QUANTIFICATION OF SUGAR IN ORANGE JUICES AND NECTARS USING CARBON ISOTOPIC ANALYSIS

Abstract:
Authenticity in orange juice products is essential for both the food industry and regulatory enforcement, as the addition of sugars compromises nutritional value and legal compliance. In this study, 27 commercial samples of orange juices and nectars available in the Brazilian market were analyzed. The samples were subjected to isotope ratio mass spectrometry (IRMS) to determine δ¹³C values of the total fraction (bulk) and of the insoluble solids (IS), used as an internal reference. The difference between these measurements allowed estimation of the amount of added sugar of C₄ origin (sugarcane). In addition, soluble solids (°Bx) were measured, and the contents of total sugars (g/100 g) and pulp (g/100 g) were calculated.
In nectars, a wide variation was observed in the proportion of added cane sugars, ranging from 21% to 75%, corresponding to 2.3–8.7 g/100 g of added sugar, while pulp content varied from 14.8 to 70.8 g/100 g. Considering that Brazilian regulations require at least 30% juice or pulp in orange nectars, some samples were compliant, whereas others presented values near or below the legal limit, suggesting excessive dilution compensated by sugar addition.
Among the orange juices, most samples exhibited isotopic profiles consistent with a 100% C₃ source, with no evidence of adulteration. However, some samples showed deviations from the expected pattern, indicating 57% to 77% of added cane-derived sugars. In these cases, calculations indicated 1.8–4.9 g/100 g of extra sugar and reduced pulp content (approximately 55–65 g/100 g), contradicting the legal requirement for 100% fruit and absence of added sugars in whole juices. The results demonstrate the usefulness of isotopic analysis combined with simple physicochemical parameters as a robust tool for detecting adulteration. The identification of noncompliance among whole juices—products of higher commercial value—highlights the need for continuous monitoring to ensure quality and protect consumers.