Effect of amylose:amylopectin ratio and rice bran addition on starch films properties

Abstract

The influence of the amylose:amylopectin ratio on the properties of pea, potato and 30 cassava starch (with a high, intermediate and low amylose-amylopectin ratio, 31 respectively) films and the effect of the incorporation of rice bran of two different 32 particle sizes were studied. The structural, mechanical (elastic modulus, tensile 33 strength and percentage of elongation at break), optical (gloss and internal 34 transmittance) and barrier (water vapour permeability and oxygen permeability) 35properties of the films were analysed after 1 and 5 weeks under controlled storage 36 conditions (25ºC and 53%RH). The properties of the films were affected by both 37 amylose-amylopectin ratio and storage time. The high content of amylose gave rise to 38 stiffer, more resistant to fracture, but less stretchable films, with lower oxygen 39 permeability and greater water binding capacity. Although no changes in the water 40vapour permeability values of the films were observed during storage, their oxygen 41 permeability decreased. Throughout storage, films became stiffer, more resistant to 42 break, but less stretchable. Rice bran with the smallest particles improved the elastic 43 modulus of the films, especially in high amylose content films, but reduced the film 44 stretchability and its barrier properties, due to the enhancement of the water binding 45 capacity and the introduction of discontinuities (fibre particles) in the matrix. 46 47

Starch-Based Coatings for Preservation of Fruits and Vegetables

“…It has a granular structure and is composed of two macromolecules: amylose and amylopectin. Amylose is a linear polymer formed by glucose units linked by α-(1,4) whereas amylopectin is a highly branched polymer of glucose units with ramifications in α-(1,6) [35,36]. However, due to their hydrophilicity starch-based films/coatings exhibit water solubility and poor water vapour barrier properties [10].…”

“…In this sense, the adequate compatibilization of lipids and polymers and the final size distribution of lipid particles in the film also affect the coating's functional properties [44]. As concerns starch coatings, the amylose-amylopectin ratio affected their functionality due to the different structure of the films generated with high-amylose starch, where linear amylose, with regions of helical conformation, exhibited better packed domains in the matrix that is more crystalline in nature [36]. The authors of [37] found that coatings made with high-amylose starch better preserved the weight losses and firmness of strawberries for longer periods than coatings of medium-amylose starch.…”

Different strategies to improve the functionality of biodegradable films based on starch and other polymers

“…One part of the samples was stored under the same conditions for five weeks in order to perform the second series of analysis of stored films (Cano et al, 2014).…”

“…Native starch has a granular structure and presents different properties depending on its amylose/amylopectin ratio. Gelatinized starch shows a great filmforming capacity and, as is well known, its two macromolecules are responsible for starch recrystallization, which leads to changes in the mechanical response of starch-based films (Cano et al, 2014;Jiménez et al, 2012a;Talja et al, 2007). Besides their poor mechanical properties, starch films are highly hydrophilic in nature, which confers a great water vapour sensitivity and poor water barrier properties.…”

“…The high amylose content contributes to improve the tensile strength and gas barrier properties of starch based films (Wolff et al, 1951;Lourdin et al, 1995;Palviainen, et al, 2001;Cano et al, 2014). The very low oxygen permeability of high amylose starch films make them very useful for preservation of foods sensitive to oxidation process, such as meat and fish products or nuts.…”