Phenolic Analysis

Many fruit juices contain ultraviolet absorbing phenolic substances. The uv-vis absorbance spectrum of an alcohol clarified solution of orange juice is shown in Figure 10. Absorbances at the key wavelengths 280, 325 and 443 nm, due to flavanoids, psoralins and carotenoids respectively, can be used to detect dilution of orange juice with sugar. The sum of these absorbances is typically in the range of 2.0-3.0. Reduced absorbance sums can indicate dilution of the juice.

Some less expensive fruit juices can be detected by HPLC analysis of polyphenolic compounds. Compounds unique to a particular fruit can be sensitive markers for the presence of that fruit. For example, analysis of the citrus flavanone glycosides naringin and eriocitrin can establish the presence of grapefruit juice or lemon juice in orange juice.

Amino Acids 
Anthocyanin Pigments 
Carbon SIRA 
Organic Acids 

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Figure 10