March 14, 2023 3 min to read

Improving rice protein hydrolysates film by various strategies

A series of articles, development of rice protein hydrolysates-based films.

A. Chitosan/rice hydrolysate/curcumin composite film: Effect of chitosan molecular weight

The composite films were prepared by adding rice protein hydrolysate (RH) into chitosan (CH). Effect of four different chitosan molecular weights (MW, 0.8- 1.0, 30, 100, 300 kDa) was evaluated and curcumin was further incorporated into the film to enhance its bioactivities. With increasing MW (<100 kDa), moisture, solubility and water vapor transmission marginally decreased while tensile strength increased. Rice hydrolysate improved the film solubility and extensibility. All films showed extraordinary extensibility ranging from 180.26% to 204.08%. DSC confirmed MW did affect the thermal stability. The lower MW, the higher antioxidant activity of the CH/RH films. The 30 kDa CH/RH film exhibited higher antibacterial activity against both E. coli and S. aureus. Curcumin effectively improved both antibacterial and antioxidant activity of the CH/RH films. Hence, chitosan molecular weight must be chosen carefully according to its application and incorporation of protein hydrolysate into film would be an efficient strategy to modify film performance.

B. Characterization of Rice Protein Hydrolysate/Chitosan Composite Films and Their Bioactivities Evaluation When Incorporating Curcumin: Effect of Genipin Concentration

The effect of genipin (GP) concentrations on the structural, mechanical, and water barrier properties of chitosan (CS)/rice protein hydrolysate (RH) composite films was investigated for further incorporating of curcumin. GP increased the stability of CS/RH conjugate in solution. The degree of CS/RH crosslinking depended on genipin concentration, as indicated in particle size and UV spectra. At optimal genipin concentration (0.4 mg GP/g total biopolymers), the CS/RH film had the lowest moisture content (10.67%) and water vapor transmission rate (829.35 g/m(2)center dot 24 h.). Genipin could enhance the tensile strength and thermal stability of the CS/RH films depending on GP addition concentration. With an increased amount of GP, the DPPH scavenging activity decreased due to the cross-linking of antioxidant peptides, and the E* value increased indicating the significant color differences caused by increasing GP. Notably, the addition of curcumin had a positive effect on the DPPH scavenging activity and antimicrobial activity of the CS/RH films. Curcumin-loaded CS/RH films had higher antibacterial activity against S. aureus than E. coli. In general, the suitable addition content of GP was a promising and green strategy to improve the properties of the CS/RH films.

C. Development of chitosan/rice protein hydrolysates/ZnO nanoparticles films reinforced with cellulose nanocrystals

In the present work, the composite films were obtained by the solution casting method from chitosan and rice protein hydrolysates, reinforced with cellulose nanocrystals (CNC) of different contents (0 %, 3 %, 6 % and 9 %). The influence of different CNC loadings on the mechanical, barrier and thermal properties was discussed. SEM showed the formation of intramolecular interactions between the CNC and film matrices, leading to more compact and homogeneous films. These interactions had a positive influence on the mechanical strength properties, which was reflected in higher breaking force of 4.27 MPa. The elongation dwindled from 132.42 % to 79.37 % with increasing CNC levels. The linkages formed between the CNC and film matrices reduced the water affinity, leading to a reduction in their moisture content, water solubility and water vapor transmission. Thermal stability of the composite films was also improved in the presence of CNC, by increasing maximum degradation temperature from 311.21 to 325.67 °C with increasing CNC contents. The strongest DPPH inhibition of the film was 45.42 %. The composite films exhibited the highest inhibition zone diameter against E. coli (12.05 mm) and S. aureus (12.48 mm), and the hybrid of CNC and ZnO nanoparticles exhibited stronger antibacterial activity than their single existent forms. The present work shows the possibility of obtaining CNC-reinforced films with improved mechanical, thermal and barrier properties.