Carbohydrates in orange juice applying pulsed amperometric detection

Significance of the topic

Accurate quantification of carbohydrates in fruit juices is essential for quality control, nutritional labeling and research into bioactive compounds. Inositol, a sugar alcohol present in orange juice, acts as an important signaling molecule in biological systems. Incorporating inositol determination alongside common sugars improves our understanding of juice composition and offers better assessment of product authenticity and functional properties.

Objectives and overview

This study demonstrates a chromatographic method for simultaneous determination of inositol, glucose, fructose and sucrose in orange juice. The approach employs a Metrosep Carb 2 – 150/4.0 column coupled with pulsed amperometric detection (PAD) to achieve baseline separation and sensitive quantification. Key objectives include method validation and evaluation of precision under routine conditions.

Methodology and applied instrumentation

The analytical workflow involves the following steps and equipment:

• Sample preparation: Orange juice diluted 1:1000 with deionized water.
• Chromatographic column: Metrosep Carb 2 – 150/4.0 with a guard column Metrosep Carb 2 Guard/4.0.
• Eluent composition: 100 mmol/L NaOH and 10 mmol/L sodium acetate.
• Flow rate and injection: 0.5 mL/min, 20 µL injection volume.
• Column temperature: 30 °C; total runtime 20 minutes per analysis.
• Pulsed amperometric detection parameters:
  • Wall-jet cell with gold working electrode and palladium reference electrode;
  • Measuring potential 0.05 V, duration 100 ms; cycle duration 550 ms;
  • Current range 200 µA; cell temperature 35 °C.
• Instrumentation:
  • 930 Compact IC Flex Oven/Deg (Metrohm) 2.930.2160
  • IC Amperometric Detector 2.850.9110
  • 858 Professional Sample Processor 2.858.0020
  • Wall-Jet cell: Carb (Au, Pd) 6.5337.010

Results and discussion

Under optimized conditions, all four analytes were well resolved. Average concentrations and precision (n = 12) were:

• Inositol: 1.5 g/L, RSD 0.5%
• Glucose: 20.6 g/L, RSD 0.3%
• Fructose: 23.2 g/L, RSD 0.3%
• Sucrose: 42.5 g/L, RSD 0.4%

These low relative standard deviations demonstrate the method’s excellent repeatability. Baseline separation was achieved without derivatization, highlighting PAD’s suitability for native carbohydrate detection.

Benefits and practical applications of the method

The procedure offers several advantages:

• Direct detection of underivatized carbohydrates, reducing sample handling.
• High sensitivity and selectivity provided by PAD.
• Robust quantification with RSD below 0.5% across key sugars.
• Applicable to routine quality control in juice production and nutritional analysis.

Future trends and applications

Emerging directions include integration of this method with high-throughput sample preparation, coupling with mass spectrometry for structural confirmation, and expansion to other food matrices. Advances in microfluidic PAD cells could further enhance speed and reduce sample volume, supporting on-line monitoring in production lines.

Conclusion

The presented PAD-based chromatographic assay enables reliable, precise determination of inositol and major sugars in orange juice. Its simplicity, accuracy and adaptability make it a valuable tool for laboratories focused on food quality, nutrition and research into bioactive carbohydrate compounds.