Lecture 5 Starch-4 - Chapter 9: Starch Chapter &...

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Unformatted text preview: Chapter 9: Starch Chapter & Chapter 10: Fiber and Plant Foods Foods HN 300 Starch Structure Starch Amylose > 200 glucose units linked by 1,4-α-glucosidic 200 1,4- -glucosidic linkages linkages Most common starches range from 17%-30% Most 17% 30% amylose amylose Corn starch: 24-28%, wheat starch: 25-26%, Corn potato starch: 20-23%, tapoica (cassava): 17% potato Starch Structure Starch Amylopectin Glucose units linked by 1,4-α-glucosidic AND Glucose 1,4- 1,6-α-glucosidic linkages 1,6Typically, amylopectin if far more abundant Typically, (75-80%) in starches (75-80%) By genetic variation – starches containing By almost all amylopectin (e.g., waxy maize; 95%) Starch Granule Starch Starch is deposited in an orderly fashion in the form of granules Concentric layers of amylose and amylopectin are formed in leucoplasts (plastids in cytoplasm of plant cells) and held together by H-bonds Properties of Starch Properties 1. 2. 3. 4. Gelatinization Gelation Retrogradation Dextrinization Gelatization Gelatization Starch is used to thicken various food Starch products products When starch is heated in water → H-bonds When heated in starch granules break → disrupts the tight organization of the starch during heating organization Water moves into starch granule (swelling) Water and some amylose molecules move into the cooking water → thickening Gelatinization Gelatinization Raw Cornstarch Cornstarch at a 5% dispersion level in 95% water (no heating) Heated to 40°C, water begins to be ADSORBED onto the surface of the granule, the H-bonding b/w the starch polymers within the granule might begin to be loosened slightly. At 50°C, more water would be ADSORBED onto the surface of the granule, the H-bonding between the starch polymers within the granule would begin to loosen. Additionally, some of the amylose may begin to work itself free of the granule surface Gelatinization cont’d Gelatinization Heated to 60-65°C; will allow even more of the water to become ABSORBED and more amylose to work itself out into the dispersion outside of the granule. Between 60-95°C gelatinization occurs. At this point, the starch granule is swollen as much as possible. When heated 95°C or > for several min.; this may allow the granules to "implode" (compress inward) and loose their contents as there is not enough structure and H-bonding to hold the polymers together → decreased viscosity Gelatization Gelatization Temperature dependent starch gradually thickens as temperature rises Refer to Fig. 9.5, 9.6 (pg 185) for comparison of Refer viscosity of different starches during heating viscosity Starch dependent (table 9.2, pg 186) (table (most effective thickening agent) Potato > waxy corn > tapioca > corn > rice > wheat flour (least effective) effective) Effect of Ingredients on Gelatinization Effect Sugar competes with starch for water → decrease viscosity and gel strength; (monosaccharides have less effect than disaccharides) less Acid (e.g., lemon juice; ph < 4) causes hydrolytic rxn that breaks down starch molecules → thinner gelatinazation gelatinazation Fats & Protein (e.g., milk) coat starch granules, delay uptake of water coat lower the temp. required for maximum gelatinization and lower viscosity Gelation Gelation Formation of a gel Occurs upon cooling of starch pastes Amylose molecules that have left the starch Amylose granules during gelatinization are free to move about in the paste about Formation of H-bonds between amylose Formation molecules → gel formation gel Amylose content of selected starches Amylose TYPE of Starch % Amylose Root/tuber Potato 20 Sweet Potato 18 Arrowroot 21 Cassava (tapioca) 17 Cereal Corn 28 W axy C orn <1 High Amylose Corn 70 W heat 26 Rice (long grain) 22 W axy rice 2 Note: low amylose starches DO NOT form gels Gelation Gelation Important factors: 1. Type & concentration of starch Low amylose starches (i.e., waxy corn) DO NOT form Low DO gels gels 2. Extent of heating For optimal gel strength: Starch pastes need