Young researcher: Alexandre Arbex de Castro Vilas Boas

Thesis abstract:
Tomato is the second most consumed vegetable in the world and a quarter of the 140 to 150 million metric tonnes produced per year worldwide is processed. The industry tomato is typically a water-demanding crop. Production is mainly in areas facing increasingly frequent periods of drought, especially due to the context of climate change. Water is a major factor affecting the yield and quality of tomatoes. There is a direct link between upstream agriculture (production) and industrial downstream (processing).

Although works to better understand pre-post-harvest links exists, better adapting production to changing climatic constraints is a challenge for the industry tomato, and is the context of this thesis. Its objectives was to analyze during the chain of production and processing, the impact of agronomic and technological factors on the quality of tomato purées, and to identify levers to improve the quality and environmental impact of manufactured products. This work was designed to analyze:
1) What are the main agronomic and technological factors responsible for the variability of the quality of fresh and processed fruit within the French production areas;
2) What are the effects of variety, water supply, ripening stages and process on the fruit quality and their suitability for processing;
3) What are the main features affecting rheological properties of the purees and which are modified by genotype and environmental effects.

Our results showed obvious differences in of fruit quality and processed products between the two major area of production in South East or West France, facing contrasted climate and especially for rainfall. Cultivars but also agronomic practices, such as planting density or production cycle duration were responsible for these differences. Both areas did not exhibited real water deficit, and the only climatic differences (thermal amplitudes and cumulative precipitation) did not seem to be a major factor of variation. This study gave also the opportunity to confirm that the commonly used harvest criteria (yield and °Brix) provided little information about the processing ability of tomatoes. In a controlled field and greenhouse experimentation, we showed that decreasing irrigation to replace only 60% of plant evapotranspiration had little effect on the yield, and increased the dry matter yield to + 27%, which is a positive result for the processing efficiency. The efficiency of water-irrigation use was thus increased by an average of 20% over the entire cycle. The composition of the fruit dry matter was not significantly affected by the water deficit in 2016. On the other hand, when these same fruits were transformed according to industrial processes, the water deficit improved the viscosity of the purees without affecting its color. It also limited the loss of viscosity obtained when fruit was processed in a Cold Break way. This result suggested that the enzymatic reactivity of the tissues was reduced. In 2017, a more drastic water stress led to significant differences in yield, but still a limited impact on dry matter content. In an industrial context, where purees are concentrated to the same soluble solid content (SSC), the purees obtain from “water deficit” fruits (WD), exhibited a lower viscosity: this results exhibit the limit of using SSC content as a quality control instead of the real dry matter content: the WD purees showed a lower viscosity, but mainly due to an un appropriate industrial process. And finally, we showed that viscosity control is a multi-factorial phenomenon and when the differences are induced by the cooking method, the viscosity of the serum was the main driving factor while it was the size and shape of the particles and their aggregation potential which were the driving factors for discriminating purees obtained from different cultivars. This thesis gives the opportunity to observe results about the influences of cultural practices and processing on the quality control of manufactured tomato products, and open discussion about the pre/post harvest interaction for the quality control from the field to the plate.

Alexandre Vilas Boas is looking for a employment or a post-doc. He can be contacted at: alexandre.boas@inra.fr or ale.boas@gmail.com