49F-34 |
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E. MERCADO-SILVA, Departamento de Investigación y posgrado en Alimentos, Universidad Autónoma de Querétaro, Centro universitario, Cerro de las Campanas, Querétaro, 76010, Mexico, E. N. Aquino-Bolaños, Centro de investigación en ciencia y tecnología de alimentos, Universidad Autónoma del Estado de Hidalgo, Av. Universidad Km. 1, Rancho Universitario, Tulancingo, 43600, Mexico, and J. Martínez-Vásquez, Centro de Investigación en Alimentos, Universidad Autónoma del Estado de Hidalgo., Avenida universidad. kilómetro 1. Rancho universitario, Tulancingo, Mexico. Jicama is susceptible to physical damage during harvesting, transport, and storage, causing browning which reduces its visual appeal. Browning is related to increased lignin content, and for this reason we hypothesized that peroxidase (POD) bonded to the cell wall and induced by this damage could play some role in this process. The purpose of this work was to relate the degree of physical damage in pieces of jicama to the activity of soluble POD and of POD bonded to the cell wall. Cylinder-shaped samples of jicama (1.8 cm diameter and 0.2, 0.87, 2.6, 4.4, and 6.2 cm long) were stored at 20°C. Soluble POD activity was measured daily in the entire tissue. In another experiment, cross sections of the root (5 cm) were stored at 20°C, and samples were taken daily at different depths from the cut surface (0-1, 1-2, and 2-3 mm). Activity of soluble POD and of POD bonded to the cell wall was measured. Soluble peroxidase was extracted in 0.1M phosphate buffer (pH 6.5) and the bonded peroxidase was extracted using the same buffer plus CaCl2 (1M). Activity was determined at 414 nm, using ABTS (50 mM) and H2O2 (0.92 mM) as subtrates. The soluble and bond to the cell wall POD activity was greater in the damaged area and less in the layers that were farther away. After 7 days, bonded POD activity was greater than soluble POD activity (1400 y 688 UAg-1 respectively). The initial soluble POD activity in the homogenized cylinders was 140.3 UAg-1, and it increased to 375 UAg-1. There were no differences among the different sized pieces. The results confirm that POD bonded to the cell wall can be induced. It was found in the damaged area, as a tissue repair response. This gives us a new way of understanding the browning of this root.
Session 49F, Fruit & Vegetable Products: Fresh vegetables
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