| Aquatic extruded feed is a environment-friendly feed with low pollution,high efficiency and high conversion rate.At present,in many countries and regions in Europe,a new mode of processing and breeding with extruded feed has been formed.In recent years,with the increasing number of aquaculture species in China,the requirements for aquaculture extruded feed are becoming higher and higher.The slow-sinking aquatic feed is for the middle and lower feeding habits of carnivorous animals(such as grouper,largemouth bass,turbot,river groups and marine fish larvae,etc.).It requires the product to sink slowly and is difficult to process.At the same time,starch plays a very important role in the processing of aquatic extruded feed,which not only enhances the viscosity of the material,but also plays a dual role of expansion and adhesion in the extruded feed.In the aquatic feed,the use of sorghum can broaden the choice of starch source for aquaculture feed and reduce production costs.Therefore,this experiment uses a single factor and response surface methods to optimize the processing parameters of the slow-sinking extruded feed,and study the effect of sorghum and pre-gelatinized sorghum as starch source on the processing quality of aquatic extruded feed.The details are as follows:(1)Using the single factor experimental method,I study the effect of the template hole area per ton(300-500 mm~2/(t/h)),the moisture content(23~31%)and die temperature(100~140°C)on the aquatic slow-sinking extruded feed product quality.The research results show that with the increase of the template hole area per ton,the bulk density gradually increases,the expansion rate gradually decreases,and the unit density decreases first and then increases.When the template hole area per ton is 400 mm~2/(t/h),as the moisture content increases(23~31%),the bulk density and unit density gradually decrease,the expansion rate gradually increases,and the floating phenomenon gradually appears.When the template hole area per ton is 450 mm~2/(t/h),the bulk density and unit density increase first and then decrease with the increase of moisture content(22~27%),and the expansion rate first decreases and increases.As the die temperature increases,the bulk density,unit density and sinking speed gradually decrease,and the expansion rate gradually increases.When the template hole area per ton is about 450mm~2/(t/h),the moisture content is about 25%,and die temperature is about 130°C,suitable for the production of slow-sinking aquatic extruded feed.(2)Using response surface methods,the moisture content(23~27%),the die temperature(100-140°C)and the screw speed(180-300 rpm)for the slow-sinking aquaculture extruded feed were studied and optimized,and I made standards for slow-sinking extruded feed.The research results show that as the moisture content increases,the bulk density and unit density decrease gradually,and the expansion rate gradually increases.The difference in sinking speed between different die temperatures under the same conditions gradually increases.As the die temperature increases,the bulk density and unit density gradually decrease,the expansion rate gradually increases,and the sinking speed gradually decreases.After 30 minutes,the sinking rate first increases and then decreases,and the SME gradually increases.When the template hole area per ton is about 450 mm~2/(t/h),the moisture content is 27%,the die temperature is 125°C,and the screw speed is 220 rpm,It can produce the optimal slow-sinking aquatic product.At this time,the sinking speed was 5.04cm/s,the sinking rate was 77%at 0min,and the sinking rate was 95%at 10min.A slow-sinking extruded feed is defined:the sinking speed is≤8cm/s,≥70%sinking at 0 min,≥95%sinking at 10 min..Under this definition,the main evaluation index of slow-sinking feed:sinking speed 5.22~7.81cm/s,bulk density 504~550g/L,expansion rate 1.27~1.37,unit density 900.93~1007.78g/L(3)Two-factor experimental method was used to study the effect of sorghum as a starch source instead of flour on the quality of aquatic extruded feed under different moisture content(25%,28%and31%).The results showed that the sorghum as a starch source,the extruded effect of aquatic feed decreased with the increase of moisture content.The flour as a starch source,the extruded effect increased with the increase of moisture content;sorghum replaced flour would reduce the extruded of aquatic products.Under the optimal moisture content,the bulk density increased from 400.83±1.15 g/L to484.33±0.76g/L,the expansion rate decreased from 1.66±0.01 to 1.39±0.01,and the maximum oil absorption rate decreased from 50.93±0.36%to 31.65±0.91%,the oil leakage rate increased from4.99±0.61%to 10.44±0.42%,and the dissolution rate increased from 8.27±0.26%to 49.84±3.70%.(4)Using two-factor experimental method,I study the effect of pre-gelatinized sorghum on the quality of aquatic extruded feed under different moisture content(25%~33%).The results showed that after sorghum pre-gelatinized,the extruded effect of aquaculture feed increased with the increase of moisture content;sorghum starch as a source,extruded effect decreased with the increase of moisture content;sorghum will improve the extruded effect of aquatic extruded feed after pre-gelatinization treatment.Under the best moisture content respectively,the bulk density is 484.33±0.76 g/L under the optimal tempering water respectively.Reduced to 433.33±0.29g/L,the expansion rate increased from1.39±0.01 to 1.55±0.02,the maximum oil absorption rate increased from 31.65±0.91%to 43.59±0.58%,and the oil leakage rate decreased from 10.28±0.16%to 6.84±.0.16%,the dissolution rate decreased from49.84±3.7%to 10.26±0.10%. |
