Effects of Ultrasound-Assisted Extraction Parameters on Antioxidant Properties, Antimicrobial Activity, and Colour Retention of Curry Leaf (Murraya Koenigii) Extract

Yap, Shuang Yun (2026) Effects of Ultrasound-Assisted Extraction Parameters on Antioxidant Properties, Antimicrobial Activity, and Colour Retention of Curry Leaf (Murraya Koenigii) Extract. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Driven by the clean-label movement, the food sector seeks natural alternatives to replace synthetic additives. Curry leaf (Murraya koenigii) provides potent antioxidants that are efficiently recovered via ultrasound-assisted extraction (UAE). However, the lack of optimized and standardized extraction parameters limits its commercial application in the food industry. This study aimed to determine the effects of UAE extraction temperature and time on the antioxidant properties, antimicrobial activity, and colour retention of curry leaf extract to identify most desirable extraction conditions. Curry leaf powder was subjected to the UAE at temperatures (30 °C, 40 °C, 50 °C) and times (15, 30, 45 minutes). Extracts were analyzed for Total Phenolic Content (TPC), DPPH and ABTS free radical scavenging activities, antimicrobial efficacy (against S. aureus and E. coli), and colour retention (CIELAB). For extraction yield, 30 °C for 45 min (21.69 ± 0.30%) was considered the most desirable extraction condition due to its lower energy requirement and highest yield at this temperature, although extraction temperature showed no significant effect on yield. On the other hand, results indicated that extraction time and temperature have significant effects on the TPC, antioxidant activities, and colour retention of the extracts (p < 0.05). The most desirable condition for TPC and ABTS was 50 °C/15 mins, yielding 1993.70 ± 7.30 mg GAE/100g and 2705.82 ± 10.88 mg TE/100g (52.96 ± 0.22%), respectively. While 50 °C/30 mins maximised DPPH activity (666.89 ± 2.90 mg AAE/100g; 29.37 ± 0.14%) and colour retention (L* = 21.40 ± 0.10; a* = 23.03 ± 0.15; b* 30.17 ± 0.38; C* = 37.97 ± 0.29 and h° = 52.60 ± 0.50). No antimicrobial activity was observed, likely due to solvent-solute polarity mismatch and insufficient antimicrobial compound extracted. Overall, UAE conditions significantly influenced the antioxidant properties and colour retention of curry leaf extracts, while no antimicrobial activity was observed. Results indicated UAE parameters lack a one-size-fits-all approach. Hence, it must be application-tailored to optimize either mass yield, phenolic recovery, or colour stability, thereby providing a viable strategy for producing high-quality natural food additives.