Abril Zoraida Graciano-Verdugo

Extruded films of blended chitosan, low density polyethylene and ethylene acrylic acid

The obtaining of chitosan extruded films was possible by using low density polyethylene (LDPE) as a matrix polymer and ethylene-acrylic acid copolymer as an adhesive, in order to ensure adhesion in the interphase of the immiscible polymers. The obtained blend films were resistant; however, a reduction in the mechanical resistance was observed as chitosan concentration increased. The thermal stability of the films showed a certain grade of interaction between polymers as seen in FTIR spectra. The antifungal activity of the extruded films was assessed against Aspergillus niger and high inhibition percentages were observed, which may be mainly attributed to barrier properties of the extruded films and the limited oxygen availability, resulting in the inability of the fungi to grow. A low adherence of fungal spores to the material surface was observed, mainly in areas with chitosan clumps, which can serve as starting points for material degradation.

Functionalization of chitosan by a free radical reaction: Characterization, antioxidant and antibacterial potential

Chitosan was functionalized with epigallocatechin gallate (EGCG) by a free radical-induced grafting procedure, which was carried out by a redox pair (ascorbic acid/hydrogen peroxide) as the radical initiator. The successful preparation of EGCG grafted-chitosan was verified by spectroscopic (UV, FTIR and XPS) and thermal (DSC and TGA) analyses. The degree of grafting of phenolic compounds onto the chitosan was determined by the Folin-Ciocalteu procedure. Additionally, the biological activities (antioxidant and antibacterial) of pure EGCG, blank chitosan and EGCG grafted-chitosan were evaluated. The spectroscopic and thermal results indicate chitosan functionalization with EGCG; the EGCG content was 25.8mg/g of EGCG grafted-chitosan. The antibacterial activity of the EGCG grafted-chitosan was increased compared to pure EGCG or blank chitosan against S. aureus and Pseudomonas sp. (p<0.05). Additionally, EGCG grafted-chitosan showed higher antioxidant activity than blank chitosan. These results indicate that EGCG grafted-chitosan might be useful in active food packaging.

Biochemical, Physical, Chemical, and Microbiological Assessment of Blue Shrimp (Litopenaeus stylirostris) Stored in Ice

Postmortem changes in blue shrimp (Litopenaeus stylirostris) muscle were studied on the basis of biochemical, chemical, physical, and microbiological changes during an 18 day storage period at 0°C. Adenosine 5′-triphosphate (ATP) content, breakdown products, K-value, pH, trimethylamine nitrogen (TMA-N), total volatile basic nitrogen (TVB-N), water holding capacity (WHC), color, and texture (shear force) changes were examined. Also, total mesophilic and psychrophilic bacterial counts were measured. K-value increased linearly (r2 = 0.98) from an initial value of 1.37 ± 0.59 to 59.42 ± 6.05% at Day 18. Spoilage indicators TVB-N and TMA-N increased from 29.56 ± 1.33 and 0.69 ± 0.25 to 39.04 and 2.04 ± 0.59 mg of N/100 g at Day 18, respectively; meanwhile, the total viable counts of mesophilic and psychrophilic bacteria increased from 3.48 ± 0.44 and 2.61 ± 0.29 log CFU/g to 6.27 ± 0.21 and 7.14 ± 0.39 log CFU/g, respectively, which indicated spoilage at the end of the storage period. The pH, texture, WHC, and color were affected (p < 0.05) during the storage period. Overall, results indicate that blue shrimp muscle quality was maintained for 12 days of storage in ice.

Preparation and characterization of films made of poly(l-lactic acid)/poly(l-lactic acid) grafted maleic anhydride/epigallocatechin gallate blends for antibacterial food packaging

The antimicrobial activity of films made of poly(l-lactic acid)/poly(l-lactic acid) grafted maleic anhydride(copolymer)/epigallocatechin gallate(EGCG) blend was determined. The effect of epigallocatechin gallate incorporation (0.03, 0.5, 5, and 10 wt%) as a natural antibacterial was determined by direct contact, solid and liquid culture media. The film antimicrobial activity was evaluated against two bacteria (gram-negative: Pseudomonas spp.; gram-positive: Staphylococcus aureus). The copolymer was prepared and characterized by Fourier transform infrared analysis and Molau test. Furthermore, the degree of grafting was determined. The epigallocatechin gallate migration profile through the films were determined and the minimum epigallocatechin gallate concentration in films required to show antibacterial activity was evaluated. The results showed that only the films with 10 wt% epigallocatechin gallate significantly affected (p < 0.05) the cell morphology and inhibited the growth of S. aureus (56% with copolymer and 55% inhibition without copolymer) and Pseudomonas spp. (28% inhibition, with and without copolymer). Incorporating copolymer inhibited the growth of Pseudomonas spp. and induced morphological changes in S. aureus. The diffusion coefficient was dependent on the presence of copolymer, which increased the epigallocatechin gallate release rate. Incorporating epigallocatechin gallate and copolymer modified the film properties. Fourier transform infrared analysis indicated hydrogen bonds which were attributed to the interaction between copolymer and epigallocatechin gallate. The results demonstrate the potential application of poly(l-lactic acid) (biodegradable polymer) and copolymers in active packaging, as well as the importance of incorporating epigallocatechin gallate as a natural antibacterial agent.

Engineering and antibacterial properties of low-density polyethylene films with incorporated epigallocatechin gallate

The antibacterial activity of low-density polyethylene/adhesive resin (10%)/epigallocatechin gallate (0.03, 0.5, 5, and 10%) extrusion cast films were evaluated against Staphylococcus aureus (gram positive) and Pseudomonas sp. (gram negative) via direct contact and in solid and liquid culture media. The epigallocatechin gallate concentration in the active films was established per the in vitro antibacterial analysis of pure epigallocatechin gallate against S. aureus and Pseudomonas sp. The epigallocatechin gallate migration profile and concentration required to inhibit bacterial growth in broth were determined. In addition, the effects of epigallocatechin gallate and adhesive resin on the mechanical, color, and thermal film properties were investigated. The results indicate that pure epigallocatechin gallate inhibited the growth of both bacteria. However, only the films with 10 wt% epigallocatechin gallate (with and without adhesive resin) induced morphological changes and inhibited the growth of S. aureus (p < 0.05). In addition, the films with 10 wt% epigallocatechin gallate (with adhesive resin) induced morphological changes in Pseudomonas sp. (p < 0.05). The adhesive resin increased the epigallocatechin gallate release rate in the migration profile (p < 0.05). The epigallocatechin gallate and adhesive resin modified the film properties (p < 0.05). Fourier transform infrared analysis indicated hydrogen bonds between the adhesive resin and epigallocatechin gallate. This study demonstrated that epigallocatechin gallate is a potential antibacterial agent and that adhesive resin provides advantages to active films.