2. 湖南大北农农业科技有限公司, 长沙 410200
2. Hunan Dabeinong Agricultural Technology Limited Company, Changsha 410200, China
全球石油资源有限，为寻找可替代能源，人们用玉米生产生物乙醇。乙醇生产过程中将产生副产物干酒糟及其可溶物(DDGS)，干磨法每蒲式耳(约50.8 kg)玉米生产17磅(1磅=0.453 6 kg) DDGS，而湿磨法生产1.6磅玉米油、2.6磅蛋白粉和13.5磅麸质饲料[1]。据美国农业部统计，全美40.5%的玉米都用于生产乙醇，其副产物DDGS 50.4%用于肉牛，33.5%用于奶牛，9.1%用于猪，7.0%用于鸡生产行业，DDGS代替了畜禽生产中65%的玉米和35%的豆粕[2]。但是，尽管40.5%的玉米用于生产乙醇，但以玉米副产物在饲料业的应用来计算，这个值仅仅为25%[2]，这意味着很多乙醇工业副产物被丢弃或未能用于饲料生产行业。按照现在的发展趋势，到2026年，DDGS用于猪和禽生产行业的比例将大幅度增加。因此，有必要对DDGS的品质进行更细地探究，促进其在单胃动物上的应用，提高其利用率。过去，因为人们对DDGS不太重视，导致其质量变异很大，粗蛋白质和中性洗涤纤维(NDF)消化率降低。经过这么多年的发展，乙醇生产工艺不断在改进，伴随着的是其副产物DDGS质量的变化。因此，本文将从近十年来DDGS的生产工艺、营养组成、营养价值特点等方面探讨其潜在价值及在猪生产上的应用现状及可能的改善途径，力争能提高DDGS的利用率，扩大其在单胃动物上的应用，为缓解全球能量原料短缺提供有效途径。
1 DDGS的生产及营养组成 1.1 DDGS的生产工艺DDGS是酿酒酵母发酵谷物生产乙醇过程中的副产物。乙醇燃料大多以玉米经干磨(67%)或湿磨(33%)方法生产[1]。传统工艺干磨法是将酵母添加到玉米、水和酶的糊状物中，发酵其中的糖分生产乙醇，产物蒸馏分离后，将蒸馏出的固体干燥生产蒸馏干燥谷物蛋白；湿磨法是将从固体中分离出的淀粉溶液和可发酵糖进行发酵生产乙醇。在生产过程中，谷物的胚芽被剔除以提取玉米油，余下的胚芽粉再混合以纤维和壳形成玉米蛋白质饲料，麸质部分也会分离出来形成玉米蛋白粉，新工艺副产物为无蒸煮酒精糟(DDGS-BPX)。高蛋白蒸馏谷物(HP-DDG)是将谷物种皮、胚芽去除后再加酶，加酵母对谷物进行发酵产乙醇的副产物。乙醇生产工艺改良集中在几个方面：1)尽可能地将所有淀粉和糖转化为乙醇；2)通过菌种的发酵将玉米中的纤维转化为淀粉和糖再发酵生产乙醇。工艺改良后，乙醇的生产量增加了，但DDGS的淀粉含量相对下降了，同时其粗蛋白质和粗纤维等的相对比例得以增加。
1.2 DDGS的营养组成由于发酵过程中酿酒酵母主要利用谷物中的淀粉进行生长和产乙醇，所以其副产物中残留的淀粉非常少；而粗脂肪、粗纤维、粗蛋白质却相应得到浓缩，比例大幅度增加。过去，对DDGS的养分研究集中在其粗蛋白质、粗纤维和植酸磷等方面，对其赖氨酸的质量、多聚不饱和脂肪酸(PUFA)以及粗纤维含量颇为头痛。但实际上，DDGS还含有很多其他养分，能更有效地用于猪生产。
