Understanding the principles and procedures to retain green and red pigments in thermally processed peels-on pears (Pyrus communis L.) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xs55mg053

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  • Thermal stabilization of chlorophyll and anthocyanin on pear peels during thermal process was investigated in this study. The green color of peels-on thermally processed (canned) pears was successfully retained by complexation of magnesium-free chlorophyll with zinc ions, and the red pigments were stabilized through anthocyanin-stannous complexation and polymerization of pear peel materials Blanching de-waxed green pears (Bartlett and Comice) in zinc solution (1,300-5,200 ppm) prior to canning resulted in attractive green color on the peels-on canned pears. Zinc pheophytin a was found to be the major zinc chlorophyll derivative created from pheophytin a and zinc ions in finished canned pears. The higher the zinc concentration in blanching solution and the longer the blanching time (6-18 min), the higher the chromacity of the color in canned green pears. The color of canned pears was highly stable during storage and did not show significant change after 19 wk of storage at 38 °C or at least 35 wk of storage at 10 °C under intensive illumination. Red D'Anjou pears were tested with various individual metallic ions in aqueous solutions for pigment complexation with anthocyanins. A formula containing stannous, hydrochloric acid, formalin, and tannic acid was then developed as a pretreatment for stabilizing anthocyanins on the peels of red pears during thermal process. The stabilization was achieved through complexation with stannous ions which integrated the pigments in a cross-linked macromolecular matrix. Tannic acid and formaldehyde were the key reagents for the polymerization of pear peels. The effectiveness of the developed formula was found to be significantly enhanced by steam-heating of treated red pears prior to canning. This study significantly improved our understandings on the principles of pigment retention during thermal process, especially for red anthocyanins in processed fruits and vegetables. Developed procedures can be used to stabilize green and red pigments on pears, as well as other fruits with pigmented peels, contributing in developing high value processed fruit and vegetable products.
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