Extrusion studies of mixtures containing certain meat offals: Part 1-Objective properties

A study was made of thermoplastically extruded products prepared from soy grits incorporating varying percentages of offal. Beyond 35% incorporation no satisfactory extrudate could be prepared. A comparison was therefore made of the expansion ratio, density and hydratability of extrudates prepared from mixes containing 20% and 35% of bovine or porcine offal with those containing soy grit alone. The offal sources consisted of untreated or alkali-extracted bovine and porcine lung and bovine tripe (rumen and reticulum) and bovine tripe extracted by sodium dodecyl sulphate (SDS). Under the determined optimum operating conditions, extrudates from all offal/soy mixtures had lower expansion ratios and rehydratability than those from soy grits alone. Nevertheless, mixtures containing 20% or 35% alkali-extracted offal protein expanded more (greatest expansion at 170°C), had lower density and greater hydratability than those containing these proportions of untreated offal or SDS-extracted offal protein. (The latter expanded most between 175-180°C.) Whereas the incorporation of SDS-extracted bovine or porcine lung protein failed to yield textured extrudates, the incorporation of SDS-extracted bovine tripe protein at the 20% level did so. Effects due to source were otherwise small.