| A 74-breed-corn chemical components analyse was conducted to investigate the variation information of different corns. Meanwhile, according to amylose-amylopectin ratio reflecting the quality of the com, three samples with great variations were chosen to be basic materials for further research. The following experiment was about the effect of four factors(amylose-amylopectin ratio, storage time, storage temperature and storage humidity) on digestable starch and resistiance starch formation in vitro. At last, trials in vivo were conducted in company to make further proof of the influences of extrusion proceeding and amylose-amylopectin ratio on starch digestibility, digestibility of energy, and digestible energy of com & soybean meal diets. These researches are expeted to give more academic surports for weaning piglets’diets and optimal proceeding manner.In experiment 1:General chemical components analysis includes water, ether extract, crude fibre, curde protein, ash, ADF, NDF, total starch and AP/AM and their variation degree. Relativity analyses were made among general chemical components, AP/AM and general energy to seek the influence of non-starch proportion on starch content and starch charater on energy value. In this trial, main reason of variation among different corns is expected and a few samples will be choson for next two trials.Results were as follows:(1) Based on DM, TS, CP, EE, CF, Ash, ADF, NDF, GE and AP/AM are 67.85%±4.41%,9.29%±0.97%,4.56%±0.73%,2.36%±0.60%,1.37%±0.20%, 3.44%±0.63%,12.70%±1.30%,19.09±0.39MJ/kg,2.36±0.37%, respectively. CV of starch is 6.50% and AP/AM 15.68%.(2) Total starch and gross energy has a very significant correlation (r=0.3115, P<0.01); EE and GE (r=0.3461, P<0.05); AP/AM, TS and GE has no significant coorelation (P>0.05).(3) Total starch and crude protein of corn has a close negative correlation (r=-0.2532, P<0.05).In experiment 2:Corn sample No.88, No.35, No.1311 (AP/AM=1.66,2.26,2.56, respectively) were choson out from trial one and five minuites extrusion treatment was given with 0.2MPa at 120℃. According to method from Goni(1996) and Englyst(1992), 3×2×2×4 trial in vitro with AP/AM, storage temperature, storge humidity and storage time of extruded corn was designed to investigate the effect on amount of digestible starch and formation of resistant starch.Results were as follows:(1) Having stored extruded corn with 2.56,2.26,1.66 ratio of AP/AM for 4 weeks, which contains resisitant starch for 1.56±0.37%,1.99±0.64%,2.17±0.68%, respectively. The amount of RS with Low AP/AM is higher than the high AP/AM (P<0.01). With digestable starch being 92.65%±1.81%,90.49%±1.71% and 89.19%±2.30%, the amount of digestable starch with high AP/AM is significantly higher than the one with low AP/AM (P<0.01).(2) The amount of resistant starch is 1.97%±0.66% and 1.84%±0.60% under storage condition at 15℃and 25℃. Resistant starch forms easier at low temperature (P<0.01); The amount of digestiable starch is 90.66%±2.50% and 90.90%±2.33% and has no significant coorelation with storage temperature (P>0.05).(3) The amount of resistant starch is 1.76%±0.48% and 2.06%±0.72% under storage condition with 50% and 80%, which has a significant increase under storage condition at high humidity (P<0.01); The amount of digestiable starch is 91.49%±2.03% and 90.07%±2.58% and has a atrong significant coorelation with storage humidity (P<0.01).(4) On common condition, four-week storage of extruded corn has a rise on the amount of resistant starch form 1.13%±0.09% to 2.45%±0.51%, which increases significantly(P<0.01) by time. However, digestiable starch decreases from 93.67%±1.63% to 89.49%±2.27%, with a strong significant coorelation (P<0.01) in day0～7, and no significant correlation (P>0.05) in day 7-28.(5) Resistant starch and digestable starch has a close negative correlation (r=-0.8284, P<0.01); AP/AM and the amount of resistant starch of extruded corn also has a strong negative correlation (r=-0.3674, P<0.01); AP/AM and the amount of digestable starch has a very significant correlation (1=0.5565, P<0.01). Fat and protein has a positive coorelation with resistant starch and negative correlation with digestable starch (P>0.05).In experiment 3:In this trial, two varieties of corn (No.80, No.1311) with different AP/AM (1.66,2.56) were non-vapor extruded at 120℃with rate of feeding 300RPM, screw speed 250RPM, thus four trial groups (Nor.1311, Nor.80, Ext.1311, Ext.80) being ready for further experiments. According to NRC (1998) standards, six groups of experiment diets are Control 1, Extrusion 1, Control 2, Extrusion 2, Amylase-adding 1, Amylase-adding 2. The Amylase-adding groups were based on Control groups with additional mixed exogenous amylase. In general, the six groups of diets contained the same digestable energy, crude protein and total starch. In this trial in vivo, six homogenetic healthy Landrace×Largewhite piglets (13.20±0.94kg) were operated with simple T-cannula. Designed by 6×6 Latin Square, six groups of experiment diets were given to piglets in turn within six trial phases, one phase a week. For each phase, fresh faeces were collected on the fifth day, and chyme was collected during the sixth to seventh day for 10 hours. After determining starch components and enerty from faeces and chyme of six diets, the information of CTTAD of starch and energy was gained for further study on AP/AM of corn starch and extrusion processing factors and correlations between them.Results were as follows:(1)The piglets weighed between 12-30kg that had no mater low or high AP/AM corn had significantly high CIAD of energy and ileum DE of starch than Control Group and enzyme-adding Group (P<0.05). Corn with additive mixed amylase has no obvious effect on CIAD of energy and starch, starch digestibility (P>0.05). It is wortwhile to note that raw corn with high AP/AM has significiantly high CIAD of starch and energy and ileum DE than the low one (P<0.01).(2) Corn with extrusion or additive mixed amylases has no obvious difference with Contral Group on CTTAD of energy and DE (P>0.05). There are also no obvious differences within a same Control Group.(3) The energy digestibility and digestable energy of total tract or ileum have significant correlations (r=0.4027, r=0.3837, P>0.05). at ileum, correlations among energy digestibility, digestable energy and starch digestibility, AP/AM have significant correlations (P<0.05); CIAD of energy, energy digestibility have significant positive correlations with starch digestibility (r=0.7258, r=0.8215, P<0.01) and AP/AM (r=0.3166, r=0.4409, P<0.05).From the results all above, the conclusions are as follows:(1) Being a kind of nergy source feedstuff, variation of AP/AM of corn is the main reason that leads to unstable nutrition value. (2) The form of resistant starch directly affects digestibility of extruded corn starch. Low humidity and long-term storage make corn with low AP/AM easy to form resistant starch.(3) Extrusion processing significantly improved starch digestibility and digestable energy at ileum on weanling pigs. Additive amylase has no obvious improvement. As to raw corn diet, the one with high AP/AM significantly improves starch digestibility and digestable energy at ileum of weanling pigs. |
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