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Corrosion of copper by food acids containing colourants and sweetening agents – Part IV: Corrosion by lactic acid
Author(s) -
Talati J. D.,
Patel A. S.
Publication year - 1988
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19880390106
Subject(s) - lactic acid , chemistry , sucrose , corrosion , fructose , copper , corrosion inhibitor , amaranth , glycerol , nuclear chemistry , food science , biochemistry , organic chemistry , bacteria , genetics , biology
The corrosion of copper in lactic acid containing various colourants and sweetening agents has been studied. In plain lactic acid the corrosion increases with acid concentration up to 0.5 M and then decreases, but it increases continuously with the time of immersion and temperature. Pure buffalo milk (pH 6.45) and curd (pH 3.70) have almost no effect on copper. Addition of food dyes to lactic acid increases corrosion, the order of corrosivity being: amaranth < fast red E ⩽ sunset yellow ⩽ tartrazine ⩽ ponceau 4 R < carmoisine. Saccharin in plain as well as coloured lactic acid has an accelerating effect. The other sweeteners have an inhibitive effect, in the order: glycerol < glucose ⩽ fructose < sucrose in plain lactic acid, while in coloured acid the effect increases in the order: glycerol < sucrose < glucose < fructose. Copper in 0.1 M plain as well as coloured and/or sweetened lactic acid shows a corrosion potential of −70 mV (+ 5 mV) vs SCE. Galvanostatic polarisation curves show very little anodic but appreciable cathodic polarisation. Preservatives like sodium benzoate confer 30% protection.