to be heated until enough amylose is released, Starch but not so much that granules start to split apart into fragments but With vigorous stirring or prolonged heating , considerable With fragmentation occurs → pasty texture and weakened gel 3. Agitation For maximum gel strength, starch mixtures should be For allowed to cool without disturbance allowed Agitation disrupts H-bonds between amylose molecules → Agitation weak gel weak Gelation Gelation 4. Effects of other ingredients: Sugar Acids (lemon juice or vinegar) Hydrolyzes starch molecules → shorter amylose chains → Hydrolyzes tender/soft gel tender/soft Fats and proteins Makes more tender and soft gel Competes w/ starch for water Tender and soft gels 5. Syneresis the separation of liquid from a gel (e.g., yogurt) As a gel ages, there is some drawing together of amylose As molecules molecules Some water (trapped within the gel) is squeezed out Some Retrogradation Retrogradation Gradual ↑ in crystalline aggregates in starch gels Gradual during storage during Is the breaking of H-bonds and reformation of other Is H-bonds as amylose molecules shift around in the gel H-bonds Amylopectin participates in retrogradation, but at Amylopectin slower rate slower Gritty texture on the tongue e.g., Staling of bread, develops slightly harsh texture e.g., after several days of storage → heat bread (breaks Hafter bonds and allows amylose to move in the gel again) Dextrinization Dextrinization Processing of heating starch without water Processing without Degradation of starch to dextrins by uptake of Degradation water (naturally present in the flour) Splits the starch molecule at one or more Splits linkages between glucose units linkages Occurs at very high temperatures e.g., when browning meat dredged in flour Examining Starches Examining Basic structure of grains: 1. Bran covering Bran Contains fiber, some Contains oil, most niacin (B3) oil, and pyridoxine (B6) and 2. Germ/embryo High in lipid, High thiamine (B1), thiamine ), protein, iron protein, 3. Endosperm *Starch 70-75% protein Unmodified vs. Modified Starches Unmodified Unmodified “native” or pure state native” Grain (e.g., wheat), root (e.g., arrowroot), tuber (e.g., Grain potato) starches potato) Waxy Starch Waxy contains mostly amylopectin Gets thick but won’t gel (e.g., pie fillings) Modified starch that has been altered from its native state by starch physical or chemical means physical Result of genetic research and breeding Modified Starches Modified 1. Pregelatinized Starches (pre-cooked) Cooked w/ water to gelatinize them and then dehydrated after Cooked they become swollen they Starch swells to desirable thickness when water is added; no Starch heating is necessary heating e.g., instant pudding Cold water-swelling (CWS) - pregelatinized starches for microwave use microwave 2. Thin-Boiling Starches Treatment of starch with hydrochloric acid or nitric acid Treatment hydrochloric nitric Cleavage of 1,6-α-glucosidic linkages ↑ solubility of starch and ↓ thickening power solubility Forms thin sol when hot and strong gel when cold e.g., gum drops 3. Oxidized Starches Treatment with sodium hypochlorite (alkaline) Treatment sodium Limited use in processed foods; forms soft gels Modified Starches cont’d Modified 4. Cross-linked Starches Starch produced under alkaline conditions, usually with Starch acetic anhydride or succinate anhydride acetic succinate Form gels that undergo very limited retrogradation during Form long storage long Used as thickeners and stabilizers in salad dressing and Used related products related 5. Starch Phosphates Starch derivative by reactionn with phosphates (e.g., Starch phosphates sodium tripolyphosphate) sodium Increases stability and improves the texture of starch pastes Increases (smooth texture) and gels with little or no syneresis CHAPTER 10 CHAPTER Fiber and Plant Foods F&V Structure F&V Tissue systems 1. Dermal (skin, rind) (skin, 2. Vascular (transports fluids, nutrients, wastes) fluids, 2 parts: Xylem (tubular cells, transports water) transports Phloem (transports nutrients) nutrients) 3. Ground (bulk