楊 燦 唐小武 賓冬梅 陳思遠(yuǎn) 賀 瑜 雷 涵

(1.衡陽師范學(xué)院，生命科學(xué)與環(huán)境學(xué)院，衡陽421008；2.湖南大北農(nóng)農(nóng)業(yè)科技有限公司，長沙410200)

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干酒糟及其可溶物的營養(yǎng)價值及其在豬生產(chǎn)上的應(yīng)用

楊 燦1唐小武2賓冬梅1陳思遠(yuǎn)1賀 瑜1雷 涵1

(1.衡陽師范學(xué)院，生命科學(xué)與環(huán)境學(xué)院，衡陽421008；2.湖南大北農(nóng)農(nóng)業(yè)科技有限公司，長沙410200)

干酒糟及其可溶物(DDGS)是乙醇生產(chǎn)工業(yè)副產(chǎn)物，隨著生物能源的應(yīng)用增加，DDGS產(chǎn)量上升。DDGS最先用于反芻動物生產(chǎn)中，近年來，也有很多報道將DDGS用于豬、雞等單胃動物生產(chǎn)行業(yè)。本文從DDGS的生產(chǎn)工藝、營養(yǎng)組成、對豬的營養(yǎng)價值及其在豬生產(chǎn)上的應(yīng)用現(xiàn)狀以及改進(jìn)措施等幾個方面對近十年來國外學(xué)者在DDGS上的研究進(jìn)行了綜述。雖然DDGS能替代部分豆粕和玉米用于豬生產(chǎn)中，但由于其質(zhì)量的不穩(wěn)定、蛋白質(zhì)品質(zhì)的低下和粗纖維含量過高影響了其大量使用。通過過篩、發(fā)酵、加酶、不同原料組合使用等方法能擴(kuò)大并提高DDGS在養(yǎng)殖行業(yè)的應(yīng)用。

DDGS；豬；粗纖維；蛋白質(zhì)

全球石油資源有限，為尋找可替代能源，人們用玉米生產(chǎn)生物乙醇。乙醇生產(chǎn)過程中將產(chǎn)生副產(chǎn)物干酒糟及其可溶物(DDGS)，干磨法每蒲式耳(約50.8 kg)玉米生產(chǎn)17磅(1磅=0.453 6 kg)DDGS，而濕磨法生產(chǎn)1.6磅玉米油、2.6磅蛋白粉和13.5磅麩質(zhì)飼料[1]。據(jù)美國農(nóng)業(yè)部統(tǒng)計，全美40.5%的玉米都用于生產(chǎn)乙醇，其副產(chǎn)物DDGS 50.4%用于肉牛，33.5%用于奶牛，9.1%用于豬，7.0%用于雞生產(chǎn)行業(yè)，DDGS代替了畜禽生產(chǎn)中65%的玉米和35%的豆粕[2]。但是，盡管40.5%的玉米用于生產(chǎn)乙醇，但以玉米副產(chǎn)物在飼料業(yè)的應(yīng)用來計算，這個值僅僅為25%[2]，這意味著很多乙醇工業(yè)副產(chǎn)物被丟棄或未能用于飼料生產(chǎn)行業(yè)。按照現(xiàn)在的發(fā)展趨勢，到2026年，DDGS用于豬和禽生產(chǎn)行業(yè)的比例將大幅度增加。因此，有必要對DDGS的品質(zhì)進(jìn)行更細(xì)地探究，促進(jìn)其在單胃動物上的應(yīng)用，提高其利用率。過去，因為人們對DDGS不太重視，導(dǎo)致其質(zhì)量變異很大，粗蛋白質(zhì)和中性洗滌纖維(NDF)消化率降低。經(jīng)過這么多年的發(fā)展，乙醇生產(chǎn)工藝不斷在改進(jìn)，伴隨著的是其副產(chǎn)物DDGS質(zhì)量的變化。因此，本文將從近十年來DDGS的生產(chǎn)工藝、營養(yǎng)組成、營養(yǎng)價值特點等方面探討其潛在價值及在豬生產(chǎn)上的應(yīng)用現(xiàn)狀及可能的改善途徑，力爭能提高DDGS的利用率，擴(kuò)大其在單胃動物上的應(yīng)用，為緩解全球能量原料短缺提供有效途徑。

