Research: Unlocking Tomato Leaf Protein Potential

In line with the growing global focus on sustainable resource management and the valorization of agricultural by-products – a topic we have consistently explored, notably with our previous articles on reusing tomato skins and seeds for cosmetic products – new research continues to emerge. The ambition to further utilize these by-products has particularly spotlighted tomato leaves as a promising source for plant-based proteins. Estimates suggest that efficient protein recovery from leaves could significantly boost global protein supply, with millions of tons per year from EU cultivation alone. However, despite their rich crude protein content, achieving efficient extraction has remained a challenge, especially as the tomato plant matures, with a noted drop in protein extractability in later developmental stages. To address this, a recent study by a team of researchers from Wageningen University embarked on a deeper investigation into the underlying factors influencing protein extractability from tomato leaves.

This study conducted a comprehensive protein analysis across four key plant developmental stages: vegetative growth, flowering, fruit-forming, and mature fruit. The findings revealed a clear and marked differentiation in the protein composition of tomato leaves as the plant progresses. Younger leaves, particularly in the vegetative and flowering stages, are characterized by a high abundance of proteins involved in fundamental building processes, such as the synthesis of new proteins and photosynthesis, primarily located within the plant’s energy-producing chloroplasts. In contrast, as the plant moves into the fruit-forming and mature fruit stages, the leaf’s protein profile shifts. There’s a notable increase in proteins associated with breakdown processes, including enzymes (proteases) that degrade existing proteins, and a greater presence of proteins involved in plant defense or stress responses. This indicates a functional transition in the leaf from being a primary builder to recycling resources and protecting the plant as it focuses on fruit development.

Ultimately, the research concluded that the decline in protein extraction yields from tomato leaves across developmental stages is directly linked to these fundamental changes in protein composition and leaf function. Specifically, as the plant matures, the proportion of easily extractable (soluble) proteins decreases while the harder-to-extract (insoluble) proteins increase. Concurrently, the activity of protein-breaking enzymes (proteases) enhances, further reducing the amount of protein available for recovery. Furthermore, the study suggests that certain “inhibitory molecules” accumulate over the plant’s development, which directly hinder the protein extraction process by reducing protein solubility.

Looking ahead, the findings offer clear directions for improving the utilization of tomato leaf protein. To address the limitations of decreasing soluble protein and increasing protease activity, future efforts should focus on tomato breeding strategies aimed at developing new varieties with enhanced proportions of soluble proteins and reduced expression of these protein-degrading enzymes. To overcome the challenge posed by inhibitory molecules, further research is critical to identify these specific compounds. Once known, these inhibitors could potentially be minimized through continued breeding efforts or managed effectively through optimized protein extraction protocols designed to mitigate their impact on protein solubility. This integrated approach, combining plant science with processing technology, is essential for unlocking the full protein potential of tomato leaf by-products.

Source: ScienceDirect

DOI: https://doi.org/10.1016/j.fochx.2024.102114