The effect of gelatin inclusion in high protein extruded pet food on kibble physical properties

Pet food is a $23 billion industry that continues to grow. Owners continue to humanize their pets and their dietary needs, thus the pet food industry tends to mirror human dietary trends. Currently, pet food is trending towards higher levels of protein, thus lower levels of starch. Decreasing starch, one of the main structure forming ingredients in extruded foods, creates issues of lower rates of expansion and decreased kibble durability. Consumers tend to dislike ingredients that do not serve a nutritional purpose; therefore, gelatin may be a plausible binding ingredient for high protein pet foods. Gelatin is a pure protein derived from collagen and is sold as a dry, odorless, tasteless powder. High-bloom gelatins find numerous uses in human food as a stabilizer, foaming agent, and capsule base among other uses. Low-bloom gelatin may find a value-added opportunity as a nutritional binder in pet food. Four extrusion experiments were performed to test this hypothesis. Experiment 1 compared gelatin at 0, 50, 100, and 150 g/kg inclusion and 150 g/kg gelatin at 3 different extruder screw speeds. Results showed a decrease in expansion but an increase in hardness and pellet durability index (PDI); however, there may have been inadequate preconditioning. It was unclear whether the decrease in expansion or presence of gelatin improved product durability. Experiment 2 analyzed two levels of gelatin, 0 and 100 g/kg, under two extruder screw speeds, 300 rpm and 500 rpm, and two hydration ratios, 170 and 280 g/kg. In this experiment, there were no differences in density, expansion, hardness, or PDI. This indicated preconditioning was more ideal and may indicate gelatin does not decrease product expansion. Experiment 3 analyzed two levels of gelatin, 0 and 100 g/kg, at two target densities, low and high. Results indicated that gelatin created a more expanded product when processed under similar conditions as a control formula. Experiment 4 analyzed different strengths of gelatin to determine if the low-bloom gelatin experiments were repeatable with more conventional strength gelatins. Treatments were a control with no gelatin, and a 100, 175, and 250 bloom gelatins. Results showed increased gelatin strength increased product expansion, likely through a foaming effect. However, durability declined with mid- and high-bloom gelatins; thus, low-bloom gelatin may be the most promising to improve product characteristics and preserve durability. Based on these experiments, low-bloom gelatin may find use as a nutritional binder in high protein pet foods.