Active films from rice starch/carboxymethyl chitosan (RS/CMCh) incorporated with propolis extract (ppl) were developed and characterized. The effect of the ppl content (0–10% w/w based on RS/CMCh) on the developed films’ properties were determined by measuring the optical, mechanical, thermal, swelling, barrier, antimicrobial, and antioxidant attributes. The thermal stability and biodegradability of the films were also investigated. As the ppl content increased, free radical scavenging and a* and b* color values increased, whereas luminosity (L*) and swellability of the films decreased. The active films with 5–10% ppl possessed antimicrobial ability against Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus). The active film with 10% ppl displayed increased flexibility and thermal stability, without a change in oxygen permeability. The results indicated that incorporation of ppl into RS/CMCh film could enhance the films’ antioxidant and antimicrobial properties.

Wolffia globosa is an interesting alternative plant-based protein source containing up to 40% protein dry weight. Dried duckweed protein extract (PE) was obtained using ultrasound-assisted extraction (UAE) before isoelectric precipitation (pH 3.5) to yield protein concentrate (PC) and protein solution (PS). The PC was hydrolyzed using Alcalase enzyme to obtain protein concentrate hydrolysate (PCH). Among all fractions, PCH exhibited antimicrobial properties by decreasing populations of Vibrio parahaemolyticus and Candida albicans at 0.43 ± 1.31 log reduction (66.21%) and 3.70 ± 0.11 log reduction (99.98%), respectively. The PE and PS also showed high solubilities at pH 8 of 90.49% and 86.84%, respectively. The PE demonstrated the highest emulsifying capacity (EC) (71.29%) at pH 4, while the highest emulsifying stability (ES) (~98%) was obtained from the PE and PS at pH 6 and pH 2, respectively. The major molecular weights (Mw) of the PE, PC, PCH and PS were observed at 25, 45, 63 and 100 kDa, with a decrease in the Mw of the PCH (<5 kDa). The PCH contained the highest total amino acids, with aspartic acid and glutamic acid being the major components. The results revealed the antimicrobial and functional properties of duckweed protein and hydrolysate for the first time and showed their potential for further development as functional food ingredients.

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Carboxymethyl chitosan (CMCH) from different chitosan sources (shrimp, crab, and squid) and molecular sizes (polymer and oligomer) were synthesized via carboxymethylation reaction. The CMCH films were prepared by solution casting. All the CMCH films had high water solubility, higher than 85% of the dry matter of the films. The sorption isotherm of the CMCH films was evaluated at several values of relative humidity (0% RH, 23% RH, 34% RH, 43% RH, 65% RH, 77% RH, and 86% RH) at 25 ± 1°C. The equilibrium moisture content values of all the CMCH films were low at lower aw but increased considerably above aw = 0.65. The sigmoidal moisture sorption isotherms of this product can be classified as type II. Understanding of sorption isotherms is an important prerequisite for the prediction of moisture sorption properties of films via moisture sorption empirical models. The experimental data were analyzed and fitted by the nine sorption models. The various constants determined by linear fitting of the sorption equation with r2 values were in the range of 0.7647 to 0.999. The GAB model was found to be the best-fitted model for CMCH films (aw = 0.23–0.86, 25 ± 1°C), and the model presented the optimal root-mean-square percentage error (%RMS) values when compared with other models. In conclusion, it can be stated that the GAB model was found to be better estimated for predicting the CMCH films than other models. Therefore, the constant derived from different sorption models were applied for use in terms of information and for the determination of the stability of CMCH packaging films for specific end uses.

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