Effect of microwave-assisted extraction pre-treatment on the yield and quality of agar from red seaweed (Gracilaria sp.)

Conventional agar extraction from Gracilaria sp. requires prolonged boiling at high temperatures (100 °C for 2 h) and often yields low-quality agar with unstable gel strength and inconsistent yield. Microwave-assisted extraction (MAE) offers an innovative and sustainable alternative to improve agar recovery from red seaweed while reducing processing time and energy consumption. This study employed a 2 × 3 factorial design using microwave power levels (136 and 440 W) and extraction time (10, 15, and 20 min) to evaluate their effects on the yield and physiochemical properties of agar. Following MAE pre-treatment, the seaweed was boiled (100 °C, 30 min), followed by frozen, thawed, and dried to produce agar, while control samples were proceeded without MAE treatment. Physicochemical characteristics analyses included agar yield, colour, gel strength, gelling and melting temperatures, pH, and syneresis, with functional groups characterised by FTIR spectroscopy. Results indicated that control agar and MAE-treated agar (136 W, 10 min) exhibited significantly higher (p < 0.05) gel strength than other treatments. Chroma values were unaffected by MAE, but hue angle decreased significantly (p < 0.05) at 136 W (20 min) and 440 W (15 - 20 min). Gelling temperature was significantly higher (p < 0.05) in MAE (136 W) samples, while melting temperature increased in MAE (440 W) treatments. Control agar showed significantly higher pH (p < 0.05) than MAE-treated agar, and syneresis was greatest at 440 W for 20 min. The optimised MAE condition (136 W, 10 min) produced agar with superior gel strength and substantially reduced processing time. These findings demonstrate the potential of MAE as a time and energy efficient pretreatment for agar extraction from Gracilaria sp.