Effect of bulking process on the utilization rate of nutrient composition in feed
Effect of bulking process on the utilization rate of nutrient composition in feed
1 Expansion principle
Puffing is a process of mixing, heating, kneading and forming. The extruder can be divided into single screw extruder and double screw extruder according to the number of screws. The temperature and water content of the powder material can reach the requirement of producing expanded material when the powder material with certain proportion of starch is processed by DDC. Then the prepared material enters the expansion chamber and moves forward in an axial direction under the extrusion and promotion of the screw and screw. As a result of material and screw, material and barrel and material internal mechanical friction, so that the material is strongly extrusion, mixing, compression and shear and in the state of high pressure and high temperature. At this point, the starch in the material gelatinization and cracking, the entire material into molten plastic. When the paste material is pushed out of the die hole, the pressure and temperature drop, under the combined action of temperature difference and pressure difference, the water evaporates quickly and the feed volume expands rapidly. At the same time, as the temperature decreased, gelatinized starch immediately coagulated and then was cut into short grains by a cutter to form expanded feed (Lin shimei, 2001).
2 Effect of bulking process on nutrient composition of feed
2.1 effect of bulking process on protein amino acid
In expanded in the process of high temperature and high pressure conditions can make the protein structure changes, such as protein tertiary and quaternary structure is weaker, intermolecular disulfide bond, hydrogen bond, etc combining with the key part of the fracture, lead to protein denaturation, the digestive enzymes to increase the sensitivity of protein and passivation antinutritional factors in plant sex protein (antitrypsin, urease), improve the utilization rate of protein has a certain role in promoting. Cheng Yi feng (2008) study found that in less than 135 ℃, puffed feed protein in vitro digestion rate increases with puffed by the rise of temperature. As reported by peng-bin shi et al. (2000), raw soybean can significantly reduce the content of urease and trypsin inhibitor after puking treatment (P<0.05). Further study also found that with the increase of temperature, the puking process has an enhanced destructive effect on urease and trypsin inhibitor in soybean. This is consistent with the research results of zuo jinhua et al. (2008). In the aspect of amino acids, more attention is paid to lysine, which may react with reducing sugars or other carbonyl compounds in the feed in maillard reaction during the expansion process, resulting in the loss of lysine. Gan zhenwei et al. (2009) showed that after the expansion treatment, the content of lysine in the feed decreased by 19.54% compared with that before the expansion (P<0.05). Meanwhile, methionine, cystine, valine, aspartic acid and crude protein also decreased by 5.71% (P>0.05), 40.35% (P<0.05), 26.39% (P<0.05), 16.81% (P<0.05) and 6.46% (P<0.05), respectively. Cattle hin, etc (2013) crystal is added in the diet and microcapsule amino acid (lysine and methionine), compares the different swelling temperature (90 ℃, 120 ℃ and 150 ℃) to feed the effect on the stability of the amino acids. The results show that compared with the control group, 90 ℃, 120 ℃ and 150 ℃ expanded set of crystal lysine content were reduced by 9.83% (P < 0.05), 18.73 (P < 0.05) and 26.66% (P < 0.05); The content of microcystic lysine decreased by 6.68% (P<0.05), 7.69% (P<0.05) and 8.35% (P<0.05), respectively. In methionine, with the increase of swelling temperature, the content of crystal methionine and microcapsule methionine in the feed decreased compared with the control group, but there was no significant difference (P>0.05). The above results suggest that when puffed temperature over 90 ℃, puffing process technology of microcapsule and the crystalline amino acid loss not only have a significant impact, and crystalline amino acid loss is significantly higher than microcapsule amino acid; In addition, the amino acid loss of crystal methionine and microencapsulated egg was less than that of lysine with the increase of expansion temperature.
