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Title: Histological effects of calcium chloride in stored apples

item Conway, William

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2008
Publication Date: 4/21/2008
Citation: Trentham, R.W., Sams, C.E., Conway, W.S. 2008. Histological effects of calcium chloride in stored apples. Journal of the American Society for Horticultural Science. 133:487-491.

Interpretive Summary: Many physiological and pathological disorders of apples are associated with the calcium content of tissues. We had previously pressure infiltrated calcium chloride solutions into apple fruit and significantly increased the tissue calcium content, which alleviated both physiological and pathological problems, but injury to the peel sometimes resulted. In this research project, we examined the possible basis of injury resulting from postharvest pressure infiltration of calcium chloride into "Golden Delicious" apples. We found that there was an alteration of the apple cuticle and underlying tissues which may lead to the fruit injury exhibited by a browning of the peel and therefore advise against the use of calcium chloride treatment of apples in some cases. This information is of use to the apple packing and shipping industry.

Technical Abstract: Mature apples, Malus domestica Borkh., cv. 'Golden Delicious' were immersed for 2 min in 0, 0.14, 0.27, or 0.41 mol L-1 (0, 2%, 4%, or 6%, respectively) aqueous solutions (w/v) of CaCl2 at 0 or 68.95 Kpa, and stored at 0°C. Histological samples of peel/cortex were taken at harvest and at four monthly intervals in storage. Paraffin sections were stained with either an aqueous mixture of alcian blue 8GX, safaranin 0 and Bismark brown Y, or with the periodic acid - Schiff (PAS) reaction. No histological difference was observed in fruit treated with 2% CaCl2. However, fruits infiltrated with 4% and 6% CaCl2, both with and without pressure, exhibited flattened epidermal cells and hypodermal cavities particularly after three and four months in storage. Cuticles were also affected at the 4 and 6% CaCl2 treatment levels (with regard to staining with Bismark brown), becoming more condensed and uniform. Both cuticle and hypodermis were stained differentially with PAS in the 6% CaCl2 treatment. All tissues, including the cuticle, were stained magenta red indicating a possible chemical alteration of the cuticle and the underlying tissue by calcium.