Iodine value, FFA, refractive index, and fatty acid composition in edible oils

Importance of the topic

Edible oils supply essential dietary fatty acids and quality traits such as iodine value, free fatty acids (FFA), refractive index, and detailed fatty acid profiles are critical for nutrition, safety, and process control.

Objectives and overview

This study aimed to develop and validate a rapid, solvent-free near-infrared spectroscopy (NIRS) method on the Metrohm DS2500 Liquid Analyzer for simultaneous determination of eight quality parameters in edible oils within one minute per sample.

Methodology and used instrumentation

A total of 397 samples covering sunflower, rapeseed, sesame, and soybean oils were measured in transmission mode at 40 °C using 8 mm disposable vials on the Metrohm NIRS DS2500 Liquid Analyzer.

• Spectral range: 400–2500 nm
• Sample holder: 8 mm vials
• Temperature control: 40 °C
• Software: Vision Air Complete for data acquisition and chemometric model development

Reference values were obtained by gas chromatography (iodine value and fatty acids) and standard titration or refractometry for FFA and refractive index.

Main results and discussion

Calibration models showed excellent agreement with reference methods, with correlation coefficients (R²) exceeding 0.94 for all parameters and low prediction errors:

• Iodine value: R² = 0.999, SEC = 0.29 g/100 g, SECV = 0.30 g/100 g
• FFA: R² = 0.983, SEC = 0.08 g/100 g, SECV = 0.08 g/100 g
• Refractive index: R² = 0.996, SEC = 0.0001, SECV = 0.0001
• Palmitic acid (C16:0): R² = 0.980, SEC = 0.29 %, SECV = 0.30 %
• Stearic acid (C18:0): R² = 0.967, SEC = 0.18 %, SECV = 0.18 %
• Oleic acid (C18:1): R² = 0.999, SEC = 0.57 %, SECV = 0.62 %
• Linoleic acid (C18:2): R² = 0.999, SEC = 0.33 %, SECV = 0.37 %
• Alpha-linolenic acid (C18:3): R² = 0.990, SEC = 0.32 %, SECV = 0.34 %

High R² values and low errors confirm the method’s reliability for routine quality control.

Benefits and practical applications

The NIRS approach offers:

• No sample preparation and no hazardous solvents
• Analysis time below one minute per sample
• Reduced labor, waste, and operational costs
• High throughput for in-line or at-line process monitoring

Future trends and possibilities

Potential developments include:

• Integration with robotic sample handling for automated workflows
• Extension to other oil matrices and value-added products
• Implementation of advanced chemometric and machine-learning algorithms
• Real-time monitoring in production lines for process optimization
• Cloud-based data management and remote QA/QC platforms

Conclusion

The Metrohm DS2500 Liquid Analyzer combined with Vision Air chemometrics delivers a rapid, accurate, and eco-friendly solution for multiparameter analysis of edible oils, streamlining QC operations and supporting industry demands for high throughput and safety.