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NHM 253 Exam 2 Study Guide

by: Regan Dougherty

NHM 253 Exam 2 Study Guide NHM 253

Regan Dougherty
GPA 4.0

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Vegetable, Fruit, and Grain Science
Food Science
Dr. Crowe
Study Guide
50 ?




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Popular in Nutrition and Food Sciences

This 13 page Study Guide was uploaded by Regan Dougherty on Friday March 11, 2016. The Study Guide belongs to NHM 253 at University of Alabama - Tuscaloosa taught by Dr. Crowe in Fall. Since its upload, it has received 144 views. For similar materials see Food Science in Nutrition and Food Sciences at University of Alabama - Tuscaloosa.

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Date Created: 03/11/16
Friday, March 4, 2016 NHM 253 Exam 2 Study Guide - Vegetables Classification of Edible Plants Fruits (contain seeds) Seeds Flowers Stems/Shoots Leaves Tuber (modified nutrient storage unit) Root (anchor) Bulb • Composition - Vegetables are primarily carbohydrates. • 3 forms of carbohydrates: - sugar - starch - fiber • cellulose hemicellulose • lignin • plant gums • pectic substances • • resistant starches - starches that act halfway like fiber (the body only breaks half of it down) 1 Friday, March 4, 2016 - Vegetables also contain non-nutritive substances (plant pigments/ phytochemicals), vitamins, minerals, and small amounts of protein (incomplete). • Complete proteins contain the 9 essential amino acids: phenylalanine, valine, tryptophan, threonine, methionine, histadine, isoleucine, leucine, lysine. - Essential amino acids cannot be produced by the body an must be obtained through diet. • Why are phytochemicals considered non-nutritive if they provide health benefits? - because they do not provide calories • Structure of Plant Cells - Plant cells have a double outer layer. • Fiber is found in the outer layer of plant cells. Turgor - pressure exerted on a cell by the water bound within • - Turgor is important for texture; it results in rigidity of the plant. - Vacuoles - storage vessels in plant cells. • Organic acids contained in the vacuoles inhibit bacterial growth (act as preservatives). - These organic acids can influence the color of plants. • When a plant is intact, organic acids will not impact color. The organic acids impact color when vacuoles are opened up. • Color can be an indicator of nutritive value. - Plant cell walls consist of fibrous strands of cellulose intertwined with other less rigid forms of fiber, like pectin or hemicellulose. • Ripening and Aging - A plant is still exchanging gases with its environment (respiring) even after it is picked. (plants still ripen after they are picked) - Upon aging, the cell wall structure loses water (turgor) and begins to collapse. • Why do some edible plants turn brown with aging? 2 Friday, March 4, 2016 - Enzymatic browning (see enzymatic browning section under Fruits) - Release of organic acids Plant Pigments Fat soluble or Colors Associated insoluble? Fruits/Vegetables Carotenoids - •carotenes soluble • orange • carrots most stable •lycopene This results in • yellow • pumpkin •lutein great heat stability • red • colored bell •xanthophyll because the peppers •zeaxanthin pigments do not leach out during moist heat preparation. Chlorophyll •chlorophyll a soluble • variations of • broccoli •chlorophyll b green • leafy greens Flavonoids - least •anthocyanins insoluble • anthocyanins - • red cabbage stable •anthoxanthins (soluble in water) red/purple • beets betalains anthoxanthins - • • cream/white • betalains - red/ yellow/purple Stability of Plant Pigments Heat pH - Acidic pH - Basic Oxygen Carotenoids stable; prolonged can cause pigment heat destroys stable stable oxidation vitamins Chlorophyll stable with minimal not easily acted up heat; unstable with unstable stable by oxygen prolonged heating Flavonoids unstable stable unstable can cause pigment oxidation and loss of antioxidant properties • Additional Notes on Pigments - Some carotenoids can be converted to vitamin A and are considered to have pro- vitamin A activity. - Degradation of chlorophyll upon aging reveals secondary pigments. - Why do greens become duller in color with prolonged cooking? 