Legumes

Nutritional Quality, Processing and Potential Health Benefits

Maria Ángeles Martín-Cabrejas

• Publisher: Royal Society of Chemistry
• Year: 2019
• eBook ISBN: 9781788016759
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Nutrition, Dietics & Bariatrics
• Index: Biological Sciences

Legumes have high potential for improving the nutritional quality of foods, but limited data on their bioactive compounds exists. Results of clinical and epidemiological studies suggest that natural antioxidants can protect us against oxidative stress that is closely associated with cancer and cardiovascular disease. Legumes are a valuable source of bioactive compounds such as phenolic compounds, peptides and non-nutritional factors. They are rich in several important micronutrients, including potassium, magnesium, folate, iron, and zinc, and are an important source of protein in vegetarian diets. They are among the only plant foods that provide significant amounts of the amino acid, lysine. Commonly consumed legumes are also rich in total and soluble fibre as well as in resistant starch.

This book provides a comprehensive overview of the antioxidant activity and health aspects of legumes. The international spread of contributors will describe the key factors that influence consumer acceptance of legumes in the diet, as well as the known functional properties of legumes and legume based food products. It will serve as an excellent and up-to-date reference for food scientists, food chemists, researchers in human nutrition, dietetics and the chemistry of natural compounds.

Part I Introduction

CHAPTER 1

Legumes: An Overview

M. A. Martín-Cabrejas^*a, ^*b

^a Instituto de Investigación en Ciencias de la Alimentación, CIAL (CSIC-UAM), Universidad Autónoma de Madrid, Madrid, Spain

^b Departamento de Química Agrícola y Bromatología, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid, Spain
^*E-mail: [email protected]

In recent years, there has been a clear breakthrough in the discovery of new bioactive compounds and the development of functional food ingredients for the prevention of diseases. Traditionally, legumes have been considered as foods with beneficial effects for human health. Legumes are plants of the family Fabaceae whose seeds represent a basic pillar of human nutrition since ancient times. In addition to a very adequate nutrient content in carbohydrates, proteins, dietary fiber, vitamins and minerals, legumes also contain a great variety of non-nutrient compounds considered bioactive compounds with antioxidant, hypoglycemic, hypolipidemic and anticarcinogenic properties. Nowadays, there is an increasing trend and research activity for incorporating legumes in innovative food products and formulations, which will help towards increasing legume consumption and improving human diet throughout the world.

1.1 Introduction

Legumes belong to the family Fabaceae whose seeds represent a basic pillar of human nutrition since ancient times. Nowadays, legumes play an important role due to their nutritional and health associated benefits,^1,7 together with economic and environmental factors crucial in our sustainable future.⁸ Legumes are safe for consumption, relatively inexpensive and also easily available, being present in the diet of millions of individuals around the world. From academic and governmental institutions, a great effort is being made to promote the value and use of legumes throughout the food system, and to make everyone aware of their benefits. To achieve this objective, it is necessary to increase their global production, integrating them into cropping systems, improving the research of new legume varieties, developing novel management strategies and overcoming the current market challenges.⁹ In this sense, the Food and Agriculture Organization (FAO) of the United Nations (UN) announced the International Year of Pulses in 2016.¹⁰ FAO-UN supported them on the following areas: (i) pulses are highly nutritious, (ii) pulses are economically accessible and contribute to food security at all levels, (iii) pulses have important health benefits, (iv) pulses contribute to climate change mitigation and adaptation, (v) pulses promote biodiversity.¹⁰

In general, legumes are characterized as providing high contents of proteins and complex carbohydrates such as dietary fiber and resistant starch, and low levels of lipids, as well as being an important source of minerals such as Fe, Zn and Ca.¹⁰ They contain important levels of vitamins, such as folate, which reduces the risk of neural tube defects. In addition, they provide bioactive compounds that contribute to the prevention of chronic diseases.¹¹ Researchers have reported that these compounds are associated with a reduction in the risks of cardiovascular diseases (CVD), diabetes and some types of cancer, particularly colorectal cancer.^1,3,5,7

Legumes are one of the most nutritious foods in the world and combined with other products are the basis of diet for a large part of the world's population, especially in poorer areas where meat, dairy products and fish are economically inaccessible.¹⁰ Legumes are densely packed with proteins, twice the amount found in whole grain cereals. When combined with other foods, such as cereals, the protein quality of legumes is further increased.

The legume crops are essential for sustainable agriculture and they can adapt to climate change, being cultivated in arid climates with limited or erratic rainfall. Scientists are currently working on the development of legume varieties that can grow at temperatures that are 4 or 5 degrees higher than the usual temperature.¹² The goal is to adapt legumes to the effects of climate change such as rising temperatures. In addition, legumes can also fix biological nitrogen into the soil, increasing its fertility and allowing less use of agrochemicals and fertilizers. For example, 85 million hectares of pulses were grown worldwide that fixed from 3 to 6 tons of nitrogen in 2014. Consequently, these crops can help to achieve an adequate and efficient use of fertilizers, resulting in reduced greenhouse gas emissions.¹⁰ One factor that is of concern today is the excessive accumulation of salts in the soil and the use of saline groundwater in legume production worldwide.¹³ It is known that saline stress alters the photosynthetic process and hormonal regulation and contributes to the nutritional imbalance in legumes, decreasing yield and grain quality.⁸ One solution would be to consider the development of transgenic crops and management strategies to achieve an increase in the yield of grain legumes in saline soils. In addition, legumes are also highly efficient in the use of water, especially in comparison with other sources of protein. For example, 1 kg of cooked beef requires 10 times more water than 1 kg of lentils.¹⁰ Furthermore, intercropping with legumes increases biodiversity creating a more diverse landscape for animals and insects. Therefore, legumes must be preserved and enriched through the development of new varieties resistant to adverse crop conditions, improving their nutritional value and optimizing their health benefits.

