30G-31 |
Effect of suppressed levels of tomato fruit polygalacturonase (PG) and expansin (EXP) on the viscosity of tomato concentrates |
M. KALAMAKI1, A. Powell2, A. Bennett2, and D. S. Reid1. (1) Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616, (2) Dept. of Vegetable Crops, Univ. of California, Davis, Mann Laboratory, Davis, CA 95616 The viscosity of a product prepared by evaporating tomato juice directly to its final concentration (based on °Brix) is significantly higher than that of a similar product prepared by diluting a more concentrated tomato paste to the appropriate soluble solids concentration. This results in an increased solids content being necessary for products prepared from paste if they are to match directly prepared products. This lower product yield has an economic cost. We have evaluated pastes prepared from two lines of genetically modified tomatoes with suppressed levels of cell wall enzymatic activities to determine whether they have improved viscosity characteristics upon dilution. Pastes were prepared from juice using a bench scale concentrator which requires only 2 liters of juice to give pastes that have properties similar to those produced from the same raw material in industrial scale concentrators. Viscosity measurements were performed using the Haake, Rotovisco 20 rheometer. NMR T1 and T2 relaxation measurements and diffusion measurements were performed using a Bruker Advance 500 spectrometer. Particle size determinations were performed using the Malvern Mastersizer. Biochemical and physical studies have shown that the consistency characteristics of tomato concentrates and diluted tomato concentrates is influenced by the cell wall polymer types whose integrity is influenced by expansin and polygalacturonase (PG); these are the proteins whose levels are reduced in our modified tomato lines. When fruit PG activity is reduced, concentrates produced from those fruits have relatively greater pectin polymer sizes and better consistency. Our studies thus far indicate that diluted concentrates from the genetically modified lines have improved Bostwick and viscosity values relative to diluted concentrates from unmodified control lines. Analytical data for pectin, hemicellulose, and cellulose composition and polymer sizes are being correlated to the rheological data. Fruits in which both polygalacturonase and expansin production are suppressed produced pastes with higher recoverable viscosities that the control fruits. Cell wall swelling on redilution appears to be enhanced in the modified fruit. Hence reducing the activity of these cell wall enzymes may be a route to the selection of improved pasting tomato varieties.
Session 30G, Fruit & Vegetable Product: Processed Fruits and Vegetables
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