Understanding interactions in wet alginate film formation used for in-line food processes

Recently some major sausage manufacturers have begun using co-extruded alginate, collagen, or alginate-collagen hybrid casings for their sausage products. Despite their use commercially, little is known about co-extruded alginate casings. In this study ‘wet’ alginate films (~ 90-95 % water content) were used as a model to understand co-extruded alginate casings. The study examined how various proteins (gelatin, soy, heated and unheated whey protein) and carbohydrates (iota- and kappa- carrageenan, low methoxyl pectin, modified and unmodified potato starch, commercial and extracted cellulose, or gellan gum) affected the mechanical and microstructural properties of ‘wet’ alginate films. Pectin, carrageenan, and modified potato starch increased (P < 0.05) the tensile elongation of the films, while soy protein, whey protein, modified potato starch, and cellulose decreased (P < 0.05) the puncture strength of the films. These results suggest that the mechanical properties of ‘wet’ alginate films can be altered by adding various proteins and carbohydrates to the films. The type of divalent cation (Ba2+, Ca2+, Mg2+, Sr2+, or Zn2+) used to gel the alginate and the presence of added NaCl in the alginate solution also affected (P < 0.05) the mechanical properties of the films. In the transmission electron microscopy images, certain added carbohydrates were easily identifiable in the alginate matrix by their unique morphology while others were less distinguishable. Another objective of the study was to explore the impact of drying the ‘wet’ alginate films. As expected, the dried films (conditioned at both 57 % and 100 % RH) had very different mechanical properties than their corresponding ‘wet’ films. Several peak shifts in the Fourier transform infrared spectra were observed when the alginate, alginate-pectin, and alginate-kappa-carrageenan solutions were gelled and dried. Differences (P < 0.05) in the mechanical properties of the dried films conditioned at 57 % and 100 % RH were also observed. These differences were attributed to the plasticizing effect of water in the films. Understanding the characteristics of ‘wet’ alginate films is important for future development and optimization of these films for use on food products, such as sausages.