1 DDGS的生產(chǎn)及營養(yǎng)組成

1.1 DDGS的生產(chǎn)工藝

DDGS是釀酒酵母發(fā)酵谷物生產(chǎn)乙醇過程中的副產(chǎn)物。乙醇燃料大多以玉米經(jīng)干磨(67%)或濕磨(33%)方法生產(chǎn)[1]。傳統(tǒng)工藝干磨法是將酵母添加到玉米、水和酶的糊狀物中，發(fā)酵其中的糖分生產(chǎn)乙醇，產(chǎn)物蒸餾分離后，將蒸餾出的固體干燥生產(chǎn)蒸餾干燥谷物蛋白；濕磨法是將從固體中分離出的淀粉溶液和可發(fā)酵糖進(jìn)行發(fā)酵生產(chǎn)乙醇。在生產(chǎn)過程中，谷物的胚芽被剔除以提取玉米油，余下的胚芽粉再混合以纖維和殼形成玉米蛋白質(zhì)飼料，麩質(zhì)部分也會分離出來形成玉米蛋白粉，新工藝副產(chǎn)物為無蒸煮酒精糟(DDGS-BPX)。高蛋白蒸餾谷物(HP-DDG)是將谷物種皮、胚芽去除后再加酶，加酵母對谷物進(jìn)行發(fā)酵產(chǎn)乙醇的副產(chǎn)物。乙醇生產(chǎn)工藝改良集中在幾個方面：1)盡可能地將所有淀粉和糖轉(zhuǎn)化為乙醇；2)通過菌種的發(fā)酵將玉米中的纖維轉(zhuǎn)化為淀粉和糖再發(fā)酵生產(chǎn)乙醇。工藝改良后，乙醇的生產(chǎn)量增加了，但DDGS的淀粉含量相對下降了，同時其粗蛋白質(zhì)和粗纖維等的相對比例得以增加。

1.2 DDGS的營養(yǎng)組成

由于發(fā)酵過程中釀酒酵母主要利用谷物中的淀粉進(jìn)行生長和產(chǎn)乙醇，所以其副產(chǎn)物中殘留的淀粉非常少；而粗脂肪、粗纖維、粗蛋白質(zhì)卻相應(yīng)得到濃縮，比例大幅度增加。過去，對DDGS的養(yǎng)分研究集中在其粗蛋白質(zhì)、粗纖維和植酸磷等方面，對其賴氨酸的質(zhì)量、多聚不飽和脂肪酸(PUFA)以及粗纖維含量頗為頭痛。但實際上，DDGS還含有很多其他養(yǎng)分，能更有效地用于豬生產(chǎn)。

1.2.1 粗蛋白質(zhì)

DDGS的蛋白質(zhì)含量受乙醇生產(chǎn)工藝、谷物種類及DDGS的加工處理等因素影響，含量并不一致。濕磨法生產(chǎn)乙醇前，去除多糖和其他可溶性碳水化合物，其DDGS的蛋白質(zhì)濃縮物、蛋白質(zhì)分離物和篩后副產(chǎn)物的粗蛋白質(zhì)含量分別為48%、52%和51%，傳統(tǒng)DDGS相應(yīng)值為33%、37%和40%，因此，濕篩步驟能增加DDGS的蛋白質(zhì)含量[3]。此外，DDGS-BPX與DDGS的蛋白質(zhì)含量沒有顯著差異，但前者含有的緩沖液可溶蛋白質(zhì)含量顯著高于DDGS，酸性洗滌不可溶蛋白質(zhì)含量顯著低于DDGS[4]；HP-DDG的粗蛋白質(zhì)含量高于玉米DDGS(cDDGS)[5]；小麥DDGS(wDDGS)的粗蛋白質(zhì)含量顯著高于cDDGS(388 g/kg DM vs. 302 g/kg DM)，中性洗滌不可溶蛋白質(zhì)及酸性洗滌不可溶蛋白質(zhì)含量則以wDDGS低于cDDGS，cDDGS中谷氨酸含量高于wDDGS[5]。對玉米進(jìn)行溶劑提油后再發(fā)酵生產(chǎn)的DDGS的粗蛋白質(zhì)和氨基酸含量比傳統(tǒng)DDGS高，干物質(zhì)基礎(chǔ)的粗蛋白質(zhì)含量為35.6%[6-7]。對蒸餾谷物回收處理再發(fā)酵所產(chǎn)生的DDGS的蛋白質(zhì)含量比常規(guī)DDGS高30%～40%，而抑制因子是常規(guī)DDGS的2～5倍[8]，賴氨酸損失更多[9]。氨基酸組成方面，賴氨酸、組氨酸、甘氨酸以小麥濕蒸餾可溶物(wWDS)高于wDDGS，其他氨基酸均以wDDGS高于wWDS[10]。對韓國1個新品種玉米進(jìn)行98 ℃預(yù)處理1.5 h后，其DDGS中總氨基酸含量為230～310 mg/g，是玉米的3倍，而賴氨酸占2.5%～2.7%，必需氨基酸總量超過美國玉米21.1 mg/g[11]。

1.2.2 粗纖維

大多數(shù)玉米副產(chǎn)物都含有很多不溶性纖維，要降解這些纖維，需要很多酶的協(xié)同作用。DDGS含有36.74% NDF、16.2%酸性洗滌纖維(ADF)、10.22%粗纖維[12-13]、0.77%酸溶木質(zhì)和5.84%酸不溶木質(zhì)素[14]。干磨法產(chǎn)乙醇產(chǎn)生的DDGS的半纖維素組分主要以阿拉伯木糖以及戊糖來源的木糖和阿拉伯糖組成[15]，其中木糖為10.2%、阿拉伯糖為5.6%[16-17]。乙醇生產(chǎn)工藝變化后，DDGS纖維含量有所改變。wWDS的NDF低于wDDGS(23 g/kg vs. 312 g/kg)[10]。DDGS-BPX的NDF、ADF及木質(zhì)素含量均顯著低于DDGS[4]。

