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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Healthy Processed Foods Research » Research » Publications at this Location » Publication #309136
Title: Effect of heat treatment, pH, sugar concentration, and metal addition on green color retention in homogenized puree of Thompson seedless grape

Author
item ZHENG, YONGIU - Northwest Agriculture And Forestry University
item SHI, JUNLING - Northwest Agriculture And Forestry University
item Pan, Zhongli
item CHENG, YONGLE - Northwest Agriculture And Forestry University
item ZHANG, YAN - Northwest Agriculture And Forestry University
item LI, NAN - Northwest Agriculture And Forestry University

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2013
Publication Date: 6/26/2014
Citation: Zheng, Y., Shi, J., Pan, Z., Cheng, Y., Zhang, Y., Li, N. 2014. Effect of heat treatment, pH, sugar concentration, and metal addition on green color retention in homogenized puree of Thompson seedless grape. LWT - Food Science and Technology. 55:595-603.

Interpretive Summary: The objective of this research is to study the optimum treatments in retaining green color of Thompson seedless grape puree, which is important as a quality indication of green raisins made from white grape cultivar of Thompson Seedless. The puree of Thompson seedless grape was treated under different heating time, temperature, pH, and additions of various types and concentrations of sugars and salts. The temperature, pH, metal ions, and sugar type and concentration had influence on the relative chlorophyll pigment retention in the puree of Thompson seedless grapes while the effect of sugar concentration and metal ion on chlorophyll pigment retention depended on the pH values of grape puree. To produce puree with the highest chlorophyll pigment retention value, the conditions of 23.3°C, pH 4.5, and 120 g/kg fructose and 210 g/kg glucose could be applied in puree production.

Technical Abstract: Homogenized puree of Thompson seedless (Vitis vinifera ‘Thompson Seedless’) grape was treated under different conditions, including heating time (5-30 min), temperature (20-80°C) and pH (2-10). Treatments with separate additions of glucose, fructose, and sucrose at concentrations of 100-600 g/L and salts of MgCl2, ZnCl2, GuSO4, and KCl at concentration of 1 g/L were also tested at 20°C up to 30 min. Relative chlorophyll pigment retention (CR) was measured at 664 nm. The chlorophyll pigments were the most stable at 20°C and the nature pH of grape puree (pH 3.4). Increasing temperature and changing pH reduced CR. After 30 min treatment at 80°C, CR decreased to lower than 20% and 50% at pH 2 and 5, separately. Increasing fructose and sucrose concentrations reduced CR at pH 3, but increased it at most levels at pH 4. Increasing glucose concentration protected chlorophyll pigment from reduction in some cases at pH 3 and 4. CR increased with addition of metal ions increased at pH 4, but decreased at pH 3. Conditions of 23.3°C, pH 4.5, and 120 g/kg fructose and 210 g/kg glucose produced the highest CR value.