Food, rancidity

As triglycerides get hydrolyzed to form free acids, glycerol is also formed. Due to volatility of free short chain fatty acids, a light rancid smell may be observed. Free fatty acids and glycerol also change the taste of the oil or oil based food. Rancidity due to the free fatty... 

Fatty acids are susceptible to oxidative attack and cleavage of the fatty acid chain. As oxidation proceeds, the shorter-chain fatty acids break off and produce progressively higher levels of malodorous material. This condition is known as rancidity. Another source of rancidity in fatty foods is the enzymatic hydrolysis of the fatty acid from the glycerol. The effect of this reaction on nutritional aspects of foods is poorly understood andhttie research has been done in the area. 

One disadvantage of fats contained within foodstuffs is the deterioration of the fat through oxidative rancidity. Many consumers find the aroma and flavor of deteriorated fats in foods repulsive, while others are fond of country ham and butter which owe thek aroma and flavor to fat rancidity and other breakdown products. The use of antioxidants (qv) makes such products commercially viable. 

A few spices, particularly rosemary and sage, are known to act as antioxidants which prevent rancidity due to oxidation in fats and fatty foods. 

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

The effectiveness of antioxidants as preservatives for fats and oils is evaluated by determining the rate of peroxide development using the Active Oxygen Method (AOM) (29). The development of a rancid odor is used to evaluate the stabiUty of food items (Schaal Oven StabiUty test) (30). 

Butter is used in some, usually more expensive, bakery foods, and is prized for its flavor contribution. Fats are used in some products such as pie cmst, croissants, or puff pastry, up to 60%, based on flour. StabiHty of fats and oils in perishable items such as breads, cakes, or pastries is of no consequence because shelf life is so limited that rancidity does not occur. In cookies and crackers, however, stable fats must be used in the formula since prolonged shelf life could lead to product deterioration with fats that develop rancidity. 

The calcium form of EDTA instead of free EDTA is used in many food preparations to stabilize against such deleterious effects as rancidity, loss of ascorbic acid, loss of flavor, development of cloudiness, and discoloration. The causative metal ions are sequestered by displacing calcium from the chelate, and possible problems, such as depletion of body calcium from ingestion of any excess of the free chelant, had it been used, are avoided. 

You may have noticed Ca-EDTA on the list of ingredients of many prepared foods, ranging from beer to mayonnaise. EDTA acts as a scavenger to pick up traces of metal ions that catalyze the chemical reactions responsible for flavor deterioration, loss of color, or rancidity. Typically, Ca-EDTA is added at a level of 30 to 800 ppm. 

One of the most prominent problems confronting the modem food processor is the prevention of rancidity. Rancidity affects not only the palatability of the food but the nutritive value as well—for example, oxidative spoilage of fats has been shown to be responsible for the partial destruction of the essential fatty acids (6) and of other dietary nutrients such as vitamins A (12) and E (9), and perhaps D (26) and certain members of the B complex (5, 29, SO). When one considers that nearly every food contains some fat and that this fat is subject to oxidative spoilage, the magnitude of the problem of rancidity is at once obvious. 

There is no completely objective chemical test for rancidity. Rancidity is determined ultimately by taste and smell, and stability is determined ultimately by placing the food in storage and allowing it to become rancid. But numerous chemical tests can be applied by the experienced chemist as an aid to objectivity. 

In spite of inadequacies in laboratory methods, much valuable time is saved through accelerated tests, and much valuable information is obtained. The foods chemist, through the judicious application of these tests, is making rapid progress in the prevention of rancidity, and in improving the quality of fats and fatty foods. 

BHA is an antioxidant. It reacts with oxygen free radicals. It can thus slow down the rate at which ingredients in a product oxidize in direct contact with air, a process that can cause changes in the taste or color. BHA can be added to the food itself, or to the packaging material, and it is used primarily to prevent fats from becoming rancid. 

Nitrites prevent foods from getting rancid by preventing the formation of toxic maldonadehyde, which is formed as foods get rancid. 

RAMANATHAN L and DAS N p (1993) Natural products inhibit oxidative rancidity in salted cooked ground fish, J Food Sci, 58, (2), 318-20. 

Robards, K, Kerr, A.F. and Pastalides, E (1988) Rancidity and its measurement in edible oils and snack foods. Rev. Analyst. 113, 213 (and references cited therein). 

Davidow (19), of the Food and Drug Administration, has described a colorimetric method applicable to technical chlordan. The method is based on the observation that when technical chlordan is heated with a mixture of diethanolamine and methanolic potassium hydroxide, a purple color is produced. When known amounts of this insecticide were added to cabbage, pears, and fresh and rancid rat fat, recoveries of 74 to 104% of the insecticide were obtained. However, because two crystalline isomers of chlordan isolated from the technical product do not give a colored reaction product with the reagent, further investigation of the method is being made. The red color obtained when technical chlordan is heated with pyridine, alcoholic alkali, and ethylene glycol monoethyl ether, as described by Ard (2), likewise fails with the crystalline isomers of this insecticide. 

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

From the legal point of view, antioxidants are substances which prolong the shelf-life of foodstuffs by protecting them against deterioration caused by oxidation, such as fat rancidity, colour changes and loss of nutrient value. Hundreds of compounds, both natural and synthesised, have been reported to possess antioxidant properties. Their use in food, however, is limited by certain obvious requirements, not the least of which is adequate proof of safety. 

Ehnholt et al.8 produced a broad paper covering raw materials, and in-process and final-product measurements. While the uses are primarily in the food industry, the rancidity was often caused by microorganisms. One case involved off-flavor materials being produced in drying and curing ovens. Marker compounds (concomitant) released during the breakdown process (of saturated and unsaturated compounds) were nonenal, decenal, and octenone for the unsaturated aldehydes and ketones, and nonanal, decanal, and octanone for the saturated molecules. A 10-m folded path gas cell was used with an FT-IR for measurements down to 1 Lig/m3. 

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