Extraction of Fat from Animal Feed Products using a Waters MV-10 ASFE System

In this note, we have demonstrated that SFE can be used as an alternative extraction technique to the industry-dominant ASE technique for determining the fat content in animal feed. The SFE-based approach also has the potential to eliminate hydrolysis steps, often required when other extraction techniques are used.

Benefits

• SFE can be used as an alternative extraction technique to ASE for fat analysis.
  
• Software-controlled extraction process offers superior accuracy and precision for fat extraction and ensuing analysis.
• The SFE-based approach has the potential to eliminate hydrolysis steps associated with fat analysis.
• Positive impact on environmental sustainability, and substantial cost savings.

Fat content is an important nutritional and quality control parameter in the manufacturing of animal feed. As a result, a fast and reliable measurement is required for process optimization. Various solvent extraction techniques, including soxhlet and accelerated solvent extraction (ASE), followed by gravimetric analysis, are commonly used for fat content determination. Typical solvents used for these extractions include hexane and ether. 

With the increasing awareness of environmental sustainability, supercritical fluid extraction (SFE) has been used to remove fat in various matrices. The low polarity of supercritical CO₂ (SC-CO₂) makes it an ideal solvent for fat.^1-2 Furthermore, the solvation power can be tuned by varying the pressure and temperature, and/or mixing with organic solvents to achieve the desired selectivity. Other advantages of SFE include: carbon dioxide is relatively nontoxic, noncombustible, and inexpensive; easy recovery of the extract; and reduced organic solvent consumption and disposal.

In this application note, we present the performance evaluation of a Waters MV-10 ASFE System for the extraction of fat from a variety of animal feed products. The results are compared to those obtained using an ASE-based methodology. The prospect of adopting SFE for routine fat analysis is also discussed.

Sample description

Various commercially available animal feeds were used as received unless noted otherwise.

Method conditions

SFE conditions 

For each SFE experiment, approximately 3 g of finely ground animal feed were loaded into a 5-mL extraction vessel. The extracted fat content was collected into a pre-weighed scintillation vial. After the solvent in the extract was removed, using a Zymark Turbovap LV, the vial was reweighed. The weight difference was considered the fat content in the sample.

ASE conditions 

For each ASE experiment, approximately 3 g of finely ground animal feed were loaded into a 10-mL extraction cell. The extracted fat content was collected into a pre-weighed collection bottle vial. After the solvent in the extract was removed, using a Zymark Turbovap LV, the bottle was reweighed. The weight difference was considered the fat content in the sample.

Comparison between SFE and ASE

Table 1 summarizes the fat analyses of 15 different animal feed products. To gauge the general applicability of SFE in fat analysis, a conscious effort was made in sample selection to ensure the sample diversity in both product form and intended animals. It is also noteworthy that samples 8 and 9 were hydrolyzed by acid prior to ASE. In ASE-based methodology, it is a common practice to include a hydrolysis step prior to extraction to disintegrate the sample, to disrupt the plant cell walls, and to liberate the fat.

The hydrolysis step, however, didn’t seem necessary for the SFE approach. For both samples 8 and 9, the fat content extracted by SFE was slightly higher than those by ASE. This is likely due to the unique properties of SC-CO₂. Its gas-like diffusivities and liquid-like solvating strengths enable CO₂ to easily penetrate those otherwise difficult matrices, such as glutenous particles in dried bakery product (sample 8), and dissolve and transport the fat contents.

Figure 1 shows the correlation of the fat content extracted by SFE and ASE. It is evident there is a general agreement between the two extraction techniques, suggesting SFE could become a potential alternative to ASE in fat analysis.

Figure 2 shows the distribution of the Fat%, based on the SFE approach. The Fat% ranges from 95% to 132%, with the majority of the samples (11 out of 15) ranging from 95% to 110%, showing excellent agreement with the label claims.  

Table 2 summarizes a reproducibility study of the SFE-based approach for fat analysis. The RSD% of the five replicate experiments is less than 2%. The MV-10 ASFE System is controlled by ChromScope Software. After samples are loaded onto the extraction vessels, there is no user intervention required for the extraction; thus, offering superior precision for the ensuing analyses.

It should be noted that an excessive extraction time (25 min) was used for all SFE experiments to ensure the thoroughness of the extraction. In practice, the fat content started to elute out in less than 5 min. Preliminary time course study indicated that the optimal extraction time for fat analysis can be shortened to less than 10 min.

In this note, we have demonstrated that SFE can be used as an alternative extraction technique to the industry-dominant ASE technique for determining the fat content in animal feed. Software controlled extraction process offers superior accuracy and precision for the overall analyses. The SFE-based approach also has the potential to eliminate hydrolysis steps, often required when other extraction techniques are used. Finally, in addition to the positive impact on environmental sustainability, the use of methanol in SFE compared to hexane used in ASE could also result in substantial cost savings. 

1. Taylor SL, King JW, List GR. Determination of oil content in oilseeds by analytical supercritical fluid extraction. J Am Oil Chem Soc. 1993 Apr; 70(4):437-9.
2. King JW, Eller FJ, Snyder JM, Johnson JH, McKeith FK, Stites CR. Extraction of fat from ground beef for nutrient analysis using analytical supercritical fluid extraction. J Agric Food Chem. 1996 Sept; 44:2700-4.