of edible portion of the plant) portion Contains parenchyma Contains parenchyma cells (predominant cell type cells in fleshy part in Fruits and vegetables) vegetables) Parenchyma Cells Parenchyma 1. Middle lamella Material b/w adjacent Material parenchyma cells mostly composed of pectic mostly substances substances 2. Primary cell wall Composed of complex CHO Composed (cellulose, hemicellulose, pectic substances, and noncellulosic polysaccharides polysaccharides 3. Plasmalemma Thin membrane between cell Thin wall and interior of the cell wall 4. Protoplasm (contains subcellular structures – plastids, mitochondria, and nuclues) mitochondria, Parenchyma cells (cont’d) Parenchyma 5. 3 types of Plasmids Chloroplasts – contain Chloroplasts Chlorophyll Chlorophyll Chromoplasts - Carotenoids Carotenoids Leucoplasts – Starch Starch Granules Granules 6. Tonoplast Membrane separating the Membrane protoplasm from interior of cell cell 7. Vacoule 7. Vacoule contains: flavor components, contains: sugars, acids, organic compounds, flavonoid pigments (e.g., anthoxanthins, anthocyanins), 90% of water, nutrients including protein nutrients Special Tissue Types Special Collenchyma tissue Elongated cells found in fibrous strands of celery; Elongated chewy and resistant to much softening when cooked; contributes to overall structure cooked; Sclerenchyma cells Woodlike cells contribute to gritty texture of some Woodlike plant foods (e.g., pears); as result of scleroids, a scleroids type of sclerencyma cell type Have thick cell walls containing lignin, a woodlike Have compound (e.g., asparagus, green beans) compound Fiber Fiber Middle lamella and primary cell wall Soluble Can be digested to a limited extent to provide Can 1-3cal/g 1-3cal/g Sources: citrus fruits, oats, legumes *β-glucan in oats helps reduce cholesterol levels Insoluble Cannot be digested; not a source of energy Provide stool bulk Speeds transit time, promoting excretion of waste from the Speeds body *Prevention of colon cancer Sources: wheat, rice, many vegetables Fibers Fibers Soluble Fibers Insoluble Gums - guar, locust bean (carob), gum arabic, gum tragacanth, gum ghatti, gum karaya, alginates, agar, carrageenan (red/brown algae, giant kelp), xanthan, gellan, cellulose gums cellulose Pectic substances Cellulose Hemicellulose Lignin Gums Gums Hydrocolloids composed of large polymers of Hydrocolloids monosacharides other than glucose monosacharides 2 characteristics: Ability to attract and bind water (used as food Ability additives because of the water-holding capacity of gums increases stool bulk and digestion) gums Very limited caloric contribution results in limited Very digestion and absorption in the large intestine (provide b/w 1-3 calories per gram) (provide Gums - Function Gums Thickening agents - used to replace fats/oils (e.g., salad Thickening dressings, ice creams and baked products) dressings, Increase fiber reduces caloric content of foods Enhance mouth feel when fats are reduced Extend shelf life Delay staling Sources of gums: seeds – guar and locust bean (carob) plant exudates (fluids) – gum arabic, tragacanth, karaya, and ghatti and seaweed extracts – red and brown algae (aka Irish moss and giant kelp) provide agar, carageenan, and algin gums and Microorganisms – Xanthomonas campestris produces xanthan gum xanthan Synthetic gums - CMC (sodium carboxymethylcellulose) GUMS (refer to Table 10.3 pg 225-6) (refer GUM GUM LOCUST BEAN (CAROB) APPLICATIONS GUAR GUM Desserts, baked products, ice cream Desserts, stabilizers, sauces, soups, salad dressings dressings GUM ARABIC Candies to retard crystallization, Candies flavor fixative, soft drinks, beer (foam stabilizer) (foam AGAR Culture medium, stabilizer in Culture puddings, pie fillings, cheese, icings, sherbets icings, CARRAGEENAN (IRISH CARRAGEENAN MOSS) MOSS) Pet food (meats w/ gravy), low Pet sugar jams/jellies, lowfat/nonfat dressings, chocolate milk, cheese analogs, bakery fillings and icings analogs, Stabilizes ice cream, bologna, Stabilizes cheese, sauce, processed meats cheese, CHO Structural Constituents CHO 1. 2. 3. 