Polysaccharides in Food Science

Carbohydrates: Part 2

• Reducing sugars, under certain conditions, can produce brown colours. These colours can be desirable or undesirable.

• Examples of desirable browning:

• Browning of baked goods in the oven.

• Examples of undesirable browning:

• Browning of stored sugar

• Overcooking browning

Maillard Reaction

• This browning reaction is caused by the reaction of glucose with amino groups on protein molecules.
• It is a non-enzymatic browning process.
• It alters proteins, notably those containing the essential amino acid lysine.
• The loss of lysine can be a concern for ensuring nutritional content in food products.
• For example, bread can lose up to 40% of its lysine through this reaction.

Total Maillard Effects

• Factors affecting Maillard reaction:

• Time

• Temperature (increased temp speeds up the reaction)

• pH (increased pH increases the rate, decreased pH slows the rate)

• Fructose, compared to glucose, reacts with protein at a slower rate in the Maillard reaction.

Caramelization

•  Caramelization is a reaction that occurs when carbohydrates, especially sucrose, are heated.
•  It is a non-enzymatic polymerization.
• Results in characteristic brown color and flavors through linking unsaturated carbohydrate rings.
• The reaction does not involve any C=O bonds.

Polysaccharides

• Polymers of monosaccharides

• Made up of sugar units arranged linearly or branched.

• Most have 200 to 3000 sugar units; some, like cellulose, have 7,000 to 15,000.

• Starch amylopectin contains more than 60,000 sugar units.

• Estimated that 90% of carbohydrate mass in nature is polysaccharide.

• Sometimes referred to as 'glycans'

• If all sugar units are the same, it is a 'homoglycan'.

•  Examples: Cellulose, starch amylose, starch amylopectin.

• Cellulose has a linear arrangement of glucose units. Hydrogen bonding between the homoglycans causes the strength and insolubility of cellulose fibers (found in cotton and wood). Enzymes have difficulty breaking down these structures.

• Branched heteroglycans(like Guar Gum, Algins, Locust Bean Gum) typically are more soluble in water compared to homoglycans.

Polysaccharide Solubility

• Polysaccharides have strong affinity for water due to hydroxyl units of the molecules.
• They absorb water and swell; may hydrolyze; hydrated water does not freeze.
• This characteristic is important in avoiding phase separation of solutes in frozen foods.

Starch

• A major plant food reserve.
• Estimated to provide 70-80 % of global human caloric intake.
• In nature, starch appears as granules.
• Granules are insoluble and hydrate only when heated; this makes them easy to transfer and mix.
• Composed of amylose (linear polysaccharide) and amylopectin (highly branched polysaccharide).
• Rice starch granules are the smallest, tuber starch are the largest.

Starch Granule Gelatinization

• Starch granules are insoluble in cold water.
• When heated, starch granules gelatinize which disrupts the molecular order within them due to the water absorption.
• Gelatinization depends on several factors such as Starch/water ratio, Granule type, and Heterogeneity among granule population.
• As water is absorbed, the granules swell and amylose molecules migrate to the surrounding solution, which can create problems for processors.

Starch Hydration Viscosity/Temperature Curve

• Viscosity increases as starch granules swell making it difficult for them to move past each other.
• Excessive heating may lead to starch granule fracture, lower viscosity, water loss and phase separation, and loss of product structure.

Starch Retrogradation and Staling

• The solubility of starch decreases as it cools.
• This process is called retrogradation;
• Problems associated with retrogradation include bread staling, and precipitation in soups and sauces.

Starch Modification

• Modifications lead to more consistent behavioral properties than natural starches regardless of seasonal variations in starch supply.
• This is helpful in the production of pastes and gels from starch.
• Some desirable characteristics of modified starch include:
• Heat tolerance
• Shear resistance
• Introduction of specific functionalities.
• Chemical modifications often involve the hydroxyl groups of the starch molecules using chemical transformations.
• Increased cross-linkages between starch molecules will increase gelatinization temps and viscosity of the matrix

Cold Water Starches

• Gelatinized starches that have been thoroughly cooled.
• Many starch granules are broken allowing fast release of amylose/amylopectin.
• Soluble in cold water, do not require cooking, and have high shear tolerance. Good for dry mixes (e.g. pudding mixes).

Cellulose

• Made of flat linear chains of polymerized glucose, linked by hydrogen bonds, resulting in insolubility in water.
• Cellulose provides structural strength to plant fibers.
• Considered as crude fiber by dieticians and is not digested by humans.
• Used to add bulk to food products like bread, minimal flavour, minimal color change, minimal microbial contamination.

Guar and Locust Bean Gum

• Used as thickening agents; Guar gum produces the highest viscosity among natural commercial gums..
• Found in the endosperm of seeds.
• Locust Bean gum has fewer branched units and works well in combination with other gums.
• Widely used in dairy, frozen food and dessert industry; Guar gum is widely used in ice cream.

Xanthan Gum

• Produced by bacterium Xanthomonas campestris.
• Has a similar polysaccharide chain structure to cellulose.
• Increases viscosity of products it is added to.
• It also shows a synergistic effect with guar gum.
• Soluble in both hot and cold water, constant viscosity over a broad temperature range.
• Ideal for pourable products (like gravy), especially those that are hot or refrigerated.

Carrageenan

• A glycan extracted from red seaweed.
• Increases viscosity of food matrices.
• Forms gels in milk and water and binds to proteins, holding them in suspension.
• Used in the chocolate milk industry to suspend cocoa particles.
• Can also assist in brine absorption in cold processed meats and poultry foods.
• Issues with dissolving in hot acids.

Agar

• Seaweed origin.
• Used as a moisture holder in canned meat products and bakery mixes.

Pectin

• Found in plant cell walls and between the cell walls.
• Commercially obtained from citrus and apple peels.
• Acid resistant and useful in forming spreadable gels.

Dietary Fiber and Carbohydrate Digestibility

• Cellulose (insoluble fiber) and some gums are dietary fiber.
• Some carbohydrates (and their component parts) are broken down in the large intestine and simple sugars are absorbed giving the product a caloric value.
• Dietary fiber has several important effects incl. proper functioning of the intestinal tract, increasing fecal bulk, and increased intestinal throughput.
• It's often thought to lower cholesterol levels and reduce the risk of heart and colon cancer.