Comparative study on physicochemical properties of starch films prepared from five sweet potato (Ipomoea batatas) cultivars

Five different sweet potato (Ipomoea batatas) cultivars (Daeyumi, Gogeonmi, Sincheonmi [SCM], Singeonmi, and Sinyulmi [SYM]) were used to extract sweet potato starch (SPS) for developing starch-based films. After the chemical composition and amylose contents of all SPSs were evaluated, the morphological, moisture, mechanical, and barrier properties of the SPS-based films were investigated. As one of the film characteristics, the X-ray diffractograms revealed that the SCM-based film with the highest amylose content (26.34%) had the highest relative crystallinity (24.31%). The SCM-based film also showed higher tensile strength (3.05-fold) and elastic modulus (2.38-fold) than the SYM-based film with the lowest amylose content (21.84%). The water vapor and oxygen permeabilities of the SPS-based films were negatively correlated with the amylose content. Thus, the SCM-based film was less permeable for water vapor (3.16-fold) and oxygen (1.81-fold) than the SYM-based film. These results demonstrated that the sweet potato cultivar, especially the amylose content, plays a significant role in determining the physicochemical properties of the SPS-based films.

Development of chia seed (Salvia hispanica) mucilage films plasticized with polyol mixtures: Mechanical and barrier properties

Food packaging is one of the main contributors to the high rates of environmental contamination; therefore, interest has emerged on the use of biopolymers as alternative materials to replace conventional food packaging. Chia seed (Salvia hispanica) is recognized by having a high content of a polysaccharide called mucilage. The aim of this study was to evaluate the feasibility using of chia seed mucilage (CSM) and a polyol mixture containing glycerol and sorbitol for the development of films. CSM films with higher sorbitol content showed superior tensile strength (3.23 N/mm²) and lower water vapor permeability (1.3*10^-9 g/m*s*Pa), but had poor flexibility compared to other treatments. Conversely, high glycerol content showed high elongation at break (67.55%) and solubility (22.75%), but poor water vapor permeability and tensile strength. Film formulations were optimized implementing a factorial design according to response surface methodology. Raman spectra analysis showed shifts from 854 to 872 cm^-1 and 1061 to 1076 cm^-1, β (CCO) modes, indicating an increase in hydrogen bonding, responsible for the high tensile strength and decreased water vapor permeability observed in this study. The optimum conditions of polyol concentration were 1.3 g of glycerol and 2.0 g of sorbitol per g of CSM. Based on these results, chia seed mucilage can successfully be used to develop biofilms with potential to be used in drug delivery and edible food coating applications.

Effect of starch type on the physico-chemical properties of edible films

Food preservation is mostly related to packaging in oil-based plastics, inducing environmental problems, but this drawback could be limited by using edible/biodegradable films and coatings. Physical and chemical properties were assessed and reflect the role of the starch type (wheat, corn or potato) and thus that of the amylose/amylopectin ratio, which influences thickness, colour, moisture, wettability, thermal, surface and mechanical properties. Higher amylose content in films induces higher moisture sensitivity, and thus affects the mechanical and barrier properties. Films made from potato starch constitute a greater barrier for oxygen and water vapour though they have weaker mechanical properties than wheat and corn starch films. Starch species with higher amylose content have lower wettability properties, and better mechanical resistance, which strongly depends on the water content due to the hydrophilic nature of starch films, so they could be used for products with higher water activity, such as cheese, fruits and vegetables. It especially concerns wheat starch systems, and the contact angle indicates less hydrophilic surfaces (above 90°) than those of corn and potato starch films (below 90°). The starch origin influences optical properties and thickness: with more amylose, films are opalescent and thicker; with less, they are transparent and thinner.

Innovative thermoplastic chitosan obtained by thermo-mechanical mixing with polyol plasticizers

Chitosan shows a degradation temperature lower than its melting point, which prevents its development in several applications. One way to overcome this issue is the plasticization of the carbohydrate. In this work plasticized chitosan was prepared by a thermo-mechanical kneading approach. The effects of different non-volatile polyol plasticizers (glycerol, xylitol and sorbitol) were investigated. The microstructure and morphology were determined using FTIR, XRD, TEM and SEM in order to understand the plasticization mechanism. Sorbitol, which is the highest molecular weight polyol used, resulted in plasticized chitosan with the highest thermal, mechanical and rheological properties. On the other hand, the sample plasticized with glycerol, the lowest molecular weight polyol, had the most important amorphous phase content and the lowest thermal, mechanical and rheological properties. Also, when the polyol content increased in the formulation, the plasticized chitosan was more amorphous and consequently its processability easier, while its properties decreased.