Interesterification.ppt

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1、Interesterification,In certain lipids the distribution of fatty acids at various positions of the triglyceride are not random. In some cases this is desirable, in other cases, randomness is desired. Exchange of fatty acids may occur at 250 C with no catalyst or at 0 C with the proper catalyst.,Inter

2、esterification,Melting Point F,Interesterification,Lard Performance and Interesterification,Interesterification,Catalyst is usually sodium methoxide,Interesterification,Interesterification within a triglyceride,Interesterification,Or between triglycerides. Start with,End with,Interesterification,Dir

3、ected Interesterification Native lard is too uniform and tends to from b crystals which do not incorporate air well Randomized lard has the proper crystal structure, but is too soft. Best performance when lard contains about 10% trisaturated glycerides. It is possible to have the reaction occur at a

4、 temperature that is below the melting point of GS3. This will cause these molecules to solidify and they are not able to participate in further reactions. Results in a lard with b crystals and the proper consistency.,Crystallization,Polymorphism Polymorphic forms are solid phases of the same chemic

5、al composition that differ among themselves in crystalline structure, but yield identical liquid phases upon melting.,Crystallization,Crystal Stability Monotropic - one stable crystal form that proceeds from less stable form to more stable form after heating and cooling Enantiotropic - each form has

6、 a definite temperature range of stability Triglycerides are monotropic,Crystallization,Triglycerides,Crystallization,Polymorphic Forms forms upon cooling from the melt Upon further cooling forms form Heating to its melting temperature yields forms,Crystallization,Crystallization Properties,Crystall

7、ization Properties,Crystallization,Alpha Crystals,Crystallization,Beta prime Crystals,Crystallization,Beta Crystals,Crystallization, Fats Some fats tend to spontaneously form b crystals: Soybean Peanut Corn Safflower Olive Coconut Lard Cocoa Butter,Crystallization, Fats Fats the crystallize in the b

8、 form include: Cottonseed Palm Rapeseed milkfat tallow Modified lard,Triple Chain Length,Double Chain Length,Shortenings,Incorporation of air, plasticity, consistency and solid-liquid ratio are important characteristics of shortenings that depend, in part, on polymorphism. Crystals - large amounts o

9、f small air cells- Yields whiter, creamier product that is tender and has a smooth texture Crystals - small amounts of large air cells - Yields large clustered crystals with a waxy or grainy texture,Enrobing,Cocoa Butter - 80% composed of disaturated triglycerides SOS = 20% POS = 55% POP = 5%,POS de

10、termines the texture of cocoa butter POS: Alpha form 17 C Beta Prime 27 C Beta 35.5C Beta prime gives small crystal structure which leads to bloom,Lard Natural lard mostly OPS (64%) tends to form beta crystals and is poor at air incorporation. Randomized lard is less ordered and it is harder to form

11、 beta crystals. Beta prime incorporates more air.,Melting points (oC) of Fat crystals,Frying,Mass Transfer Water in a frying food migrates from the center to the surface. As water is removed at the surface due to heating, water is pumped to the surface. The rate of water loss and its ease of migrati

12、on through the product are important to the final characteristics of the food.Heat Transfer Water evaporation from the surface of a frying food also removes heat from the surface and inhibits charring or burning at the surface. The heat of vaporization of water to steam removes much of the heat at t

13、he food/oil surface.Heat Removal As long as water is being removed at a sufficient rate, the surface of the food will not char. Subsurface water in the food will also conduct heat away from the surface and towards the center of the product.,Frying,Interior Cooking The transfer of heat to the interio

14、r of the product by water will result in cooking of the interior of the food. Want enough heat to cook the product, but not enough to cause damage - example -French fry Oil - Food Interactions Ideally the food products should have similar dimensions and thus, similar surface to volume ratios. Once a

15、n equilibrium is established all processes should be the same unless there are changes in equipment function or in oil composition.Oil The properties of oil change with frying. New oil has a high heat capacity that diminishes with use. Other factors such as viscosity may change dramatically with use

16、,Frying,Mass Transfer Heat Transfer Heat Removal Interior Cooking Oil - Food Interactions Oil The properties of oil change with frying. New oil has a high heat capacity that diminishes with use. Other factors such as viscosity may change dramatically with use,Frying - Stages of oil,Break in oil. Whi

17、te product, raw, ungelatinatized starch at center of fry; no cooked odors, no crisping of the surface, little oil pickup by the food. Fresh Oil Slight browning at edges of fry; partially cooked (gelatinization) centers; crisping of the surface; slightly more oil absorption. Optimum Oil Golden brown

18、color; crisp, rigid surface; delicious potato and oil odors; fully cooked centers (rigid, ringing gel); optimal oil absorption. Degrading Oil Darkened and/or spotty surfaces; excess oil pickup; product moving towards limpness; case hardened surfaces. Runaway Oil Dark, case hardened surfaces; excessi

19、vely oily product; surfaces collapsing inward; centers not fully cooked; off-odor and flavors (burned).,Frying - Quality of oil,Indicators of frying oil quality: Total polar compounds Conjugated dienes FFA Dielectric constant Color pH Sensory Smoke point, Fire point, Flash point,Frying - Quality of

20、oil,Flavor Reversion Special type of oxidative deterioration characterized by an objectionable flavor prior to the onset of true rancidity May develop during exposure of fat to ultraviolet or visible light or heat Reverted soybean oil described as “painty”, “beany”, “haylike” or “grassy” and in final stages as “fishy” Linolenic acid most common source,