Studies On Sterilization Of SPF Pig Feed

This paper consists of three experiments which studied the effect of sterilization process on microorganism and nutrient composition of SPF pig feed by radiation, microwave and extrusion, in order to choose the appropriate process to produce feeds which accord with SPF pig feed standard.Experiment one studied the relation between the residual colonies number and the radiation dose (0 kGy, 2 kGy, 3 kGy, 4 kGy, 5 kGy and 6 kGy), and the effects of radiation dose (0 kGy, 5 kGy, 10 kGy, 15 kGy, 20 kGy and 25kGy) and preservation time (0 days, 7 days, 14 days, 21 days and 28 days after radiation) on sterilization of SPF feed. The result is as follows: (1) The relation between the radiation dose and bacterial logarithm or mildew and yeast logarithm after irradiation is linear: y＝.0.8319x+6.5087(R²ï¼0.9958), y＝0.8928x+5.7199 (R²ï¼0.9673); (2) The D₁₀ value of the bacterial and mildew and yeast are 1.20kGy and 1.12kGy. (3) No microorganism was detected in the feed radiated by 15kGy, which initial bacterial concentration is 8.79×10⁶ cfu/g, and the mildew and yeast is 5.07×10⁵ cfu/g and the coliform is 488MPN/100g; (4) Radiation has no significant effects on crude fat, crude protein and gross energy content (P＞0.05), and has significant effects on water content and crude protein content(P＜0.01), but the variation is less than 3%. In short, the feed after radiation by 15kGy can accord with SPF pig feed standard.Experiment two studied the effects of microwave on sterilization of pig feed by means of orthogonalizing process, adopting water moisture (20%, 27% and 34%) of the feed, power (350 w, 560 w and 700w) of the microwaves, time (3 min, 6 min and 9 min) of heat treatment and thickness/average weight (4 mm/20.10g, 8 mm/40.20g and 12mm/60.30g) of the feed as factors. The conclusion is as follows: (1) The coliform, mildew and yeast are highly sensitive to microwave, so that they can be killed by microwave in three minutes. (2) Above four factors have significant effects (P＜0.01) on microorganism of the feed, and the remarkable order is: time＞thickness＞power＞water content. (3) The best process is A₃B₃C₃D₃, viz. the water content is 34%, the power is 700 watt, the time is 9 minutes, and the thickness is 12 millimeter. At the same time, reducing time can be considered. In short, the feed after sterilization by microwaves can accord with SPF pig feed standard.Experiment three studied the effects of extrusion on sterilization of pig feed. The trial were designed by single factor (90℃, 100℃, 110℃, 120℃, 130℃, 140℃,150℃, 160℃, 170℃, 180℃)test and the orthogonalizing process L₉ (3⁴): moisture content (18%, 23%, 28%), feeding rate (18 r/min, 24 r/min, 30r/min), screw speed (100r/min, 150r/rain, 200r/rain) and barrel temperature (80℃, 120℃, 160℃). The results are showed as follows: (1) The process of extrusion has very perfect effects on sterilization of pig feed. The coliform, mildew and yeast were not detected after extruding at 80℃, and no microorganism was detected after extruding at 90℃. (2) The four determined factors all have significant effects (P＜0.01) on microorganism of the feed, among which barrel temperature is the more remarkable.(3) The best process is A₂B₂C₂D₂, that is, the moisture content is 23%, feeding rate is 24 r/min, screw speed is 150 r/min and barrel temperature is 120℃. In short, producing SPF animal feed by extrusion is possible if the secondary pollution can be avoided. Radiation is the best sterilization process for SPF pig feed considering all of the experiments and the advance. The radiating dose of 15 kGy is enough, and the feed can keep 28 days in ordinary circumstances.