1.2.3 粗脂肪及維生素

DDGS的粗脂肪含量為8.4%～9.7%[18]，其脂肪酸組成多為不飽和脂肪酸。在生產(chǎn)過程中DDGS的PUFA容易發(fā)生過氧化導(dǎo)致其過氧化值高達(dá)84.1 meq/kg[19]。wDDGS的脂肪含量顯著低于cDDGS(38 g/kg DM vs. 115 g/kg DM)[5]。HP-DDG的粗脂肪含量比DDGS-BPX以及DDGS低[4]。低可溶性玉米蒸餾干燥谷物(LS-DDG)的粗脂肪含量為7.95%[20]。值得注意的是，DDGS中維生素E含量與粗脂肪含量呈正相關(guān)(R=0.667 7,P=0.147 3)，6個DDGS樣本的維生素E平均含量為6.8 mg/kg,并且還含有其他B族維生素如維生素B17.7 mg/kg、維生素B22.3 mg/kg、維生素B63.5 mg/kg及維生素B310.9 mg/kg[21]。

1.2.4 粗灰分及礦物元素

wDDGS粗灰分含量為5.4%，但硫、氮、磷、鉀含量都很高[22]，硫含量是其他農(nóng)副產(chǎn)物殘渣如棕櫚仁壓榨粕和橄欖殘渣的3～4倍[23]。DDGS-BPX比DDGS含有更多的硫、鈉、錳、銅、鉬和硒，但鋅含量以DDGS更高[4]。DDGS中的總磷含量較高，多為植酸磷，利用率較低。DDGS、HP-DDG和玉米胚芽的總磷含量分別為0.76%、0.33%和1.29%，生物學(xué)利用效率分別為60%、56%和25%[以磷酸二氫鉀(KH2PO4)為對照][24-26]。加植酸酶可分解清亮浸泡液中和整個蒸餾物中植酸，釋放4.52或0.86 mg/g的磷[27]。并且，植酸酶處理能使DDGS蛋白質(zhì)含量增加，淀粉殘渣減少[28]。在發(fā)酵時使用帶有植酸酶的酵母，則干酒糟的植酸磷含量下降89.8%，游離磷含量增加142.9%[29]。

1.2.5 其他成分

DDGS的酚酸組成和其相應(yīng)的玉米一致，但酚酸含量是玉米的3.4倍。其中，阿魏酸和p-香豆酸占總酚酸的80%以上，香草酸、咖啡酸、p-香豆酸、阿魏酸、芥子酸和總酚酸含量分別為0.22、0.14、0.72、4.59、0.33和5.99 mg/g DM[30]。DDGS是霉菌毒素嚴(yán)重污染原料。來源于北京的17個DDGS樣品均含有嘔吐毒素和玉米赤霉烯酮，平均濃度分別為1.36 mg/kg和882.7 μg/kg，超標(biāo)88%和41%[31]。臺灣的30個DDGS樣本有50.8%的樣品同時感染5種鐮刀菌屬毒素[32]。此外，DDGS中還殘留有抗生素以及微生物。對來源于美國9個州43個工廠的20個DDGS樣本進(jìn)行檢測發(fā)現(xiàn)有13%的樣本含有小于1.12 mg/kg的抗生素如紅霉素、青霉素、四環(huán)素等[33]。wDDGS的微生物菌群主要是乳酸桿菌如Lactobacillusamylolyticus、Lactobacilluspanis、Lactobacilluspontis和偶爾可檢測到的酵母菌[19]。

1.3 物理特性

用含有DDGS的原料制作飼料時，飼料的紅度增加，但亮度降低[34-35]。而添加DDGS到面包或圓餅中能提升其粗脂肪和粗纖維含量，使產(chǎn)品偏金黃色[36-37]。

