Effect Of Ultrasonic On NMR Transition Point Of Sucrose Concentration And Structure Of High Methoxy Pectin

Pectin is a kind of linear polysaccharide polymer with stability, gelcharacteristics and emulsibility. Pectin has been widely used in food, medicine andcosmetic industries due to its natural, non-toxic and inexpensive properties. However,pectin has limitations on practical applications because of its large molecular weightand complicated structure varieties. Therefore, more and more researches are recentlyfocusing on the modification of pectin (modifying molecular weight or structure) inorder to meet the different needs. Ultrasound, as a new and non-pollution way tomodify the pectin, has been widely used in the studies of polysaccharide polymer. Inthe process of pectin gel, the pectin gradually transforms into gel state from the flowof abnormal. Such transition is mainly due to the change of the water distribution inthe pectin system.Nuclear magnetic resonance (NMR) is a technology to study water distributionin the food systems and fluid mechanics by the measurements of relaxationparameters T1and T2. The NMR technology used in the food systems utilizes theresonant features of hydrogen protons and hydrogen protons in the water from foodsprovide a favorable condition for the use of the technology. The nature property offood samples determines the relaxation time parameters T1and T2, which are closelyrelated to the physicochemical environment of the food systems. Therefore, it is aviable way to study the physicochemical properties of food samples by themeasurements and analysis of T1and T2. In addition, NMR technology also has therapid and non-destructive advantages, which are very important to food research.This study investigated the pectin by using the NMR technology for the firsttime. The relationship between relaxation time parameter T1and the co-solutionconcentration was established in order to study the effects of ultrasonic treatment onthe properties of pectin.The main results and conclusions were listed as follows:1The relationship between relaxation time T1and the gel property of highmethoxy pectin A good linear relationship between relaxation time T1and the pectin gel strengthhas been found, which means that NMR technology could be used in themeasurement of the pectin gel strength.2Effect of pH on NMR transition point of sucrose concentration of highmethoxy pectinpH could change the relaxation time T1of the pectin system. When the sucroseconcentration was under40%, T1value decreased as the increase of sucroseconcentration. When the sucrose concentration was40%~50%, the effect of the pHon T1values was reduced. And when the sucrose concentration was above50%, pHhad little effect on the T1values.The NMR transition point of sucrose concentration increased as the decrease ofpH value. Meanwhile, when pH value decreased, the change of the structure of pectinrequired higher concentration of sucrose. When the pH was2.0,2.5and3.0, thecorresponding transition points of sucrose concentration were62.11%（w/w,60.15%(w/w) and53.93%(w/w), respectively.3Effect of ultrasonic treatment on the water distribution and water migration inthe high methoxy pectinThe results of NMR study showed: As the time of gel processing increased, theflowing water in the pectin system gradually transformed into non-flowing water.Such transformation became faster when the time and power of the ultrasonictreatment increased.4Effect of ultrasonic treatment on NMR transition point of sucroseconcentration of high methoxy pectinUltrasonic treatment could reduce the strength of the gel of pectin. As the powerincreased, the strength of the gel decreased and the gel rate decreased.Both the time and power of ultrasonic treatment could affect the NMR transitionpoint of sucrose concentration. The NMR transition point of sucrose concentrationincreased as the increase of the time and power.5Effect of ultrasonic treatment on the molecular structure of pectinThe results showed that the molecular weight of pectin decreased when thepower and time of ultrasonic treatment increased. Meanwhile, within a certain period of time, the rate decreased and ultrasound degradation did not alter the structure ofthe pectin. The degree of esterification of the pectin decreased with the ultrasounddegradation. However, the pectin side chains were degraded. The stability ofinteraction between the molecules has been destroyed by the ultrasound degradationThis study was the first research on the properties of the pectin and modifiedpectin by using NMR technology for the measurement and determination of thelowest sucrose concentration that affects the pectin transformation into gel. This couldbuild a foundation for further applications of ultrasound in food industry in the future.