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Relationships carotenoid composition-antioxidant activity. Assessment of possible interaction effects

Final Report Summary - INTERCAROTEN (Relationships carotenoid composition-antioxidant activity. Assessment of possible interaction effects)

The in vitro antioxidant capacity (AC) of some carotenoids has been much studied although data on the individual contribution of carotenoids to the AC of extracts and on the possible existence of interactions among them are scarce. Studies on this topic are interesting for the food industry since carotenoid-containing extracts can be used as food ingredients with both functional and technological benefits. It is important to consider that these compounds are very versatile. They are much more than pigments, since they could also act as antioxidants (in their natural milieu, foods or in the human body), provide health benefits and, some of them, be used to improve the intake of vitamin A. Since the interest of carotenoids in the food industry is beyond doubt, it is important to use rapid methodologies for their quality control. The instrumental objective measurement of colour can be harnessed for this purpose as they are the main contributors to the coloration of many products. This approach offers advantages like rapidity, non-destructiveness, simplicity, affordability, versatility, portability, possibility of automation and easy interpretation of results, among others. In this sense, it is tempting to assess whether this kind of measurements can also be harnessed for the rapid estimation of the AC of carotenoid extracts from foods.

In this project we evaluated the carotenoid profile and the AC of lipophilic extracts from a wide variety of orange juices, tomatoes and tomato products. The main objectives were two: to gain insight into the contribution of individual compounds to the AC of the extracts and to assess the existence of possible interactions. Likewise the colour of such products was thoroughly characterised by different instrumental approaches to assess the validity of colour measurements for the rapid estimation of the AC attributable to carotenoids.

The analysis of the carotenoid content of fresh tomato fruits and processed tomato products revealed that both kinds of products showed very similar proportions of (Z)-lycopene isomers with respect to the total content, although the total lycopene (LYC) levels were clearly higher in the processed samples. The main contributors to the AC of the lipophilic extracts of these samples were LYC and alpha-tocopherol (ATOC). On average, the highest AC values corresponded to the processed tomato products. Considering the tomato fruit samples, the lowest AC values were observed in the resistente a fusarium (RAF) variety and the highest in the Pera variety. The simple regression coefficients between the trolox-equivalent antioxidant capacity (TEAC) values and the levels of LYC and ATOC (0.91 and 0.83) were significant. By multiple regression analysis it was observed that the contribution of the LYC levels to the AC of the extracts was higher than that of ATOC. On the other hand, from experiments with model extracts containing AC and ATOC it has been observed that their AC do not seem to be additive.

The colour of tomato fruits and products was measured by two methodologies, spectroradiometry (SPR) and digital image analysis (DIA), which were compared. The commission internationale de l'eclairage luminance (l*) red-green axis (a*) blue-yellow axis (b*) (CIE Lab) colour parameters obtained by both methodologies were well correlated. This seems to indicate that DIA, a newer methodology, is appropriate to evaluate the coloration of tomato products. By means of multiple regression analyses it was observed that the TEAC values were significantly correlated with the set of colorimetric parameters L*,a*,b* obtained by DIA (R = 0.77). A virtually identical value of R was obtained when the set of parameters L*,hab,C*ab was considered. Higher values of R (R = 0.80) were obtained when both sets of colour parameters obtained by SPR were considered. These results seem to indicate that a rapid estimation of the AC of lipophilic extracts from tomatoes and derived products could be obtained by considering colorimetric information, despite ATOC, one of the main contributors to the AC, is colourless.

Concerning the orange juices, over 40 samples from more than 20 different varieties grown in an experimental field were analysed. The study of their carotenoid profile revealed that the great majority of the xanthophylls were esterified and that, overall, epoxycarotenoids were the main carotenoids in quantitative terms. Important quantitative differences in the carotenoid profile were found between varieties and as a result of different ripening stages. Such differences had a clear impact on the TEAC values of the lipohilic extracts obtained from the samples. The samples with the highest AC were those from Valencia Delta and Navel Rhode oranges. The AC of some varieties (Pera, Navel Cara Cara, Salustiana, Cadenera) at two different points of the ripening stage were observed to be ca. 5-10-fold different. Our preliminary results indicate that the meaningful interpretation of the contribution of individual compounds to the TEAC value and the assessment of possible interactions in these samples require further statistical analysis and data processing as the carotenoid pattern of oranges is far more complex than that of tomatoes.

The colour of the orange juices was assessed by SPR using white (WB) and black backgrounds (BB). Independently of the background the R values obtained when correlating the TEAC values with the sets of colour parameters (L*,a*,b* and L*,hab,C*ab) were considerably lower (ranging from 0.40 to 0.49) compared to those obtained for the tomato samples.

The results of this project indicate that the study of the weight of different antioxidant species in extracts in order to detect synergistic and antagonistics combinations of them requires further investigation, above all in products with complex carotenoid patterns like orange juices. The generation of more knowledge on this topic is useful for the food industry in relation to the formulation of carotenoid-containing products with higher nutritional quality and shelf-life. The color of tomatoes and derived products was found to be highly correlated with their TEAC values. Such correlations are not as good in the case of orange juices, which have a more intricate carotenoid pattern. Taken together these preliminary data indicate that the instrumental colour measurements offer possibilities to rapidly estimate the carotenoid-related AC of some carotenoid-containing foods.