Evaluation of different pomegranate powder concentrations in active starch-based films

Pomegranate (Punica granatum) is a fruit from Central Asia. Due to its high antioxidant and anti-inflammatory activity, interest in nutraceutical and functional potential of pomegranate has increased. Some authors demonstrate the antioxidant potential of pomegranate alcoholic extract, however, it is not observed in the literature works adding pomegranate powder directly to films. Therefore, the aim of this study was to evaluate the properties and antioxidant activity of active starch-based films added with different concentrations of pomegranate mesocarp powder. Films were prepared by tape-casting technique using 5g starch/100g film-forming solution and 40g sorbitol/100g starch. It was produced films without addition of pomegranate powder (PP0), with 1g of pomegranate powder/100g of film-forming solution (PP1) and with 2g of pomegranate powder/100g of film-forming solution (PP2). The pomegranate mesocarp was manually separated from the fruit and dried at 40ºC, followed by trituration. The granulometry was standardized using a 100 MESH sieve, and the powder was stored in freezer at -18ºC in the absence of light until the films were produced. For the film production, starch was dispersed in aqueous solution containing sorbitol and pomegranate powder, using continuous mechanical stirring (600 rpm and 83.5ºC) until complete solubilization. The solution was cooled to 28ºC, poured on acrylic plates and dried at 40ºC in oven for 24 hours. Before the analyses, it was conditioned in desiccators with NaBr (58% RH, 25 ± 2ºC) for 5 days. Samples were submitted to the following tests: moisture content, contact angle, phenolic compound and antioxidant capacity. All the analyses were carried out in triplicates. Analysis of variance test (ANOVA) and Tukey's multiple range test was done to evaluate the significant differences between values using SAS (version 9.2, SAS Inc.). Moisture content of films was 15.9 ± 2.0g H2O/100g film, and there was no significant difference between films with or without pomegranate powder. For contact angle analysis, the pomegranate samples had no significant difference between them (74.1 ± 1.7º for PP1 and 69.0 ± 4.6º for PP2). However, there was an increase in films hydrophobicity when compared to films without pomegranate addition (PP0 = 61.7 ± 4.7º), possibly due to its hydrophobic character. PP2 assay showed higher concentration of total phenolics (3391± 171mg GAE/100g dry weight) compared to PP1 (575 ± 10mg GAE/g dry weight). For the antioxidant capacity, the same effect was observed to FRAP method, with 251.6 ± 6.2 and 1162.9 ± 109.1µmolTEq/100g dry weight for PP1 and PP2 assays, respectively. Although the results were below those found in the literature for pomegranate extract, the starch-based films added with pomegranate mesocarp powder showed antioxidant potential and can be applied in industry as active films.
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.