Nutrient Enhancement of Ground Sago (Metroxylon sagu Rottboll) Pith by Solid State Fermentation with Rhizopus oligosporus for Poultry Feed

Abstract

<p>Utilization of ground sago pith (GSP) as poultry feed ingredient is limited due to its high fibre content and negligible amount of protein. Hence, to enhance its utilization in poultry feed formulations, proper treatment method is necessary. This study was aimed to improve the nutritive value of GSP through solid state fermentation (SSF) using <em>Rhizopus microspores </em>var. <em>oligosporus</em> isolated from fermented cooked soybean seeds (local name <em>tempeh</em>). Fermentation of GSP was first conducted in 500 ml Erlenmeyer flasks to determine the optimized conditions. The substrate was prepared by mixing 50 g of GSP with 50 ml mineral solution and sterilized by autoclaving. The autoclaved GSP was inoculated with 5 ml of <em>R. oligosporus </em>spore suspension (1 × 10⁶ spore/mL). Four factors were investigated; moisture levels (35, 45, 55, 65 and 75 ml liquid/50 g substrate), pH values (4.5, 5, 5.5, 6, 6.5, 7 and 7.5), incubation temperatures [ambient temperature (28 ± 2), 30, 32.5, 35 and 37.5 °C] and inorganic nitrogen (ammonium sulphate, ammonium phosphate, ammonium carbonate, ammonium nitrate, ammonium chloride and ammonium molybdate) sources at 1 % (w/v) concentrations. Fermentation was conducted for 3 days and the parameters measured were reducing sugar, soluble protein and hydrolytic enzyme activities. The optimized conditions in the flask system were moisture level of 55 ml liquid/50 g substrate, citrate buffer pH 6.0, incubation temperature 30 °C and ammonium sulphate as the inorganic nitrogen source. A time course study for 7 days under optimized conditions showed that the reducing sugar reached maximum from 15.7 ± 0.5 to 183.8 ± 22.6 mg/g (dmb) at 1.5 days and the soluble protein increased from 9.5 ± 0.5 to 11.4 ± 0.7 µg/g (dmb) at the end of fermentation period. Amylase and CMCase activities were maximum at 3 days of fermentation; 3.58 0.73 ± and 4.44 ± 1.50 U/mg protein, respectively but FPase activities did not show apparent changes during the time course study. Using the optimized condition, scaling up in a horizontal drum laboratory fermenter was conducted using 3 kg of GSP in the presence of air at 4 L/min flow rate. The nutrient composition of fermented GSP produced in the fermenter was 89.1% dry matter, 3.4% crude protein, 5.5% crude fiber, 6.3% ash and 3495 kcal/kg gross energy as compared to 88.2% dry matter, 1.6% crude protein, 6.0% crude fiber, 5.3% ash and 3608 kcal/kg gross energy for untreated GSP. Solid state fermentation by <em>R. oligosporus</em> had increased the reducing sugar by 61%, glucose and fructose by more than 100%, soluble protein by 1% and amino acids by 1.5 to 38.2%. Cysteine which was undetected in the unfermented GSP was produced during the fermentation at a concentration of 222 ppm. The other amino acids were increased by 1.5% (arginine), 2.1% (glutamic acid), 16.2% (isoleucine), 16.5% (leucine), 6.2% (phenylalanine), 25.7% (proline), 38.2% (serine), 27.3% (threonine)and 5.7% (tyrosine). The results showed that the nutritive value of GSP was enhanced by solid state fermentation with <em>R. oligosporus</em>.</p>