Optimizing γ-aminobutyric acid content of fermented mulberry leaves by using Taguchi design and analyzing antioxidant capacity of whole extract

Abstract

This study utilized the Taguchi method to optimize the conditions for the hydrothermal extraction of γ-aminobutyric acid (GABA) from fermented mulberry leaves (FMLs) and evaluated the antioxidant capacity of FML extract powder (EP). Four extraction factors—the leaves-to-water ratio, temperature, duration, and pH—were considered, and a series of experiments were conducted in accordance with a Taguchi design. The results indicated that the optimal hydrothermal extraction conditions were a leaves-to-water ratio of 1:10, temperature of 100 °C, duration of 15 min, and pH of 4. Under these conditions, the GABA content of an FML infusion was 75.04 mg GABA/g EP. Further analysis revealed that the pH had the strongest impact on GABA extraction, with the corresponding signal/noise ratio ranging from 27.36 to 31.60. Additionally, experimental results for antioxidant capacity showed that the total phenolic and flavonoid content of the EP were 12.94 mg gallic acid equivalent/g EP and 81.77 mg quercetin equivalent/g EP, respectively. The IC₅₀ values for ABTS and DPPH free-radical-scavenging ability were 0.58 mg/mL and 0.20 mg/mL, respectively. The reducing power of the EP was 81.69 mg vitamin C equivalent/g EP. These findings provide an important foundation for further applications of FMLs.

Keywords:

• γ-aminobutyric acid
• Taguchi
• mulberry
• antioxidant

Reviewing Editor:

• M. Luisa Escudero-Gilete, Universidad de Sevilla, Spain

Subjects:

• Food Chemistry
• Food Engineering
• Food Additives & Ingredients
• Chemical Engineering

Authors contributions

Conceptualization: Yung-Sheng Lin and Chia-Hung Shih; investigation: Yung-Sheng Lin and Chia-Hung Shih; data curation: Ji-Hong Zheng, Cheng-You Chen, and Chiu-Hsun Liao; funding acquisition and supervision: Yung-Sheng Lin and Chia-Hung Shih; writing – original draft: Yung-Sheng Lin and Chia-Hung Shih; writing – review and editing: Yung-Sheng Lin and Chia-Hung Shih. All authors have read and agreed to the published version of the manuscript.

Ethical approval

Ethical approval was not required for the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data and materials are available on request.

Additional information

Funding

The was supported by National Science and Technology Council, Taiwan (112–2622-E-239-004).

Notes on contributors

Yung-Sheng Lin

Dr. Yung-Sheng Lin is a professor in Department of Chemical Engineering, National United University, Taiwan. He specializes in biomaterials and functional analysis in plant.

Ji-Hong Zheng

Ji-Hong Zheng holds a master’s degree in Department of Chemical Engineering, National United University, Taiwan.

Cheng-You Chen

Dr. Cheng-You Chen is a postdoctoral researcher and an adjunct assistant professor in Department of Chemical Engineering, National United University, Taiwan. He specializes in natural product extraction and detection technique.

Chiu-Hsun Liao

Chiu-Hsun Liao is an associate researcher in Miaoli District Agricultural Research and Extension Station, Ministry of Agriculture, Taiwan. She also holds a doctor’s degree in Ph.D. Program in Materials and Chemical Engineering, National United University, Taiwan.

Chia-Hung Shih

Dr. Chia-Hung Shih is the researcher and deputy director in Miaoli District Agricultural Research and Extension Station, Ministry of Agriculture, Taiwan. He is also an adjunct assistant professor in Department of Chemical Engineering, National United University, Taiwan. His area of research interest is agronomic and horticulture crops cultivation improvement, postharvest treatment and management.