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- Features and performance of edible films, obtained from whey protein isolate formulated with antimicrobial compoundsPublication . Ramos, Óscar L.; Silva, Sara I.; Soares, José C.; Fernandes, João C.; Poças, M. Fátima; Pintado, Manuela E.; Malcata, F. XavierThe goal of this research effort was to assess the efficacy of edible films produced fromwhey protein isolate (WPI) and glycerol, including incorporation of lactic acid (LA) and propionic acid (PRO), chitooligosaccharideswith nominal MW of 3 kDa (COS) and natamycin (NA) as antimicrobial agents. Their features were evaluated in vitro via agar diffusion and viable cell counting, against spoilage microflora often found contaminating cheese surfaces. The effect of incorporating the aforementioned compounds upon thickness, moisture content (MC), solubility (S), density (ρs),water activity (aw) and water vapor permeability (WVP), as well as upon tensile and optical properties of those films were also evaluated. Films formulated with LA, PRO or COS exhibited antimicrobial activity against all microorganisms tested, yet the viable cell count assay was more sensitive and reproducible. COS was the most active against Gram-negative bacteria, whereas LA was the most active against Gram-positive ones. NA was not active against bacteria, but displayed the strongest effect against yeasts. Incorporation of said antimicrobial compounds did not significantly (pN0.05) affect film thickness, yet it significantly (pb0.05) reduced tensile strength (TS). Incorporation of LA and NA in particular did not significantly (pb0.05) affect MC, S, ρs, WVP, elongation at break (EB) and Young's modulus (YM) values; however, a statistically significant increase (pb0.05) of MC, S andWVP, together with a statistically significant decrease (pb0.05) of ρs were attained upon incorporation of PRO or COS. Moreover, PRO produced the highest variation (pb0.05) in EB, TS and YM,whereas COS produced the highest change (pb0.05) in optical properties.
- Effect of whey protein purity and glycerol content upon physical properties of edible films manufactured therefromPublication . Ramos, Óscar L.; Reinas, Isabel; Silva, Sara I.; Fernandes, João C.; Cerqueira, Miguel A.; Pereira, Ricardo N.; Vicente, António A.; Poças, M. Fátima; Pintado, Manuela E.; Malcata, F. XavierThis manuscript describes the detailed characterization of edible films made from two different protein products e whey protein isolate (WPI) and whey protein concentrate (WPC), added with three levels of glycerol (Gly) e i.e. 40, 50 and 60%(w/w). The molecular structure, as well as barrier, tensile, thermal, surface and optical properties of said films were determined, in attempts to provide a better understanding of the effects of proteinaceous purity and Gly content of the feedstock. WPI films exhibited statistically lower (p < 0.05) moisture content (MC), film solubility (S), water activity, water vapor permeability (WVP), oxygen and carbon dioxide permeabilities (O2P and CO2P, respectively) and color change values, as well as statistically higher (p < 0.05) density, surface hydrophobicity, mechanical resistance, elasticity, extensibility and transparency values than their WPC counterparts, for the same content of Gly. These results are consistent with data from thermal and FTIR analyses. Furthermore, a significant increase (p < 0.05) was observed in MC, S, WVP, O2P, CO2P, weight loss and extensibility of both protein films when the Gly content increased; whereas a significant decrease (p < 0.05) was observed in thermal features, as well as in mechanical resistance and elasticity e thus leading to weaker films. Therefore, fundamental elucidation was provided on the features of WPI and WPC germane to food packaging e along with suggestions to improve the most critical ones, i.e. extensibility and WVP.