4. Cellulose Hemicellulose Pectic Substances Lignins CHO Structural Constituents CHO 1. Cellulose Contributes to structure of foods (primary cell wall Contributes or parenchyma cell) or Glucose polymer joined by 1,4-β-glucosidic -glucosidic linkages; unable to digest linkages; 2. Hemicelluloses Key component of cell wall Present in smaller quantities than cellulose Contain a variety of sugars in its long chains – Contain xylose, arabinose – and glucuronic acid xylose, Become mushy when heated in alkaline (e.g., Become baking soda) cooking water baking Structural Constituents Structural 3. Pectic Substances member of family of member polygalacturonic acid componds includes protopectin, includes pectin, pectinic acid, and pectic acid Location: Middle lamella b/w Middle cells Primary cell wall Primary where they combine w/ hemicelluloses w/ 1,4-α linkages Pectins Pectins 1. Protopectin Water-insoluble, methylated (-CH ), very long polymer of 3 ), galacturonic acid (GA) joined by 1,4-α linkages galacturonic Immature fruits, and to lesser extent vegetables Contributes to firm texture of unripe fruits 2. Pectins As fruit ripens, some demethylation occurs (randomly) When limited demetylation occurs = pectins When pectins Most, if not all, GA is esterified with methanol Valued for gel-forming properties in making jams and Valued jellies jellies Pectins cont’d Pectins 3. Pectinic acid {4. Pectinates} ¼ to ½ of GA are esterified with methanol Formed as fruits begin to ripen Compounds resulting from combination of pectinic acid or Compounds pectins with calcium or other ions to form salts pectins Usually enhance gel-forming capability 5. Pectic acid The smallest pectic substances NO methyl esters Occurs in overly ripe, very soft fruits and veg. Loses all gel-forming ability PECTINS PECTINS Protopectin Protopectin Pectin Pectin *Protopectinase Pectinic Pectinic Acid Acid Pectic Acid IMMATURE/UN-RIPE OVER-RIPE ALL METHYLATED NONE METHYLATED ENZYMES 1) *Protopectinase Catalyzes cleavage of protopectins to shorter Catalyzes chains of pectins chains 2) Pectinerases Demethylates (-CH3) protopectins and pectin Loss of gel forming ability Loses gel-forming ability Structural Constituents Structural 4. Lignin Lignin Located in primary cell wall A non-CHO polymer of aromatic structures linked together non-CHO forms an extremely large, complex molecule forms gives a woody quality to plant foods Tough and rigid texture (often removed during processing) Changes of Fruits & Vegetables Changes During Maturation During Cooking Post-Harvest changes & Post-Harvest Storage Storage Changes During Maturation Changes As fruits and vegetables mature: They gradually ↑ content of cellulose, They hemicelluloses, and lignin (↑ structural support of the cell wall) the Vegetables ↑ lignins, results in tough, woody Vegetables texture texture Pectic substances undergo cleavage resulting in Pectic shorter polymers and demethylation → softening of fruits of During Cooking During Softening of cellulose, breaking down of Softening hemicellulose and lignins hemicellulose Dissolving of pectins in solution Gelatinization of starches Acid increases resistance to softening Alkali (e.g., baking soda) speeds softening Calcium (hard water) increases cooking time Post harvest changes and Storage Post 1. Respiration Rate (RR) (↑ O2 consumption /CO2 prodn) (↑ Senescence (↑ in RR and loss of moisture in F & V after maturation) Refrigeration retards RR and extends shelf-life Most well stored b/w 4-7°C (except bananas, mushrooms, tomatoes) Atmosphere (ratio of O2:CO2): influences RR of fresh produce Carbon dioxide: Strawberries can tolerate as much as 45% Apples are injured with levels as low as 2% Climacteric Period - period of max RR just prior to full ripening of many fleshy fruit Climacteric fruits Fruit that continue to ripen after picked (peaches, pears, bananas) Non climacteric fruits Fruit that need to be harvested when ripe b/c RR does not accelerate Fruit after harvesting (citrus fruits, grapes) after Post harvest changes and Storage Post 2. Enzyme Changes Lipase, pectic enzymes, invertase, chlorophyllase, and Lipase, peroxidase peroxidase Hemicellulases and cellulase – release sugars in cell walls ↑ sweetness in ripening fruits sweetness 3. Ethylene gas (H2C=CH2) (H gas produced by plants accelerates ripening accelerates Note: Tomatoes, for example, are often picked green and hard so that they can survive harvesting and long-distance transport, and then ripened in rooms pumped full of ethylene gas, which artificially initiates the ripening process. process. 