Kalamaki Mary S, Powell Ann L T, Struijs Karin, Labavitch John M, Reid David S, Bennett Alan B
Department of Food Science, Vegetable Crops, University of California, Davis, California 95616.
J Agric Food Chem. 2003 Dec 3;51(25):7465-71. doi: 10.1021/jf0341666.
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.
抑制番茄中与成熟相关的扩展蛋白基因LeExp1的表达可增强果实硬度，而LeExp1的过表达则导致果实软化加剧。由于新鲜果实质地与加工产品稠度之间的关系尚未完全明确，我们研究了LeExp1过表达对番茄果实加工特性的影响。通过博氏稠度测定法和控制应变流变学测定发现，由LeExp1表达受抑制的转基因番茄制备的果汁和果泥，其粘度高于对照果实制备的产品。然而，由LeExp1过表达果实制备的果汁和果泥的粘度显著高于对照或LeExp1表达降低品系的产品。与对照相比，LeExp1表达受抑制的品系中，果汁的博氏稠度增加了9%，果泥增加了6%；而LeExp1过表达品系中，果汁的博氏稠度增加了27.5%，果泥增加了19.5%。通过激光衍射测定发现，LeExp1表达降低的转基因果实制备的果汁和果泥中的颗粒较小，而LeExp1过表达果实制备的产品的粒度分布表明有更多大颗粒。细胞壁多糖大小分析表明，LeExp1过表达增强了水溶性果胶以及紧密结合的基质聚糖的解聚作用。LeExp1过表达可能使细胞壁水合作用增强，导致颗粒尺寸增大和产品粘度增加。由于LeExp1的抑制或过表达均能改善稠度，因此导致产品最佳流变学特性的相互作用较为复杂。
