Carbohydrates

1. Carbohydrates

2. What are carbohydrates? • Carbohydrates include sugars, starches, cellulose and glycogen. • Carbohydrates are needed for storage and liberation of energy. • All carbohydrates contain the following elements: carbon, hydrogen, oxygen • Carbohydrates may be used a sweeteners, thickeners, stabilizers, gelling agents, and fat replacers

3. Carbohydrates can be divided into three groups • Monosaccharide-”single sugars” eg glucose. • Disaccharides –”double sugars” eg sucrose. • Polysaccharides-”multiple sugars” eg starch • Monosaccharide and disaccharides are sugars that are sweet and soluble. • Polysaccharides are polymers that are not sweet or soluble.

5. Carbohydrates Glucose Lactose Less water soluble, Less sweet • Water soluble • Sweet (Image: Wikipedia)

6. Glucose Reactive aldehyde group. A reducing group Linear form Ring forms (Image: Wikipedia)

7. Maltose Reactive aldehyde group Monosaccharides Disaccharide Glycosidic bond

8. Sucrose Fructose Glucose No free reactive aldehydes. A non-reducing sugar

9. Polysaccharides • Polysaccharides are formed from thousands of glucose molecules and are classified as polymers. • There are three polysaccharides that need to be studied: • Starch • Glycogen • Cellulose

10. Polysaccharides • Monosaccharides linked by glycosidic bonds • Simple chemistry, variable structure (Image: Wikipedia)

11. Polysaccharide sources • Higher plant sources: Starch, cellulose, pectin • Physically modified: starch, cellulose • Chemically modified: starch, cellulose • Seaweeds: alginate, carageenan • Seeds: guar, locust bean • Tree extrudates: Gum arabic • Microbial fermentations: xanthan gum

12. Starch granule • Amylopectin • A large molecule • Crystalline structure • Held together by hydrogen bonds • Amylose • A small molecule • Amorphous

13. Types of Starch Granules FYI: One pound of cornstarch has approx. 800 billion starch granules Rice – small granule Cornstarch Potato Larger starch granules gelatinize first

14. Gelatinization • Starch granules in water • Heat – overcome the hydrogen bonds • Swelling of starch granules • https://www.youtube.com/watch?v=L6vYxYE1jOg

15. Thickening Sol Suspension

16. Thickening ability • Thickening ability of various starches • What starch has the greatest thickening ability? • Which on has the least? • At what temperature does thickening occur?

17. Q: What causes lumping? • Dry starch • Exterior granules gelatinized first and clings together • Interior granules remains dry

18. Ways to avoid lumping • Separation of starch granules • Agitation - stirring • Mix with a fat - roux • Mix with a sugar

19. Gelation • Gelatinized starch mixture as cools can form a colloidal gel • Hydrogen bonding between amylose molecules

20. Gelled Dispersions Suspension Sol Gelled solid

21. Gel structure

22. Gels • May be clear and form at low concentrations • Often stretch a long way before breaking • Examples: gelatin, starch, carrageenan, pectin Image flickr user Furryscaly

23. Retrogradation and Syneresis • Retrogradation • The crystallization and matrix forming of starch molecules • Amylose retrogrades quickly • Starches with low levels of amylose do not form gels well • As gel ages there is a continued drawing together of the gel and water is extruded. • Syneresis • Separation of liquid from the gel

24. To Gel, or Not to Gel • Starches High in Amylose content are able to gel • Starches without amylose thicken, and do not gel

25. Waxy starch • Contains only amylopectin • Useful for making pies in which a thickened but ungelled consistency is desirable • Waxy starches are derived from some natural strains of barley, corn, rice and sorghum • Root starches are naturally low in amylose (cassava, arrowroot)

26. Modified Starches • Pregelatinized starch is gelatinized then dried (instant pudding) • CWS may be gelling or non-gelling (low-fat items for mouthfeel) • Cross-linked starches withstand low pH, high shear, or high temperatures (bbq sauce, pizza sauce) • Stabilized starches are used in frozen foods to prevent gelling and syneresis • Acid-modified starch forms a strong gel upon cooling and less viscous when hot.

27. Pectin • Pectinic acids are dispersible in water and can form gels • It is not easy to form pectin gels: it requires a delicate balance of pectin, water, sugar, and acid • Sugar competes for water, thus making less water available for the pectin molecules • Acid makes the pectin molecules less likely to repel each other

28. Gums (hydrocolloids) • Complex hydrophilic carbohydrates containing thousands of monosaccharide units • Do not form gels, but trap large amounts of water • Thickening agent (replacing starch) • Stabilizer of emulsions and maintain texture • Mouthfeel of low-fat foods

29. Gums (hydrocolloids) • Gums can be used synergistically to form gels • Guar and carrageenan • Locust bean and xanthan • Seaweed polysaccharides • Can form gels under certain conditions (iota carrageenan with calcium) • Can also be used with other gums • Agar forms a heat-reversible gel • Alginates are used to produce specialized food products (synthetic fruits)