The ultrasound technology as a novel non thermal physical processing

The ultrasound technology, as a novel non-thermal physical processing technology, has many applications in food [5] and its related fields [6]. Acoustic cavitation, resulting from the mechanical interaction between sound waves and bubbles in liquids, is regarded as the fundamental effect that is responsible for the initiation of most of the sonochemical reactions in liquids [7–10]. The collapse of cavitation bubbles, which are formed rapidly and exploded violently during sonication, generates violent physical forces, such as micro jets, shear forces, shock waves and turbulence [11,12]. The ultrasonic frequency is one of the factors that influence the yield and intensity of cavitation in liquids [13]. It was found that the ultrasonic cavitation yield can be enhanced by multi-frequency sonication [14,15]. Recently, the power ultrasound (20–100kHz) is widely employed in protein enzymolysis to produce bioactive peptides [16–19], improvement of the functional properties of proteins [20–23] and synthesis of lysozyme microspheres [24]. It is reported that power ultrasound pretreatment can improve the reaction rate of enzymolysis, and the conversion rate of substrate proteins, and the bioactivity of target products significantly [4,25,26]. Moreover, ultrasound treatment can lead to changes in the secondary structure [18,27] as well as in the microstructure of protein, resulting in the exposure of more hydrolysis sites to be accessible to protease [28,29]. However, systematic research on the molecular mechanism of ultrasound-accelerated enzymatic hydrolysis process of CGM is unavailable.

Materials and methods

Results and discussion

Conclusions
Multi-frequency power ultrasound (SFPU, SDFU) pretreatment can improve the enzymatic hydrolysis of CGM significantly. The molecular mechanism of multi-frequency power ultrasound which promoted enzymolysis includes the exposure of BTL-105 groups, redistribution of the secondary structure, decrease in the SS bonds content, and changes in the microstructures. In addition, it can BTL-105 be concluded from the results that it is better to take the hydrophobicity of a protein into consideration when choosing the type of ultrasound (bath or probe) because SDFU induced aggregation of zein was observed in the present study. Generally, the SFPU is superior to SDFU provided that the hydrophobicity of the protein is strong, otherwise the SDFU is more suitable. However, from the perspectives of energy efficiency, the SFPU pretreatment is still the best method.

Acknowledgements
The authors wish to express their appreciation for the support obtained from grant (2013AA100203) of the Project of National 863 Plan of China, National Natural Science Foundation of China (31471698, 31301423), Research-Innovation Program of Postgraduate in General Universities of Jiangsu (CXZZ13-0695), Natural Science Foundation of Jiangsu Province (BK2012708), Key University Science Research Project of Jiangsu Province (12KJA550001), Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

Introduction
The “extremely thin lamellae of carbon” [1], later called graphene, was prepared in 1962 by chemist Hanns-Peter Boehm [2] using a procedure based on the oxidation of graphite to graphite oxide, which was published in 1859 [3] and modified by Hummers in 1957 [4].
Edwards and Coleman [5] highlighted the different methods available for the synthesis of graphene and discussed the viability and practicality of using the materials produced via these methods for different graphene-based applications. The aim of that review [6] article was to provide a comprehensive overview of the scientific progress of graphene to date and evaluate its future prospects. Wu et al. [7] summarized the state-of-the-art self-assembly strategies that have been established to construct chemically modified graphene-based nanomaterials. The versatility of graphene-based devices goes beyond conventional transistor circuits and includes flexible and transparent electronics, optoelectronics, sensors, electromechanical systems, and energy technologies [8]. Machado and Serp [9] presented the most relevant synthetic routes to obtain graphene and focused attention on the properties and characterization techniques of graphene that are of relevance to catalysis, with emphasis on adsorption.