Effects of Oven Drying and Freeze Drying on the Antioxidant, Antimicrobial, and Color Properties of Avocado (Persea Americana) Seed for Potential Food Applications

Tong, Suet Ling (2026) Effects of Oven Drying and Freeze Drying on the Antioxidant, Antimicrobial, and Color Properties of Avocado (Persea Americana) Seed for Potential Food Applications. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

The increasing global demand for avocado has led to a rise in agricultural waste, particularly avocado seeds, which contribute to environmental concerns. However, avocado seeds are known to be rich in bioactive compounds and may serve as a potential source of natural food additives and colorants for food applications. Drying is an important processing method for converting agricultural by-products into valuable materials. However, it may influence their functional properties. Therefore, this study aimed to compare the effects of oven and freeze drying on the phytochemical content, antioxidant activity, antimicrobial activity, and colour properties of avocado seeds. Two drying methods were applied: oven drying (85℃) and freeze drying (-101℃) for 24 hours. The extracts were analyzed for total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, antimicrobial activity using the disc diffusion method, and color characteristics. Freeze-dried samples exhibited higher TPC (11.06 ± 0.01 mg GAE/g), TFC (58.48 ± 0.64 mg QE/g), and antioxidant activity (24.10 ± 0.26%) compared with oven-dried samples. In addition, freeze-dried samples demonstrated stronger antimicrobial activity against both Gram-positive bacteria (Staphylococcus aureus: 12.92 ± 1.06 mm; Bacillus cereus: 14.82 ± 0.84 mm) and Gram-negative bacteria (Escherichia coli: 8.51 ± 0.72 mm), with the highest inhibition observed at 100 mg/mL. Colour analysis further showed that freeze-dried samples were lighter and more yellow, indicating higher L* and b* values than oven-dried samples. This may be attributed to the low-temperature conditions of freeze-drying, which reduce thermal degradation and oxidation of bioactive compounds while enhancing the release of phenolic compounds through ice crystal formation. Overall, these results suggest that freeze-drying is a more effective method for preserving bioactive compounds, antioxidant capacity, antimicrobial activity, and colour properties of avocado seed, highlighting its potential as a natural food ingredient.