The number of bacteria in steam-pelleted or crumbled chicken food was compared with the number in individual ingredients and in mash. A few bacteria were detected in white-fish meal processed Alaska pollack. Highest yields were from alfalfa meal. Colonies numbering 3.5 x 10(3)-4.2 x 10(5) were obtained by heart-infusion agar culture, and 2.1 x 10(2)-7.0 x 10(4) with deoxycholate hydrogen sulphide lactose agar, from 1 g mash. After pelleting or crumbling the number of colonies in 1 g was reduced to 0-1.9 x 10(3) and 0-3.0 x 10(0) respectively. Bacteria in the lactose medium, mostly coliform, were observed in only 1 of 18 samples.
SummaryPellet feeds were prepared at 70, 80, 83 and 90°C under constant steam pressure of 4·0 kg/cm 2 • Under these conditions, the food received 10 seconds of heat treatment, but treatment at 90°C was found inappropriate since the food became slushy.Pelleting conditions examined in this study did not eliminate all contaminating bacteria, but coliforms from ingredients were killed when pelleting was conducted at over 80°C. Concentrations of vitamins were not decreased during pelleting. The optimum temperature for pelleting food is considered to be 83°C under the conditions investigated in this study.In a previous report (Furuta, Morimoto & Sato, 1980) Carlson, 1969;Quadri & Deyoe, 1975). Halls & Tallentire (1978) also found a marked reduction in the numbers of bacteria contaminating a commercial laboratory animal diet during the pelJeting process. However, agreement has not been reached on pelleting conditions such as temperature, pressure and period of steaming in the manufacture of formulated chicken food. This paper deals with the effect on the numbers of viable bacteria and on the vitamin content of food of steam supplied at various temperatures at a constant pressure during the pelleting process of chicken food.Materials and methods Formulated pelJet layer food which has been supplied to specified-pathogen-free (SPF) chickens maintained in the Poultry Disease Laboratory, National Institute of Animal Health, was used in this study. Composition of the food was presented in our previous report (Furuta et al., 1980). The mixer consisted of an insulated cylinder (90 cm in length, 23·5 cm in diameter) and 3 injecting nozzles distributed steam evenly in the cylinder. The pelJeting die (pelJet diameter, 3·5 mm) was attached to the outlet of the pelleting chamber. A chute was connected between the mixer and the pel1eting chamber. Temperature of the food in the pelleting chamber was nearly the same as that in the mixer. The time required for the food to pass from the inlet of the mixer to the outlet of the die was recorded.Bacterial counts and vitamin estimations were repeated on a total of 5 and 3 lots respectively, each lot of food consisting of 1 ton. Control samples for bacterial count and vitamin estimation were collected from 3 different parts of the mash prior to pelleting. 200 kg samples of the mash were processed at 70, 80 and 90°C, and the rest of the lot, i.e. 400 kg, was processed at 83°C. 3 pelJet samples of each lot, totalling more than 500 g, were collected for the determination at regular intervals just after the pelleted food ran out from the die.Bacterial counts were performed as described previously (Furuta et al., 1980), using heart-infusion (HI) agar for all bacteria and deoxycholate hydrogen sulfide lactose (DHL) agar for enteric bacteria. Enrichment culture was carried out using heartinfusion broth for cultivation of all bacteria, EC broth for coliform bacilli, and Hajna tetrathionate broth for Salmonella. 2 g amounts of the sample from a single lot was soaked in 20 test tubes containing 1...
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