Author(s)

Hannah Han¹, Shusheng Wang², Milan Rakita³, Yanting Wang⁴, Qingyou Han³, Qin Xu^4*

¹Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, CA, USA.
²School of Life Sciences, Jilin Agricultural University, Changchun, China.
³School of Engineering Technology, Purdue University, West Lafayette, IN, USA.
⁴School of Agriculture, Purdue University, West Lafayette, IN, USA.

Walnuts are one of nature’s more waste-heavy products. 67% of the nut is shell and husk, low value by-products that are rich in phenolic compounds. The phenolic compounds extracted from walnut shells are potentially good natural sources of antioxidants for the food and pharmaceutical industries. In this study, phenolic compounds were extracted using an ultrasonic bath, an ultrasonic probe and a standard shaking method. The extraction yield achieved with an ultrasonic probe was 51.2 mg GAE/g DW, two times higher than both the shaking method and the ultrasonic bath method which were 20.6 mg GAE/g DW and 25.8 mg GAE/g DW, respectively. Phenolic extraction was further improved by a size reduction of the walnut shells. The best extraction yield of 52.8 mg GAE/g DW was attained when the particle size was between 45 - 100 mesh. The ultrasonic probe treatment is the best method for extraction of phenolic compounds from walnut shells. Scanning electron microscopy (SEM) imaging indicated that the ultrasonic probe treatment could better rupture the hard structure of the cells, increasing the penetration of solvents and thus the extraction yield.

Walnut Shell, Ultrasound-Assisted Extraction, Total Phenolic Content (TPC), Particle Size, SEM Analysis

Han, H. , Wang, S. , Rakita, M. , Wang, Y. , Han, Q. and Xu, Q. (2018) Effect of Ultrasound-Assisted Extraction of Phenolic Compounds on the Characteristics of Walnut Shells. Food and Nutrition Sciences, 9, 1034-1045. doi: 10.4236/fns.2018.98076.