The incorporation of natural fillers such as seaweed may potentially enhance the properties of biopolymer films. In this study, we investigated the effect of seaweed powder as a bio-filler in alginate-based films at different concentrations (10, 30, and 50%, w/w alginate) and particle sizes (100 and 200 μm) on the mechanical, barrier, antioxidant, and antimicrobial properties of alginate which are essential for food packaging applications. Initially, mechanical properties of the alginate films prepared at different temperatures were evaluated to find the optimal temperature for preparing alginate solution. The addition of seaweed powder did not have any positive effect on the mechanical properties of the alginate films. However, the barrier (water vapor transmission rate) and antioxidant properties were improved with the addition of seaweed filler regardless of concentration. In addition, selected films were prepared in plasma-activated water (PAW). The mechanical properties (tensile strength, but not elongation at break) of the films prepared with PAW improved compared to the films prepared in distilled water, while a significant decrease was observed when incorporated with the seaweed filler. The films prepared in PAW also showed improved barrier properties compared to those prepared in distilled water. The antimicrobial activity of the alginate-seaweed film-forming solution was in general more pronounced when prepared with PAW and stored at 10 °C, particularly at the highest concentration of the film-forming solution (83.3% v/v). A more pronounced inhibitory effect was observed on the Gram-positive S. aureus than on the Gram-negative E. coli, which has been attributed to the different composition and structure of the respective cell walls. This study has demonstrated the potential of seaweed filler in combination with PAW towards enhanced functionality and bioactivity of alginate films for potential food packaging applications.

No abstract

Background: LEUCINE CARBOXYL METHYL TRANSFERASE 1 (LCMT1) transfers a methyl group from the methyl donor S-adenosylmethionine (SAM) to the catalytic subunit of PROTEIN PHOSPHATASE 2A (PP2A). This post-translational modification of PP2A is manifested throughout eukaryotes from yeast to plants and animals. Although highly conserved, the importance of the methylation is poorly understood. Since Arabidopsis plants with knocked out LCMT1 grow and develop fairly normally, we decided to search for conditions that may reveal the benefits of this regulation. We compared the effects of various stressful conditions on Arabidopsis wild type (WT) and a lcmt1 mutant possessing only non-methylated PP2A. Results: Seedlings were grown in Petri dishes for 5-12 days, or in rock wool and soil for up to 7 weeks. A significant increase in sodium concentration was found for lcmt1 relative to WT, but this was not linked with stressful conditions. Plants were exposed to variable levels of the chelator EDTA, iron, zinc, aluminium, heat, and hydrogen peroxide. The lcmt1 mutant was clearly more sensitive than WT to all the various stresses, as demonstrated by effects on seedling root growth and on shoots of rosette stage plants on rock wool. When omitting EDTA, expression of genes known as signature genes for iron deficiency, FIT1, bHLH100, IMA1, IRT1 was strongly enhanced in lcmt1. Although an iron starvation response was induced, Fe homeostasis was apparently maintained by slowed growth in lcmt1 and the Fe level related to tissue dry weight was not changed. Among genes induced in lcmt1 were also the Zn induced gene ZIF1, and heat shock protein HSP90-1. Concentrations of non-iron transition metals, Cu, Mn and Zn, increased significantly in response to lack of EDTA for both lcmt1 and WT tissue, and especially the growth of lcmt1 was strongly hampered. Conclusions: Presence of the LCMT1 gene was necessary to cope efficiently with an imbalance in the micronutrients, heat stress, and oxidative stress. Methylation of PP2A appears important to ameliorate the toxic effects of metals present in unfavourable high concentrations as well as heat or oxidative stress. The experiments establish LCMT1 as a key component in broad stress tolerance.