Lifen Zhang

Effect of high-intensity ultrasound on the physicochemical properties and nanostructure of citrus pectin

BACKGROUND Modified pectin has been found to have various biological activities. The preparation of modified pectin is generally accomplished by either chemical or enzymatic depolymerisation processes, but both methods have several disadvantages. Ultrasound treatment is simple and requires shorter times and lower temperatures than conventional techniques used for processing plant materials. In recent years the application of ultrasound to modify polysaccharides has received increasing attention. The objective of this study was to use ultrasound to modify citrus pectin. RESULTS The average molecular weight of citrus pectin decreased under different ultrasonic conditions. The average molecular weight decreased from 464 to 296 kDa after 30 min of sonication. The degree of methylation of citrus pectin changed slightly and its monosaccharide component remained unchanged when high-intensity ultrasound was applied. The reduced (Gal+Ara)/Rha ratio after ultrasonication suggested degradation in the neutral sugar side chains of citrus pectin. Atomic force microscopy results confirmed the degradation of citrus pectin chains by ultrasound at nanolevel. CONCLUSION Ultrasound is an effective way to pretreat or modify pectin. The degradation of citrus pectin is due to the cavitational effects of ultrasound. Thus ultrasound may be useful in establishing environmentally friendly extraction and modification technologies for pectin.

Nanostructural difference of water-soluble pectin and chelate-soluble pectin among ripening stages and cultivars of Chinese cherry

Nanostructure of water-soluble pectin (WSP) and chelate-soluble pectin (CSP) of two Chinese cherry (Prunus pseudocerasus L.) cultivars (soft cultivar ‘Caode’ and crisp cultivar ‘Bende’) with two different ripening stages were characterised using atomic force microscopy. Both cultivars shared some common values of chain widths for WSP or CSP, and both pectins shared several values of chain widths including 37, 55 and 61 nm. The results indicate that different cultivars shared similar components of pectin, and cultivar textural difference might be related to the interaction between pectin and other cherry components or the dissociation of pectin. During ripening, the wide WSP and CSP gradually dissociate in width. The results demonstrated that the changes of WSP and CSP of Chinese cherry in widths were a dissociation process. †The manuscript is a contribution for the special issue on the 70th birthday of Prof. Dr. Atta-ur-Rahman.

Kinetics of Protein Extraction in Reverse Micelle

Sodium bis (2-ethylhexyl) sulfosuccinate (AOT)-sodium dodecyl sulfate (SDS)/isooctane-octanol reverse micelle extraction was tested an efficient and effective approach to separate peanut protein from full-fat peanut powder. Here, important kinetic factors including pH, ion strength, and temperature were studied during reverse micelle backward extraction. The extraction conditions were obtained by response surface experiments as follows: pH 7.5, ion concentration 1.1 mol/L at temperature 35°C. Under these optimum extraction conditions, the extraction rate of protein reached 79.03%. A model on the kinetic partitioning of peanut protein was also developed. The backward extraction in this reverse micelle system was controlled by interfacial resistance instead of diffusion resistance in reverse micelle and aqueous phase with the total mass transfer rate of 0.8×10−5 m3·s−1. A two-film theory may be the mechanism for flat interface. Results of mass transfer process are helpful for creating an reverse micelle extraction process, and used for purification of peanut proteins, promoting the development of food industry.

Effects of Extruded Soy Protein on the Quality of Chinese Steamed Bread

Five different extruded soy protein isolates (ESPIs) were obtained by extrusion and denoted by IVD1, IVD2, IVD3, IVD4, and IVD5. Then the SDS-PAGE results showed that the subunits of SPI decreased after extrusion, especially the subunits of 90.8, 32.8, and 31.3 kDa, whereas no isopeptide bond was formed. Although SPI improved both the development time (DT) and stability (S) of dough, ESPIs increased S but the DT decreased from 4.3 min to 1.8–2.0 min. Texture profile analysis (TPA) results showed that the hardness and chewiness of Chinese steamed bread (CSB) decreased in the order wheat flour

Combined effects of ultrasound and calcium on the chelate-soluble pectin and quality of strawberries during storage

The combined effects of ultrasound and calcium on the water migration, quality, and chelate-soluble pectin (CSP) properties of strawberries were investigated using nuclear magnetic resonance (NMR), high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM). The relationship among water migration, firmness, and CSP properties was also determined. Treatment with ultrasound and calcium (U + Ca) prevented the decrease in firmness of strawberries during storage (17 days). Measurements of physicochemical parameters (titratable acidity (TA), soluble solid content (SSC), CSP and Ca content) showed that U + Ca treatment maintained better fruit quality. AFM showed a larger percentage of wider and longer CSP molecules in the U + Ca group (width ≥90 nm; length ≥800 nm). These results, together with the HPLC results, confirmed that U + Ca treatment effectively inhibits CSP degradation. This study revealed that the application of ultrasound and calcium could preserve the quality of stored strawberries.

Comparison of Two Soy Globulins on the Dynamic-Mechanical Properties of the Dough and the Quality of Steamed Bread

To investigate the effect of the soy protein concentrate (CSP) and 7S and 11S soy globulin on wheat dough and steamed bread (SB), mixing properties of the dough were assessed by farinograph and dynamic-mechanical analyzer (DMA). The quality attributes of SB were assessed by texture profile analyzer (TPA), sensory analysis, and scanning electron microscope (SEM). The results showed that CSP, 7S, or 11S (each from 2.0 to 4.0%) significantly decreased gluten content (from 29.4 to 26.0, 36.7 to 31.8, and 31.6 to 30.7%), when those were added to wheat flour. The CSP/wheat dough stability was increased (from 6.5 to 8.4, 6.5 to 8.5, and 6.5 to 8.3 min) and the degree of softening was decreased (from 71.0 to 68.0, 71.0 to 64.0, and 71.0 to 62.0 min), but 7S or 11S had the opposite result. Moreover, the ratio of 7S and 11S has a significant effect on the quality of the dough. The storage modulus and loss modulus of soy/wheat dough decreased in the order of CSP, control, 11S soy globulin, and 7S soy globulin. The hardness, chewiness, and cohesiveness of SB decreased in the order of control, CSP, 11S soy globulin, and 7S soy globulin. Microstructure demonstrated that gluten network was interfered by SPC, 7S, and 11S soy protein, which was in agreement with the texture analysis index. The quality of SB with 3% 11S was the best in texture, microstructure, and sensory. These findings indicate that 11S has the potential to be used as a special soy protein for SB making.