1.2.1 粗蛋白质DDGS的蛋白质含量受乙醇生产工艺、谷物种类及DDGS的加工处理等因素影响，含量并不一致。湿磨法生产乙醇前，去除多糖和其他可溶性碳水化合物，其DDGS的蛋白质浓缩物、蛋白质分离物和筛后副产物的粗蛋白质含量分别为48%、52%和51%，传统DDGS相应值为33%、37%和40%，因此，湿筛步骤能增加DDGS的蛋白质含量[3]。此外，DDGS-BPX与DDGS的蛋白质含量没有显著差异，但前者含有的缓冲液可溶蛋白质含量显著高于DDGS，酸性洗涤不可溶蛋白质含量显著低于DDGS[4]；HP-DDG的粗蛋白质含量高于玉米DDGS (cDDGS)[5]；小麦DDGS (wDDGS)的粗蛋白质含量显著高于cDDGS (388 g/kg DM vs. 302 g/kg DM)，中性洗涤不可溶蛋白质及酸性洗涤不可溶蛋白质含量则以wDDGS低于cDDGS，cDDGS中谷氨酸含量高于wDDGS[5]。对玉米进行溶剂提油后再发酵生产的DDGS的粗蛋白质和氨基酸含量比传统DDGS高，干物质基础的粗蛋白质含量为35.6%[6-7]。对蒸馏谷物回收处理再发酵所产生的DDGS的蛋白质含量比常规DDGS高30%~40%，而抑制因子是常规DDGS的2~5倍[8]，赖氨酸损失更多[9]。氨基酸组成方面，赖氨酸、组氨酸、甘氨酸以小麦湿蒸馏可溶物(wWDS)高于wDDGS，其他氨基酸均以wDDGS高于wWDS[10]。对韩国1个新品种玉米进行98 ℃预处理1.5 h后，其DDGS中总氨基酸含量为230~310 mg/g，是玉米的3倍，而赖氨酸占2.5%~2.7%，必需氨基酸总量超过美国玉米21.1 mg/g[11]。
1.2.2 粗纤维大多数玉米副产物都含有很多不溶性纤维，要降解这些纤维，需要很多酶的协同作用。DDGS含有36.74% NDF、16.2%酸性洗涤纤维(ADF)、10.22%粗纤维[12-13]、0.77%酸溶木质和5.84%酸不溶木质素[14]。干磨法产乙醇产生的DDGS的半纤维素组分主要以阿拉伯木糖以及戊糖来源的木糖和阿拉伯糖组成[15]，其中木糖为10.2%、阿拉伯糖为5.6%[16-17]。乙醇生产工艺变化后，DDGS纤维含量有所改变。wWDS的NDF低于wDDGS (23 g/kg vs. 312 g/kg)[10]。DDGS-BPX的NDF、ADF及木质素含量均显著低于DDGS[4]。
1.2.3 粗脂肪及维生素DDGS的粗脂肪含量为8.4%~9.7%[18]，其脂肪酸组成多为不饱和脂肪酸。在生产过程中DDGS的PUFA容易发生过氧化导致其过氧化值高达84.1 meq/kg[19]。wDDGS的脂肪含量显著低于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]。低可溶性玉米蒸馏干燥谷物(LS-DDG)的粗脂肪含量为7.95%[20]。值得注意的是，DDGS中维生素E含量与粗脂肪含量呈正相关(R=0.667 7, P=0.147 3)，6个DDGS样本的维生素E平均含量为6.8 mg/kg, 并且还含有其他B族维生素如维生素B1 7.7 mg/kg、维生素B2 2.3 mg/kg、维生素B6 3.5 mg/kg及维生素B3 10.9 mg/kg[21]。
1.2.4 粗灰分及矿物元素wDDGS粗灰分含量为5.4%，但硫、氮、磷、钾含量都很高[22]，硫含量是其他农副产物残渣如棕榈仁压榨粕和橄榄残渣的3~4倍[23]。DDGS-BPX比DDGS含有更多的硫、钠、锰、铜、钼和硒，但锌含量以DDGS更高[4]。DDGS中的总磷含量较高，多为植酸磷，利用率较低。DDGS、HP-DDG和玉米胚芽的总磷含量分别为0.76%、0.33%和1.29%，生物学利用效率分别为60%、56%和25%[以磷酸二氢钾(KH2PO4)为对照][24-26]。加植酸酶可分解清亮浸泡液中和整个蒸馏物中植酸，释放4.52或0.86 mg/g的磷[27]。并且，植酸酶处理能使DDGS蛋白质含量增加，淀粉残渣减少[28]。在发酵时使用带有植酸酶的酵母，则干酒糟的植酸磷含量下降89.8%，游离磷含量增加142.9%[29]。
