Determination of Total Solids in Milk

Significance of Total Solids Analysis in Milk

Determination of total solids in milk is critical for assessing product quality, consistency and safety. Moisture content affects texture, taste and microbial stability, while solids content underpins purity, yield calculations and nutritional labeling. Accurate measurement supports regulatory compliance and informs process control in dairy production.

Study Objectives and Overview

This application note evaluates the performance of the LECO TGM800 thermogravimetric analyzer for total solids determination in various milk types. The objectives were to establish method parameters, verify repeatability across sample types (skim milk, half-and-half, vitamin D milk, heavy whipping cream and cream), and compare fixed drying time and mass-constancy protocols using different crucible sizes and sample masses.

Methodology

The analysis is based on a loss-on-drying technique where sample mass loss is recorded under controlled temperature and gas flow. Two protocols were applied:

• Fixed Drying Time: Samples (∼3 g or ∼1 g) heated from 25 °C to 102 °C at 10 °C/min with a 180 min hold.
• Mass Constancy: Samples (∼1 g) heated under the same ramp but held until mass change stability within 0.0005 g over 9 min.

Each protocol used aluminum foil crucibles (1.5 in or 2.4 in) and compressed air (oil- and water-free) at 5 L/min. Moisture and solids percentages were calculated via mass ratio equations in the TGM800 software.

Instrumentation

• Thermogravimetric Analyzer TGM800 (LECO Corporation)
• Aluminum foil crucibles: 1.5 in (621-010-236), 2.4 in (621-010-956)
• Carousels: 11-place (621-011-237) and 17-place (621-010-642)
• Compressed air supply (oil and water free)

Main Results and Discussion

Across all methods and sample types, moisture values were highly consistent and reproducible. Average solids content and standard deviations for the fixed drying time (2.4 in crucible) were:

• Skim milk: 9.43 % ± 0.05
• Half-and-half: 19.28 % ± 0.04
• Vitamin D milk: 12.34 % ± 0.05
• Heavy whipping cream: 41.58 % ± 0.02

Results using 1.5 in crucibles and mass-constancy method yielded similar averages within ±0.1 %, indicating method robustness. Minor variations reflect sample heterogeneity and crucible size differences, but all data meet AOAC accuracy requirements.

Benefits and Practical Applications

Reliable solids determination by the TGM800 supports:

• Quality assurance and control in dairy processing
• Labeling compliance and nutritional analysis
• Yield optimization and cost management
• Verification against official methods (AOAC 925.23)

Future Trends and Potential Applications

Advancements may include higher ramp rates (up to 20 °C/min) for faster throughput, automated sample handling for increased efficiency, coupling thermogravimetry with spectroscopic sensors for compositional profiling, and integration with data-driven analytics and AI for predictive quality control. Extensions to other food matrices and real-time monitoring are promising directions.

Conclusion

The TGM800 thermogravimetric analyzer demonstrates high precision and reproducibility in total solids determination across milk varieties. Both fixed time and mass constancy methods provide consistent moisture and solids data, facilitating robust quality control and compliance with standard methods.

Reference

• AOAC Official Method 925.23: Solids (Total) in Milk.