2 DDGS在豬生產(chǎn)上的應(yīng)用

2.1 DDGS對豬的營養(yǎng)價值

2.1.1 DDGS的能值

DDGS的總能比玉米高(22.75 kJ/kg DM vs. 18.82 kJ/kg DM)，但能量消化率比玉米低(76.8% vs. 90.4%)[24]，所以兩者的消化能和代謝能沒有顯著差異[38]。因為原料的變化，能值有些許差異。如對28個DDGS樣品進(jìn)行分析，表觀代謝能(AME)為5.94～12.21 MJ/kg，真代謝能(TME)為7.29～13.56 MJ/kg[39]。LS-DDG的消化能和代謝能分別為13.53和12.39 MJ/kg DM，與DDGS相當(dāng)[20]。溶劑提油后的cDDGS的代謝能和凈能分別為11.96和8.56 MJ/kg DM，比DDGS低[7]。在18.5 kg豬的玉米-大豆基礎(chǔ)飼糧中添加0、15%、30%小麥-玉米DDGS，用比較屠宰試驗測得其凈能分別為10.17、10.16和10.17 MJ/kg DM，通過間接測熱法測得凈能分別為10.82、10.52和10.55 MJ/kg DM，通過化學(xué)分析法測得凈能分別為10.24、10.26和9.91 MJ/kg DM[40]。DDGS在飼糧中的添加會降低飼糧干物質(zhì)和能量的消化率[10]，即使配方凈能和可消化氨基酸一致，飼糧的干物質(zhì)和能量的表觀總腸道消化率(ATTD)也隨小麥-玉米DDGS的增加而線性下降，同時NDF的ATTD線性增加[41]。乙醇生產(chǎn)過程中的加工和發(fā)酵在一定程度上改善了纖維的消化率，所以DDGS的總飼糧纖維(TDF)的表觀回腸消化率(AID)和ATTD比玉米高，但整個腸道發(fā)酵的TDF不足50%，暗示DDGS中超過50%的TDF沒有被豬消化吸收[42]。對玉米副產(chǎn)物進(jìn)行分析表明，阿拉伯木聚糖含量能極顯著解釋干物質(zhì)的ATTD的變異(R2=0.67)，而非淀粉多糖木糖殘渣能解釋干物質(zhì)(R2=0.78)、NDF(R2=0.63)、蛋氨酸(R2=0.40)和蘇氨酸(R2=0.11)的ATTD的變異[43]。用T瘺管豬測試去油DDGS的養(yǎng)分消化率，賴氨酸的AID隨DDGS的增加(0、20%和40%)而降低，并且去油DDGS和大豆油對NDF和酸洗乙醚提取物的AID和ATTD均有顯著影響，飼糧酸洗乙醚提取物含量最高而NDF最低時，其NDF的AID和ATTD最高[44]。

2.1.2 DDGS的蛋白質(zhì)和氨基酸利用效率

小麥DDGS所有的氨基酸中，賴氨酸在肥育豬(82 kg)的AID最低，僅36%[45]，而且其標(biāo)準(zhǔn)回腸消化率(SID)變異很大(9%～82%)[46-47]。cDDGS中賴氨酸消化率變異也非常大[47]。wWDS的粗蛋白質(zhì)、賴氨酸和組氨酸的回腸標(biāo)準(zhǔn)消化率系數(shù)(CSID)顯著高于wDDGS，而蛋氨酸、半胱氨酸、異亮氨酸、亮氨酸和纈氨酸的CSID卻顯著低于wDDGS[10]。對DDGS進(jìn)行去脂或加熱處理會改變氨基酸消化率。添加玉米油使飼糧等脂肪含量時，高脂(11.5%)DDGS組的蛋白質(zhì)和脯氨酸、色氨酸以外的所有必需氨基酸的AID和SID均顯著高于低脂組(7.5%和6.9%)，額外加玉米油都無法補(bǔ)償這種消化率的損傷[48]。對玉米DDGS進(jìn)行130 ℃熱處理10、20和30 min后，生長豬粗蛋白質(zhì)的SID從77.9%下降到72.1%、66.1%和68.5%，賴氨酸的SID從66.8%下降到54.9%、55.3%和51.9%[49]。Yoon等[50]研究證實DDGS在60 kg豬飼糧中的增加會降低粗蛋白質(zhì)的ATTD，不過甘露聚糖酶可以改善粗蛋白質(zhì)的ATTD?？赏ㄟ^蛋白質(zhì)中賴氨酸的含量預(yù)測賴氨酸的SID，賴氨酸占粗蛋白質(zhì)的比例少于1.9%或2.8%的玉米DDGS不再適宜飼喂豬[46-47]。賴氨酸/粗蛋白質(zhì)(R=0.63)以及賴氨酸的SID(R=0.68)與亮度均呈顯著正相關(guān)[46]，代謝能和黃度顯著正相關(guān)(R=0.39)[39]，所以，在DDGS的使用中，亮度是很重要的衡量指標(biāo)。如果補(bǔ)充DDGS到飼糧中，應(yīng)根據(jù)可消化氨基酸和可消化磷來配置含DDGS的飼糧，10%的DDGS可替代4.25%的大豆和5.7%的玉米，同時補(bǔ)充0.1%的賴氨酸[51]。DDGS在飼糧中含40%會降低氮的消化率[20]，但氮儲備未受小麥DDGS含量的增加而影響[52]，這可能與氮排放增加有關(guān)[53-54]。

2.1.3 DDGS的礦物質(zhì)應(yīng)用

磷的ATTD高達(dá)59.1%，所以DDGS中可利用磷比較豐富(0.36%)[24]。與玉米-大豆飼糧組相比，以有效磷一致為基礎(chǔ)配方時，DDGS組仔豬的糞磷顯著下降，與100 g/kg DDGS組相比，200 g/kg DDGS組降低了鈣的儲留以及鈣ATTD[55]。

