Ultrasonic Processing Induced Activity and Structural Changes of Polyphenol Oxidase in Orange (Citrus sinensis Osbeck)

Lijuan Zhu; Linhu Zhu; Ayesha Murtaza; Yan Liu; Siyu Liu; Junjie Li; Aamir Iqbal; Xiaoyun Xu; Siyi Pan; Wanfeng Hu

doi:10.3390/molecules24101922

Ultrasonic Processing Induced Activity and Structural Changes of Polyphenol Oxidase in Orange (Citrus sinensis Osbeck)

Molecules. 2019 May 18;24(10):1922. doi: 10.3390/molecules24101922.

Authors

Lijuan Zhu^{1

2}, Linhu Zhu^{3

4}, Ayesha Murtaza^{5

6}, Yan Liu^{7

8}, Siyu Liu⁹, Junjie Li^{10

11}, Aamir Iqbal^{12

13}, Xiaoyun Xu^{14

15}, Siyi Pan^{16

17}, Wanfeng Hu^{18

19}

Affiliations

¹ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. lijuanzhu2019@hotmail.com.
² Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. lijuanzhu2019@hotmail.com.
³ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. orion_zhu@webmail.hzau.edu.cn.
⁴ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. orion_zhu@webmail.hzau.edu.cn.
⁵ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. ayeshamurtaza@webmail.hzau.edu.cn.
⁶ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. ayeshamurtaza@webmail.hzau.edu.cn.
⁷ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. y20170022@mail.ecust.edu.cn.
⁸ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. y20170022@mail.ecust.edu.cn.
⁹ Key Laboratory of Structural Biology, School of Chemical Biology & Biotechnology, Peking University Shenzhen Graduate School, Shenzhen 518055, China. siyuliu@pku.edu.cn.
¹⁰ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. junjieli2019@hotmail.com.
¹¹ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. junjieli2019@hotmail.com.
¹² College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. aamirraoiqbal@webmail.hzau.edu.cn.
¹³ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. aamirraoiqbal@webmail.hzau.edu.cn.
¹⁴ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. xiaoyunxu88@gmail.com.
¹⁵ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. xiaoyunxu88@gmail.com.
¹⁶ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. drpansiyi.hzau.edu@outlook.com.
¹⁷ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. drpansiyi.hzau.edu@outlook.com.
¹⁸ College of Food Science and Technology, Huazhong Agricultural University, No.1, Shizishan Street, Hongshan District, Wuhan 430070, China. wanfenghu@mail.hzau.edu.cn.
¹⁹ Key Laboratory of Environment Correlative Dietology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, China. wanfenghu@mail.hzau.edu.cn.

Abstract

Apart from non-enzymatic browning, polyphenol oxidase (PPO) also plays a role in the browning reaction of orange (Citrus sinensis Osbeck) juice, and needs to be inactivated during the processing. In this study, the protein with high PPO activity was purified from orange (Citrus sinensis Osbeck) and inactivated by ultrasonic processing. Fluorescence spectroscopy, circular dichroism (CD) and Dynamic light scattering (DLS) were used to investigate the ultrasonic effect on PPO activity and structural changes on purified PPO. DLS analysis illustrated that ultrasonic processing leads to initial dissociation and final aggregation of the protein. Fluorescence spectroscopy analysis showed the decrease in fluorescence intensity leading to the exposure of Trp residues to the polar environment, thereby causing the disruption of the tertiary structure after ultrasonic processing. Loss of α-helix conformation leading to the reorganization of secondary structure was triggered after the ultrasonic processing, according to CD analysis. Ultrasonic processing could induce aggregation and modification in the tertiary and secondary structure of a protein containing high PPO activity in orange (Citrus sinensis Osbeck), thereby causing inactivation of the enzyme.

Keywords: aggregation; browning reaction; polyphenol oxidase; structural changes; ultrasonic processing.

MeSH terms

Catechol Oxidase / chemistry*
Catechol Oxidase / isolation & purification
Catechol Oxidase / metabolism
Circular Dichroism
Citrus sinensis / chemistry*
Citrus sinensis / enzymology
Enzyme Activation
Maillard Reaction
Molecular Weight
Particle Size
Plant Proteins / chemistry*
Plant Proteins / isolation & purification
Plant Proteins / metabolism
Protein Conformation / radiation effects*
Spectrum Analysis
Ultrasonic Waves*

Substances

Plant Proteins
Catechol Oxidase