Whole Grains and Health

Rikard Landberg, Nathalie Scheers, Rikard Landberg, Nathalie Scheers

• Publisher: Wiley-Blackwell
• Year: 2021
• Print ISBN: 9781118939437
• eBook ISBN: 9781118939406
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

WHOLE GRAINS AND HEALTH

The updated guide to whole grains and their integral role in nutritional health

In an increasingly health-conscious society, the potential benefits of whole grain products are of paramount importance to manufacturers, dieticians, and consumers alike. Whole Grains and Health covers all aspects of this crucial topic, presenting a data-driven study of whole grains' functional components, associated biomarkers and overall impact upon human health. Now in its second edition, the text has been revised and expanded to include six new chapters and groundbreaking new data. This essential guide features:

• Summaries of large research projects on the health effects of whole grain in Europe and the US
• New data on the associations between whole grain consumption and risk of developing chronic diseases
• Discussions of metabolomics and their use in addressing health effects and finding new biomarkers of both dietary exposure and health effects related to the diet
• Information on the use of genomics in studies of how gene-expression profiles change in response to whole grain intake
• Newly identified bioactive compounds in whole grains and whole grain fractions
• The new EU regulations on health claims that affect whole grain food products

Providing information that will be of interest to food scientists, healthcare specialists and food industry professionals alike, the second edition of Whole Grains and Health is an essential resource for anyone concerned with the impact whole grains may have upon health.

1
The Structure of Cereal Grains and Their Products

Maud Langton¹, and José Luis Vázquez Gutiérrex^1,2

¹Department of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden

²Department of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden Present address: Centro Technológico ITENE, Valencia, Spain

1.1 Introduction

Through the senses, consumers can subjectively detect properties in food. However, other qualities such as long‐term health benefits of food that cannot be easily detected. A deep knowledge of cereal grain structure and how it is modified by processing is necessary to understand the physical and health properties of the different cereal products. This chapter focuses on the microstructure, at different levels, of cereal grains and their products. The structure of the grain is briefly overviewed and followed by the effect of processing on the structure of different food products. Based on the microstructure of the final product, three groups are distinguished: rolled cereals and porridge, protein network‐based products and starch network‐based products. This different organization is important for food production and technological aspects. The impact on the health‐related aspects of the product is currently investigated.

1.2 Grain structure

Cereals are the most important crops in the world and are destined to become both human food and animal feed. Cereals, which belong to the grass family (Gramineae), produce dry, one‐seeded fruits. These fruits are, botanically speaking, caryopses, but they are commonly referred as “grains” or “kernels.” The cereal grains such as wheat, rice, maize, barley, oats, rye, sorghum and millet provide 50% of the food energy and 50% of the protein consumed on earth. Wheat, rice and corn constitute around 75% of world’s grain production (Ramaswamy and Riahi 2003). In this chapter, wheat is used as reference to explain the structure of cereal grain. Its kernels contain three main parts: embryo, endosperm and their covering layers. The last are, in milling, often separated as the bran fraction (Figure 1.1A). If all the parts of the kernel are retained in processing, one can speak of whole grain. If either the bran or germ is separated from the kernel during milling, then it is a “refined grain.”

Figure 1.1 A: General structure of a cereal grain); B: Epifluorescence micrograph of parts of rye grain. The sections were stained with Acid Fuchsin and Calcofluor: protein appears red, cell walls rich in β‐glucan appear light blue and lignified cell walls of the pericarp appear yellowish‐orange. Structure of cereal foods

(Source: Hemery et al. 2007).

1.3 Embryo

The embryonic axis (rudimentary root and shoot of the next generation) and the scutellum (storage organ) together constitute the embryo, which makes up 2.5% to 3.5% of the weight of the entire kernel in wheat. It is often referred to as germ, although, strictly speaking, the germ is the embryo‐rich fraction of the kernel produced during milling. Wheat germ contains protein (25%), sugar (18%), oil (16% of the embryonic axis and 32% of the scutellum), and it is also rich in vitamins B and E (Delcour and Hoseney 2010a). In the case of rye, the embryo constitutes about 3.8% of the weight of the grain and contains 37.2% of protein, 13.4% of lipids and 43.6% of carbohydrates (Lasztity 1999; Ellis 2007).

