The rate of degradation by oxygen of lycopene in solution varies according to temperature. Catalytic effects of traces of copper lead to a marked increase in rate of oxidation of solutions.
Solid lycopene is degraded into small fragments and derivatives of acetone, methylheptenone, laevulinic aldehyde, laevulinic acid and of an α‐dicarbonyl, probably glyoxal, have been obtained.
Degradation of lycopene occurs during the heating of serum-free tomato pulps in the The rate of breakdown as measured by colour loss varies according to Acetone and methylpresence of oxygen. availability of oxygen, temperature and intensity of illumination. heptenone appear as volatile degradation products.Many general studies have been made of colour losses during the processing of tomato products. Earlier work, e.g. that of MacGillivray,l drew attention to factors associated with such losses and indicated that these could be due to (a) heating effects alone, (b) the presence of oxygen, and (c) the presence of copper and iron. Recently, Montselise & Berk2 have reported on losses of lycopene occurring in tomato puree after different methods of heat treatment, and have indicated that removal of air checks destruction of the pigment. In part I,3 it was shown that oxidative degradation of lycopene at 50" leads to fragmentation of the molecule, giving acetone, methylheptenone, laevulinic aldehyde and probably glyoxal as products. It is now shown that similar products are obtained from serum-free tomato pulps heated in an atmosphere of oxygen. Further, the rate of colour loss has been shown to vary with availability of oxygen, temperature and intensity of illumination.
Experimental (a) Preparation of serum-free pulpMarket tomatoes were ripened in the dark at 28" during four days, for development of maximum colour. After mashing in a Waring Blendor, serum was separated by centrifuging and the pulp repeatedly suspended in distilled water and centrifuged until free from soluble carbohydrates (negative Molisch test).
(b) Lycopene estimationsLycopene was extracted and estimated by McCollum's method, which involves measurement of absorption by the extracted pigment at 472 mp. As previously discussed (Cole & Kapur3) there is a difference of about 13% between the molecular extinction coefficients of all-trans-and of thermally-isomerized-lycopene (cf. Zechmeister & Polgars). Thus loss of absorption at 472 mp may be due to loss by isomerization and/or by degradation. The possible contribution of each of these factors was studied by modifying the conditions of heating as outlined below. For the same reason results in all cases have been expressed in terms of ' apparent loss '.
(c) Effect of heating under various conditionsThe prepared pulp (250 g.) was placed in a 2-neck flask provided with a reflux condenser and gas inlet to the surface of the contents and heated in a bath under conditions indicated in Tables I and 11, shaking vigorously at intervals.A black lacquered flask was used for experiments in the dark, and a flow of carbon dioxide to obtain an oxygen-free atmosphere.The effect of different light intensities was studied by illuminating with a tungsten lamp placed at various distances from the flask. Intensities were measured a t the surface of the flask using a Valec ' light meter.
Characterization of volatile degradation productsIn each series of experiments effluent gas from the top of the condenser was passed through...
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