Hydrolysis alkaline saponification base

Extraction of Active Compounds from Food. Vitamins are the group of compounds more usually extracted from foods using SFE (83). A method for the analysis of the natural contents of vitamins A and E in milk powder based on SFE, a miniaturized alkaline saponification procedure, and HPLC was proposed by Turner and Mathiasson (84). Modifications of the sample matrix, the combination of static and dynamic extraction modes, and the effect of changes in extraction parameters such as temperature, flow rate, time, collection solvent, and collection temperature were optimized, obtaining recoveries of 99% and 96% for vitamins A and E, respectively. Another method for the determination of vitamins A and E based on the coupling of SFE-enzymic hydrolysis-HPLC has also been proposed providing recoveries between 79% and 152% (85). 

Saponification. Before solvent is added for extraction, saponification (alkaline hydrolysis) is a step used in most extractions of tocopherols and tocotrienols. It should be noted that acetate forms of tocopherols or tocotrienols in a sample are changed to free tocopherols and tocotrienols after saponification. This process breaks down the ester bonds of lipids and sample matrices as well. In most extraction procedures, a 60% to 80% (w/v) aqueous solution of KOH is used to perform the saponification. The volume of KOH required varies according to the amount of lipid contained in the sample. Also, ethanol is needed to stabilize the saponified solution and prevent the precipitation of soap material. Usually, the ratio of KOH, ethanol, and fat (in sample) during saponification is 3 (g) 15 (ml) 1 (g), respectively (Ball, 1988). The ratio may need to be adjusted based on the types of fats in the sample. Although ethanol concentration has no effect on the extraction of a-tocopherol by hexane, a concentration above 30% may cause lower recoveries of other tocopherols (Ueda and Igarashi, 1990). For most food samples, saponification for 30 min at70°C is sufficient. 

Enzymatic hydrolysis is a nondestructive alternative to saponification for removing triglycerides in vitamin K determinations. For the simultaneous determination of vitamins A, D, E, and K in milk- and soy-based infant formulas and dairy products fortified with these vitamins (81), an amount of sample containing approximately 3.5-4.0 g of fat was digested for 1 h with lipase at 37°C and at pH 7.7. This treatment effectively hydrolyzed the glycerides, but only partially converted retinyl palmitate and a-tocopheryl acetate to their alcohol forms vitamin D and phyllo-quinone were unaffected. The hydrolysate was made alkaline in order to precipitate the fatty acids as soaps and then diluted with ethanol and extracted with pentane. A final water wash yielded an organic phase containing primarily the fat-soluble vitamins and cholesterol. 

The preparation of a solution of soap by the reaction of fat with water in the presence of base was probably one of the earliest chemical processes discovered by humans. Although the details of this discovery are lost in antiquity, we can imagine early humans finding that water that had been in contact with wood ashes from the campfire could be used to remove grease from hands and other objects and that this water became a more effective cleaning agent as it was used. The water leaches some alkaline compounds from the ashes, and this basic water hydrolyzes the esters of the fat or grease to alcohols and soap. This is why the hydrolysis of esters under basic conditions is called saponification (the Latin word for soap is sapo). 

Saponification is the base-promoted hydrolysis of the ester linkages in fats and oils (review Section 21-7B). One of the products is soap, and the word saponification is derived from the Latin word saponis, meaning soap. Saponification was discovered before 500 b.c., when people found that a curdy material resulted when animal fat was heated with wood ashes. Alkaline substances in the ashes promote hydrolysis of the ester linkages of the fat. Soap is currently made by boiling animal fat or vegetable oil with a solution of sodium hydroxide. The following reaction shows formation of soap from tristearin, a component of beef fat. 

Base catalyzed hydrolysis. Historically, soaps were produced by alkaline hydrolysis of oils and fats, and this process is still referred to as saponification. Soaps are now produced by neutralization of fatty acids produced by fat splitting (see below), but alkaline hydrolysis may still be preferred for heat-sensitive fatty acids. 

The reverse of the reactions in Eqns 2.3 and 2.4 is achieved by hydrolysis, so named because it involves the splitting of the molecule with the addition of water. Hydrolysis reactions can be speeded up (catalysed, see Box 2.6) by the presence of an acid or base (e.g. the alkalis NaOH and KOH). The alkaline hydrolysis of fatty esters is often termed saponification. 

For some reactions small samples of the reaction mixture can be removed and then analysed by performing an acid-base or redox titration (Chapter 1) with a standard solution (Figure 6.39). This will allow the amount of a particular reactant remaining to be determined. The small sample of the reaction mixture is usually added to a large volume of cold water so the reaction is stopped, or at least slowed down. It suffers from being a destructive technique. This method can be used to measure the rate of saponification (alkaline hydrolysis) of ethyl ethanoate (Chapter 1) ... 

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