綜上所述，DDGS的蛋白質(zhì)品質(zhì)不高，但通過補(bǔ)充晶體氨基酸能解決這個問題。DDGS的能值和玉米大致一樣，只是如果在工藝中對其去油能值則會下降，所以，在使用中需要關(guān)注DDGS的生產(chǎn)工藝。運用DDGS替代單胃動物飼糧中的玉米豆粕時，建議將其凈能、回腸可消化氨基酸、有效磷配平，這樣才不會導(dǎo)致生產(chǎn)性能的下降。

2.2 DDGS對豬的飼用價值

2.2.1 在仔豬飼糧中的應(yīng)用

凈能和可消化氨基酸一致時，cDDGS在5.2 kg仔豬飼糧中添加7.5%對平均日增重(ADG)、平均日采食量(ADFI)和飼料轉(zhuǎn)化效率(G/F)沒有影響[56]，在6.4 kg仔豬斷奶后1～7 d添加7.5% cDDGS是可行的，8～42 d用量可增加到15%，7.1 kg仔豬采食含高達(dá)25% cDDGS的飼糧也不會對ADG、ADFI和G/F產(chǎn)生影響[57-58]。但cDDGS在仔豬飼糧中添加比例高達(dá)30%時會顯著降低ADFI[59]。如果讓豬斷奶后先適應(yīng)一段時間(21 d)再添加高達(dá)30%的cDDGS則不會影響其生產(chǎn)性能[60]，當(dāng)然，如果cDDGS已經(jīng)溶劑提油處理過[7]，或仔豬已經(jīng)足夠大(11 kg)[57]，則30%的玉米DDGS也不會影響其生產(chǎn)性能。高粱DDGS在11 kg仔豬飼糧中添加30%降低了G/F[61]。wDDGS在6.2 kg的斷奶豬中添加10%不會影響其采食量和終體重，但添加15%時會顯著降低采食量和體增重[62]。仔豬(6.7 kg)前期飼糧中香料的添加對仔豬后期采食DDGS或HP-DDG飼糧不利，并且有顯著降低ADG的趨勢[63]。DDGS的添加能增加5.2 kg仔豬回腸中炎性因子的mRNA表達(dá)量[56]。含硫高的DDGS能增加斷奶8周閹公豬血清中α-生育酚和肝臟中谷胱甘肽的含量，即高含硫的DDGS可能保護(hù)了仔豬免受高度氧化的DDGS的損傷[19]。

2.2.2 在生長肥育豬飼糧中的應(yīng)用

大多數(shù)試驗表明在生長肥育豬飼糧中添加高達(dá)15%[50，64]、20%[53，65]或30%[54]的cDDGS不會降低其生產(chǎn)性能。也有例外，如Xu等[66-67]報道在22～115 kg豬飼糧中添加高達(dá)30%DDGS時降低了ADFI以及ADG(29.8 kg豬)。DDGS的添加比例高達(dá)40%會顯著降低ADG和ADFI[68]。保持飼糧可消化賴氨酸和色氨酸一致，用DDGS替代33 kg生長豬配方中的玉米和豆粕，其ADG顯著下降[69]。保持飼糧可利用磷、可消化回腸賴氨酸及代謝能一致，飼糧中添加30%的DDGS不會降低ADFI，可如果同時添加30% DDGS和5%的牛油，則ADFI會顯著低于玉米豆粕對照組[70]。相同情況下，以粉料形式向小豬提供含30% DDGS飼糧時，其ADFI相對于玉米豆粕對照組顯著增加，G/F降低，而顆粒料形式的DDGS不會影響ADFI和G/F[71]。豬對DDGS有個適應(yīng)過程，保持凈能和可消化賴氨酸一致時，在小豬飼糧中添加30% DDGS顯著降低第1階段(29～50 kg)的ADFI和ADG，但對全期(29～120 kg)生長性能沒有顯著影響[72]。在飼糧中突然引入20%的DDGS不會對51.3 kg 的肥育豬造成不良影響，但突然引入40%的低可消化賴氨酸，DDGS會顯著降低ADG[73]。原料種類也對DDGS的使用效果產(chǎn)生不同影響。在25.5 kg豬的玉米-大麥-豆粕基礎(chǔ)飼糧上添加0～30%的小麥-玉米DDGS，保持凈能和可消化氨基酸一致時，ADG隨著小麥-玉米DDGS的增加而線性降低，G/F有降低的趨勢[41]。與玉米-大豆飼糧相比，在18.6 kg豬飼糧中添加15%或30%小麥-大豆DDGS使ADFI和ADG線性下降，但對G/F沒有顯著影響[74]。此外，溶劑提油后的cDDGS在飼糧中從0逐漸增加到30%時，29.6 kg生長豬的ADG、ADFI顯著降低，G/F也有顯著降低的趨勢[7]。而將22 kg生長豬飼糧的豆粕50%或100%都用HP-DDG替代，都不會影響其生產(chǎn)性能[65]。