3 Friday, March 4, 2016 • When the chlorophyll molecule bursts during cooking, the magnesium in the center of the molecule is removed and replaced with hydrogen. The pigment changes from chlorophyll to pheophytin. Green vegetables should be cooked uncovered because the vacuoles lyse due • to heat and organic acid is released. If the vegetables are covered, the organic acid may be evaporating and then dripping back onto the vegetable. Remember, chlorophyll is not stable in acidic conditions. Impact of Heat During Cooking Texture Cooking decreases moisture content, modifying turgor. Flavor Cooking causes organic acids to be released, altering flavor. Odor Cooking causes structure to be broken down and sulfur to be released. Color Cooking causes organic acids to be released, causing different acids to mix and change the overall color. Nutrient Retention Nutritive value decreases with cooking. *Exception: Lycopene increases in nutritive value when heated because cooking causes the molecule to take the cis configuration which allows the molecule to be better absorbed. The highest concentration of nutrients is located immediately beneath the skin of • fruits or vegetables. This is why is is important not to remove the skin! • Cooking and Nutrient Retention - Roasting - works best for vegetables with thick skin - Boiling - high nutrient loss • Simmering does not cause as much nutrient loss because it occurs at a lower temperature. - Steaming - minimal nutrient loss - Microwaving - minimal nutrient loss • Vegetable Storage - Two primary factors influencing shelf-life: • continued respiration • loss of moisture 4 Friday, March 4, 2016 - Ways to prolong shelf-life • refrigeration (slow respiration and enzyme activity) • store in a humid environment (ex. crisper drawer in refrigerator) - Why should vegetables be blanched before freezing? • Blanching destroys enzymes. • Legumes - Plant part - seeds contained within pods - Beans, peas, and lentils are an excellent source of complex carbohydrates, protein, and fiber. - 2 commonly consumed legumes that are added as a protein-rich ingredient in commercial foods: • soy and peanuts - These are 2 of the 8 common allergens. • Vegetable-Based Meat Alternatives - TVP (textured vegetable protein) - dehydrated plant protein material commonly used as meat alternative • The USDA limits TVP to 30% of a product if it still wants to go by a certain name (ex. chicken nuggets). • May decrease cost of products. - Tofu- curd made from soy milk • Organic produce - produce that is produced without added chemicals - Fruit - the ripened ovary of a flowering plant that contains the seeds • Composition - Fruits are mostly composed of carbohydrates. - Fruits also contain small amounts of protein, fat, non-nutritive substances, vitamins, and minerals. • How are fruits different from vegetables? 5 Friday, March 4, 2016 - seeds - 10-15% of their weight is sugar (only about 3-5% of vegetables’ weight is sugar) - Organic acids are much more abundant in fruit. - Pectic substances are much more abundant in fruit. • Pectic substances - polysaccharides between cell wall and membrane which imparts strength and firmness to plants Organic Acids • - Acidity varies with the age of the plant. - Acidity decreases with age and, as acidity decreases, sugar content increases. - Organic acids act as protection/preservatives (slow/inhibit microbial growth). - Volatileor Non-volatile • We smell volatile substances. • We taste non-volatile substances. Common Organic Acids citric acid (citrus fruits) malic acid (apples) tartaric acid (grapes) *more common in vegetables benzoic acid (cranberries) • Pectic Substances - Pectin contributes to the gelling properties of fruits. These gelling properties are due to the water-holding capability of methyl pectate within the pectin molecule. - Uses of Pectin: • thickener • commonly found in non-fat products • found in ice cream to prevent crystallization 6 Friday, March 4, 2016 - 3 Stages of Pectic Substances: • Protopectin - found in immature fruits; no gel • Pectin - found in ripe fruit; gel (contains methyl pectate) • Pectic acid - found in overripe fruit; no gel • Enzymes that are responsible for ripening fruit aid in the breakdown of protopectin to pectin. - Ethylene - fruit-ripening hormone • Phenolic compounds - compounds assisting in repair of plant cells; their structure allows them to work like an antioxidant - Not all plants have the same amount of phenolic compounds. - When fruits undergo enzymatic browning, they lose the nutritive value of the phenolic compounds. • Enzymatic browning - phenolic compounds react with polyphenol oxidase (PPO) in the presence of