20 wt% polyamide 12 （PA1212） pellets were dissolved in molten caprolactam. The caprolactam was then catalyzed at 180℃ and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the...20 wt% polyamide 12 （PA1212） pellets were dissolved in molten caprolactam. The caprolactam was then catalyzed at 180℃ and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6 （PA6） and PA 1212. Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder. Scanning electron microscopy （SEM） observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix, no phase-separation existed in the in situ blends. The results of thermal analysis by differential scanning calorimetry （DSC） showed that single melting peak and crystallization peak existed for the in situ blends, while two melting and crystallization peaks appeared for the mechanical blends. The in situ blend film and the mixed blend film, both cast from a dilute formic acid solution with a concentration of 0.5 g/L, remained similar crystallization and melting behavior as above. It is proved by solution 13C-NMR analysis that transamidation took place during the in situ blending, and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation. Furthermore, it is proposed that the interchange reaction between PA 1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.展开更多
Gluten is essential to the rheological and functional properties of wheat dough.Microbial transglutaminase is often used to enhance gluten functionality through cross-linking and,when combined with amine nucleophiles,...Gluten is essential to the rheological and functional properties of wheat dough.Microbial transglutaminase is often used to enhance gluten functionality through cross-linking and,when combined with amine nucleophiles,can reduce its immunogenicity.ε-Poly-L-lysine(ε-PL),a GRAS-status natural homopolymer of lysine with anti-microbial activity,can efficiently act as an amine nucleophile for transamidation,yet its effects on gluten microstructure and rheology remain unexplored.This study investigates the concentration-dependent impact of covalently linkedε-PL on gluten structure and functionality.Polymeric structure was analyzed using asymmetric flow field-flow fractionation,and rheological behavior was evaluated through small and large deformation tests.A preliminary antimicrobial assessment was also conducted.At a 1:1ε-PL:glutamine mol ratio,protein polymer size and resistance to extension increased,indicating a reinforced gluten network due to enhanced cross-linking.In contrast,a 5:1 ratio reduced polymer size and elasticity while enhancing extensibility,consistent with a plasticizing effect.These findings demonstrate thatε-PL modulates gluten structure and mechanics in a concentration-dependent manner.Moreover,ε-PL incorporation reduced yeast viability,suggesting added antimicrobial potential.Overall,this work provides new insights intoε-PL-mediated transamidation as a strategy to tailor gluten polymerization,dough rheology,and microbial stability.展开更多
基金This work was financially supported by the National Natural Science Foundation of China(No.50373037).
文摘20 wt% polyamide 12 （PA1212） pellets were dissolved in molten caprolactam. The caprolactam was then catalyzed at 180℃ and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6 （PA6） and PA 1212. Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder. Scanning electron microscopy （SEM） observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix, no phase-separation existed in the in situ blends. The results of thermal analysis by differential scanning calorimetry （DSC） showed that single melting peak and crystallization peak existed for the in situ blends, while two melting and crystallization peaks appeared for the mechanical blends. The in situ blend film and the mixed blend film, both cast from a dilute formic acid solution with a concentration of 0.5 g/L, remained similar crystallization and melting behavior as above. It is proved by solution 13C-NMR analysis that transamidation took place during the in situ blending, and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation. Furthermore, it is proposed that the interchange reaction between PA 1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.
基金the financial support from the Portuguese Foundation for Science and Technology(FCT)to CQ-VR(https://doi.org/10.54499/UIDB/00616/2020 and https://doi.org/10.54499/UIDP/00616/2020).
文摘Gluten is essential to the rheological and functional properties of wheat dough.Microbial transglutaminase is often used to enhance gluten functionality through cross-linking and,when combined with amine nucleophiles,can reduce its immunogenicity.ε-Poly-L-lysine(ε-PL),a GRAS-status natural homopolymer of lysine with anti-microbial activity,can efficiently act as an amine nucleophile for transamidation,yet its effects on gluten microstructure and rheology remain unexplored.This study investigates the concentration-dependent impact of covalently linkedε-PL on gluten structure and functionality.Polymeric structure was analyzed using asymmetric flow field-flow fractionation,and rheological behavior was evaluated through small and large deformation tests.A preliminary antimicrobial assessment was also conducted.At a 1:1ε-PL:glutamine mol ratio,protein polymer size and resistance to extension increased,indicating a reinforced gluten network due to enhanced cross-linking.In contrast,a 5:1 ratio reduced polymer size and elasticity while enhancing extensibility,consistent with a plasticizing effect.These findings demonstrate thatε-PL modulates gluten structure and mechanics in a concentration-dependent manner.Moreover,ε-PL incorporation reduced yeast viability,suggesting added antimicrobial potential.Overall,this work provides new insights intoε-PL-mediated transamidation as a strategy to tailor gluten polymerization,dough rheology,and microbial stability.
