Food Science Lipid Reactions

Anitoxidants overview

they react with oxygen and donate a H to free radicals

Which oils are most susceptible to oxidation

unsaturated oils because their double bonds are good sites for oxidation.

what can food producers do to avoid synthetic antioxidants

use real antioxidants from fruits or vegies or phytochemicals but this is more expensive, it is used in stores like trader joes.

High fat foods

when exposed to O2 become rancid to minimize this effect you vaccum seal, flush with nitrogen, add antioxidants

Propyl Gallate

white crystalline soild synthetic anitoxidant some water solubitly. used in cereals and snack foods. helps stabilize vegetable oils but decomposes at melting point 148.

Sensory affects of degradation on oils

fishy acetaldehyde like bitter cardboard paint like smoky swampy woody pungent plasticlike musty

Off Flavor in Hydrolysis

FFA and their oxidized compounds produce off flavor and make oil less acceptable.

Changes in nutrients during frying

Vitamin E decomposes maillard reaction causes nutrient loss from aa carbonyl compounds formed in lipid oxidation react with amino acids and produce acrylamide (UNSAFE) and many othe rvolatile compounds produced (benzene, toluene, hexylbenzene, TOXIC)

Oxidation natural?

YES natural process that takes place between molecular oxygen and unsaturated fatty acids

Lipid Oxidation Storage problems

a challenging problem in storage of fats and oils and lipid containing foods. characteristic changes associated with oxidative deterioration of vegetable oils and fats--> development of unpleasant tastes, odors, as well as color, viscosity and solubility changes

What is oxidative rancidity

a chemical change that results in unpleasant odors and taste in fat. WOF(warmed over food) first recognized by Tims and Watts in 1958 who defined it as rapid onset of rancidity in cooked meats after refrideration. oxidized flavors are readily detectable after 48 hours in cooked meats. slow development of rancidity encountered in raw or fatty tissues after prolonged freezer storage

In order to function as an antioxidant

a molecule must react with free radicals more rapidly than the free radicals react with lipid. products of the reaction with the free radicals must not be pro-oxidant the molecule must be lipid soluble

Hydrogenation (don't confuse with hydrolysis)

adding H to saturate double bonds need: heat and metal catalysts Used for margarines, shortenings to increase stability and shelf life. results in a more solid plastic fat so it increases hardness of fat by saturating double bonds

BHA

butylated hydroxyanisole is a waxy white solid. Used in ice creams, candy, chewing gum, dry dessert mixes.

BHT

butylated hydroxytoulene inexpensive synthetic antioxidant, works well in conjunction with BHA. effective in animal fats not as effective in vegetable oils

Termination

chain reaction is terminated by formation of nonradical products resulting from combination of two radical species. Free radicals can damage living tissues unless antioxidants are present to react with free radicals

Autooxidation

complex chain reaction that starts when lipids are exposed to oxygen. the oxygen binds to lipids and then other compounds. causes lipids to deteriorate. new compounds are formed when oxygen is added to lipids. These compounds include ketones, aldehydes, alcohol, apoxides.

Oxidation overview

complex chain reaction, starts when any food containing lipids are exposed to O2. Leads to lipid deterioration-rancidity. Unsaturated are more susceptible than saturated because the double bonds are weaker and the O2 more readily binds with lipid molecule at double bond site

Anitoxidants

compounds that quickly react with oxygen to form new substances and prevent foods from going rancid. antioxidants are fat soluble so they work well to prevent lipid degradation

Chemistry of Deep Fat Frying Oil article

deep fat fried foods have generally desirable color, and crispy texture. immerse food in hot oil in the presence of air at a H temperature. this oil acts as a heat transfer medium and contributes to texture and flavor common reactions occur mentioned above (maillard rxn, trans fatty acids formed)

Hydrolyzed triglycerides

deterioration hydrolysis=large molecules broken into smaller parts by the addition of H2O. H2O + lipids-->FFA and glycerol shorter C chain gives a fatty acid that becomes more rancid and gives off off flavors (butter: butyric and caproic acid)

Liquid Vegetable oils

don't have optimal function for baked goods process of hydrogenation was invented to convert liquid oil to semisolid with low poly unsaturated but trans fats formed from partially hydrogenating

Frying: 3 major chemical reactions

each of these produces a range of compounds that contribute to a range of desirable or undesirable products

Rancidity

form of food spoilage. but it poses no short term health risks. But the main problems are the unappetizing color and flavor changes, because of the compounds formed during oxidation.

