Effects of ultrasonic on structure, chain conformation and morphology of pectin extracted from Premna microphylla Turcz.

In this study, ultrasonic effects on structure, chain conformation and morphology of pectin extracted from Premna microphylla Turcz (PEP) and its probable mechanism were investigated. In the process of ultrasonic treatments, the chains of PEP were fractured rapidly within the initial 10 min and then the degradation rate gradually slowed down. The primary structure of PEP nearly remained unchanged after ultrasonic degradation. The rigid semi-flexible chains of PEP were converted into flexible chains, flexible coils, even compact coils. Sonication at low intensity for short time made PEP molecular chains curly collapse and tighten up. Long duration sonication at high intensity generated excessive small rigidness segments that mutually aggregated because of hydrogen bonds and inhibited the self-coiling of PEP chains. Atomic force microscopy (AFM) analysis supported the conformation transition of PEP chains. The results provided a fundamental basis for orientation design and process control of PEP structure.

Ultrasonic effects on molecular weight degradation, physicochemical and rheological properties of pectin extracted from Premna microphylla Turcz.

The high molecular weight and poor solubility of pectin extracted from Premna microphylla Turcz (PEP) limits its application. Therefore, in this paper, the degradation effects of PEP under ultrasound irradiation and the influences of ultrasonic on the PEP processing characteristics were investigated. The results indicated that the Mw of PEP decreased significantly with a narrow distribution after ultrasonic treatment. The degradation kinetics of PEP at different ultrasound intensities were sufficiently described by the 2nd-order kinetics eq. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis suggested that ultrasonic treatment destroyed the ordered structure inside the PEP, resulting in a looser microscopic morphology. Compared with the control, the thermal stability of PEP was significantly boosted after ultrasonic treatment. Rheological analysis illustrated that the sonicated PEP presented lower apparent viscosities than the original PEP. While the elasticity and thermal reversibility of the degraded products was enhanced. Ultrasonic treatment prominently weakened its shear thinning fluid behavior and thixotropy, thus improved its processing quality. Therefore, desirable PEP can be prepared by ultrasonic irradiation. The results can provide a reference for the development and application of PEP.