Fabrication and characterization of zein/ethyl cellulose composite film and its application as the coating for enhancing the storage stability of nut-containing jams

A zein/ethyl cellulose (EC) composite film was prepared for aqueous systems, with mechanical properties, water solubility, and oil permeation as evaluation indicators. The optimal conditions were zein/EC mass ratio of 1: 9, ethanol concentration of 93 mL/dL, 0.3 g/g glyceryl dioleate (GD), and curing temperature of 60 °C. Under these conditions, after one-month water soaking, the film showed a tensile strength of 11.61 MPa and an elongation at break of 43.60%, with no obvious oil permeation within one week. The film exhibited low water solubility with values ≤ 0.010%. FTIR analysis indicated zein and EC were physically combined; SEM analysis showed GD improved their compatibility, presenting more uniform surface; water contact angle analysis demonstrated composite film exhibited good hydrophobicity; and DSC analysis revealed composite film possessed better thermal stability. The film acted as a coating to apply in walnut, hazelnut, and peanut chunks for nut-containing jam preparation. A 3-month storage experiment at 25 °C showed the coating reduced the average oil seepage rate of jams from 1.97% to 0.18%, effectively inhibiting oil seepage; acid value and peroxide value of oils in all samples met the limits regulated by the National Standard. This coating significantly improves the storage stability of nut-containing jams in aqueous systems.