1.2.5 其他成分DDGS的酚酸组成和其相应的玉米一致，但酚酸含量是玉米的3.4倍。其中，阿魏酸和p-香豆酸占总酚酸的80%以上，香草酸、咖啡酸、p-香豆酸、阿魏酸、芥子酸和总酚酸含量分别为0.22、0.14、0.72、4.59、0.33和5.99 mg/g DM[30]。DDGS是霉菌毒素严重污染原料。来源于北京的17个DDGS样品均含有呕吐毒素和玉米赤霉烯酮，平均浓度分别为1.36 mg/kg和882.7 μg/kg，超标88%和41%[31]。台湾的30个DDGS样本有50.8%的样品同时感染5种镰刀菌属毒素[32]。此外，DDGS中还残留有抗生素以及微生物。对来源于美国9个州43个工厂的20个DDGS样本进行检测发现有13%的样本含有小于1.12 mg/kg的抗生素如红霉素、青霉素、四环素等[33]。wDDGS的微生物菌群主要是乳酸杆菌如Lactobacillus amylolyticus、Lactobacillus panis、Lactobacillus pontis和偶尔可检测到的酵母菌[19]。
1.3 物理特性用含有DDGS的原料制作饲料时，饲料的红度增加，但亮度降低[34-35]。而添加DDGS到面包或圆饼中能提升其粗脂肪和粗纤维含量，使产品偏金黄色[36-37]。
2 DDGS在猪生产上的应用 2.1 DDGS对猪的营养价值 2.1.1 DDGS的能值DDGS的总能比玉米高(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]，所以两者的消化能和代谢能没有显著差异[38]。因为原料的变化，能值有些许差异。如对28个DDGS样品进行分析，表观代谢能(AME)为5.94~12.21 MJ/kg，真代谢能(TME)为7.29~13.56 MJ/kg[39]。LS-DDG的消化能和代谢能分别为13.53和12.39 MJ/kg DM，与DDGS相当[20]。溶剂提油后的cDDGS的代谢能和净能分别为11.96和8.56 MJ/kg DM，比DDGS低[7]。在18.5 kg猪的玉米-大豆基础饲粮中添加0、15%、30%小麦-玉米DDGS，用比较屠宰试验测得其净能分别为10.17、10.16和10.17 MJ/kg DM，通过间接测热法测得净能分别为10.82、10.52和10.55 MJ/kg DM，通过化学分析法测得净能分别为10.24、10.26和9.91 MJ/kg DM[40]。DDGS在饲粮中的添加会降低饲粮干物质和能量的消化率[10]，即使配方净能和可消化氨基酸一致，饲粮的干物质和能量的表观总肠道消化率(ATTD)也随小麦-玉米DDGS的增加而线性下降，同时NDF的ATTD线性增加[41]。乙醇生产过程中的加工和发酵在一定程度上改善了纤维的消化率，所以DDGS的总饲粮纤维(TDF)的表观回肠消化率(AID)和ATTD比玉米高，但整个肠道发酵的TDF不足50%，暗示DDGS中超过50%的TDF没有被猪消化吸收[42]。对玉米副产物进行分析表明，阿拉伯木聚糖含量能极显著解释干物质的ATTD的变异(R2=0.67)，而非淀粉多糖木糖残渣能解释干物质(R2=0.78)、NDF (R2=0.63)、蛋氨酸(R2=0.40)和苏氨酸(R2=0.11)的ATTD的变异[43]。用T瘘管猪测试去油DDGS的养分消化率，赖氨酸的AID随DDGS的增加(0、20%和40%)而降低，并且去油DDGS和大豆油对NDF和酸洗乙醚提取物的AID和ATTD均有显著影响，饲粮酸洗乙醚提取物含量最高而NDF最低时，其NDF的AID和ATTD最高[44]。
