How Does Alkali Aid Protein Extraction in Green Tea Leaf Residue: A Basis for Integrated Biorefinery of Leaves.

Chen Zhang,Johan P M Sanders,Marieke E Bruins,Ting T Xiao

doi:10.1371/journal.pone.0133046

Chen Zhang, Johan P M Sanders + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0133046

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Abstract

Leaf protein can be obtained cost-efficiently by alkaline extraction, but overuse of chemicals and low quality of (denatured) protein limits its application. The research objective was to investigate how alkali aids protein extraction of green tea leaf residue, and use these results for further improvements in alkaline protein biorefinery. Protein extraction yield was studied for correlation to morphology of leaf tissue structure, protein solubility and hydrolysis degree, and yields of non-protein components obtained at various conditions. Alkaline protein extraction was not facilitated by increased solubility or hydrolysis of protein, but positively correlated to leaf tissue disruption. HG pectin, RGII pectin, and organic acids were extracted before protein extraction, which was followed by the extraction of cellulose and hemi-cellulose. RGI pectin and lignin were both linear to protein yield. The yields of these two components were 80% and 25% respectively when 95% protein was extracted, which indicated that RGI pectin is more likely to be the key limitation to leaf protein extraction. An integrated biorefinery was designed based on these results.

Highlights

Leaf protein has been considered as an additional protein source since 1960s [1, 2]
As protein yield increased with the increase of temperature (23% obtained by 25°C, 38% obtained by 60°C, and 84% obtained by 95°C), these figures indicate a correlation of leaf tissue disruption with protein yield under alkaline conditions
As galactose and arabinose majorly originate from rhamnogalacturonan I (RGI) pectin [20, 34], these results indicate a linearity of RGI pectin yield to protein yield, and RGI may be the limitation to protein extraction

Summary

Introduction

Leaf protein has been considered as an additional protein source since 1960s [1, 2] These proteins can be used in food [3], animal feed [4], or when hydrolysed to amino acids for Nchemicals bulk chemicals [5]. Applications of these proteins are limited by its low cost-efficient production [6], in extraction processes. This limitation was preliminarily solved by using alkaline conditions at higher than 60°C [7] Drawbacks of this technique are overuse of chemicals and low quality of (denatured) protein. To overcome these drawbacks and design an integrated process for protein and other products, the basis of alkaline protein extraction in leaf should be better understood

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