NUT1111 Lecture 3 Carbohydrates PDF

Edith Cowan University School of Medical and Health Sciences Chapter 1 Week 3 Grains and carbohydrates Edith Cowan University School of Medical and Health Sciences Learning Outcomes • Describe the parts of a grain and how it is turned into flour • Understand the storage of starch as a combinatio...

Edith Cowan University School of Medical and Health Sciences Chapter 1 Week 3 Grains and carbohydrates Edith Cowan University School of Medical and Health Sciences Learning Outcomes • Describe the parts of a grain and how it is turned into flour • Understand the storage of starch as a combination of amylose and amylopectin • Describe the process of gelatinisation and retrogradation • Describe syneresis and how it occurs • Outline the function of gluten in baking • Describe malliard and caramelisation reactions • Understand how amylose/amylopectin content impact GI Edith Cowan University School of Medical and Health Sciences Structure & composition – wheat grain https://www.glnc.org.au/grains-2/grains-andnutrition/whole-grains/ Edith Cowan University School of Medical and Health Sciences Refined vs Whole Grains https://wholegrainscouncil.org/whole-grains-101/health-studies-health-benefits/compare-nutrients-various-grains Edith Cowan University School of Medical and Health Sciences https://aegic.org.au/wp-content/uploads/2021/03/AEGIC-Grain-Note-wheat_LR.pdf Edith Cowan University School of Medical and Health Sciences Grain to flour – the ancient way Edith Cowan University School of Medical and Health Sciences How flour is made • https://www.youtube.com/watch?v=kFP-KBPwn3E Edith Cowan University School of Medical and Health Sciences Bread – A staple Edith Cowan University School of Medical and Health Sciences Food uses of cereal grains WHEAT - bread (leavened + unleavened) pasta, noodles, breakfast cereals, cakes, biscuits, porridge, extruded snack foods, bulgar RICE cooked grains, breakfast foods, extruded snack foods, sake CORN (maize)hominy, tortillas, cornbread, cooked grains, polenta, breakfast foods, popcorn, extruded snack foods, corn syrup, animal feed OATS porridge (rolled oats, oatmeal), muesli, oatcakes, animal feed RYE leavened bread, crispbread, spirits MILLETS/SORGHUM - cooked grains, porridge, unleavened breads, flatcakes, beer, animal feed BARLEY pearl barley, baby foods. Edith Cowan University School of Medical and Health Sciences Starch • Plants store carbon as starch • Most consist of 20-25% amylose and 75-80% amylopectin Edith Cowan University School of Medical and Health Sciences Starch - structure ▪ In the form of small granules [2 - 35 m] made up of: ▪ amylose (25%) linear (500-2000 glucose molecules ▪ amylopectin (75%) branched arrangement of many thousands of glucose molecules Edith Cowan University School of Medical and Health Sciences Starch - properties Insoluble in cold water, forms a paste Amylose becomes cloudy when heated with water forms a gel very quickly when cooled the more amylose present, the lower the GI Amylopectin remains translucent when heated with water does not, usually, form a gel when cooled. Expands with moist heat - becomes more digestible, dextrinises with dry heat Edith Cowan University School of Medical and Health Sciences Gelatinisation When starch is heated in surrounding water, the granule imbibes water (60o-71oC). As heating continues, starch granules take up more water and irreversibly swell. Some short chains of amylose come out into the liquid. The swollen granules take up more space and the mixture thickens. This process is called gelatinisation and is responsible for thickening food mixtures. * Cooking for 5 minutes develops flavour but over stirring can rupture the swollen starch granules resulting in a ‘thinning’ of the mixture. Edith Cowan University School of Medical and Health Sciences Gelatinisation - chemical reaction Edith Cowan University School of Medical and Health Sciences Retrogradation After standing, cooling and/or chilling, a gelatinised starch mixture will become a solid or rigid gel … and if in a container can be “unmoulded” and hold its shape. This is due to: • amylose - amylose rebonding (retrogradation) • amylopectin - amylopectin rebonding (recrystallisation) • lipid - amylose complexes being formed Edith Cowan University School of Medical and Health Sciences Syneresis After standing for a while, a cooled starch gel will “leak”. This separation of fluid from a gel is called syneresis • Occurs because of amylose re-bonding which forces the water out (“weeping”) • Accelerated by freezing … when thawed water is unable to re-bind in the fragile spongy mass. Edith Cowan University School of Medical and Health Sciences Protein - Gluten • Elastic properties makes it preferred choice for baking/breads • Proteins gliadin and glutenin become flexible when mixed with water → gluten • Proteins form cross-links and stretching and kneading increases the number formed • As the bread baked, the inflated gluten dries leaving a strong, flexible structure • Soft wheat (6-8% protein) forms weaker gluten • Hard wheat (10-14% protein) forms stronger, more elastic gluten Gluten cont. Edith Cowan University School of Medical and Health Sciences Gluten and gluten-free foods Terms used on food labels (p.657 ff) wheat, bran, breadcrumbs, couscous, pasta, farina, flour, tabouleh, wheat berries, bulgar, hydrolysed protein, biscuits, cake, bread, barley, oats, triticale, wheat, ‘corn starch’, kamut Edith Cowan University School of Medical and Health Sciences Dietary value of cereal and grain products • Cereals contain approximately: • 71% CHO • 11% protein (gluten is the main form of protein in most grains) • 2-3% dietary fibre • 2% minerals • 11% water + some important B vitamins • Cereals which are eaten as the whole grain (provided that they are softened by cooking) are more nutritious than the refined versions since the whole kernel contains the protein, fat, vitamins and mineral. • The carbohydrates in cereals are primarily starch, with small amounts of dextrins and other sugars. Edith Cowan University School of Medical and Health Sciences Dietary value of cereal & grain products (continued) • Cereals are