2.1.2 DDGS的蛋白质和氨基酸利用效率小麦DDGS所有的氨基酸中，赖氨酸在肥育猪(82 kg)的AID最低，仅36%[45]，而且其标准回肠消化率(SID)变异很大(9%~82%)[46-47]。cDDGS中赖氨酸消化率变异也非常大[47]。wWDS的粗蛋白质、赖氨酸和组氨酸的回肠标准消化率系数(CSID)显著高于wDDGS，而蛋氨酸、半胱氨酸、异亮氨酸、亮氨酸和缬氨酸的CSID却显著低于wDDGS[10]。对DDGS进行去脂或加热处理会改变氨基酸消化率。添加玉米油使饲粮等脂肪含量时，高脂(11.5%) DDGS组的蛋白质和脯氨酸、色氨酸以外的所有必需氨基酸的AID和SID均显著高于低脂组(7.5%和6.9%)，额外加玉米油都无法补偿这种消化率的损伤[48]。对玉米DDGS进行130 ℃热处理10、20和30 min后，生长猪粗蛋白质的SID从77.9%下降到72.1%、66.1%和68.5%，赖氨酸的SID从66.8%下降到54.9%、55.3%和51.9%[49]。Yoon等[50]研究证实DDGS在60 kg猪饲粮中的增加会降低粗蛋白质的ATTD，不过甘露聚糖酶可以改善粗蛋白质的ATTD。可通过蛋白质中赖氨酸的含量预测赖氨酸的SID，赖氨酸占粗蛋白质的比例少于1.9%或2.8%的玉米DDGS不再适宜饲喂猪[46-47]。赖氨酸/粗蛋白质(R=0.63)以及赖氨酸的SID (R=0.68)与亮度均呈显著正相关[46]，代谢能和黄度显著正相关(R=0.39)[39]，所以，在DDGS的使用中，亮度是很重要的衡量指标。如果补充DDGS到饲粮中，应根据可消化氨基酸和可消化磷来配置含DDGS的饲粮，10%的DDGS可替代4.25%的大豆和5.7%的玉米，同时补充0.1%的赖氨酸[51]。DDGS在饲粮中含40%会降低氮的消化率[20]，但氮储备未受小麦DDGS含量的增加而影响[52]，这可能与氮排放增加有关[53-54]。
2.1.3 DDGS的矿物质应用磷的ATTD高达59.1%，所以DDGS中可利用磷比较丰富(0.36%)[24]。与玉米-大豆饲粮组相比，以有效磷一致为基础配方时，DDGS组仔猪的粪磷显著下降，与100 g/kg DDGS组相比，200 g/kg DDGS组降低了钙的储留以及钙ATTD[55]。
综上所述，DDGS的蛋白质品质不高，但通过补充晶体氨基酸能解决这个问题。DDGS的能值和玉米大致一样，只是如果在工艺中对其去油能值则会下降，所以，在使用中需要关注DDGS的生产工艺。运用DDGS替代单胃动物饲粮中的玉米豆粕时，建议将其净能、回肠可消化氨基酸、有效磷配平，这样才不会导致生产性能的下降。