4. Degradation of Pectins 4. Demethylation and hydrolysis (protopectins) Climacteric Fruits Climacteric Nonclimacteric Fruits Apple Apricot Avocado Banana Peach Peach Pear Pear Plum Tomato Tropical fruits (papaya, Tropical mango, passion fruit) mango, Cherry Citrus fruits Fig Grapes Melons Pineapple Strawberry Pigments (vacoule) Pigments 1. 2. 3. Chlorophyll Carotenoids Flavonoids Anthocyanins Anthoxanthins (tannins) Betalains Chlorophyll Green pigment Chlorophyll a More abundant *Methyl group (CH ) 3 Blue-green color Chlorophyll b *Aldehyde group (CHO) Yellowish-green color The amt of chlorophyll a and b The varies depending on specific plant or even w/in the plant plant e.g., broccoli Blue-green florest (a) Yellow-green stalks (b) Chlorophyll diminishes w/ Chlorophyll ripening ripening W/ Cooking, intensification of W/ bright green color as air is * Chlorophyll Chlorophyll Pheophytin a and b formed when chlorophyll a and b are heated d/t elimination of central Mg and replacement by d/t Hydrogen, after 5-7 min. Hydrogen, Chlorophyll a → Pheophytin a (greenish gray) Chlorophyll Pheophytin Chlorophyll b → Pheophytin b (olive-green) Chlorophyll Pheophytin (olive-green) Added acids and acids released during cooking facilitate Added conversion to pheophytin conversion Methods to Retain chlorophyll: Boiling vegetables w/out a cover may eliminate acids Heating water to boil b/f adding vegetables Heating Add more water to dilute acids Add Addition of baking soda ↑ retention of chlorophyll but affects texture Addition of calcium (acetate or salt) prevents mushiness (by blocking Addition breakdown of hemicellulose) but not feasible in home preparation breakdown Blanching-quick boiling in water prior to freezing vegetables, causes Blanching-quick expulsion of air → very green Carotenoids Carotenoids Isoprene group Yellow, orange, red pigments Isoprene polymers β-carotene 2 groups: 1. Carotenes (only C, H) α-, β-, and ξ-carotene -, -, Lycopene (C40H56) Acyclic High in tomatoes and High tomato based products tomato Possible health benefits Possible (cancers, CHD, LDL) (cancers, 2. Xanthophylls (C, H, O) Lutein (C H O ) 40 56 2 Crytoxanthin (C H O) (C40 56 Zeaxanthin (C H O ) 40 56 2 Lycopene Xanthophylls Carotenoids Carotenoids Pigment Carotenes α-carotene β-carotene Lycopene Lycopene ξ-carotene Xanthophylls Lutein Lutein Zeaxanthin Zeaxanthin Cryptoxanthin Cryptoxanthin Color Yellow-orange Orange Red Pale yellow Yellow Orange Orange Flavonoids Flavonoids Anthocyanins highly pigmented, water-soluble pigments range in color from red to purple to blue Basic Flavonoid Struture Contained in the vacoule of plant cells Contained vacoule e.g., cherries, red apples, berries, blue/red grapes, e.g., pomegranates, red cabbage pomegranates, Oxygen in central ring has (+) charge charge 3 prominent anthocyanins: 1. Pelargonidin (red) 2. Cyanidin (reddish-blue) 3. Delphinidin (blue) Anthoxanthins (tannins) colorless or white and may change to yellow Oxygen in central ring is uncharged Oxygen uncharged e.g., Bananas, Onions, Cauliflower, Parsnips, Garlic, Potatoes, Ginger, Turnips, Jicama, Mushrooms Anthocyanins Anthocyanins RED REDDISH BLUE BLUE Note: Structures differ by # of hydroxyl (-OH) groups on the right side of formula Examples of Anthocyanins in food Examples Food Pigment Strawberry Pelargonidin Raspberry Cyanidin Cherry Cyanidin and peonidin Cranberries Cyanidin and peonidin Apple Cyanidin Orange Cyanidin and delphinidin Black currants Cyanidin and delphinidin Blueberry Cyanidin, delphinidin, malvidin, peonidin, and petunidin Grape Cyanidin and petunidin Peach Cyanidin Plum Cyanidin