Because legumes provide numerous benefits they may act as an affordable ally against malnutrition. Nowadays, they may be considered as a superfood for the future, enabling us to reach zero hunger at a time when one in five children under 5 years of age is chronically malnourished.¹⁴ Legumes are more accessible to lower-income families and have a beneficial influence on physiological functions by improving the state of well-being and health, and reducing or preventing the risk of diseases. In fact, promising progress has been observed in the areas of South America and the Caribbean in the fight against hunger.¹⁵ However, as the production of legumes is still lower than that of other basic products, such as cereals, starchy roots and vegetables, it is necessary to raise awareness about their benefits and encourage greater production of these crops. For this reason, it is convenient if the design of farming systems is local and based on regional expert knowledge.⁸

However, at a global level, the consumption of legumes has been reduced by an increase in the consumption of products of animal origin, especially in developed countries, which has led to a number of important health problems. The profile of the consumer has been changed and new preferences and needs in the food market have emerged. There are different reasons to develop new food products, such as the nutritional and health demands of the different sectors of the population and the reduction and/or elimination of certain nutrients, as well as the incorporation of others (dietary fiber, vitamins, minerals, antioxidants, polyunsaturated fatty acids, etc.), which can provide a health benefit and a better quality of life for consumers.¹⁶

In this sense, legumes are of special interest as a healthy and tasty alternative to the high-calorie diets prevalent in developed countries. In some population groups a low risk of suffering from chronic diseases, such as cardiovascular diseases and certain types of cancer, has been identified, and this has been attributed to a diversified eating style, either in food or in its components.¹⁶

1.2 Nutritional Quality of Legume Seeds

The chemical composition of the legumes varies between the different types of seeds. The average energy content of legumes is, in general, high (330–374 kcal/100 g dry matter).¹⁰ The amount of proteins in legumes varies greatly depending on the species, and ranges between 20 and 35%. The protein content is considered high compared with cereals and is rich in the amino acid lysine and sulfur amino acids such as methionine, both of which are limited in most plant foods. Legumes in combination with other cereals such as corn and other products rich in starches and with low protein value significantly increase the nutritional value of the diet.¹⁷ However, their nutritional value is poor compared to proteins of animal origin. Several factors are involved, such as the legume proteins have a storage function, their quaternary structure is more compact, which makes the action of digestive enzymes difficult, and the presence of protease inhibitors inhibits the activity of proteases, the digestive enzymes.^18,19 A priori, all these factors seem to affect their digestibility. However, during their traditional culinary preparation, the nutritional value can be improved because the thermal treatments inactivate the protease inhibitors as will be described in Chapter 10.

The processing induces structural changes in proteins, which facilitates the accessibility of the digestive enzymes, and favors protein metabolism.¹⁸ In addition, the protein content is often overestimated, since legumes have a high proportion of non-protein nitrogen (peptides, free amino acids and other nitrogenous compounds) that is quantified as total protein and this should be taken into account for the nutritional studies.

On the other hand, carbohydrates in legumes are considered complex, which, unlike simple carbohydrates such as sugars, are slowly digested and absorbed by the intestine, which favors their consumption by diabetic individuals.⁷ Starch is the predominant carbohydrate in legumes (75–80%), except in oilseeds; in peanuts the starch content accounts for one third of the total carbohydrates, while soybeans exhibit a very low starch content. Legumes are also rich in dietary fiber, and it is the soluble fiber fraction that is relevant (approximately 16–20%).^21,26 This type of fiber plays a leading role because it facilitates water adsorption in the intestine. Thus, the intestinal bolus increases, facilitating intestinal movement and preventing constipation.²⁰ Clinical trials and epidemiological studies have reported that dietary fiber contained in beans, helps to lower blood cholesterol levels. This fact is very important in the prevention and reduction of risk of cardiovascular diseases.²⁷ In this regard, legumes are also low in fat, with values from 1 to 4%, except for oilseeds that show mean values of 18% for soybeans and 50% for peanuts. The lipid fracti...

Table of contents

• Cover
• halftitle
• Series Editor
• Title
• Copyright
• Preface
• Contents
• Part I Introduction
• Chapter 1 Legumes: An Overview
• Part II Bioactive Compounds of Legumes
• Chapter 2 Leguminous Seeds as a Source of Phenolic Acids, Condensed Tannins, and Lignans
• Chapter 3 Phenolic Compounds: Flavonoids in Legumes
• Chapter 4 Role of Dietary Fiber in Legumes
• Chapter 5 Legume Bioactive Peptides
• Chapter 6 Melatonin
• Chapter 7 Non-nutritional Factors: Lectins, Phytic Acid, Proteases Inhibitors, Allergens
• Part III Processing Of Legumes: Changes Of Bioactive Compounds
• Chapter 8 Obtaining, Chemically Characterizing and Nutritionally Evaluating Seasonal Legume Sprouts as a Feed Alternative
• Chapter 9 Impact of Fermentation on the Nutritional Quality, Bioactive Compounds and Potential Health Properties of Legumes
• Chapter 10 Thermal Processing of Legumes
• Chapter 11 Innovative Legume Foods
• Part IV Health Benefits Of Legumes
• Chapter 12 Legumes and Oxidative Stress
• Chapter 13 Legumes and Inflammation
• Chapter 14 Legumes and Obesity
• Chapter 15 Legumes and Cancer
• Subject Index