2.2.3 DDGS對胴體品質(zhì)和肉質(zhì)的影響

盡管大多數(shù)試驗證實在飼糧中添加一定比例的DDGS不會影響生長肥育豬的生產(chǎn)性能，但DDGS對肉質(zhì)的影響卻是負(fù)面的并且顯著的。隨飼糧中DDGS含量的增加(0～30%)，生長豬畜體重和屠宰率下降[7，64，66]；保持回腸可消化氨基酸一致時，20%的DDGS就會降低屠宰率[20]；與對照組相比，飼糧添加30% DDGS平均減輕了5.1 kg胴體重[75-76]。屠宰率降低的原因可能與DDGS蛋白質(zhì)不平衡，內(nèi)臟代謝活動增強(qiáng)，內(nèi)臟重量增加相關(guān)[77]，也可能與DDGS粗纖維含量高，導(dǎo)致飼料通過速率增加，使得小腸生長增加相關(guān)[78-79]。在凈能和可消化賴氨酸一致時，生長豬采食含30%DDGS的飼糧將顯著降低眼肌面積和無脂瘦肉率[72]。飼糧中的DDGS從10%增加到30%，背肌大理石花紋會下降[66]。DDGS對肉質(zhì)最大的影響是增加了肌肉中PUFA含量，增加其碘價，導(dǎo)致豬肉不易加工和儲存。給100 kg公豬用20%或30% DDGS替代基礎(chǔ)飼糧中的玉米和豆粕會降低其屠宰時(130 kg)腹部脂肪硬度[65-67，70]，增加腹部脂肪的碘價[80]。40%的DDGS降低了肥豬的眼肌面積，背脂的不飽和程度也更高[73]。隨著DDGS在生長肥育豬飼糧中從0增加到15%、30%和45%，豬的背膘厚線性下降，皮下脂肪的飽和脂肪酸和單不飽和脂肪酸濃度線性下降，PUFA濃度線性增加，背脂內(nèi)外碘價線性增加[69]。Stein[24]總結(jié)了8個試驗報道的DDGS對碘值的影響，7個試驗表明碘值增加，1個不變。高碘值的豬肉十分柔軟，不利于加工，容易氧化變質(zhì)。飼糧中DDGS比例太高(30%)會影響儲存期肉品的脂質(zhì)過氧化值(TBARS)，降低肉貨架壽命[81]。造成腹脂硬度降低和碘值增加的原因為DDGS高的不飽和脂肪酸含量導(dǎo)致脂肪及肌肉組織中不飽和脂肪酸增加[7，66]。所以，當(dāng)DDGS的脂肪含量從16.0%降低到5.6%時，導(dǎo)致豬肉PUFA濃度以及碘價降低[82]。同時添加30%的DDGS和5%的牛油能降低腹部脂肪的碘價[70]，只是改善幅度小[83]。LS-DDG[20]和10%的玉米胚芽[65]能在一定程度上緩解DDGS對豬肉的負(fù)面影響。維生素E能降低TBARS和肉的揮發(fā)性鹽基氮(TVB-N)濃度，部分緩解DDGS比例太高引起肉貨架壽命降低的負(fù)面影響[81]。在100 kg公豬的20% DDGS飼糧中添加0.6%的共軛亞油酸(CLA)能降低碘價，增加瘦肉率，但CLA對新鮮、冷藏或冷凍儲存方式下的肉品質(zhì)影響非常小[84]。Xu等[67]證實15%和30% DDGS飼糧組屠宰時和屠宰前3、6、9周去除DDGS會線性降低C18∶2及碘價，所以要避免DDGS對豬肉品質(zhì)的影響，最好在屠宰前3周停止飼喂DDGS飼糧，這與Hill等[85]的建議非常一致。

2.3 DDGS在母豬飼糧中的應(yīng)用

早期研究表明妊娠母豬飼糧中添加40%～80%的DDGS對母豬的體重、采食量、產(chǎn)仔數(shù)和仔豬體重?zé)o影響[86-87]。Hill等[85]研究表明僅在哺乳期添加15% DDGS和5%甜菜渣時，飼糧對仔豬增重和死亡率及母豬哺乳期失重?zé)o顯著影響。將代謝能和賴氨酸配平后，在第2或3胎母豬的妊娠晚期及哺乳期飼糧中同時添加20%或40%飼糧的cDDGS，母豬繁殖性能沒有受影響[88]。Wilson等[89]研究表明，妊娠期添加50% DDGS的同時在哺乳期添加20% DDGS，斷奶仔豬的死亡率高，但是第2個產(chǎn)仔期這種現(xiàn)象消失，而且第1胎飼糧中添加DDGS縮短了第2胎母豬的發(fā)情間隔，所以哺乳母豬飼糧中DDGS的添加量可以達(dá)到20%。

