Preliminary LC-IRMS Characterization of Italian Pure Lemon Juices and Evaluation of Commercial Juices Distributed in the Italian Market

LC-IRMS determinations of the δ13C values for organic acids and sugars in 20 genuine lemon juices squeezed in the laboratory were obtained from fruits derived from two producer regions of Italy (Campania and Sicily). These samples were used to deduce four ratios to use as indices of the natural variation of these compounds in Italian lemon juice. The corresponding confidence limits were also determined. According to EU laws, addition of acidifying agents to lemon juice is allowed and must be declared on the label, while addition of exogenous sugars is not permitted. We have used the four indices to identify the exogenous addition of these organic compounds to 42 samples of commercial juice lemon distributed on the market. Due to more positive values of δ13C produced by addition of citric acid and sugar from sources with C4-type metabolism, the four judgment ratios permitted us to identify the addition of citric acid and sugars. A nonquantitative method for determination of added compounds is needed, and these LC-IRMS measurements permitted us to obtain the status of the most common additions made to lemon juices in the Italian market.