Conjugation of soy protein isolate (SPI) with pectin: effects of structural modification of the grafting polysaccharide.

Recently, there has been a great interest in enhancing the emulsifying properties of soy protein isolate (SPI) by Maillard reaction. As a commonly-used grafting polysaccharide, pectin has proved useful in modifying proteins. However, effects of its structural characteristics on conjugation are still not fully understood. To address this problem, we employed alkaline or/and enzymatic treatments to modify pectin and obtained three modified samples. Structural characteristics of pectin, including the molecular weight, degree of methoxylation and acetylation, and monosaccharide compositions were measured. When conjugated with SPI, pectin with lower molecular weight and less main chains induced higher conjugate yield. Fluorescence intensity and surface hydrophobicity of all conjugates markedly reduced compared to the original SPI, suggesting a more loosened protein structure after Maillard reaction. In this study, the enzymolysis pectin proved an optimum grafting polysaccharide considering the simple preparation procedures and the highest emulsifying properties of its resulting conjugates.

Development of pullulan/carboxylated cellulose nanocrystal/tea polyphenol bionanocomposite films for active food packaging.

In this study, novel active films based on pullulan and carboxylated cellulose nanocrystal (C-CNC) incorporated with tea polyphenol (TP) was prepared by solution casting method. The effect of TP addition on the microstructural, mechanical, barrier, optical, functional properties of the resultant pullulan/C-CNC/TP (PC-TP) bionanocomposite films was systematically evaluated. Scanning electron microscopy showed that an appropriate TP adding was well distributed within the PC-TP bionanocomposite matrix. Fourier-transform infrared further revealed that new hydrogen bond was formed among the pullulan, C-CNC, TP. Addition of TP at an appropriate level (3%, w/w, on a dry basis of the weight of pullulan and C-CNC) led to stronger intermolecular interactions and more compact microstructure, and thus enhanced the water barrier properties, thermal stability and tensile strength of the resultant bionanocomposite films. Nevertheless, overloading of TP in the bionanocomposite films might produce some aggregations and thus have negative effects on their performance. In addition, the incorporation of TP significantly improved the UV-barrier properties, antioxidant activity and antimicrobial activity of PC-TP bionanocomposite films, while induced a decrease in the transmittance. These results revealed that PC-TP bionanocomposite films with TP at appropriate levels had potential to be used as active food packaging.

Dry heating and annealing treatment synergistically modulate starch structure and digestibility.

To modulate starch digestibility, dry heating combined with annealing treatment was employed to synergistically modulate structure and digestibility of normal maize starch (NMS) and potato starch (PS). Dry heating decreased starch molecular weight and created small molecular fractions with suitable chain length, resulting in starch better rearrangement during annealing treatment. Accordingly, after dry heating combined with annealing treatment starches had the highest pasting temperature, the thinnest and the thickest of crystalline lamellae for NMS and PS, respectively, and the highest ordered structures of cooked-starch compared with single dry heating or annealing modified starches. The results revealed that the synergistic modification altered starch lamellar thickness and increased double helices orders. Thereby, dry heating combined with annealing treated starches exhibited the lowest enzymatic digestibility with increased ca. 7.90% of slowly digestible starch for NMS or elevated ca. 5.04% of resistant starch for PS. The differential changes caused by dry heating combined with annealing treatment between NMS and PS were comprehensively discussed and the difference should result from the different starch crystalline structure and average chain length. This study provides a promising pathway for modulating starch structures and enzymatic digestibility.

Synergistic effect of hydrothermal treatment and lauric acid complexation under different pressure on starch assembly and digestion behaviors.

To control starch digestion, debranched high amylose maize starch (dG50) was forced to re-assemble through hydrothermal treatment combined with lauric acid (LA) complexation under high pressure (dG50-LA-HP) and atmospheric pressure (dG50-LA-AP). Both dG50-LA-HP and dG50-LA-AP complexes showed B + V hybrid crystalline structures, but mainly V-type for dG50-LA-AP and apparently B + V-type for dG50-LA-HP. Besides, those two type complexes significantly decreased starch digestibility, and the dG50-LA-HP changed in a higher magnitude since dG50-LA-HP contained more compact and ordered aggregates. The different starch assembly behavior under synergistic effect of hydrothermal treatment and LA complexation combined with different pressure should be responsible for the variation in starch digestibility. The formation of B-type crystallite contributed to the increase of slowly digestible starch, whereas the type I and type II starch-LA inclusion complexes increased the resistant starch fractions. This study offers a novel understanding on starch reassembly under hydrothermal treatment and lipid complexation combined with different pressure.