title: Transgenic overexpression of expansin influences particle size distribution and improves viscosity of tomato juice and paste.
abstract: Suppression of the expression of a ripening-related expansin gene, LeExp1, in tomato enhanced fruit firmness and overexpression of LeExp1 resulted in increased fruit softening. Because of the incompletely understood relationship between fresh fruit texture and the consistency of processed products, we examined the effects of LeExp1 overexpression on the processing characteristics of tomato fruit. As determined by Bostwick consistency and by controlled strain rheometry, juices and pastes prepared from transgenic tomatoes with suppressed LeExp1 expression had a higher viscosity than preparations from control fruits. However, the viscosity of juice and paste prepared from fruit overexpressing LeExp1 was significantly greater than products from controls or lines with reduced LeExp1. Bostwick consistency increased by 9% (juice) and 6% (paste) in lines with suppressed LeExp1 expression but increased by 27.5% (juice) and 19.5% (paste) in lines overexpressing LeExp1, relative to controls. Determined by laser diffraction, the particles in juice and paste prepared from transgenic fruits with reduced LeExp1 expression were smaller, and preparations from fruits overexpressing LeExp1 had a size distribution indicating more large particles. Analysis of cell wall polysaccharides size indicated that LeExp1 overexpression enhanced depolymerization of water soluble pectins as well as tightly bound matrix glycans. LeExp1 overexpression may allow increased cell wall hydration, resulting in expanded particle size and increased viscosity of products. Because either LeExp1 suppression or overexpression leads to improved consistency, the interactions that contribute to optimal product rheological properties are complex.
authors.affiliation: Department of Food Science, Vegetable Crops, University of California, Davis, California 95616.
authors.forename: Mary S
authors.initials: MS
authors.lastname: Kalamaki
authors.forename: Ann L T
authors.initials: AL
authors.lastname: Powell
authors.forename: Karin
authors.initials: K
authors.lastname: Struijs
authors.forename: John M
authors.initials: JM
authors.lastname: Labavitch
authors.forename: David S
authors.initials: DS
authors.lastname: Reid
authors.forename: Alan B
authors.initials: AB
authors.lastname: Bennett
mesh_terms: D001628:Beverages; D005511:Food Handling; D005524:Food Technology; D005638:Fruit / Q000737:chemistry; D015870:Gene Expression; D018551:Solanum lycopersicum / Q000737:chemistry* / Q000235:genetics; D010316:Particle Size; D010940:Plant Proteins / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000737:chemistry*; D012212:Rheology; D013489:Suppression, Genetic; D014783:Viscosity
chemical_list: D010940:Plant Proteins; C095825:expansin protein, plant