Introduction to Foods Gelatins Define gel * fluid trapped in rigid structure * work together (fluid in gel, gel in fluid) * polymers (chains) linked together Types of polymers 1. starch 2. egg protein 3. gelatin 4. pectin * gelatin made from collagen * connective tissue * nutritional value is low * bacteria growth concerns made in three forms 1. granular 2. pulverized 3. sheets * when using, ratio of 1-3 parts gelatin to 97-99 parts water Hydration * swelling due to absorption of water (diffusion) * dependent upon 1. size of gelatin particles 2. percentage of water 3. presence of salts accelerates process 4. presence of sugar inhibits process Dispersion * when the mixture reaches a temperature of approximately 35 C or 95 F * separation of molecules that form structure * therefore, add hot water to aid in separation Gelation * reversal of dispersion process * temperature plays important role * normally requires a long time to set properly * rapid cooling affects strength (melts easier due to lack of strength) Factors that affect Gel Formation Concentration of gelatin * increase the concentration of gelatin * increases firmness * decrease time of setting Gel Foam * air bubbles increase the volume (2-3 times) * dispersion of the gel network structure * decreases the firmness of the network (possible weeping) Acidity * high concentrations of acid inhibits gel formation and strength Addition of other ingredients * salts increase strength * sugars weaken gel due to water absorption Enzymes * hydrolyze protein (breakdown bond structure) * weaken structure Emulsions Definition * one liquid dispersed in another liquid which is immiscible * can not mix or blend the liquids together Three types 1) Temporary Emulsion * do not hold together for long periods o example: oil and vinegar dressings that need to be shaken before service 2) Semi permanent Emulsion * stabilizer added to decrease the tendency to separate o example: French salad dressing 3) Permanent Emulsion * use of stabilizer / emulsifier to produce a product that will not separate * example: mayonnaise Oil in water emulsion * Oil droplets suspended in water * Most emulsions of this type o Examples: milk, cream, egg yolks, puddings Water in oil emulsion * Water droplets suspended in oil Examples: butter, margarine * Both types of emulsions use an Amphiphilic molecule * Polar in nature with two sides to each 1. hydrophilic or water liking 2. lipophilic or oil liking Reasons for Breakdown of Emulsions 1. Oil particles coalesce (join together) 2. Liquid added too fast 3. Saturated solution 4. Temperature Mayonnaise * oil in water emulsion * 65% edible oil by weight emulsified in vinegar or lemon juice * egg lecithin acts as emulsifying agent Factors affecting Mayo * Temperature * harder to start with cold oil or eggs but end product is thicker * Ingredients * Salt aids in stabilization (crystalline structure) Fats and Oils Difference between and fat and oil * Fat comes from animals, oils from plants Triglycerides * One glycerol molecule plus 3 fatty acids Saturated Fatty acid * Full hydrogen capacity * Body produces low-density-lipoproteins to move cholesterol around body (promotes plaque in arteries) Unsaturated fatty acid * Has one or more bonds not with hydrogen * Mono-unsaturated has 2 less hydrogen molecules * Poly-unsaturated has room for four or more hydrogen atoms Melting point * based on three points 1. Number of saturated fatty acids (increase melting point) 2. Number of triglycerides (increase the number of carbon atoms) 3. crystalline structure shape * More unsaturated a fat, the more liquid it remains at room temperature * More saturated a fat, the firmer its consistency at room temperature * Remember that the product will melt over a range of temperatures due to mixture of triglycerides (quality of refining) Plasticity * ability to mold or shape (spread ability) * liquid held in network of crystals * increases melting point * the more unsaturated a fat is, the more plastic it tends to be Hydrogenation * Addition of hydrogen molecule to chain * increases plasticity and melting point * reduces oxidation and spoilage Winterization * cloudy in fridge * crystallization of molecules due to melting points (triglycerides) Five types of oils 1. Butter * two and a half quarts of milk to make ¼ lb of butter * consists of 80% milk fat, no more than 16% water and 4% milk solids 2. Margarine * created in 1869 * consists of 80% fat and 4% milk solids 3. lard or tallow 4. hydrogenated shortening (Crisco) 5. refined oils Olive Oil * three classifications based upon Italian law * based upon the levels of acidity left in the oil * the lower the level of acid, the higher the grade Grades 1. Extra Virgin * approximately 1% acid * the first cold press of the olives 2. Virgin * second cold press or mixture of two * contains from 1 to 3.3% acid 3. Refined * heat extraction, third press or different blends Rancidity * Chemical deterioration of fat * Molecules break off of the triglycerides and contribute to the off odors and tastes * free acids and glycerol produced * glycerol under high heat converts to acrolein and water (smoke and odor) Hydrolytic Rancidity * Breaking of chemical bonds by the addition of water Oxidative Rancidity * Breaking of chemical bonds by the addition of oxygen Deep Frying * Water on the surface instantly converts to steam * Creates a barrier for oil penetrating into the food