Crocin oxidation

Saffron extract contains many carotenoids such as crocetin, crocetin di-glucose ester, crocetin gentiobiose glucose ester, and crocin (crocetin di-gentiobiose ester), whose chemical structures are shown in Figure 58.1. These carotenoids scavenge free radicals, especially superoxide anions, and so may protect cells from oxidative stress. Indeed, it has been demonstrated that these carotenoids are useful in sperm cryoconservation and in protecting heptocytes from toxins. 

Another group of methods relies on the destruction of an indicator by an oxidant, leading to a decrease of its characteristic absorbance or fluorescence. Usually this decrease is not linear with time, so the method of choice for the analysis of data is the either the lag time measurement or the area-under-curve approach, that is, comparing the areas under curves of absorbance or fluorescence versus time for a reference sample and a sample studied. Antioxidants protecting the oxidizable substrate increase the area under the kinetic curve (Fig. 4). An absorptiometric method used the bleaching of the carotenoid crocin induced by ABAP (L23, T7). However, crocin is rather expensive and the recommended method of its preparation (by extraction of saffron) may lead to extracts of different composition and properties varying from batch to batch. 

Since the crocin-bleaching method is based on competition kinetics, it can also be used to detect pro-oxidant activity (POA), for example, of early MRPs the DPPH method cannot. In fact, in the presence of antioxidants, the crocin-bleaching rate [reaction (1)] is slowed down, because the antioxidant reacts with the radical first and the antioxidant radical formed [reaction (2)] reacts only slowly with the crocin [reaction (3) ]. On the contrary, the pro-oxidant competes with the radical for the crocin [reaction (4)], thus increasing the extent of crocin bleaching 446... 

Manzocco et a/.483 compared the redox potential and the POA of some potent oxidants with those of some foods (milk, bread). For the POA, hydroxy radicals generated from H202, peroxy radicals from ABAP, and DPPH, as well as milk and bread, were allowed to react with crocin in aqueous solution at 40 °C and the POA was taken as the ratio of the decrease in Acrocin at 5 min to oxidant concentration ... 

L. Manzocco, S. Calligaris, and M. C. Nicoli, Assessment of pro-oxidant activity of foods by kinetic analysis of crocin bleaching, J. Agric. Food Chem., 2002, 50, 2767-2771. 

Resveratrol analogs have been extensively studied for their anti-oxidative properties. Some were found to be more active than resveratrol (1). The SARs of some resveratrol analogs have been discussed [388,395,466,497]. Several resveratrol derivatives from Yuccapericulosa F. Baker showed inhibitory activity on bleaching of crocin induced by alkoxyl radicals and scavenging properties toward DPPH. This may later contribute to their insect growth regulatory activities [498]. 

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