## 1 Introduction  
Sunflower seeds are not only an important source of oil, but also a high-quality source of protein, which have the advantages of few anti-nutritional factors, low allergenicity, reasonable and balanced amino acid (AA) composition, etc. The protein content of sunflower seed is between 20% and 30%, and its proper utilization can effectively alleviate the protein resource shortage [1]. After enzymatic sunflower seeds oil extraction, the alkali-soluble acid precipitation method is usually used to extract sunflower seeds protein (SSP) in the byproduct. However, there is abundant content of chlorogenic acid (CGA) in the by-product [2]. Under high pH conditions, the oxidatively polymerized CGA dimers tend to covalently bind to the polar groups of the protein, thereby generating green quinones [3] and affecting the sensory quality, functional properties and nutritional value of SSP [4, 5, 6]. This is the reason why SSP has been regarded as waste or low valuable animal feed, leading to financial loss and low utilization. CGA is an ester formed by the condensation of a molecule of caffe acid and a molecule of quinic acid [7]. It is widely found in natural plants, such as sunflower seeds, eucommia, coffee beans and potatoes [8, 9, 10]. The CGA content in sunflower seeds can reach 71.4% of the total phenolic content in sunflower seeds and play a critically negative role in protein quality.  
In view of the above situation, the removal of CGA by physical and chemical methods in the initial stage was not able to completely remove all CGA in SSP, and the unacceptable green color still existed after treatment [11]. The enzyme biodegradation is becoming an emerging way to eliminate hazardous substances in food byproducts. An _Aspergillusstrain_ SD14 was isolated from CGA-rich soil, which could produce an enzyme with CGA hydrolytic activity. Whole genome sequencing (WGS) is the individual genome sequencing of species with unknown genome sequences, which can detect all the genetic information in the genome [12]. The whole genome sequencing analysis showed that the _Aspergillus strain_ SD14 is a strain of _Aspergillus aculeatus_, and the fertile esterase is an enzyme capable of hydrolyzing CGA. Two genes encoding ferulic esterase were also annotated. This is consistent with some previous reports stating that some types of ferulic esterase can hydrolyze CGA [13; 14; 15]. However, in previous reports, CGA was only used as one of the substrates to react in the specific analysis of ferulic acid esterase (FAE), and very little attention has been paid to further practical application research. Because of its low enzyme activity (4.35 U/g) and long fermentation cycle (11 d), the wild ferulic esterase from _Aa_SD14 was difficult to apply in the food industry. There is an urgent need to obtain efficient expression of engineering bacteria, by means of genetic engineering, to shorten fermentation time, to reduce fermentation cost, and to further improve CGA hydrolysis activity.  
In the present research, we aimed to express these two novel genes (GME3292 and GME11122) encoding FAE efficiently in engineered _E. coli_ BL21 (DE3), and to disclose the possibility of their heterogeneous expression. The recombined ferulic acid esterases (reFAEs) were characterized and applied to confirm its CGA hydrolysis activity. To the best of our knowledge, this is the first study in which ferulic esterase has been used in an attempt to remove CGA from SSP.