Effect of plasticizer on edible film properties

Hydrolyzed whey protein isolate (WPI) provided film water vapor permeability (WVP) and oxygen permeability (OP) similar to film WVP and OP from unhydrolyzed WPI at comparable plasticizer content. However, film solubility from hydrolyzed WPI was much higher than that from unhydrolyzed WPI. Moreover, hydrolyzed WPI required less glycerol to achieve the same film mechanical properties compared to unhydrolyzed WPI. Therefore, hydrolyzed WPI films with mechanical properties similar to those of unhydrolyzed WPI films had better oxygen barrier.; Beta-lactoglobulin (β-Lg) films with different plasticizers were investigated for mechanical properties and oxygen permeability. Propylene glycol (PG) plasticized β-Lg films were the most brittle, with mechanical properties independent of plasticize content, and provided excellent oxygen barrier. Films with other plasticizers studied (glycerol (Gly), sorbitol (Sor), polyethylene glycol (PEG 200 and PEG 400) and sucrose (Suc)) exhibited negative exponential dependence on plasticizer content for elastic modulus (EM) and tensile strength (TS), while they exhibited linear dependence on plasticizer content for percent of elongation (%E). The EM_o, TS_o and %E_o of β-Lg films without plasticize from the fitted equations were 1500 MPa, 37.28 MPa and zero, respectively. The k_EM, k_TS and k_E values determined from the fitted exponential relationships for EM, TS and fitted linear relationship for %E data, respectively, reflect the efficiency of plasticizers. Gly- and PG-plasticized films had similar OP values and their OP values were higher than OP of Sor-plasticized films. PEG 200- and PEG 400-plasticized films were the poorest oxygen barriers. Suc-plasticized films showed the best oxygen barrier. Linear empirical equations were fitted to OP vs. plasticizer content to determine plasticizer efficiencies for OP. Plasticizer efficiency ratios between mechanical and OP properties of β-Lg films (k_EM /k_OP or k_TS/k_OP) showed the relative efficiency of plasticizers in modifying mechanical and OP properties. A large ratio is desirable. The plasticizer efficiency ratios found were in the order Suc > Sor > Gly > PEG 200 > PEG 400.