Free fatty acid during frying

Autoxidation is the most common process leading to oxidative deterioration and is defined as the spontaneous reaction of atmospheric oxygen with lipids (3). The process can be accelerated at higher temperatures, such as those experienced during deep-fat frying, which is called thermal oxidation, with increases in free fatty acid and polar matter contents, foaming, color, and viscosity (4). Lfnsaturated fatty acids... 

Not surprisingly, heat treatment, such as commercial and household frying, accelerates autoxidation. In addition to undergoing autoxidation, when fats are heated in the presence of moisture, as often is the case in food applications, fatty acids are released via hydrolysis of the ester linkages (233). The free fatty acids can accelerate oxidation of the oil. During heat treatment, the formation of dimeric and cyclic compounds seems to be the predominant thermolytic reaction of unsaturated fatty acids. In the presence of oxygen during heat treatment, however, oxidative... 

Free fatty acids are probably the most widely used characteristic of oil quality control (AOCS Ca 5a-40). Deodorized oUs, generally, have a free fatty acid level of less than 0.05%. During use for frying, there is a buildup of free fatty acids. In the initial... 

In many operations, an oil treatment system is used. This takes out the fines and treats the oil to reduce free fatty acid, color, and oxidized material and soap from the fryer oil. This has been proven to improve the fry-life for the oil and extend product shelf life. The oil can be treated at the end of frying or during frying. In the former case, a batch system is used. In the latter case, a small amount (typically 5%) of the fryer oil is treated through a system. 

Phospholipids, if not removed from oils before deodorization, can lead to dark-colored oils and serve as off-flavor precursors (53, 54). Chlorophyll (55), pheophytins and pyropheophytins (56), and metal ions (57, 58) are prooxidants that decrease oil stability. Iron and copper at levels as low as 0.01 and 0.1 ppm, respectively, are capable of lowering flavor and oxidative stabihty (59). Free fatty acids, besides representing a refining loss, have also been shown to act as prooxidants (60) and to lower smoke points (61) of oils during frying. Uinolenic acid has... 

During frying, hydrolytic, oxidative and pyrolytic (Pokomy, 1989) reactions occur and these lead to the formation of volatiles, nonpolymeric polar compounds of moderate volatility, dimeric and polymeric acids and partial acylglycerols as well as free fatty acids (Chang et aL, 1978). These reactions are responsible for a variety of physical and chemical changes that may be observed in the oil during frying. These physical and chemical... 

The types of adsorbents mentioned above can be chemically reactive. The alkali, as well as the alkali earth metals present in these adsorbents, can produce soap. The reduction of free fatty acids in the oil could be equated to the amount of soap formed in the oil. The soap thus generated in the oil then promotes rapid oxidation as well as hydrolysis of the oil during subsequent frying. Therefore, the apparent benefit of oil cleaning by this method could be overshadowed by the detrimental effects experienced later in subsequent use of the oil. A series of patents have been awarded for various adsorbent materials. However, the concept of soap formation and the need for their removal have not been dealt with effectively. 

John Gyann in his US Patent (4,764,384, 1988) proposed a blend of amorphous silica, synthetic amorphous magnesium silicate, diatomaceous earth and synthetic silica alumina for rejuvenating spent frying oil. In this invention, the inventor claims that the adsorbent would remove some free fatty acids and other oil breakdown products. It does not clearly specify if the adsorbent also removes the soap that is formed during adsorption due... 

Fatty acids are much more volatile than glycerides therefore, smoke, flash, and fire points of oils depend principally on the content of free fatty acids, and decrease if hydrolytic degradation is extended during frying. The smoke point of cottonseed, corn, or peanut oils, e.g., decreases from about 232°C at a free fatty acid content of 0.01% to 93°C at a free fatty acid content of 100%i. The unsaturation of oil has hardly any effect on its smoke, flash, and fire points. 

Lipase, phospholipase and lipoxygenase are the enzymes primarily responsible for poor-quality rice bran oil. They are activated during the bran removal process (Vetrimani et al., 1992 Takano, 1993), and can cause the rate of free fatty acid (FFA) formation to be as high as 5-7% per day (Nasirullah et al., 1989). Thus, inactivation of lipases is important for producing high-quality rice bran oil. The quality of rice bran oil is inversely related to the level of FFA, and this must be kept low if the oil is to be edible and acceptable in frying applications. However, the removal of FFA is not a simple process and is accompanied by the loss of important antioxidants (Krishna et ai, 2001). This loss must be kept to a minimum if rice bran oil is to be used as a functional food component. 

FIGURE 5.5 Formation of free fatty acids in oils during rotational frying. 

The amount of free fatty acids increased in all oils during frying, but the highest increase was found for PO, HOSO and PHCO. The three high-oleic canola oils had significantly lower rates, but the differences between these oils were not significant. 

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