Many partially and poorly digested organic compounds are being investigated as potential fat substitutes and these are discussed in a comprehensive review by Artz and Hansen (1994). Since none of these are allowed for use in foods to date, the range of compounds is discussed only very briefly in the section below.
Esterification of (poly-) pentaerythritol and other polyhydric alcohols with selected fatty acids produces noncaloric, nondigestible, heat resistant organic compounds that retain the functional attributes of fats or oils. Alcohols with the neopentyl nucleus (-(CH2)4C), pentaerythritol, trimethyloethane, trimethylol-propane, trimethylolbutane, and neopentylalcohol, can be esterified with fatty acids to produce potentially acceptable fat substitutes (Artz and Hansen, 1994; Barth et al., 1944; Minich, 1950).
Polyvinyl alcohol (PPVA) fatty acid esters have been suggested for use as fat substitutes (D'Amelia and Jacklin, 1990). The polyvinyl alcohol fatty acid esters can be synthesized by direct esterification of low MW polyvinyl alcohol with excess fatty acids, chlorides or anhydrides; interesterification of polyvinyl acetate with fatty acid methyl esters; or transesterification of polyvinyl alcohol with an excess of unsaturated fatty acid esters.
Trialkoxytricarballylate (TATCA) (Best Foods Division of CPC International Inc., Englewood Cliffs, NJ) is similar to a triglyceride with polycarboxylic acids with two to four carboxylic acid groups such as tricarballic acid replacing glycerol and saturated or unsaturated alcohols replacing the fatty acids (Schlicker and Regan, 1990). TATCA is sometimes called "retrofat" (Dziezak, 1989) and its synthesis has been described by Hamm (1984). TATCA has been suggested as a substitute for vegetable oils in margarine and salad dressings (Anon., 1990; Hamm, 1984; LaBarge, 1988). Margarines prepared with TATCA melted more quickly and were softer than vegetable oil margarine (Hamm,
1985). TATCA is not digested by animals, but when fed at medium to high concentrations (9%) resulted in anal leakage, depression, weakness, and fatalities. The deaths were attributed to starvation or laxative effects as a result of interference with nutrient absorption rather than to toxicity (Hamm, 1984 and 1985; LaBarge, 1988).
Trialkoxycitrate (TAC) and trialkoxyglyceryl ether (TGE) were also investigated by Hamm (1984). Because the ester bonds in TAC are reversed from corresponding esters in triglycerides, the esters in the polycarboxylic acid fat substitutes are not susceptible to lipase hydrolysis, and do not contribute calories to the diet. Polymorphic behavior is exhibited during melting and TAC viscosity and surface tension are similar to corn oil. Thermal decomposition problems may prevent TAC from being used in frying oils. Trialkoxyglyceryl ether (TGE) production on a large scale is difficult and time-consuming (Hamm, 1984; LaBarge, 1988). TGE exhibits viscosities and surface tensions similar to vegetable oils at room temperature. While functional properties may allow TGE use as a fat substitute, synthesis problems will make commercial production difficult (Artz and Hansen, 1994; Hamm, 1984; LaBarge, 1988).
Dialkyl dihexadecylmalonate (DDM) (Frito-Lay, Inc., Dallas, TX) is a mixture of hexadecyl dioleylmalonate and dihexadecyl dioleylmalonate fatty acid esters of malonic and alkylmalonic acids which exhibit thermal stability (Dziezak, 1989; Fulcher, 1986; Gillis, 1988). Small molecular weight DDM are synthesized by reacting a malonyl dihalide with a fatty alcohol. Larger molecular weight DDM require the addition of an alkyl halide in a basic solvent (Artz and Hansen, 1994). DDM is noncaloric and absorption is negligible (Fulcher, 1986). Frying of potato and tortilla chips in DDM produces crisp chips with reduced oiliness (Anon., 1990).
Esterified propoxylated glycerols (EPG) (Arco Chemical Company, Newtown Square, PA) are produced by reacting glycerine with propylene oxide to form a polyether polyol subsequently esterified with fatty acids (Anon., 1990; Gillis, 1988; Schlicker and Regan, 1990; Sowinski, 1991; White and Pollard, 1989). The structure of EPG is similar to triglycerides, except that an oxypropylene is incorporated between the glycerol and the fatty acids. Although many polyols are acceptable, the glycerol triol is preferred. Preferred fatty acids are in the C14 to C18 range, and preferred sources of fatty acids are soybean, olive, cottonseed, corn oil, tallow, and lard (Whilte and Pollard, 1989). EPG is low-to-noncaloric, heat stable (Anon., 1990; Arciszewski, 1991; Dziezak, 1989), and partially digestible (White and Pollard, 1989). EPG feeding studies with rats indicate no toxicity (White and Pollard, 1989).
Polydextrose, derived from glucose, sorbitol, and citric acid, can also be esterified with C8-C22 fatty acids to produce polydextrose derivatives of potential value as fat substitutes (Vianen et al., 1991).
Phenylmethylpolysiloxanes (Dow Corning 550 Gluid, Contour Chemical Co., North Reading, MA) are organic derivatives of silica (SiO2) with a linear polymeric structure consisting of the generic formula [-R2SiO], where the R is an organic radical such as a methyl, phenyl, or other aliphatic or aromatic hydrocarbon (Bracco et al., 1984). Polysi-loxanes are chemically inert, nonabsorbable, and nontoxic, with viscosities ranging from 0.65 to 106 centistokes (cs) at ambient temperature depending on molecular weight. Phenylmethylpolysiloxane is an oil that is similar in functionality to soybean oil, is oil-soluble, and exhibits lipid-like character in organic solvents.
Similarly, phenyldimethylpolysiloxane (PDMS) (Dow Corning Corp., Midland, MI) is another potential noncaloric heat stable fat substitute (LaBarge, 1988). PDMS exhibits thermal and oxidative stability, minimal change in viscosity over a broad temperature range, water repellant ability, and biological inertness. The polysiloxanes possess physical, functional, and organoleptic properties of fats and oils that are inherent to unique silicon chemistry and are totally unrelated to glyceride structure. Polysiloxane has been shown to be a safe and effective calorie diluent in foods fed to experimental rats (Bracco et al., 1987).
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