nasal mucosa and conjunctiva (rhinoconjunctivitis), lip or other edema, hives (urticaria), difficulty breathing (laryngospasm, dyspnea, asthmatic attacks), abdominal pain, nausea, and even anaphylactic shock. 36.
Lupine protein lowers cholesterol levels
By incorporating 25g of lupine protein per day into various foods, total cholesterol and LDL cholesterol levels were reduced in samples of individuals with hypercholesterolemia (high cholesterol levels in the blood). 37. Additionally, triglyceride, homocysteine, and uric acid levels were reduced. Elevated levels can be indicators of metabolic disorders such as gout.
By consuming 35g of lupine protein per day over a period of six weeks, 43 subjects were able to lower their LDL cholesterol levels. 38. HDL cholesterol levels remained unchanged. Triglyceride, homocysteine, and amino acid levels in the plasma were not or only minimally affected.
Even with the consumption of lupine protein bars along with cellulose (fiber), a cholesterol-lowering benefit (-4.2%) was achieved in subjects with hypercholesterolemia. 39.
Another study over eight weeks also shows that 25g of lupine protein can reduce total cholesterol (-5%) and LDL cholesterol levels (-12%) over a short period of time 40. The LDL:HDL ratio improved by 16%. Additionally, systolic blood pressure levels were also lowered. According to the scientists, lupine protein could offer a safe and non-pharmacological approach as a dietary supplement to mitigate the extent of hypercholesterolemia, thereby reducing the risk of cardiovascular diseases.
Foods enriched with lupine could have a positive impact on reducing risk factors of cardiovascular diseases 41.
Blood Pressure-lowering Benefit
Lupin proteins have a moderate blood pressure-lowering benefit, which is attributed to the ACE inhibitors released during digestion. 42 43. The two storage proteins, α-conglutin and β-conglutin, are believed to be responsible for the ACE inhibitor activity. ACE inhibitors are drugs used, among other things, in the treatment of hypertension. ACE (Angiotensin Converting Enzyme) regulates blood pressure by influencing water balance.
Lupin protein can be consumed as a vegan protein powder after training, mixed with water or plant-based drinks, as a protein shake. However, it is recommended to combine it with other protein powders such as rice protein and hemp protein, which contain high levels of methionine, thus balancing the limiting amino acids.
In addition, the rather taste-neutral lupine protein is excellent as a component of smoothies.
Due to its functional properties (excellent solubility, good emulsifying capacity, foaming and gelling properties), lupine protein can be considered as a potential substitute for soy protein in food 44 45.
Therefore, lupine protein offers further applications in ice cream, yogurt, pudding, spreads, sauces, plant-based drinks, as well as bread, baked goods, and pasta 46 47 48 49. Additionally, it is possible to produce meat substitute products such as patties, cutlets, burgers, sausages, and strips from lupin protein. According to studies, lupin proteins have been well accepted and tolerated in such products 50. According to scientists, they could provide a good option for the nutrition of high-performance athletes before training.