Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2025 Jun 25;14(13):2245.
doi: 10.3390/foods14132245.

Biorefining of Walnut Shells into Polyphenol-Rich Extracts Using Ultrasound-Assisted, Enzyme-Assisted, and Pressurized Liquid Extraction Coupled with Chemometrics

Busra Acoglu Celik  1 , Muhammed Alpgiray Celik  2 , Laura Jūrienė  3 , Jovita Jovaišaitė  3 , Rita Kazernavičiūtė  3 , Erturk Bekar  1 , Perihan Yolci Omeroglu  1 , Petras Rimantas Venskutonis  3 , Senem Kamiloglu  1
Affiliations

Biorefining of Walnut Shells into Polyphenol-Rich Extracts Using Ultrasound-Assisted, Enzyme-Assisted, and Pressurized Liquid Extraction Coupled with Chemometrics

Busra Acoglu Celik et al. Foods. .

Abstract

Walnut (Juglans regia L.) shells are valuable agro-industrial by-products rich in polyphenols. This study investigated traditional (maceration) and advanced extraction techniques-ultrasound-assisted extraction (UAE), enzyme-assisted extraction (EAE), pressurized liquid extraction (PLE), and combined ultrasound-enzyme extraction (US-EAE)-to recover bioactive compounds from walnut shells. Extraction efficiency, total phenolic content (TPC), antioxidant capacity (ABTS•+, DPPH•), and polyphenol composition were evaluated. UPLC-ESI-MS/MS identified key polyphenols including ellagic acid, 4-hydroxybenzoic acid, vanillin, taxifolin, and quercitrin. The highest TPC (5625 mg GAE/100 g dw) was found in extracts subjected to US-EAE, in which ultrasound pretreatment (200 W, 10 min) was followed by enzymatic extraction using 0.06 mL/g Viscozyme® L at pH 3.5 and 45 °C. Under the same extraction conditions, UAE alone yielded the second highest TPC (4129 mg GAE/100 g dw). The highest ABTS•+ scavenging activity (14,478 mg TE/100 g dw) and enhanced DPPH• activity (45.38 mg TE/100 g dw) were also observed in US-EAE extracts. Chemometric techniques (PCA and HCA) revealed meaningful clustering and variation patterns among methods. These findings highlight the potential of walnut shells as a sustainable source of polyphenols and demonstrate the effectiveness of innovative extraction technologies in maximizing bioactive compound recovery for potential functional applications.

Keywords: Juglans regia L. shell; antioxidant capacity; combined extraction; green extraction; phenolic compounds; principal component analysis.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
(a) Walnut shell, (b) walnut shell powder, (c) PLE-EtOH, (d) PLE-AC, (e) EAE, (f) UAE, (g) US-EAE, (h) M-Water, (i) M-EtOH extractions.
Figure 2
Figure 2
Pearson correlation analyses.
Figure 3
Figure 3
Principal component analysis (PCA) loading plot of walnut shell extracts.
Figure 4
Figure 4
Principal component analysis (PCA) score plot of walnut shell extracts.
Figure 5
Figure 5
Cluster map of walnut shell extracts.
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Gullón P., Gullón B., Romaní A., Rocchetti G., Lorenzo J.M. Smart advanced solvents for bioactive compounds recovery from agri-food by-products: A review. Trends Food Sci. Technol. 2020;101:182–197. doi: 10.1016/j.tifs.2020.05.007. - DOI
    1. Sharif T., Bhatti H.N., Bull I.D., Bilal M. Recovery of high-value bioactive phytochemicals from agro-waste of mango (Mangifera indica L.) using enzyme-assisted ultrasound pretreated extraction. Biomass Convers. Biorefinery. 2023;13:6591–6599. doi: 10.1007/s13399-021-01589-5. - DOI
    1. Nguyen T., Vu D. A review on phytochemical composition and potential health-promoting properties of walnuts. Food Rev. Int. 2023;39:397–423. doi: 10.1080/87559129.2021.1912084. - DOI
    1. FAOSTAT Food and Agriculture Organization Corporate Statistical Database. [(accessed on 1 March 2025)]. Available online: https://www.fao.org/faostat/en/#search/walnut.
    1. Statista The Statistics Portal for Market Data. [(accessed on 1 March 2025)]. Available online: https://www.statista.com.

LinkOut - more resources