88C-22 |
Use of confocal microscopy to correlate microstructure and properties of different whey protein-based edible films. |
M. S. ZUTARA, Dept. of Nutrition and Food Sciences, University of Vermont, 221 Terrill Hall, Burlington, VT 05405 and H. Chen, Dept. of Nutrition and Food Sciences. Microstructural information of the interactions of protein matrix and functional ingredients is fundamental to understanding and predicting the performance of protein-based edible films. Laser Scanning Confocal Microscopy (LSCM) is one of powerful techniques to study material microstructures. The objectives of this work were (1) to examine the distribution of hydrophobic additives in different whey protein-based films using LSCM, and (2) to correlate structural information with film functional characteristics. Whey protein concentrate (WPC, 76.5% protein), and whey protein isolate (WPI, 93.6% protein) films were made of two different protein:lipid ratios (2:0 & 2:1). Three lipids, namely beeswax (BW), milkfat of high melting point (MFHM), and milkfat of very high melting point (MFVHM), were used. Samples for confocal imaging were stained by dipping a piece of film (0.5cm x 1.0cm) in 4ml of 1:1 mix of FITC (0.025% in water) and DiI (0.025% in a 1:1 water DMSO mix) solution for 20min. Dyed samples were then washed in 3:1 water:DMSO solution for 20min to eliminate residual dye. The confocal images of the films were immediately obtained using a Noran Oz system. Film water vapor permeability (WVP), moisture content (MC), tensile strength (TS) and elongation (EL) were also evaluated. All experiments were carried out in triplicates. Confocal results revealed that different lipids were distributed differently throughout the protein matrix. BW was distributed more discretely and crystalline-like while milkfat was more amorphous and clustered. Lipids were better spread out in WPI than in WPC films. WVP and EL of BW composite films were significantly (P<0.000l) lower than milkfat films. Structural observations correlate with film WVP and mechanical values. Moisture values of composite films were significantly lower than simple protein film. Confocal technique can effectively differentiate the film structures containing different lipids.
Session 88C, Food Engineering: Physical and Chemical Properties
|