excellent sources of dietary fibre - most of it is insoluble cellulose and hemicellulose. • Oat bran and barley have soluble dietary fibre, which dissolves in water, swells, and traps bile acids. • The fatty acid composition of the lipids in cereals is: 72-85% unsaturated, and, 11-26% saturated • The lipids are subject to rancidity ….Vit E acts as a natural antioxidant, but milling will allow the cereal to be stored for long periods. Edith Cowan University School of Medical and Health Sciences FSANZ definitions • Wholegrain food • Any food which uses every part of the grain including the outer layers, the bran and the germ • Definition applies even if these parts are separated during processing or milled into smaller pieces • Wholemeal food • Wholemeal means the product containing all the milled constituents of the grain in such proportion that it represents the typical ratio of those fractions occurring in the whole cereal. Edith Cowan University School of Medical and Health Sciences Food additives and grains • Thiamin is added to bread making flour (mandatory) (Tiong, 2014) • Wholegrain cereals are rich in thiamine, however milling removes scutellum and germ. • 0.64 mg/100g of bread flour • Iodised salt used in bread making from 2009 • Acetic Acid (Vinegar) is often added to bread to increase shelf life • Preservatives 282 (Propionates) also increase shelf life https://www.youtube.com/watch?v=kFP-KBPwn3E Edith Cowan University School of Medical and Health Sciences Sugars • Three monosaccharides (one molecule) • Glucose, Fructose, Galactose • Simple sugars are found as either monosaccharides OR disaccharides • Sucrose = glucose + fructose • Maltose = glucose + glucose • Lactose = glucose + galactose • Australian sugar relies on sugarcane farming Edith Cowan University School of Medical and Health Sciences Caramelisation • Applying heat to sugars results in a non-enzymatic browning called caramelisation • Caramelisation occurs at around 160°C for sucrose and glucose and at 110°C for fructose • Volatile chemicals are produced and the sugars break down and release water, resulting in the nutty flavour and brown colour Edith Cowan University School of Medical and Health Sciences Malliard Reaction • The browning that occurs when baking a loaf of bread or cake is due to a malliard reaction • Complex series of reactions producing colours, flavours and aromas of cooked food • Require - carbohydrates + protein + heat https://www.scienceofcooking.com/maillard_reaction.htm Edith Cowan University School of Medical and Health Sciences Malliard Reaction cont. https://www.researchgate.net/publication/272962881_Food_Processing_and_Maillard_Reactio n_Products_Effect_on_Human_Health_and_Nutrition Edith Cowan University School of Medical and Health Sciences Fibre • Challenging to define as not a single compound • Unrelated compounds which escape digestion but have differing physiological effects and health impacts • Traditional methods of quantifying fibre: soluble and insoluble • Solubility does not correlate with physiological outcomes • Previously thought only to be a bulking agent for the stool • Now known to impact cholesterol, gut microbiome composition, inflammation, glucose response, blood pressure and weight control [Genoni, 2018] Edith Cowan University School of Medical and Health Sciences Resistant Starch • The portion of starch which escapes digestion in the small intestine is termed ‘resistant’ • Component of fibre naturally present in starch-rich foods: cereal grains, legumes, root vegetables and bananas. • Food determination is difficult – dependent on cooking method, temperature, food matrix and individual variations in digestion • Fermentation by bacteria in the colon produce short chain fatty acids – mainly butyrate, which have significant health promoting qualities for the colon and systemic outcomes. [Genoni, 2018] Edith Cowan University School of Medical and Health Sciences Glycaemic Index (GI) • Humans are able to hydrolyse starch from 4mths age • Glycaemic Index (GI) is a measure of how quickly a food can be converted to glucose; it is NOT an indication of nutrient value • The presence of fat and protein and dietary fibre influence the GI of a meal • GI is measured from the amount of the food which provides 50 g glucose (used as standard, GI:100) Edith Cowan University School of Medical and Health Sciences Glycaemic Index Edith Cowan University School of Medical and Health Sciences Glycaemic Index (Whitney et al., 2014, p. 103) Edith Cowan University School of Medical and Health Sciences Glucose Homeostasis • • • • Blood glucose must be constantly maintained to nourish cells Low vs high blood glucose Hormonal control Normal BGLs - 3.9 and 5.5 mmol/L Edith Cowan University School of Medical and Health Sciences MC questions Coeliac disease is an expression of an allergic reaction to: a) Glucose b) Globulins c) Glycogen d) Gluten Retrogradation in a cooked starch/liquid mixture is due, in part, to: a) Amylose-amylose rebonding b) Amylose-amylopectin rebonding c) Protein-amylose complexes being formed d) Lipid-amylose complexes being formed Edith Cowan University School of Medical and Health Sciences Practice revision questions • Define and explain the terms: – retrogradation; and – gelatinisation; in relation to starch. • Illustrate the structure of a single grain and add notations to your diagram which detail the major nutrient composition. • Cereals and grains provide a wealth of nutrients to humans. Discuss the nutrient value of these staple foods in the diet • Cereals and grains are a source of what can be termed ‘non’-nutrient components in the human diet. Discuss the positive and negative contributions of these components. • Answer the critical thinking questions about GM and food. Edith Cowan University School of Medical and Health Sciences For discussion: • What do you think, the community perception of whole grains is? • Can you think of any recent media/social media about grains? • Was it positive or negative? • How, did you believe this information? Why or why not? • Practise using the library search engines and see if you can find any journal articles about grains and human health.