A comparison of pilot scale trials to recover protein from tomato seeds and from tomato pomace

Background

Tomato seeds contain a significant source of protein with valorization potential. The seeds by weight comprise between 0.1% to 0.25% in whole tomatoes but are greatly enriched in tomato pomace to 70% when extracting tomato paste.
Methods

The procedure to recover protein from tomato seeds that had been separated from the tomato pomace was performed at pilot scale with 2.8 kg of seeds using the combination of high shear mixing and wet milling. At each step in the process, soluble protein was quantified using the Bradford assay and the total soluble protein recovered per g dry seeds was calculated based on measurement of the total liquid volume. Further steps involved centrifugation, ultrafiltration and spray drying.
Results

The results revealed an extraction of 22 mg protein per g dry seeds during the first extraction step and much lower protein concentrations in the subsequent steps. The additional steps were performed using only stirring in contrast to the first step where high shear mixing and wet milling were used. Four sequential extractions were pooled together and the soluble protein concentration recovered was 52 mg per g dry seeds. Protein concentration by ultrafiltration through a 10 kDa membrane reduced the expected recovery to 4 mg per g dry seeds. A final protein powder of 28 g was recovered using spray drying having a total protein content of 40%. Processing of the tomato pomace without separation of the seeds resulted in a lower recovery of 1.7 mg per g dry seeds when extractions were pooled together. A green protein powder of 42 g was recovered having a protein content of only 7%. Additional processing using hexane extraction and protease digestion of crude protein samples was also investigated.
Conclusions

These results revealed that highest protein recovery was obtained from the seeds that were separated from the tomato pomace and that high shear mixing was important in releasing the protein into the suspension.