and peonidin Radish Pelargonidin Red Cabbage Cyanidin Anthocyanins Anthocyanins Sensitive to pH, Heat, Oxygen, Metallic ions pH Heat Intense boiling and prolonged shelf life results in gradual Intense change from pleasing red to dull reddish-brown (e.g., strawberry jam) strawberry Oxygen Oxidation of anthocyanins responsible for color change (red →dull reddish brown) (red In Acidic Medium: red As pH increases to weak acid/neutral: violet As eak In Alkaline medium: blue Anthocyanins Anthocyanins Metallic ions Metallic Contact w/ iron, aluminum, copper, tin → results in green/slate blue Contact results Special enamel linings in cans used for heat-processed foods Ascorbic acid + copper or iron (e.g., worn utensils/knives) accelerates Ascorbic oxidation and undesirable color change oxidation Effect of Enzymes: Anthocyanase Catalyzes rxns that result in loss of color of anthocyanins (strawberry jam: undesirable/ white wine: helpful) Peroxidase & Phenolases Naturally present in F&V Catalyze oxidative rxns → undesirable color changes Glycosidases Split the sugar from anthocyanins to form very unstable Split anthocyanins anthocyanins Betalains Betalains 2 groups of pigments that groups contribute anthocyanin-like color to beets, but differ chemically Betacyanins – reddishpurple color of beets Betaxanthins – yellowish pigment yellowish Used as natural food Used colorant in food industry colorant Anthoxanthins (taninns) Anthoxanthins Phenolic compounds, colorless to white to yellow (e.g., Phenolic cauliflower) cauliflower) Acidic medium (pH < 7) – white colored veg. Acidic Alkaline medium (pH > 7) – yellow color Subdivisions of anthoxanthins: Flavones Isoflavone – anthoxanthin in soybeans Flavonols (Kaempferol, Quercetin, Myricetin) Flavonones Flavanols Flavanols Catechins (color and flavor of tea) Leucoanthocyanins (aka proanthocyanidins) Pigments Pigments Natural Natural Color Color Anthocyanin Red to purple Red Colorless, Anthoxanthin Colorless, white white Acidic Acidic Medium Medium Alkaline Alkaline Medium Medium Blue, bluegreen White Creamy white, Creamy yellow yellow Natural color, Natural Brownish tint Brownish Carotenoids Orange, Orange, yellow, redyellow, orange, red Natural color Chlorophyll Green Brownish Bright Green Brownish green, yellowgreen, green Enzymatic Browning Enzymatic Polyphenolic compounds (e.g., tannins, lignins, Polyphenolic flavinoids) may undergo browning/blackening rxns when they are bruised, cut, or exposed to air for a pd of time of Enzyme – Polyphenoloxidase (PPO) To prevent browning/inactivate PPO: Cold storage, low temp ↓ PPO activity Cold PPO Lower pH by dipping in acid (lemon juice, citric acid, Lower ascorbic acid) ascorbic Sulfur (sulfur dioxide gas, sulfite, bisulfite) used in dried Sulfur fruit (e.g., apricots, apples) fruit Flavor of Fruits and Vegetables Flavor 1. Sugars 2. Organic acids Malic, citric, tartaric and oxalic acids, *isocitrate and *succinate Malic, (*vegetables) (*vegetables) 3. small amounts of salts 4. Flavonones Glucose (most abundant), galactose, fructose, ribose, arabinose, xylose, Glucose and other sugars and Hesperidin & naringin (orange and grapefruit peels) 5. Flavanols – astrigency or “puckering” (wines, ciders) “puckering” 6. Volatile compounds Esters, aldehydes, acids, alcohols, ketones, ethers Flavors Flavors Sulfur-containing compounds Propensylsulfenic acid Allium – genus including onions, chives, garlic, leeks chives, Sinigrin in Cruciferous veg. (Brussels sprouts, broccoli, cabbage, rutabagas, turnips, cauliflower, kale, mustard) Compound in onions causing eye Compound irritation and tears irritation Alliin Odorless precursor in garlic that Odorless ultimately is converted to diallyl disulfide (key flavor aromatic compd.) disulfide Allin Diallyl thiosulfinate allinase (unstable) Diallyl disulfide (key flavor aromatic compd.) ...
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This note was uploaded on 10/21/2011 for the course HUMAN NUTR 300 taught by Professor Staver during the Spring '11 term at Ill. Chicago.

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