Environmental conditions affect pectin solubilization in cherry tomato fruits grown in two experimental Mediterranean greenhouses

Considering the economic importance of the tomato and its nutritional benefits for human health, we studied how different environmental factors [temperature, solar radiation and vapour-pressure deficit (VPD)] influenced the pectin solubilization and the calcium concentration in cherry tomato fruits (Solanum lycopersicum cv. Naomi) grown in two experimental greenhouses: improved parral type (low-technology) and multispan type (high-technology). For three years (2004, 2005 and 2006), three fruit samples were taken over the entire production period: at the beginning of harvest [16 weeks after transplanting (WAT)], at mid-harvest (26 WAT), and at the end of harvest (35 WAT). Values for temperature, solar radiation, and VPD peaked in the third sampling in both greenhouses during the three years, being higher in the parral greenhouse during the production cycle. No-market production and peroxidation indicators [measured as H2O2 and malondialdehyde (MDA) concentrations] significantly increased at the end of the productive period in both greenhouses, indicating the presence of oxidative stress caused by the rise in temperature, solar radiation, and VPD, which was more pronounced in the parral greenhouse. Water-soluble pectins, pectate, and protopectin contents were measured, revealing an increase in the former two and a reduction in the latter under environmental stress. This indicates a clear pectin solubilization in cherry tomato fruit. The enzymes pectolytic polyglacturonase (PG), pectin methylesterase (PME), and pectate lyase (PEL), altered their activities during the third sampling, while the calcium concentration fell drastically. Therefore, both the increase in pectin solubilization as well as the reduction in the Ca concentration during harshest environmental stress in the third sampling, especially in the parral greenhouse, could degenerate the textural properties of the cherry tomato, reducing its quality and consumer acceptance.