Retaining Green Pigments on Thermally Processed Peels-on Green Pears

Abstract

: The interest in developing peels‐on thermally processed (canned) green pears has prompted the investigation of retaining green pigments during thermal processes. Use of zinc ions as a processing aid for the retention of green pigment and surface pretreatment to remove waxy layer and a part of the top cuticle layer of the peels for enhancing reactions of zinc ions with chlorophylls in peel tissues were studied. Whole pears or pear chunks were subjected to zinc treatment during presoaking in 5200 ppm Zn2+ solutions for 60 min or blanching at 94 °C for 6, 12, and 18 min in a 1300, 2600, or 5200 ppm Zn2+ solution for identifying the most appropriate procedures for retaining green peel pigments. Pears were then thermally processed in glass jars at 94 °C for 20 min after commercial canning. Canned pears were subjected to an accelerated shelf life test in rooms set at 10 °C, 21 °C, and 38 °C under fluorescent light. CIELAB L*, a*, and b* color values of pear samples were monitored during storage up to 35 wk. Results showed that surface pretreatment is essential for ensuring the reactions of zinc ions with green pigments, thus retaining green pigment during thermal treatment. Blanching pears in zinc solution containing about 1300 ppm Zn2+ was effective in obtaining attractive green‐colored canned pears. Hue angle and ‐a* (greenness) values of canned pears were significantly (P < 0.05) associated with blanching time and zinc concentration in blanching solutions, and remained stable over 19 wk of storage under intensive illumination at all 3 temperatures. The technology used zinc ions as a processing aid, thus significantly minimizing the zinc content in the final processed pears.

Development of a novel Zn fortified table olive product

“…Changes in the physicochemical characteristics of olives during shelf life Divalent cations are usually associated with the improvement of firmness in fermented cucumbers (Walter, Fleming, Thompson, & Fine, 1996) and table olives (Brenes, García, & Garrido, 1994). Zn preserved the green colour of pears (Ngo & Zhao, 2005). The presence of Zn salts in the packing brine can then affect the firmness and colour of the novel olive products during shelf life.…”

“…Technology has been recently applied to retaining green pigments in thermally processed, peels-on, green pears (Ngo & Zhao, 2005).…”

Spray-Drying of Green or Gold Kiwifruit Juice–Milk Mixtures; Novel Formulations and Processes to Retain Natural Fruit Colour and Antioxidants

“…The addition of alkaline agents such as zinc and copper salts during heating is an approach to preserve the green colour via the formation of Zn 2+ /Cu 2+ -chlorophyll complexes (Ngo and Zhao 2005;Guzmán et al 2002;Maharaj and Sankat 1996). The pH range of 4.0-8.5 favors the zinc complex formation and the development of green colour (Ngo and Zhao 2005;LaBorde and von Elbe 1990).…”

The Effect of Mg2+, Cu2+ and Zn2+ pre-treatment on the color of yerba maté (Ilex paraguariensis) leaves

“…Lioutas (1989) determined that a pH between 7.0 and 9.0 was important for the stability of chlorophyll. and chlorophyll-derivative concentrations (Ngo and Zhao, 2005). The effect of both the cations in avocado puree has been studied by Guzmán et al (2002).…”

“…They found that color was best preserved when the material was treated with a salt solution (120 ppm of ZnCl 2 and 12 ppm of CuCl 2 ) and micro-waved for 30 s. Better results were obtained with zinc chloride than with copper chloride treatment. Ngo et al (2005) studied the formation of Zn 2+ -chlorophyll complexes in thermally processed green peas. They found that zincpheophytin complexes were the dominant green compound.…”