Development and characterization of edible films and coatings from peanut protein

Food proteins have been used to develop edible and biodegradable protein films and coatings. However, limited information is available on the method to prepare peanut protein based films, and on their characteristics. Deposition technique (involving preparation of film forming solution with peanut protein (3%), adjusted to a pH of 9.0, cast on a non-stick flat surface and then dried at {dollar}90spcirc{dollar}C) was found to be most suitable. The films were tested for their permeability and mechanical properties. Attempts were made to enhance the film properties by using chemical, enzymatic and physical methods. The water vapor permeability improved slightly with the incorporation of 20% stearic acid (w/w of protein film). Several plasticizers including glycerin, sorbitol, polyethylene glycol and propylene glycol were used to improve handling ability and use of glycerin (glycerin:protein ratio of 3:5) showed the best performance. Peanut protein film was found to be very hydrophilic. Equilibrium moisture content of film increased sharply with an increase in RH from 75 to 93% at pH 7.5 and 9.0. Film thickness depended on the RH and film at pH 6.0 showed the greatest change in film thickness with increasing RH.; Diffusivity of sorbic acid in the film and model food (cheese analog) were estimated as 8.18-{dollar}rm 12.60times10sp{lcub}-12{rcub} msp2/s (Dsb{lcub}f{rcub}){dollar} and {dollar}rm 1.14times10sp{lcub}-10{rcub} msp2/s (Dsb{lcub}m{rcub}),{dollar} respectively. Lower value of {dollar}rm Dsb{lcub}f{rcub}{dollar} implied that peanut protein film can be used to retard migration of sorbic acid from surface to interior of the food. Mathematical models were developed to determine sorbic acid profiles in model food coated with peanut film. This implication was examined by a microbial study in which Staphylococcus aureus was used as challenge microorganism to determine the effectiveness of edible coating. Contrary to the prediction, the peanut protein film did not show any improvement in extending the shelf life of the model food when compared to the food dipped only in potassium sorbate. This could be attributed to the thickness of the film and increasing it might improve the performance of peanut protein film.