Legume flours: Nutritionally important sources of protein and dietary fiber

Peer-reviewed | Manuscript received: June 12, 2015 | Revision accepted: October 15, 2015

Introduction

Demand is increasing for grain legumes, such as pea, lupin, beans, and lentils. An increase in the content of grain legumes in food would support sustainable agriculture and nutrition, and would be good for health. The use of grain legumes in Europe needs to be developed. This is why both scientists and politicians are attempting to promote human consumption of these valuable foods. One result has been that the area in Germany under cultivation for pea and broad beans doubled in 2015 relative to the previous year.

Highly processed foods are now consumed in large quantities, but have a lower content of protein than conventionally produced foods. “Tasty”, cheap, and energy dense components are deliberately selected for processing and manufacturing, with the consequence that the proportions of carbohydrate and fat increases at the expense of protein. Analysis of the nutrient supply in the USA between 1971 and 2006 found that the protein fraction decreased by 1 energy percent (En%) and the carbohydrate and fat fraction increased by 8 En% [1]. Other studies too have indicated “protein dilution” in highly processed food. This leads to an imbalance, which is evident in increased energy uptake from carbohydrates and fat and decreased energy uptake from proteins. Although the German Nutrition Society (DGE) specifies a reference value of 15 En% from protein, there are demands to increase this to 30 En% [2].

Summary

Vegetarian and vegan nutrition have become fashionable. Some consumers now see themselves as partial vegetarians and greatly restrict their consumption of animal products. This has led to an increase in the demand for alternative sources of protein, in the form of legumes and their processed products. Proteins enhance the feeling of fullness and can contribute to lowering blood pressure. Moreover, plant proteins have a favorable effect on lipid metabolism. For this reason, legume flours are important sources of plant protein.

Flours from soya, lupin, chickpea and green pea have been studied. The highest content of protein was found in soya and lupin, which both contained ca. 35 g protein per 100 g. Lupin flour had the highest content of kernel fiber, corresponding to 35 g/100 g soluble kernel fiber. In addition, lupin and soya flour only had a low content of easily digestible carbohydrates: ca. 8–10 g/100 g.

Cereal flour had a high content of starch and a low content of protein and is used in making bread, cakes and pastries; one possibility would be to replace 10–20% of this with legume flour. The amino acids contained in the legume flour would enhance the nutritional value of the cereal protein.The fat content in legume flours other than soya flour was clearly under 10 g/100 g. The omega-6/omega-3 ratio in lupin and green pea flour was in accordance with the recommended maximal ratio of 5:1. Most legume flours are a good source of magnesium, iron and zinc, as well as of vitamin E, the B vitamins, and carotenoids. Aside from their nutritional and physiological benefits, legume flours are cheaper than protein and fiber extracts from legumes.

For ecological and nutritional/physiological reasons, only plant protein should be used to enrich protein relative to fats and carbohydrates. Lupin is an interesting alternative to soya beans in Europe, as it has a high content of protein. Legume flour can be used to enrich bread, cakes or pastries, or meat products. It supports good health and is easy to process.

Keywords: legume flour, pulses, plant protein, dietary fiber, protein quality, fat quality, carotenoids, vitamins, trace elements

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