Regarding lard

even lard uses anitoxidants anything with unsaturated fats needs it (added to walnuts)

Polymerization

fats particually the ones from polyunsaturated fatty acids tend to form some larger molecules (polymers) when heated under high temperature for a long time. although the process isn't understook completely it is believed that polymers in fats and oils arise by formation of either C to C bonds or O2 bridges (results in the sticky residue occurs after hydrolysis and oxidation)

Antioxidant functions

function by interfering with the chain reaction. If the number of free radicals can be kept low enough oxidation will not occur. O2 would rather react with BHA or BHT rather than oxidizing fats or oils thereby protecting them from spoilage. In addition to being oxidizable BHA and BHT are fat soluble (work well for manufacturers)

Examples of secondary oxidation products

hexanal, pentanal, malonaldehyde

Three chemical processes in frying

hydrogenation, oxidation, polymerization

Steps of oxidation

initation propagation termination

Steps of oxidation

initiation, propagation, termination

Factors that initiate oxidation

light oxygen heat time metal cataylsts

Controlled use antioxidants

manufactures add synthetic antioxidants to keep foods fresh they include BHA, BHT, propyl gallate, and TBHQ

Frying oils

oxidized polymers accelerate the oxidation of the oil polymers accelerate further degradation of oil, increase oil viscosity, produce foam, develop undesirable color in food and cause high oil absorption in foods. Polymers are highly conjugated dienes, produce a brown resin-like residue along sides of fryer

Oxidation

oxygen reacts with unsaturated fatty acids. initially peroxides are formed which break down into hydrocarbons, ketones, aldehydes, and smaller amounts of epoxides, and alcohols. Oil becomes part of the food we eat so it is a major factor in the quality and nutritional value of the food.

Hydrolysis

partial hydrolysis of triglycerides--> mono and diglycerides and fatty acids water attacks the ester linkage of triacylglycerols which produces di, monogylcerols, glycerol, and FFA. FFA increase as the number of fryings increase. when the hydrolysis is carried to completion with H2) in the presence of an acid catalyst the mono, di, and tri will hydrolyze to glycerol and fatyy acids

Fats and oils in food prep

production of fat includes lard (pigs) and tallow (beef) meat scraps are heated and the melted fat is skimmed of the top. Oils from plants are extracted by heating and then percolate hexane through seeds to collect containing oil, solvent distilled from oil and can be resused

BHT and BHA

reacts by using its OH group to prevent oxidation, all used to preserve foods. BHT also added directly to shortening, cereals, and other foods containing fats and oils.

Propagation

resultant alkyl free radical reacts with oxygen to form unstable peroxy free radical which abstracts a H from another unsaturated fatty acid to form ROOH and a new alkyl free radical-this radical initiates further oxidation and contributes to chain reaction. ROOH is a hydroperoxide, one of the major initial oxidation products that decompose to form secondary compounds responsible for off flavors

Initiation

starts with abstraction of H atom adjacent to a double bond in a fatty acid RH--> R + H where RH is an unsaturated fatty acid and R is a free radical. this is catalyzed by light heat/metal and other things

TBHQ

tertiary-butylhydroquinone synthetic antioxidant, white to tan powder. works well in vegetable oils after extensive testing approved as an additive in 1972. works best in frying applications. developed to be used in stabilizing various veg oils, fats and foods against oxidative deterioration, thus preventing rancidity

Frying

the convective heat transfer in which foods are immersed in hot oil. may reactions in which water in food evaporates and is replaced by oil fried snacks are as much as 30% oil