Effects of extrusion specific mechanical energy and dryer conditions on the survival of Bacillus coagulans GBI-30, 6086 for commercial pet food applications

Abstract

In companion animal nutrition, probiotics (direct-fed microbials) are considered functional ingredients that benefit the gastrointestinal and immune health of the host. Bacillus coagulans GBI-30, 6086 is a spore-forming bacterial strain that has been reported to survive environmental stresses, heat processing, and extreme-pH conditions. Extrusion cooking is the most widely used method to produce commercial dog and cat foods, however the thermal and mechanical forces exerted during extrusion and drying present a challenge for guaranteeing the viability of live microorganisms after processing. Two experiments were conducted to determine the reduction in viability of the microorganism at graded flour inoculation levels (0, 6.2, 6.7, and 7.3 log10 colony forming units per gram (CFU/g)) subjected to extrusion cooking under varied levels of specific mechanical energy that were achieved by adjusting the extruder water input (10, 12, and 20 kg/h), and extruder screw speed (400, 500, and 600 rpm). A second experiment was conducted to determine the survival of the microorganism subjected to three dryer conditions (49 °C for 10 min; 107 °C for 16 min; and 66 °C for 46 min). Enumeration of bacterial colony forming units was performed on pre- and post-processing samples. Extrusion data were analyzed using a general linear model using the GLIMMIX procedure, and dryer data were analyzed as a completely randomized design with one-way analysis of variance (SAS v. 9.4, SAS Institute, Inc., Cary, NC) with significance accepted at a level of 95% confidence (α = 0.05). The results indicate that the low SME extrusion conditions (in-barrel moisture of 35%, extruder screw speed of 400 rpm, and specific mechanical energy of 129 kJ/kg) resulted in the greatest retention (P < 0.05), with a mean log10 reduction of viable spores of 0.44, 2.15, and 2.67 for the low, moderate, and severe extrusion conditions, respectively. Viability of the spores through three dryer conditions were observed to be similar across all treatments. This study also demonstrated that the greatest losses of viability occurred during extrusion rather than drying, and that in-barrel moisture and extruder screw speed are two operational parameters may be modified for the optimization of Bacillus coagulans survival in extruded foods.