oxygen to produce brown pigments - phenolic compounds + enzymes (PPO) + oxygen = enzymatic browning - Phenolic compounds in fruit are usually separated from oxygen and enzymes by vacuoles (and the cell wall keeps out oxygen), but when the fruit is cut, its structure is compromised and the phenolic compounds are exposed to enzymes and oxygen. Methods for Preventing Enzymatic Browning Target Enzymes • Temperature: Heat denatures enzymes and cold temperatures slow the rate of enzymes. • Low pH Oxygen • Coating food with sugars/syrup prevents oxygen from coming into contact with phenolic compounds and/or enzymes. • Addition of food antioxidants or sulfur compounds causes these substances to react with oxygen, causing the oxygen to be unavailable for the browning process. Sulfates, sorbates, and benzoates can also be added to prevent enzymatic browning. Many people have sensitivities to these. 7 Friday, March 4, 2016 - Primary metabolites - essential for growth - Secondary metabolites - compounds that are not required for the plant to survive (but may provide some benefit) - Changes in Fruit During Ripening • 1. decrease in acid content (loss of sourness) - results from the break down of organic acids • 2. conversion of starch to glucose, causing increases in sugar content - Starch (which is used for storage in plants) is no longer needed because the plant is near the end of its life. • 3. formation of volatile compounds like ethylene (ripening hormone) • 4. destruction of chlorophyll, unmasking secondary pigments • 5. softening in texture as pectic substances break down - Respiration - chemical process where the plant converts sugars and oxygen and releases carbon dioxide • How do you stop a plant from respiring? - take away the oxygen - Fruit Ripening • Fruits differ in respiration rate and, in turn, their rate of ripening. • Climacteric fruits - continue to ripen after harvest Ethylene is the ripening hormone associated with fruit maturation. • - If oxygen is removed from the environment, the environment is considered a modified atmosphere. - Storage and Handling of Fruits • To hasten the ripening of climacteric fruits, place them in a bag with a bruised banana (or any ripening fruit) because the banana will be release ethylene. - *The bag makes sure that the ethylene remains concentrated and does not diffuse. 8 Friday, March 4, 2016 • Once fruits are fully ripe, storage time may be increased by loosely covering with a plastic bag and placing them in the refrigerator. - Exception: You should never put bananas in the refrigerator. The fibers in the skin will cause the banana to undergo enzymatic browning. - Changes in Composition During Heating • pH - Organic acids are released when fruit is heated. • Texture - protopectin is converted to —> pectin is converted to —> to pectinic acid - weakening of cellulose and hemicellulose - denaturation of cell membrane which alters fruit turgor - Osmosis - the movement of water through a selectively permeable membrane from areas of low solute concentration to high • Application of Osmosis - Addition of water - as water moves from an area of low solute concentration (sugar) to a higher one, water is drawn into fruit cells causing swelling or plumping of the fruit - Addition of sugar - What is the effect of sprinkling sugar in the outside of cut fruit? • Water leaches out of the fruit - Cereal Science Components of a Grain • protective outer coating Husk • We do not eat the husk. • Husks can be stripped from grains and processed into fiber supplements. Bran • protective coating of the endosperm • high in fiber, B vitamins, and minerals Endosperm • part of the grain where the starch is stored • serves as the basis of flours Germ • embryo of the plant • The germ is the part of the plant that sprouts. • high in fat, vitamin E, and B vitamins • Classification of Cereal Grains 9 Friday, March 4, 2016 - Whole Grains - contain the entire grain kernel (bran, endosperm, and germ) - Refined Grains - grains that have been milled to remove the bran and the germ • finer texture • increased shelf life - Why? • The germ (lipid portion) of the whole grain is the most easily oxidized. The process of refinement removes fiber, iron, and B vitamins, so refined • grains must be enriched. • Land Use for Cereal Production - 4 most abundantly grown grains (by amount of land used): wheat, rice, corn, barley • Use of Cereal Grains - Flour • Wheat flour is the most predominant choice of flour (because of its protein content and ability to provide structure to baked goods). - Pasta - Breakfast cereal (primarily made from wheat, corn, and oats) - Alcoholic beverages (made through fermentation of rice, barley, corn, or rye) • Grains are used as food for the microorganisms responsible for fermentation. - Animal feed • For every 15 lbs of animal feed, 1 lb of beef is produced; for every 6 lbs of feed, 1 lb of pork is produced. • Barley - Barley can be processed into malt. It is used primarily in the malt form for flavorings, color additives, and in the manufacture of beer or whiskey. • Additional uses: soups and cereals, livestock feed 10 Friday, March 4, 2016 Processing Barley to Malt Pearling removal of the hull, bran, germ, and/or part of the endosperm (the endosperm is the only component left) Sprouting gently drying barley to stop germination (the temperature should be below 110° to preserve the enzymes that are responsible for converting starches to sugars) Amylase enzymes (alpha and beta) break down Malt becomes food for fermenting organisms. starches to sugars such as maltose (glucose + glucose) and glucose. Functions of Carbohydrates in Foods • - sweetness - color (caramelization and Maillard browning) - moisture absorption - texture - thickening • Grains to be avoided by individuals who have a sensitivity to gluten: - barley - rye - wheat - oats • Oats do not naturally contain gluten-forming proteins. However, oats may be processed in a facility that processes barley, wheat, or rye. - Gluten-free flours do not have the same function as wheat (they result in a different texture). • Complex Carbohydrates - Digestible polysaccharides are not sweet and they are not soluble in water. Classification of Complex Starches Amylopectin bulky, branched structure • less able to interact with water due to bulky structure • 11 Friday, March 4, 2016 Amylose • linear molecule • interact with water easily due to linear structure • function: thicken and swell when heated with water • taste impact: dry, fluffy • Responses of Starch in Food Systems - Dextrinization - breakdown of amylose and amylopectin molecules that results in shorter and sweeter glucose chains • Starches become sweeter in the presence of heat. • ex. white bread vs. toasted white bread (sweeter) • dextrose - glucose derived from starch • DE = dextrose equivalents - Gelatinization - cooking of starch granules causing water absorption resulting in the swelling and softening of granules • water + heat + starch • uses: thickener in sauces or gravies; development of structure/texture in cakes or breads Factors Influencing Gelatinization Temperature the higher the temperature, the faster the rate of gelatinization Stirring increases the rate of gelatinization Acidity/Alkalinity of Cooking Medium decrease the rate of gelatinization Sugar decreases the rate of gelatinization (because sugar molecules will bind more readily to water) - Gel formation - upon cooling, some gelatinized starches will convert into a semi- solid paste or gel • dependent on the presence of amylose • Amylose molecules bind to each other (through hydrogen bonds), forming a gel. Water molecules that were bound between amylose molecules are released into the environment. - The higher the amylose concentration, the firmer the gel. • ex. yogurt 12 Friday, March 4, 2016 - Retrogradation - the seepage of water out of an aging gel as a result of amylose re-association (forming an orderly structure of amylose molecules); occurs with very cool temperatures under prolonged storage • opposite of gelatinization also known as syneresis • • negative attribute of food • component of staling (becoming stale) - sequence: gelatinization —> gel formation —> retrogradation - Some grains take longer to cook than others because: • size (how long does it take water to get to the center) • amount of processing (physical breakage that allows water to bind more readily) • presence of bran (whole grain products take longer to cook) • Pasta Basics - Pasta is made with durum wheat that is processed into semolina flour. • Durum wheat has a higher protein content that other wheat varieties. - Extrusion - process in which a gelatinized starch (pasta dough) is formed into a shape by forcing it through formed plates and then drying it - Whole wheat pasta - incorporates bran and/or germ into dough prior to extrusion • firmer texture, stronger taste 13


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