Physical and chemical changes in pectins during tomato paste processing

This dissertation aimed to understand physical and chemical changes that occur in tomato juice during the course of industrial manufacture of tomato paste by elucidating the kinetics of nonenzymatic degradation of pectins and determining the roles of soluble and particle bound pectin in modulating consistency. The kinetics of p-elimination, acid hydrolysis and demethylation were determined. In order to study changes during tomato paste production, tomato samples from various steps of tomato juice concentration were collected at an industrial tomato processing plant located in California. The samples were reconstituted to 5 °Brix by adding an appropriate amount of distilled water. The Bostwick consistency, serum viscosity, viscosity profile and particle size distribution of the juice were determined. Changes in uronic acid content, molecular weight, radius and conformation of tomato pectins were monitored throughout the different steps of tomato paste manufacture. Results showed that nonenzymatic degradation of pectins occurred through acid hydrolysis at pH levels below 6.0. On the other hand, beta-elimination predominated at pH 6.0 and above. Tomato pectins degraded via acid hydrolysis and followed Arrhenius type kinetics. Concentration lead to the solubilization of particle bound pectins into the soluble serum across the entire pectin molecular weight distribution. The solubilization occurred during the late steps of production. Despite the increased soluble pectin content of the serum, there was a loss in serum viscosity. Conformational studies showed that soluble tomato pectins assumed a more compact conformation during the late steps of manufacture. During the industrial production of tomato paste, results showed that Bostwick consistency was highly correlated with the apparent viscosity of the tomato juice. Furthermore, there was a drop in Bostwick consistency early in the concentration process while the solubilization of pectins occurred late in the process. Particle size distribution of the tomato samples decreased in the early steps of processing as well. The results point out that pectins plays a major role in the modulation of serum viscosity but may only play a minor role in overall consistency changes during industrial tomato paste manufacture. Physical changes early in the process lead to the consistency loss characteristic during tomato juice concentration.