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Starches, Cellulose, Gums and Pectins.  Starches – most abundant complex carbohydrate in diet. ◦ Composed of glucose ◦ Main dietary source in U.S. is.

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Presentation on theme: "Starches, Cellulose, Gums and Pectins.  Starches – most abundant complex carbohydrate in diet. ◦ Composed of glucose ◦ Main dietary source in U.S. is."— Presentation transcript:

1 Starches, Cellulose, Gums and Pectins

2  Starches – most abundant complex carbohydrate in diet. ◦ Composed of glucose ◦ Main dietary source in U.S. is wheat flour ◦ Nature’s reserve carbohydrate supply

3  Cellulose - known as fiber in the diet ◦ Provides bulk in food – good for digestive functioning ◦ Cannot be a food source for humans like it is for cows or termites since humans lack the digestive enzymes needed to digest ◦ Forms rigid structure of plants – strings in celery and membranes surrounding kernels of corn are largely made up of cellulose.

4  Gums – available commercially for ◦ Thickeners ◦ Stabilizers ◦ Trapping color and flavor ◦ Example: gum arabic used in salad dressings and gummy candies

5  Pectins – occurs naturally in fruit; sugar acid that causes hydrogen bonding between negatively charged molecules resulting in thickened structure. ◦ Key component in jams and jellies ◦ Basic recipe for jams and jellies 1% pectin, 60-65% sugar, and 34-39%crushed fruit or fruit juice.

6  Provide structure – the starch’s ability to thicken when heated and gel when cooled enables foods containing starch to take and hold many shapes.

7  Bind – as a binding agent, complex carbohydrates tend to hold two other substances together ◦ Amylose or amylopectin molecules hold batters to vegetables and meats during deep-frying. If allowed to set 20 minutes before frying, binding is increased due to chemical reactions that take place.

8  Thicken – starch can thicken liquids. This function is possible because of ◦ Starch’s chemical structure ◦ The size of its molecules ◦ The way it reacts to heat

9  Term used by food scientists to describe thickening a liquid with starch.  As the temperature increases, so does the swelling of the granule structure.  The temperature at which maximum swelling occurs is the gelatinization point. This is the point at which starch will hold the most water and the greatest thickening power.

10  Applying heat to a starch-water mixture causes it to thicken (gelatinization).  As heat is added, starch opens up or stretches which allows water molecules to slip in the much larger starch molecules.  Heat increases the amount of water that can be trapped which will make the mixture become thicker.

11  Salt and sugar can interfere with thickening process by decreasing the strength and viscosity of the gel.

12  Each starch has different physical properties  Food scientists must determine which type of starch is best for a given food product.  Five properties are evaluated:  Retrogradation  Viscosity  Stability  Opacity vs. translucency  Texture

13  Starch and liquid combinations can be 4 types: ◦ Slurries – uncooked mixtures of water and starch ◦ Sols – thickened liquids – they are pourable. Examples: pancake, waffle and muffin batter. Cooked sols include white sauce and gravy.

14 ◦ Pastes – thickened mixtures of starch and liquid that have very little flow, but thin enough to be spread easily. Example: the start of making a gravy ◦ Gels – starch mixtures that are rigid. The stability is controlled by controlling the linear amylose starches and the branched amylopectins

15  Retrogradation – the firming of a gel during cooling and standing. ◦ Occurs because starch granules are trying to return to the structure they had before cooking. ◦ Desirable when it causes a gel to thicken during cooling. ◦ Undesirable if it continues to the point that cracks form in the gel. Ex. Gravy uncovered in refrigerator several days will develop these.

16  Retrogradation (continued) ◦ An important factor is serving temperature.  If serving a sauce immediately, then cook to desired thickness.  If served at room temperature, finish cooking while it is still thinner as it will thicken as it cools.

17  Viscosity – is the resistance of a mixture to flow. ◦ Food scientists run viscosity tests to measure how foods such as ketchup will flow.

18  Stability – is the ability of a thickened mixture to remain constant over time and temperature changes. ◦ Waxy maize starch – example of a stable starch when frozen or heated. It is a clear, soft paste that is as thick hot as cold. ◦ Cornstarch – has more thickening power than flour; smoother in texture; makes appetizing mushroom gravy. But it does not reheat well

19  Opacity vs. Translucency – refers to how much an object blocks light. ◦ Cornstarch, potato starch, and arrowroot produce gels that are more translucent. Good to use in fruit sauces, fruit pie fillings, and glazes that are translucent. ◦ Wheat flour is best used in chowders and white sauce.

20  Texture – in this context has mostly to do with mouth feel. ◦ Example: most people would not care for whole wheat flour being used to make a sauce or gravy because the texture would not be very smooth.

21  Starch can be added to liquid to make a thickened sauce three basic ways. In each method, starch granules are separated to prevent lumping.  Cold water paste  Starch and fat  Starch and sugar

22  Cold Water Paste – a method used to prevent lumps when thickening a sauce : ◦ Quickly stir an equal amount of cold water and starch. ◦ Continue stirring until a smooth paste is formed. ◦ Then more liquid such as broth can be added to make a gravy.

23  Starch and Fat – separate the starch granule with melted fat: ◦ An equal amount of starch is added to heated fat. ◦ Once starch is stirred into the fat, the liquid can be added SLOWLY, stirring constantly to keep the sauce smooth. ◦ This method is used in making white sauce and gravy from meat drippings.

24  Starch and Fat (continued) – Professional chefs often thicken soups and sauces using : ◦ Buerre manie – is a ball of equal amounts of solid fat and starch mixed together.  These balls can be added to hot soups to thicken the broth.  The balls can be prepared ahead of time and refrigerated for several days or frozen for several months.

25  Starch and Fat (continued) –Cajun cooks commonly use a roux to thicken sauces or gravy: ◦ Roux is a gravy that has had the starch heated in fat until it turns a rich red-brown.  Toasting the flour adds a distinctive flavor.  Needs low heat and constant stirring while browning the starch to prevent burning or uneven browning.

26  Starch and Sugar – to avoid lumps with this method: ◦ First thoroughly combine the starch and sugar. ◦ Then gradually add the liquid with constant stirring. ◦ Used most often in sweet sauces and puddings. ◦ Presence of sugar also reduces the viscosity of the liquid and the resulting gel will be tender and smooth rather than rigid.

27  Starches divided into two categories: digestible starches and indigestible fiber.  Starches like sugar provide 4 calories/gram  Most abundant and economical source of calories available to people.  Carbohydrates should provide over 50% of your daily caloric intake.  Carbohydrates in the form of glucose is the only energy source your brain can use.

28  Excess carbohydrates are stored as glycogen.  The liver stores about 33% of total glycogen.  The muscles store the other 66.99% glycogen.  Fiber provides bulk – contributes to feeling full, aids digestion and elimination.  Fiber sources include whole grains, fruits and vegetables.

29  Nutritional Functions of Starches – in addition to providing energy, carbohydrates: ◦ Provide bulk for digestive process ◦ Tie up bile acids, decreasing their re-absorption ◦ Lower cholesterol levels in the blood, retarding atherosclerosis ◦ Promote the utilization of fat


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