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.

No abstract

Carboxymethyl chitosan (CMCH) from two molecular sizes (oligomer and polymer) and three different sources (shrimp, crab and squid) of chitosan were prepared by carboxymethylation reaction. The CMCH films were cast and their mechanical properties. For molecular sizes, the polymer CMCH films showed higher %elongation (%E) than those of oligomer CMCH films but had no effect on tensile strength (TS). The crab polymer CMCH films showed the highest TS. The different sources of chitosan had no influence on %E of CMCH films. The effect of plasticizers [glycerol (Gly), sorbitol (Sor) and polyethylene glycol 400 (PEG)] on mechanical properties of CMCH films was also investigated. Additions of Gly and Sor into films increased %E and reduced TS of CMCH films; however, films plasticizing with PEG showed no significant difference in mechanical properties. The crab CMCH films were selected to determine water vapor transmission rate (WVTR) at 25°C and 65%RH. The crab oligomer CMCH films showed higher WVTR than those of crab polymer CMCH films. Addition of Sor as plasticizer decreased WVTR of crab polymer and oligomer CMCH films whereas WVTR of films with Gly depended on molecular sizes of chitosan. Addition of PEG had no effect on WVTR of CMCH films.

Summary Improper cooling of cooked rice at an inappropriate temperature or leaving cooked rice at room temperature can cause food poisoning attributed to Bacillus cereus. Natural food preservative of either squid or crab polymer chitosan solution was added to examine their antibacterial properties against Bacillus cereus in cooked rice during storage at 37 and 4 °C. Both types of chitosan could retard the growth of B. cereus and total aerobic counts in cooked rice stored at 37 °C up to 1 day. In addition, the effect of chitosans on the physical and textural properties of cooked rice during storage was studied. Both chitosans slightly increased the moisture content of cooked rice. However, chitosans had no effect on the whiteness and hardness of cooked rice during storage (P > 0.05). Therefore, both chitosans have a potential to be used as food preservative for cooked rice with no negative effects on rice quality.

No abstract