Evaluating Protein Extraction Techniques from Lentils (Lens Culinaris): Comparing Ammonium Sulfate, Ultrasound-assisted and Conventional Extraction

Aim: The research aims to compare and evaluate the efficiency of environmentally friendly protein extraction methods from lentils. The focus is on the applications of conventional extraction, ammonium sulfate precipitation, and ultrasound-assisted extraction. Effectiveness is assessed by protein yield and potential applications in the food industry.

Method: Yellow (YL) and red (RL) ground lentils are treated with three different extraction methods: (1) conventional extraction by alkaline solubilization and isoelectric precipitation (Al/IEP), (2) ammonium sulfate precipitation (AS), and (3) ultrasound-assisted extraction (US). Response Surface Methodology (RSM) is used to optimize conventional extraction regarding pH, solvent-to-solid concentration (%w), extraction time, and extraction temperature. The other methods are adapted to the optimal parameters of conventional extraction. The extracted proteins are analyzed for protein yield and protein content.

Results: Alkaline solubilization and isoelectric precipitation were individually analyzed using RSM, with the optimization of alkaline solubilization as the initial step. The optimal parameters were adjusted based on practical considerations and insights from the literature.

The results showed no significant differences in protein yield across methods. The highest protein yield of 69.62% was achieved using the conventional extraction on red lentil flour. Regarding protein content, it also achieved the highest level at 88.67%, with no significant difference between red and yellow lentils for this method. This suggests that red lentil flour results can likely be replicated with yellow lentil flour under similar conditions.

No significant difference was found between ultrasound-assisted extraction and the adjusted conventional extraction of yellow lentils, indicating that ultrasound does not provide a substantial efficiency advantage over the conventional method. Initial tests of ammonium sulfate precipitation at 80% concentration resulted in a high protein content of 98.39% but a lower yield of 45.01%, suggesting limited efficiency of this method. In contrast, Alsohaimy et al. (2007) reported a protein yield of 93% using a similar approach. These findings suggest further research is required to fully evaluate the effectiveness of ammonium sulfate precipitation.

Following results were obtained:

YL Al/IEP with optimal parameters: Protein content: 73,45% ± 2,1%, Protein yield: 68,87% ± 5,6%

YL Al/IEP with adjusted parameters: Protein content: 81,98% ± 2,1%, Protein yield: 69,12% ± 1,1%

RL Al/IEP with adjusted parameters: Protein content: 88,67% ± 0,4%, Protein yield: 69,62% ± 0,7%

YL US: Protein content: 84,25% ± 1,2%, Protein yield: 68,44% ± 0,6%

YL AS: Protein content: 92,12% ± 8,9%, Protein yield: 51,18% ± 8,2%

Conclusion:

With conventional extraction a protein content of 88.67% was achieved for red lentils. Ammonium sulfate precipitation yielded an even higher protein content of 98.39%, though it resulted in a lower protein yield compared to other methods. In the food industry, efficiency often prioritizes methods that provide greater product yield in a single process. Despite its advantages - such as high solubility, protein structure stabilization, purity, and low cost - ammonium sulfate precipitation requires time-intensive desalting steps, like ultrafiltration or dialysis. Therefore, further research is necessary to assess the method’s practical viability.

Ultrasound-assisted extraction, on the other hand, showed no significant improvement in protein content or yield compared to conventional extraction. This suggests that cell disruption is sufficiently achieved without ultrasound.

Overall, lentil proteins demonstrate strong potential for use in milk alternatives and other high quality foods due to their valuable sensory and technofunctional properties. To better evaluate the applicability of each method in the food industry, a detailed analysis of the technofunctional properties resulting from each extraction technique is recommended.