Thursday Lecture – Hydrogels, Latexes, Resins

Reading: Textbook, Chapter 10

ASSIGNMENT

Find labels on food products that show each of the following types of ingredients. Tape or fasten them to a piece of paper, and highlight the ingredient from each category.

1. Vegetable oil

2. Exudate Gum

3. Extractive Gum

4. Starch

5. Pectin

Due: Tuesday 4/19

HydrogelsWater-modifying Substances alter behavior of water

Example = gravy, thickening by starch so water molecules can no longer move freely

Figures 10.1, 10.2, p. 245

HydrogelsWater-modifying Substances alter behavior of water

Example = gravy, thickening by starch so water molecules can no longer move freely

Classes of Plant-Derived Hydrogels:

1. Gums

Figures 10.1, 10.2, p. 245

HydrogelsWater-modifying Substances alter behavior of water

Example = gravy, thickening by starch so water molecules can no longer move freely

Classes of Plant-Derived Hydrogels:

1. Gums

2. Pectins

Figures 10.1, 10.2, p. 245

HydrogelsWater-modifying Substances alter behavior of water

Example = gravy, thickening by starch so water molecules can no longer move freely

Classes of Plant-Derived Hydrogels:

1. Gums

2. Pectins

3. Starches

All are polymers of sugars (= polysaccharides)

Figures 10.1, 10.2, p. 245

GumsPolysaccharides composed of sugars other than glucose:

Arabinose, galactose, mannose, xylose

Figure 10.2, p. 245

GumsPolysaccharides composed of sugars other than glucose:

Arabinose, galactose, mannose, xylose

- water-soluble, or can absorb water

Figure 10.2, p. 245

GumsPolysaccharides composed of sugars other than glucose:

Arabinose, galactose, mannose, xylose

- water-soluble, or can absorb water

- gum + water gel

Figure 10.2, p. 245

GumsPolysaccharides composed of sugars other than glucose:

Arabinose, galactose, mannose, xylose

- water-soluble, or can absorb water

- gum + water gel

- only partially digested by people, mostly no adverse effects

Figure 10.2, p. 245

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

- prevent formation of ice crystals

- increase shelf life of products

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

- prevent formation of ice crystals

- increase shelf life of products

In medicines:

- used as a binder

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

- prevent formation of ice crystals

- increase shelf life of products

In medicines:

- used as a binder

- laxatives

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

- prevent formation of ice crystals

- increase shelf life of products

In medicines:

- used as a binder

- laxatives

Industrial:

- sizing material – fills in pores in paper, textiles

Uses of GumsAs foods:

- “texturize” foods

- emulsifiers – disperse fat and protein molecules evenly in water

- prevent formation of ice crystals

- increase shelf life of products

In medicines:

- used as a binder

- laxatives

Industrial:

- sizing material – fills in pores in paper, textiles

- lubricants (especially in oil drilling operations)

Sources of Plant Gums - Exudates

Exudate Gums: plant is injured to initiate gum production

- gum arabic, Acacia senegal * gum tragacanth, Astragalus

Figs. 10.4, 10.5, 10.6, 10.7, p. 247-248

Sources of Plant Gums - ExtractivesExtractive gums – from endosperm or wood of Fabaceae speciesLocust bean gum – Ceratonia siliqua, Carob; St. John’s Bread *

Guar gum - Cyamopsis * Figure 10.8, p. 249

Xanthan Gum – Made by Bacterium, Xanthomonas campestris

Fermentation Product – uses various starting materials, both plant and animal origin

Polysaccharide – somewhat complex structure, useful physical properties

Note – can be derived from wheat, so it can contain gluten

Should be avoided by those who are allergic to glutens

PectinsPectins – polysaccharide composed of units of pectic acid and its

derivatives

Different types of pectins – vary in # molecules + methylation

Pectin-rich mesocarp

Figure 10.10, p. 251

PectinsPectins – polysaccharide composed of units of pectic acid and its

derivatives

Different types of pectins – vary in # molecules + methylation

Pectins – found in middle lamella of cell wall, epidermis

Pectin-rich mesocarp

Figure 10.10, p. 251

PectinsPectins – polysaccharide composed of units of pectic acid and its

derivatives

Different types of pectins – vary in # molecules + methylation

Pectins – found in middle lamella of cell wall, epidermis

Use of pectins – mostly in jellies and jams

Pectin-rich mesocarp

Figure 10.10, p. 251

PectinsPectins – polysaccharide composed of units of pectic acid and its

derivatives

Different types of pectins – vary in # molecules + methylation

Pectins – found in middle lamella of cell wall, epidermis

Use of pectins – mostly in jellies and jams

Sources of pectins:

Apple pomace (residue after pressing for juice)

Citrus peels

Pectin-rich mesocarp

Figure 10.10, p. 251

Starches

Polymers of glucose

Starch: alpha bonds between glucose molecules

Cellulose: beta bonds between molecules of glucose

Figure 10.11, p. 252

Starches

Polymers of glucose

Starch: alpha bonds between glucose molecules

Cellulose: beta bonds between molecules of glucose

Uses: food products, sizing

Figure 10.11, p. 252

LatexLatex = mixture of organic compounds produced in laticifers

Laticifer = cells or groups of cells that form tubes, canals, or networks

Latex may be inelastic or elastic

Rubber – elastic latex composed of polymers

Figs. 10.14, 10.15, p. 254

Rubber – Hevea brasiliensis

Euphorbiaceae – known for milky latex (“milky sap”) – in laticifers

Figs. 10.17, 10.18, 10.19, p. 255-256

Guayule – Parthenium argentatum *Asteraceae – southwestern U.S./Mexico developed as alternative source of natural rubber Figure 10.20, p. 257

Chicle – Manilkara zapota

New World - Sapotaceae Figure 10.23, p. 259; Box 10.2, p. 258

Plant ResinsResins – compounds that are synthesized and secreted into specialized canals or ducts within the plant, in xylem, phloem, or bark

Chemically: resins are polymerized terpenes, usually + volatile oils

Uses of resins:

- incense (frankincense and myrrh)

Figure 10.24, p. 259

Plant ResinsResins – compounds that are synthesized and secreted into specialized canals or ducts within the plant, in xylem, phloem, or bark

Chemically: resins are polymerized terpenes, usually + volatile oils

Uses of resins:

- incense (frankincense and myrrh)

- embalming

Figure 10.25, p. 260

Plant ResinsResins – compounds that are synthesized and secreted into specialized canals or ducts within the plant, in xylem, phloem, or bark

Chemically: resins are polymerized terpenes, usually + volatile oils

Uses of resins:

- incense (frankincense and myrrh)

- embalming

- mastic *

- lacquer

- artist’s paints

- naval stores (pines)

Figure 10.26, p. 261

Plant ResinsResins – compounds that are synthesized and secreted into specialized canals or ducts within the plant, in xylem, phloem, or bark

Chemically: resins are polymerized terpenes, usually + volatile oils

Uses of resins:

- incense (frankincense and myrrh)

- embalming

- mastic *

- lacquer

- artist’s paints

- naval stores (pines)

- amber – jewel of plant origin

Figure 10.27, p. 261

Student Presentations – Gums, Latex, Resin