綜上所述，我們可看到，在一定范圍內(nèi)，讓豬有個適應(yīng)的過程，能用DDGS替代配方中的玉米、豆粕用于豬生產(chǎn)。但為了解決其PUFA引起的高碘價肉的問題，建議添加CLA和維生素E等添加劑，同時在屠宰前21 d停用DDGS。DDGS在母豬上的應(yīng)用的相關(guān)報道還比較少，其實懷孕母豬能耐受粗纖維飼糧，理論上來說，富含NDF的DDGS應(yīng)該是妊娠母豬的適宜原料。因此，有必要在母豬上加大DDGS的研發(fā)力度，觀察其使用效果。此外，DDGS在養(yǎng)豬生產(chǎn)上的應(yīng)用研究集中于生產(chǎn)性能和肉品質(zhì)兩方面，但有限的資料表明，某些富含硫的DDGS可能具有抗氧化效果，某些DDGS具有抗炎效果。除了富含植酸磷外，DDGS還富含其他礦物質(zhì)和酚酸等，這些物質(zhì)可能對豬的免疫、抗氧化等方面產(chǎn)生效果，因此，有必要對此進(jìn)行研究。

3 DDGS應(yīng)用過程中存在的問題及改進(jìn)思路

3.1 過篩

DDGS最大問題是質(zhì)量變異大，蛋白質(zhì)品質(zhì)低，粗纖維含量太高。對采用POET(Sioux Fals，SD)系統(tǒng)的27個乙醇工廠進(jìn)行DDGS采樣分析，干物質(zhì)含量的變異25.6%來自于時間，7.1%的變異源于不同生產(chǎn)地點，生產(chǎn)地點的不同解釋了粗蛋白質(zhì)、粗脂肪、ADF、NDF、粗纖維和硫含量變異的38.9%、12.5%、11.1%、17.2%和25.5%，而ADF和NDF含量的變異大部分是因為時間原因(43.6%和50.1%)，因此，在使用DDGS時盡可能采用同一時間段相同生產(chǎn)工藝廠家的原料，養(yǎng)分變異程度相對較小[90]。降低DDGS中粗纖維最簡單而有效的方法是過篩。用1 130、869、582、389 μm的篩子對干酒糟進(jìn)行過篩處理后，得到物占27.2%、22.8%、21.4%和15.0%，底盤上物料占13.5%，其NDF含量分別為38.8%、36.8%、34.6%、32.2%和27.7%[91]。過80號篩(249～177 μm)的wDDGS將粗蛋白質(zhì)含量從原來的371.6 g/kg增加到底盤中的432.4 g/kg，同時顯著降低了NDF和ADF含量[92]。過篩后再對各篩上物進(jìn)行空氣流分級能進(jìn)一步降低DDGS的粗纖維含量。對869～1 130 μm篩上部分的片段進(jìn)行空氣分級，風(fēng)力從1.75到1.92 ms-1增加，輕片段含量從7.2%增加到13.6%，其中的NDF含量從63.1%降低到59.0%，NDF分離系數(shù)從2.7下降到2.2[91]。這也在試驗工廠得到驗證，效果不錯[93]。在降低NDF方面低速率揚風(fēng)3次的效果與中速率揚風(fēng)1次效果相當(dāng)，把整個DDGS一次性揚風(fēng)效率不及過篩后再分別對篩上篩下物揚風(fēng)[94]。木聚糖酶的添加(24 000 U/kg)能增加液態(tài)DDGS飼糧的NDF的AID[95]。只是，酶的作用具有針對性，所以要有效降解DDGS中的纖維，還需要多酶混合。

3.2 發(fā)酵

對發(fā)酵過程進(jìn)行改良也能改善DDGS的質(zhì)量。對生淀粉進(jìn)行發(fā)酵能增加Pronghorn黑小麥DDGS的固醇、酚化合物和β-葡聚糖含量，增加CDC Ptarmigan DDGS的生育酚及酚化合物含量[96]。此外，發(fā)酵前對原料進(jìn)行預(yù)處理能增加DDGS營養(yǎng)價值[97]。對DDGS進(jìn)行酸堿或熱水預(yù)處理能分解纖維素釋放出糖，預(yù)處理后的DDGS還能繼續(xù)加纖維素酶等進(jìn)行酶解產(chǎn)糖[98]，由此產(chǎn)生的發(fā)酵副產(chǎn)物DDGS營養(yǎng)價值也得到提升。用含有α-淀粉酶和葡糖淀粉酶的復(fù)合酶制劑STARGEN 001在50 ℃處理生淀粉后再用釀酒酵母發(fā)酵谷物產(chǎn)乙醇所產(chǎn)生的DDGS營養(yǎng)價值更高[96]。

