DETECTION OF ADDED BEET SUGAR IN CONCENTRATED AND SINGLE STRENGTH FRUIT JUICES BY DEUTERIUM NUCLEAR-MAGNETIC-RESONANCE (SNIF-NMR METHOD) - COLLABORATIVE STUDY

A collaborative study of the site-specific natural isotope fractionati on-nuclear magnetic resonance (SNIF-NMR) method for detecting added be et sugar in fruit juices is reported. This method is complementary to the stable carbon isotope ratio analysis (SCIRA) (AOAC Official Method s 981.09 and 982.21), which can detect sugars derived from plants exhi biting C-4 metabolism (corn and sugarcane). It is based on the fact th at the deuterium content at specific positions of the sugar molecules is higher in fruit sugars than in beet sugar. The fruit juices are fer mented, and the alcohol is distilled with a quantitative yield and ana lyzed with a high-field NMR spectrometer fitted with a deuterium probe and fluorine lock. The proportion of ethanol molecules monodeuterated on the methyl site is recorded. This parameter (D/H)(I) is lowered wh en beet sugar is added to a fruit juice or concentrate. The precision of that method for measuring (D/H)(I) was observed to be similar to th at of other isotope ratio methods: S-r values ranged from 0.19 to 0.25 ppm and S-R values varied between 0.21 and 0.37 ppm. An excellent cor relation was observed between the percentage of added beet sugar and t he (D/H)(I) isotope ratio measured in this collaborative study. Conseq uently, all samples in which beet sugar was added were found to have a (DM)(I) isotope ratio significantly below the normal value for authen tic juice or concentrate of that fruit. The SNIF-NMR method for detect ion of added beet sugar in fruit juices has been adopted by AOAC INTER NATIONAL.