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

The effect of storage time on the physical properties of pea starch (PS) and polyvinyl alcohol 17 (PVA) films and their blend was studied to develop biodegradable packaging materials for 18 food applications. To this end, an analysis was performed of the microstructural and physical 19 properties (solubility, moisture content, barrier, mechanical and optical properties) of PS, 20 PVA and PS:PVA films stored for five weeks (25ºC-53%RH). Whereas SEM micrographs 21 showed a homogenous appearance for PS films, PVA presented irregularities typical of 22 semi-crystalline structures. Blend films showed a structure which was more similar to PVA 23 films. After 5 weeks, the physical properties of PVA films did not change; in the case of PS, 24 however, the elastic modulus and tensile strength increased markedly but the stretchability 25 and gloss significantly decreased, which was associated with water loss in the starch matrix. 26All the physical properties of blend films remained unchanged throughout time, except the 27 elastic modulus and the tensile strength, which slightly increased. Therefore, the 28 incorporation of PVA into pea starch films improved their physical properties and inhibited the 29 changes that occurred in the starch matrix caused by ageing. 30

No abstract

16In order to obtain antimicrobial packaging films, starch-PVA-based films with silver 17 nanoparticles (AgNPs) have been developed and characterized as to their physical and 18 antimicrobial properties and silver release kinetics to polar (A, B, C and D1) and non-19 polar (D2) food simulants. Antimicrobial activity against two bacteria, Listeria innocua 20and Escherichia coli, and two fungi, Aspergillus niger and Penicillium expansum, was 21 studied. Silver-loaded starch-PVA films exhibited antimicrobial activity against the 22 tested microorganisms, which depended heavily on the concentration of AgNPs. Their 23 addition only led to notable physical changes in the colour and transparency of the 24 films, which underwent significant changes and turned brownish-yellow and opaque, 25 this being more notable when the silver concentration rose. Silver was released into 26 aqueous simulants in its entirety within the first 60 minutes of contact. In the non-polar 27 simulant (oleic acid), the release capacity of the films drastically decreased, being the 28 only case where the established limit (60 mg/Kg simulant) was met. As a consequence, 29 the use of the developed films as food packaging materials should be restricted to fat-30 rich foodstuffs. 31 32

The effect that the incorporation of different antimicrobial substances into S-PVA films had on their disintegration and biodegradation process was analyzed. To this end, starch, PVA and S-PVA films containing different concentrations of neem oil, oregano essential oil and silver nanoparticles were submitted to composting conditions in order to determine the disintegration and biodegradability percentages for 73 and 45 days, respectively. Additionally, thermogravimetric and structural analyses were also carried out throughout the composting period. The biodegradation and disintegration behavior of S-PVA films was intermediate between S and PVA films. The addition of neem and oregano essential oils slightly affected the biodegradation and disintegration profile of starch-PVA films, enhancing both disintegration and biodegradation levels. So, the presence of these antimicrobials did not compromise the compostable and biodegradable character of the starch-PVA blend films. Nevertheless, the biodegradation capacity of films containing 9.8 % silver species was seriously affected, reaching values of only 58% after 45 days of composting, despite their high disintegration capacity. Thus, lower silver concentrations are recommended in order to avoid possible alterations in compost microbial activity.