2.2 effect of extrusion process on starch
Starch is not only an important carbohydrate, but also an adhesive in the processing of expanded feed. Gelatinization is a major change of starch during extrusion. Starch is insoluble in cold water and can be suspended by stirring. When the water temperature rises to a certain degree, starch molecules absorb a large amount of water and cause a sharp expansion. The molecular structure expands, the amylopectin on the periphery of starch particles is distensible and cracked, and the directly connected starch molecules on the inside are free and the suspension becomes sticky and thick. This phenomenon is called starch gelatinization (leaf yuan soil et al., 2013). During extrusion, gelatinized starch and other components of raw materials, such as fat and protein, together form a plastic body, which plays a key role in the forming of expanded feed. Cheng yifeng (2008) reported that, within a certain range of conditions, the gelatinization degree of starch during extrusion would increase with the increase of material moisture. The effects of expansion temperature feeding speed and screw speed on the gelatinization degree of starch were similar. This is consistent with the research results of liu tian et al. (2009) and niu hua xin et al. (2011). However, the higher the expansion temperature and feeding speed, the better. When the expansion temperature and feeding speed are too high, the degradation degree of starch molecules will increase. As reported by huan yanjun (1997), the gelatinization degree and degradation rate of starch decreased with the expansion temperature and feeding speed increasing. In addition, in the expansion process, the strong shear force caused by excessive screw rotation speed will make the fully swollen starch particles excessively shear, resulting in accelerated degradation rate of starch molecules (1995). Gomez et al. (1983) found that in the extrusion process with high compression ratio, when the moisture content of materials was 20%, the degradation of starch was obvious.
2.3 effect of bulking process on fat
Gan zhenwei et al. (2009) reported that the content of crude fat in the expanded feed was 6.46% lower than that before the expansion, which may be related to the partial hydrolysis of the fat in the extrusion expansion process, and the glycerol and free fatty acids produced were easily related to the formation of starch and protein complexes. The strong shear force produced by the screw can make the complex formed by amylose and fat in the material transform from v-type structure to stable e-type structure. Extrusion temperature and water content are the main factors affecting starch fat complex. With the increase of material water content and extrusion temperature, the production of starch fat complex decreases (Hahn et al., 1987). In addition, cis-trans isomerization of unsaturated fatty acids occurs during extrusion. When the temperature of the bulking from 55 ℃ to 171 ℃, the content of trans fatty acids increased from 1% to 1.5% (shuang-kui du, etc., 2005). At present, fish, especially Marine fish, have a high demand for fat. In the process of feed production, exogenous oil is often added to increase the fat content in the diet of Marine fish. However, when the added exogenous oil passes through the expansion chamber with high temperature and pressure, what changes will happen to its physical and chemical properties and what harmful components will be produced? There are relatively few reports on this aspect. The results showed that the acid value of extruded oil increased with the increase of extruded temperature. In addition, with the increase of screw speed, strong shear force and friction force as well as high expansion temperature can accelerate the decomposition of oil, resulting in decreased stability of oil and increased peroxide value (sun peiling et al., 2010).
2.4 effects of bulking process on vitamins and minerals
The retention rate of vitamin in the puffing process has always been the focus of attention. The vitamin in feed will be lost to some extent after puffing treatment. Among them, the loss rate of vitamin K, vitamin B1, vitamin B6, vitamin B2 and folic acid in puffing treatment was 50.83% (P<0.05), 97.33% (P<0.05), 100% (P<0.05), 84.27% (P<0.05) and 100% (P<0.05), respectively. The loss rate of vitamin A, vitamin D and vitamin E was also between 12.16% and 15.38% (gan zhenwei et al., 2009). Zhang chunyan et al. (2010) reported that Vc phosphate had a loss rate of 21.22% (P<0.05) after expansion treatment. Further studies showed that the retention rate of vitamin C activity decreased with the increase of feeding speed and screw rotation speed, but the decrease was small. The retention rate of vitamin C activity decreased rapidly with the increase of the expansion temperature. At 90 ℃ can keep 70%, at 165 ℃ survival rate is only 2% (Cheng Yi feng, 2008). Liu Wanhan etc. (2003) reported that puffing temperature rise every 5 ℃, activity of vitamin C retention rate fell by 5%, when puffed temperature is 111 ~ 115 ℃, crystalline vitamin C activity retention rate of 60%, when the puffing temperature rise to 161 ~ 165 ℃, crystalline vitamin C activity retention rate close to zero. The vitamin loss rate of different packing process was different in puffing treatment. Wang hongying et al. (2003) showed that the loss rate of vitamin C added in crystal form was as high as 80.29% (P<0.05), while that of vitamin C added in capsule form was 47.64% (P<0.05). The expansion treatment had little effect on mineral elements. From the loss ratio, although the content of most mineral elements decreased, the difference was not significant (P>0.05) (gan zhenwei et al).