Determination of exogenous water in grape juice through the isotopic analysis of ¹⁸O/¹⁶O

Determinação de água exógena em suco de uva através da razão isotópica do ¹⁸O/¹⁶O

Abstract

The consumption of grape juice has been growing significantly, so its quality is becoming an issue of great importance, both for the consumer and for the industry. However, identifying adulteration in juice is a great challenge and requires a reliable analytical process. The isotope ratio (¹⁸O/¹⁶O) is an important tool to determine the addition of exogenous water in beverages, however, there is no official method for juice in Brazil. This study aimed to develop and validate a method for detecting exogenous water in grape juice through isotopic analysis of ¹⁸O/¹⁶O. The development and validation of the analytical method were performed using Isotope Ratio Mass Spectrometry (IRMS). The effect of temperature and evaporation of δ¹⁸O in experimental juices was evaluated, and reference values were found for juices based on the δ ¹⁸O of musts. The influence of the juice industrial production process on ¹⁸O values was verified, and commercial juices were evaluated in relation to the values of reference regarding the addition of water. The temperature and evaporation parameters did not influence the results of the ¹⁸O of the juice, as they presented differences lower than the method uncertainty. The heat exchanger system did not influence the proposed method. The reference values for juice can come from the musts, without affecting the interpretation of the final results. Of the thirty real juices analyzed, nine had exogenous water, three proved to be reconstituted juices and eighteen were considered to have no exogenous water. The method proposed and validated in this study presented values for the limit of detection (LOD) of 0.24‰, the limit of quantification (LOQ) of 0.97‰ and measurement uncertainty of 0.71‰, proving to be effective for the detection of exogenous water in grape juice, through of the analysis of the isotopic ratio of ¹⁸O/¹⁶O by IRMS.

Keywords:
Isotopes; IRMS; Adulteration; Method validation; Musts; Biotechnology

HIGHLIGHTS

• This proposed and validated method can be used to detect exogenous water in grape juice.

• The isotopic reference values for juice may come from the musts.

• Of the thirty Brazilian commercial juices analyzed, nine had exogenous water in their composition.