Effect of Water Hardness on the Antioxidant Capacity of Reconstituted Pineapple Juice

Lee, Yan Zhen (2026) Effect of Water Hardness on the Antioxidant Capacity of Reconstituted Pineapple Juice. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Reconstituted juice is made by mixing fruit juice concentrate with water, which may vary considerably in mineral composition and levels of water hardness, affecting the antioxidant activity of the juice. This study evaluated the effects of different levels of water hardness on the antioxidant capacity of reconstituted pineapple juice. The reconstituted pineapple juice was prepared by mixing 1 part of concentrate with 9 parts of water of different hardness (100, 500, 1000, 2000 mg CaCO₃ equivalent/L). The effect of water types (distilled water, mineral water, simulated public water) on the antioxidant activity of the reconstituted pineapple juice were also evaluated. Antioxidant properties were determined using DPPH, ABTS, and total phenolic content (TPC) assays, over a 24-hour storage period at 8-hour intervals. Pineapple juice reconstituted with simulated public water showed a significant decrease in DPPH, ABTS and TPC values. Generally, DPPH activity increased over time, possibly due to the gradual release and enhanced accessibility of antioxidants from the juice matrix. Differences in water hardness levels ranging from 100 to 2000 mg/L did not show significant effects on the antioxidant activity after 24 hours of storage, suggesting that higher hardness concentrations may be required for further investigation. A strong positive correlation (r > 0.7) was observed among DPPH, ABTS, and TPC values, indicating consistent trends across the antioxidant assays. These findings suggested that mineral interactions may influence antioxidant activity of fruit juice and should be considered when interpreting functional claims of commercial juice products.