1.4 Endosperm

The endosperm is the largest tissue of the grain. It is the primary starch and protein storage site and the source for white flour. It contains protein, carbohydrates, iron and B‐vitamins, such as riboflavin, niacin and thiamine. However, it is nutritionally inferior to the whole grain. The endosperm comprises two different parts: the starchy endosperm and the aleurone layer. The aleurone is botanically part of the endosperm. However, in practice, it is most often part of the bran since it is removed together with the pericarp and testa during the milling process. The main part of the grain constitutes the starchy endosperm, which consists of cells packed with nutrients, mainly starch, to support the growth of the embryonic axis after germination. It is also rich in protein. In all cereals, there is an inverse gradient involving these two components. The protein content increases towards the periphery, while starch is more predominant towards the center of the kernel. Cell size also decreases towards the outside and this is accompanied by increasing cell wall thickness. The endosperm cell walls of wheat are mainly composed of arabinoxylans, while in barley and oats (1‐3)‐ and (1‐4)‐β‐D glucans predominate. The contribution of cellulose to the cereal endosperm cell wall is low except in the case of rice.

1.5 Bran

The bran consists of the hard outer layers of the kernel and, depending on the milling process, constitutes around 14% of the grain. Generally, wheat bran comprises approximately 12% water, 13–18% protein, 3.5% fat and 56% carbohydrates. Wheat bran can be chemically differentiated by the occurrence of complex structures of either C6‐sugars like cellulose or C5‐sugars like xylans. Phenolic compounds and their polymer lignin are found in different concentrations within the bran. It also contains a large quantity of B‐vitamins as well as insoluble dietary fibre (Prückler et al. 2014). From the histological point of view, wheat bran is composed of the pericarp, testa and aleurone layer.

1.5.1 Pericarp

The pericarp consists of several complete and incomplete layers of dry, largely empty cells. During development, it serves to protect and support the growing endosperm and embryo. The outer layers of wheat bran, pericarp and testa are formed by thick cell walls containing cellulose, lignin and complex xylans with high arabinose to xylose ratios and substitution by ferulic acid dehydromers as cross‐linkers between polymer chains (Hemery et al. 2007).

1.5.2 Testa

The testa is a hydrophobic, semipermeable layer under the pericarp, which contains a cuticle rich in lipidic compounds. The testa is the outermost tissue of the seed and may consist of one or two cellular layers. Almost all of the alkylresorcinols in the grain are localized in the testa of wheat, rye, triticale and, at much lower levels, in barley (Ross et al. 2003b; Landberg et al. 2008). Alkylresorcinols are antioxidant compounds whose main function is to protect the membrane against lipid peroxidation. They are commonly used as biomarkers for whole grain intake since they are absorbed and at least partially metabolized in the human intestine (Ross et al. 2003a; Linko et al. 2005).

1.5.3 Aleurone layer

The aleurone layer surrounds the starchy endosperm and part of the embryo, and makes up 5–8% of the kernel. It is usually constituted by a single cell layer except in the case of barley, which contains two to three layers. Aleurone cells do not contain starch but they have high protein content and they are rich in lipids. They release active enzymes that help the cereal grain grow into a plant. The main component of wheat and rye aleur...

Table of contents

• Cover
• Table of Contents
• Title Page
• Copyright Page
• Preface
• Editors’ Biographies
• Acknowledgments
• Contributing Authors
• Supplementary Material
• 1 The Structure of Cereal Grains and Their Products
• 2 Definition of Whole Grain and Determination of Content in Cereal Products
• 3 Whole grain Fractions and Their Utilization in Foods
• 4 Whole grain Carbohydrates
• 5 Whole grain Content of Cereal Products
• 6 Whole grain consumption and associated lifestyle and sociodemographic factors
• 7 Alkylresorcinols and Their Metabolites as Biomarkers for Whole grain Wheat and Rye
• 8 Body Composition and Weight Management
• 9 Whole Grains and Type 2 Diabetes
• 10 Whole Grains and Cardiovascular Disease
• 11 Whole Grains and Cancer Risk
• 12 Whole Grain Intake and Mortality
• 13 Whole Grains and Appetite
• 14 Modulating Glycaemia with Cereal Products
• 15 Whole Grains, Cereal Fibre and the Gut Function
• 16 Bioactive Compounds in Whole Grains and Their Implications for Health
• 17 Potential Negative Effects of Whole grain Consumption
• 18 Application of Metabolomics for the Assessment of Process‐induced Changes in Whole Grain Foods
• 19 Application of Metabolomics for the Assessment of Health Effects of Whole grain Foods
• 20 Using Transcriptomics and RNA Sequencing to Assess Health Effects of Whole Grains
• 21 Whole Grains from an Industry Perspective
• 22 Global Regulation and Labeling, Claims and Communication with Consumers
• Summary
• Index
• End User License Agreement