3.3 不同組分組合

試驗證實將去殼大麥和谷物DDGS混合后能顯著改變營養(yǎng)組分的結(jié)構(gòu)。檢測發(fā)現(xiàn)谷物和谷物副產(chǎn)物混合后與脂肪相關(guān)的分子光譜強(qiáng)度[99]以及與蛋白質(zhì)分子結(jié)構(gòu)相關(guān)的光譜特征都發(fā)生了改變[100]，最終飼料的組合改變了飼料化學(xué)和營養(yǎng)結(jié)構(gòu)，營養(yǎng)物質(zhì)的消化率和可利用率得到改變。在混合濃縮蒸餾可溶物(CDS)和濕蒸餾谷物(WDG)時，隨著CDS的減少，cDDGS的顏色變得更亮，樣品的不溶纖維含量以及氨基酸增加，而脂肪、總可溶性糖含量下降[101]。與混合飽和及不飽和脂肪相比，通過化學(xué)方法對脂肪進(jìn)行部分加氫更能有效的提高消化率，但需注意，飼糧碘價太低(20)時，消化率反倒會降低[102]。研究一般認(rèn)為是熱損傷導(dǎo)致了DDGS中氨基酸的消化率低下，但糖漿塊的氨基酸AID和SID與DDGS一致或更高，只是冷凝液可溶物和酒精廢液蒸發(fā)物的大部分氨基酸消化率低于DDGS，尤其是蛋氨酸?？扇绻菬釗p傷導(dǎo)致冷凝液可溶物的氨基酸消化率下降，下降最嚴(yán)重的應(yīng)該是賴氨酸而不是蛋氨酸，所以導(dǎo)致DDGS氨基酸消化率下降的原因可能還是因為飼糧纖維濃度太高或賴氨酸濃度太低等其他原因[103]。

3.4 生產(chǎn)活性物質(zhì)

DDGS可用于生產(chǎn)生物活性物質(zhì)，如通過紅發(fā)夫酵母(Phaffiarhodozyma，ATCC 24202)和紅擲孢酵母(Sporobolomycesroseus，ATCC 28988)共發(fā)酵或單發(fā)酵DDGS生產(chǎn)278 μg/g β-胡蘿卜素[104]；通過白腐菌發(fā)酵產(chǎn)生木質(zhì)素降解酶[105]；通過裂褶菌(Schizophyllumcommune，ATCC 20165)發(fā)酵麥芽提取物和DDGS生產(chǎn)裂褶多糖[106]。此外，也能從cDDGS和高粱DDGS中提取植物甾醇和二十八烷醇[107]。

4 小 結(jié)

雖然DDGS能生產(chǎn)生物活性物質(zhì)，但其大量的使用還是在動物生產(chǎn)中。養(yǎng)殖者需要了解原料的營養(yǎng)組分及其變異程度才能更好地選擇和利用這種原料。乙醇生產(chǎn)廠家應(yīng)調(diào)控生產(chǎn)工藝，使DDGS質(zhì)量更穩(wěn)定。同時，對DDGS營養(yǎng)價值的關(guān)注不應(yīng)僅僅在其氨基酸和粗纖維以及植酸磷方面，DDGS還富含有其他礦物質(zhì)以及維生素，也許能在免疫和抗氧化方面改善其在動物上的飼養(yǎng)效果。DDGS在母豬上的使用也有必要投入更多的研究。最終，通過乙醇生產(chǎn)企業(yè)的工藝改良以及動物營養(yǎng)專家的努力，全方面探究DDGS的營養(yǎng)價值，擴(kuò)大DDGS的利用率，將為緩解飼料行業(yè)能量飼料缺乏提供有效解決路徑。

致謝：

感謝四川農(nóng)業(yè)大學(xué)動物營養(yǎng)研究所陳代文教授和何軍研究員對文稿所提的寶貴意見。

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Author, YANG Can, lecturer, E-mail: yangcansky@163.com

(責(zé)任編輯 田艷明)

Nutrition Value of Distillers Dried Grains with Solubles and Its Application in Swine Production

YANG Can1TANG Xiaowu2BIN Dongmei1CHEN Siyuan1HE Yu1LEI Han1

(1.CollegeofLifeandEnvironmentScience,HengyangNormalUniversity,Hengyang421008,China; 2.HunanDabeinongAgriculturalTechnologyLimitedCompany,Changsha410200,China)

As a kind of ethanol production industry by-products, the distillers dried grains with solubles (DDGS) output is continuously raised with the application of biological energy. DDGS was first used in ruminant production. In recent years, there were also many reports related DDGS used in swine, chickens and other single stomach animal production industry. This review summarized research results from recent ten years abroad on production process, nutrition composition, nutrition value of DDGS on swine and its application in swine production and improvement measures, et al. Soybean meal and corn can be replaced partly by DDGS in swine production, but the instability of product quality, poor protein quality and high-fiber content limit the DDGS to the applications in swine industry. It suggests that through the sieving, fermentation, adding enzyme and certain combinations of different material can broaden the DDGS utilization in swine production.[ChineseJournalofAnimalNutrition, 2017, 29(1)：8-20]

DDGS; swine; crude fiber; protein

10.3969/j.issn.1006-267x.2017.01.002

2016-07-14

衡陽師范學(xué)院科研啟動資金(15B12)；湖南省省市聯(lián)合自然科學(xué)基金(14JJ5001)

楊 燦(1981—)，女，湖南汨羅人，講師，博士，從事動物營養(yǎng)與飼料科學(xué)研究。E-mail: yangcansky@163.com

S816；S828

A

1006-267X(2017)01-0008-13