|Authors: ||D.M. Barrett, G. Anthon|
|Keywords: ||tomato, concentration, viscosity, thickness, heating|
During the concentration of raw tomato juice to paste, losses in consistency and serum viscosity are commonly known to occur.
Storage of concentrated paste, and reconstitution of the paste back to juice with water, result in a further reduction in consistency and viscosity.
To understand the reasons for this, samples of raw juice, processing intermediates and final paste were collected from an industrial processing plant during normal commercial production, and the final paste was stored for up to 1 year.
Tomato juice consistency decreased throughout the course of juice concentration, with the greatest change occurring early in the process, as the juice was concentrated from 5 to 10 °Brix.
Total pectin content did not change as the juice was concentrated to paste, but the water-soluble proportion of the total pectin increased.
The greatest increase in pectin solubility occurred late in the process when the evaporator temperature was the highest.
The Bostwick values of tomato pastes stored at least 1 month were more than twice those of the same pastes measured on the day of paste production, indicating a significant loss of consistency during storage.
The loss of consistency during storage could be nearly completely reversed if the reconstituted paste was heated to 90°C or above.
Optimal heating times for restoring consistency were 30 min at 90°C or 12 min at 100°C. Serum viscosities also decreased during paste storage, but the change in serum viscosity was proportionally smaller than the changes in Bostwick consistency.
As with the Bostwick consistency, heating the reconstituted juice under similar conditions restored the serum viscosity.
This might be done during product formulation, when water and other ingredients are typically added to stored paste to create pizza and spaghetti sauces, salsa and other high-value products.
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