Use of Gelatin as a Strengthening Agent in Dry Extruded Pet Food

Abstract Text: Recent pet food innovations have increased protein and decreased cereal inclusions in diets, which has diminished product durability and negatively changed texture. Low-bloom gelatin is a pure protein that is used to improve some pelleted feeds.  The objective of this project was to determine the effect of low bloom gelatin (Pro-Bind Plus 100) on kibble physical properties. Two experiments were conducted on a Wenger X-20 single screw extruder. In Exp. 1, a total of 6 total treatments were extruded: 0, 5, 10, or 15% gelatin inclusion at 400 RPM and 15% gelatin inclusion at 300 or 500 RPM. Chicken by-product meal was removed to add gelatin and maintain an iso-starch formulation. In Exp. 2, a total of 6 treatments were extruded: 0 vs. 10% gelatin inclusion; 300 vs. 500 RPM; and 15 vs. 30% hydration ratio, meaning the ratio of water added in the extruder versus the preconditioner. Extrudates were analyzed for moisture, expansion ratio, specific length, piece density, hardness (TA-XT2, Stable Micro Systems), and pellet durability index (PDI; Holmen NHP 100, Tekpro). Results were analyzed using the GLIMMIX procedure of SAS. Product hardness showed a good positive correlation with PDI. Hardness and PDI improved with gelatin inclusion (P < 0.05; 5.15 vs 9.35 kg; 64.5 vs. 96.9%). It was surmised that the increase in kibble strength and durability was caused partially by the strengthening effect of gelatin on the solid matrix. Lower product expansion also had an important role in increasing hardness and durability, as radial expansion ratio increased at 10% gelatin inclusion (P < 0.05; 4.27 vs. 6.65 mm²/mm²) but decreased at 5 and 15% gelatin inclusion (P < 0.05; 4.27 vs. 3.31 or 2.40 mm²/mm², respectively). Increase in screw speed from 300 to 400 rpm and decrease in hydration ratio from 30% to 15% (impying greater degree of pre-conditoning) led to a slight increase in expansion ratio, suggesting that altering processing parameters may overcome the negative imapct of gelatin on radial expansion. Additionally, specific length (a measure of longitudinal expansion) increased at 15% gelatin inclusion (P < 0.05; 42.11 vs. 48.30 mm/g), and as less of the total water content was added in the extruder (p<0.05; 37.62 mm/g vs. 41.16). These results suggest that gelatin had a binding effect on finished product. This binding may be helpful in high protein formulation, especially those reducing the use of functional cereal grain starches.

Keywords: gelatin, pet food, extrusion