Antimicrobial and water vapour barrier properties of sago starch films

07 Feb 2011

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Sago starch-based edible films prepared using microwave irradiation have demonstrated potential to be used as antimicrobial agents in active packaging, according to new research.

The study by L Ruchi et al also measured how water vapour barrier properties of the film were influenced by its thickness and the presence of chitosan micro particles.

The team said that previous research has shown that a range of organic and inorganic active agents can be incorporated into polymeric films to prevent microbial spoilage. Citing the use of natural plant extracts as “desirable”, the study used microwave induced synthesis of ethylenediamine tetra acetic acid (EDTA)-loaded sago starch edible films to increase its antimicrobial properties.

Sago starch is a substance isolated from sago palm and is well-distributed throughout South East Asia, said the paper published in the International Food Research Journal.

The team prepared plain sago starch (PSS) films using microwave-induced gelatization. The films were characterized by the FTIR, XRD, DSC and Tensile strength measurements. The equilibrium moisture content (EMC) data, obtained at 23C and 31C was interpreted in terms of the well known GAB isotherm model, said the researchers.

Vapour permeation

The degree to which water vapour seeped into the film was found to increase with temperature and relative humidity.

“This may be simply attributed to the fact that difference in vapour pressure across the film acts as a driving force for their permeation,” said the study.

The research also found that the rate of water vapour permeation showed a linear relationship with thickness of the films – with the amount of vapour penetration falling when the thickness of the film was increased.

Thicker films meant the water vapour had to travel further through the film and that more water molecules were trapped by polar groups within the film matrix thanks to the hydrophilic nature of the starch material, explained the study.

Vapour barrier properties were also enhanced by incorporating chitosan micro particles into the film, said the India-based group.

Antimicrobial effect

The researchers also found films loaded with EDTA increased their antimicrobial efficacy against E. coli. This was attributed to its “strong chelating tendency” that weakens the stability of the outer membrane of Gram-negative bacteria. The substance also “releases a large proportion of Gram-negative lipo-polysaccharide from the outer membrane and exposing hydrophobic phospholipids that increases the susceptibility to hydrophobic and cell wall degrading agents”, said the study.

“Water vapor permeation properties of sago starch-based edible films, prepared via microwave irradiation, are greatly influenced by temperature, relative humidity, presence of chitosan microparticles,” concluded Ruchi. “These films exhibit potential to be used as antimicrobial packagings to protect food stuff from microbial infections.”

Source: International Food Research Journal