Fig. 2 shows the light microscopy images of the ‘wet’ alginate films
with 2% added gelatin, soy protein and heated and unheated whey
protein. Images of the 1% protein films followed a similar pattern as
the 2% films except that less protein was visible in each film (figures
not shown). In the original color images the protein has been stained
with H&E and appears red in color, while the alginate stained with
PAS (for carbohydrates) appears purple in color. From the images
obtained, it appears that the heated whey protein (Fig. 2b) and soy
protein (Fig. 2c) formed larger protein clumps in the film, whereas
the unheated whey protein (Fig. 2a) and gelatin (Fig. 2d) seemed to
be more integrated in the alginate film. The increased integration of
unheated whey protein and gelatin into the alginate film could
explain why these two protein films (1% added) had the numerically
highest force, distance and work to puncture values of all the
alginate–protein films (Fig. 1, Table 1). This observation supports
the idea that the decrease in puncture strength of the films is a result
of proteins disrupting the alginate structure.