Understanding the protein extraction potential of tomato leaves (Solanum lycopersicum) through mass balance modelling

Tomato leaves, the main by-product from tomato production, are a potential protein source. In this study, proteins were extracted from tomato leaves collected from different positions of the plant (top, middle and bottom) using three different purification methods: acid precipitation, ethanol precipitation and dialysis. The protein extraction process was evaluated in terms of protein yield and purity. In addition, mass balances were established to estimate the potential additional protein recovery as well as to identify the limiting factors of the extraction. Significant protein loss (0.62 g/g total proteins) occurred during the initial processing steps, which was mainly attributed to the water absorbed by the fibrous pulp and the presence of large quantities of insoluble proteins. Part of the loss may be recovered from the pulp and thus considered attainable. However, most of these proteins were inevitably lost, due to their insolubility. In general, low protein yields were found for all leaves when aiming for a protein extract with high purity, with some variations in different leaves. Top (young) leaves resulted in the highest protein yield, suggesting the presence of more intact proteins. Acid precipitation resulted in the highest protein purity, suggesting a high selectivity for proteins.