96-8 |
Turgor pressure component of calcium-induced firming of tomato pericarp tissue |
I. LUNA-GUZMAN1, K. A. Shackel2, J. M. Labavitch2, and D. M. Barrett3. (1) Dept. Food Science and Technology, University of California, Davis, One Shields Ave, Davis, CA 95616, (2) Dept. of Pomology, (3) Dept. Food Science and Technology Texture is a key quality attribute of raw tomatoes since they are often used as ingredients in other products and undergo further thermal processing. Tissue softening results from the loss of turgor pressure and occluded air, degradation of cell wall polysaccharides, and loss of cellular compartmentation. Maintenance of textural integrity of tomatoes during processing is a major concern for the industry and it has been traditionally accomplished by addition of calcium chloride solutions. The objectives of this work were: 1) to determine the effect of calcium treatments on turgor pressure of processing tomatoes, and 2) to determine the turgor contribution to calcium-induced tissue firming. Pericarp discs from Hypeel 45 tomatoes were treated with calcium chloride and/or mannitol solutions of different concentrations. Turgor pressure was measured directly by using a pressure probe while observing the sample with a microscope. A glass microcapillary probe containing silicon oil was inserted into the sample. Turgor pressure values were obtained by returning the meniscus to its original position using the interfaced pressure transducer. Puncture tests were used to determine textural parameters of the treated discs. Turgor pressure increased with increasing calcium chloride concentrations. In general, there was a positive correlation between turgor pressure and firmness values, with optimum values at 0.43% calcium chloride. However, an osmotic effect was apparent at calcium chloride concentrations equal or higher than 1% (w/v), when turgor pressure decreased. This study provides new insights into the role of calcium treatments in firming parenchymatous tissue. It is possible that such firming is not only due to calcium interacting with the pectins in cell walls and middle lamella as traditionally believed, but also to its potential contribution to the increase and/or maintenance of cellular turgor pressure.
Session 96, Fruit & Vegetable Products
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