Plant-based polymer as a thermoresistant carrier of phytase in Nile tilapia (Oreochromis niloticus) diets

A biodegradable soybean oil-based polymer produced following the Green Chemistry principles, was assessed as a thermoresistant vehicle of phytase aiming to improve the enzyme stability during fish diet processing. Juvenile Nile tilapia (70 ± 4.3 g) were submitted to a digestibility assay designed in a factorial model (3 ×2) to assess the polymer efficiency. The treatments comprised the combination of three phytase inclusion methods with two feed processing methods. The inclusion methods of phytase were: CPP- coating post processing, in which the enzyme was spread on top of pellets after processing, PAE- polymer associated to enzyme, which was adsorbed by the polymer and included in the ingredients mash prior feed processing and NE- no enzyme inclusion, playing a control role as phytase was not included. The feed processing methods were extrusion (120 °C) or pelleting (40 °C), exposing the polymer to different temperatures. Phytase was supplemented at 1500 units kg−1 using the CPP or PAE methods. There was a significant interaction for the apparent digestibility coefficient (ADC) values of phosphorus (P), calcium (Ca) and Ash (P < 0.05). CPP resulted in higher ADC values for P and Ca, compared to PAE and NE in extruded diets (P < 0.05). The PAE method resulted in higher ADC values of P, Ca, and Ash than NE in extruded diets (P < 0.05). In pelleted diets, PAE resulted in higher ADC values for P and Ca, and a similar ADCAsh in comparison to CPP (P < 0.05). As verified in extruded diets data, the polymer partially protected phytase from heat denaturation, resulting in higher ADC values in comparison to NE (P < 0.05). The polymer improved phytase effects in pelleted diets probably by reducing degradation in fish stomach. These results suggest that the polymer may be a potential protective carrier of phytase and other thermolabile additives in extruded and pelleted diets.