Factors that Affect Pellet Quality： A Review

Pelleting is the most popular thermal processing technique in poultry industry. Birds fed pelleted diets have greater feed intake and weight gain, and better feed conversion ratio. However, this better performance can only be achieved, if the pellets remain intact until they are ingested by the birds. Many factors may affect pellet physical quality, such as feed nutritional composition, ingredient particle size, conditioning temperature and time, feed moisture, etc.. Despite their importance, sometimes these factors are not managed properly, therefore, pelleted feed may not contain a high amount of intact pellets. In addition, the possible interactions among these variables may yield different responses in comparison with those expected when individual factors are considered. Very few experiments have been conducted to evaluate the impact of combined factors on pellet quality. This may be explained by the presence of many qualitative and quantitative factors in the manufacturing process. Research indicates that heat processing and feed formulation, especially fat inclusion level, are the factors which have the biggest influence on pellet quality. Strategies, such as the expansion process and fat inclusion restriction or post pellet liquid fat application could be implemented to produce high physical quality pellets. More research is needed to identify which factors have a positive or negative effect on pelleting process and to find new strategies to improve pellet physical quality.

Effect of Thermal Processing, Press Throughput and Roller-Die Gap on Physicochemical Properties of Broiler Feed Pellets

The present study aimed to evaluate the effect of thermal processing, press throughput and roller-die gap on pellet physical quality, protein solubility and starch gelatinization in a corn-soybean based broiler diet. The different processing factors were combined in a 2 × 5 × 3 factorial arrangement with eight randomized block consisting of eight production series： two thermal processing treatments （conditioning-pelleting or conditioning-expanding-pelleting）, five press throughput levels （18, 21, 24, 27 and 30 ton/h） and three roller-die gap （0.50, 0.75 and 1.00 mm）, which resulted in 30 different processed feeds. For determination of pellet durability index （PDI）, amount of intact pellets, degree of starch gelatinization and protein solubility, one composed feed sample was collected per treatment in each of eight production series, totaling eight replicates per treatment. Data concerning the amount of intact pellet and protein solubility in KOH were transformed using a variation of Box-Cox transformation in order to fit a normal distribution （P 〉 0.05）. Pellet physical quality was enhanced by conditioning-expanding treatment （P 〈 0.01）, narrower roller-die-gap （P 〈 0.01） and reduced press throughput （P 〈 0.01）. Protein solubility in KOH was impaired （P 〈 0.01） in the expander treatment and larger roller-die distance （0.75 mm and 1.00 mm） （P 〈 0.01）. Finally, greater starch gelatinization degree was achieved in expanded treatment （P 〈 0.01） and in 1.00 mm roller-die gap （P 〈 0.05）. The factors evaluated in this study resulted in interactions and significant effects on physicochemical properties of broiler feed pellets.

Impact of Particle Size, Thermal Processing, Fat Inclusion and Moisture Addition on Pellet Quality and Protein Solubility of Broiler Feeds

The present study evaluated the effect of feed particle size, thermal processing, several levels of fat inclusion and moisture addition on pellet quality and protein solubility in potassium hydroxide （KOH） in a corn, soybean meal and animal by products based broiler diets. The different processing factors were combined in a 2 x 4 x 4 x 2 factorial arrangement in an eight randomized block consisting of eight production series： two particle sizes （coarse： 1,041 microns and medium： 743 microns）, four fat inclusion levels at the mixer （15, 25, 35 and 45 g/kg of feed）, four moisture addition levels in the conditioner （0, 7, 14 and 21 g/kg of feed） and two thermal processing treatments （conditioner-pellet press treatment or conditioner-expander-pellet treatment） which resulted in 64 different processed feeds. For the determination of the pellet durability index （PDI）, the amount of intact pellets and protein solubility determinations, eight feed samples （replicates） were collected for each treatment. The data were transformed using a variation of Box-Cox transformation in order to fit a normal distribution （p 〉 0.05）. Adding moisture up to 21 g/kg of feed in the conditioner improved pellet quality of the diets （p 〈 0.05）. Expansion of diets before pelleting improved （P 〈 0.05） PDI and amount of intact pellets by 26% and 31%, respectively, as compared to a simple conditioning-pelleting feed processing. Expander treatment （at 110 ℃） decreased （p 〈 0.05） protein solubility in KOH from 686 g/kg to 643 g/kg total protein as compared to pelleting process （at 80-82 ℃）. The amount of intact pellets reduced from 773 g/kg to 746 g/kg of feed （/7 〈 0.05） as particle size increased from medium to coarse grinding. Pellet quality was significantly reduced with fat inclusion levels higher than 35 g/kg of diet.