2.2 DDGS对猪的饲用价值 2.2.1 在仔猪饲粮中的应用净能和可消化氨基酸一致时，cDDGS在5.2 kg仔猪饲粮中添加7.5%对平均日增重(ADG)、平均日采食量(ADFI)和饲料转化效率(G/F)没有影响[56]，在6.4 kg仔猪断奶后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仔猪采食含高达25% cDDGS的饲粮也不会对ADG、ADFI和G/F产生影响[57-58]。但cDDGS在仔猪饲粮中添加比例高达30%时会显著降低ADFI[59]。如果让猪断奶后先适应一段时间(21 d)再添加高达30%的cDDGS则不会影响其生产性能[60]，当然，如果cDDGS已经溶剂提油处理过[7]，或仔猪已经足够大(11 kg)[57]，则30%的玉米DDGS也不会影响其生产性能。高粱DDGS在11 kg仔猪饲粮中添加30%降低了G/F[61]。wDDGS在6.2 kg的断奶猪中添加10%不会影响其采食量和终体重，但添加15%时会显著降低采食量和体增重[62]。仔猪(6.7 kg)前期饲粮中香料的添加对仔猪后期采食DDGS或HP-DDG饲粮不利，并且有显著降低ADG的趋势[63]。DDGS的添加能增加5.2 kg仔猪回肠中炎性因子的mRNA表达量[56]。含硫高的DDGS能增加断奶8周阉公猪血清中α-生育酚和肝脏中谷胱甘肽的含量，即高含硫的DDGS可能保护了仔猪免受高度氧化的DDGS的损伤[19]。
2.2.2 在生长肥育猪饲粮中的应用大多数试验表明在生长肥育猪饲粮中添加高达15%[50, 64]、20%[53, 65]或30%[54]的cDDGS不会降低其生产性能。也有例外，如Xu等[66-67]报道在22~115 kg猪饲粮中添加高达30%DDGS时降低了ADFI以及ADG (29.8 kg猪)。DDGS的添加比例高达40%会显著降低ADG和ADFI[68]。保持饲粮可消化赖氨酸和色氨酸一致，用DDGS替代33 kg生长猪配方中的玉米和豆粕，其ADG显著下降[69]。保持饲粮可利用磷、可消化回肠赖氨酸及代谢能一致，饲粮中添加30%的DDGS不会降低ADFI，可如果同时添加30% DDGS和5%的牛油，则ADFI会显著低于玉米豆粕对照组[70]。相同情况下，以粉料形式向小猪提供含30% DDGS饲粮时，其ADFI相对于玉米豆粕对照组显著增加，G/F降低，而颗粒料形式的DDGS不会影响ADFI和G/F[71]。猪对DDGS有个适应过程，保持净能和可消化赖氨酸一致时，在小猪饲粮中添加30% DDGS显著降低第1阶段(29~50 kg)的ADFI和ADG，但对全期(29~120 kg)生长性能没有显著影响[72]。在饲粮中突然引入20%的DDGS不会对51.3 kg的肥育猪造成不良影响，但突然引入40%的低可消化赖氨酸，DDGS会显著降低ADG[73]。原料种类也对DDGS的使用效果产生不同影响。在25.5 kg猪的玉米-大麦-豆粕基础饲粮上添加0~30%的小麦-玉米DDGS，保持净能和可消化氨基酸一致时，ADG随着小麦-玉米DDGS的增加而线性降低，G/F有降低的趋势[41]。与玉米-大豆饲粮相比，在18.6 kg猪饲粮中添加15%或30%小麦-大豆DDGS使ADFI和ADG线性下降，但对G/F没有显著影响[74]。此外，溶剂提油后的cDDGS在饲粮中从0逐渐增加到30%时，29.6 kg生长猪的ADG、ADFI显著降低，G/F也有显著降低的趋势[7]。而将22 kg生长猪饲粮的豆粕50%或100%都用HP-DDG替代，都不会影响其生产性能[65]。
2.2.3 DDGS对胴体品质和肉质的影响尽管大多数试验证实在饲粮中添加一定比例的DDGS不会影响生长肥育猪的生产性能，但DDGS对肉质的影响却是负面的并且显著的。随饲粮中DDGS含量的增加(0~30%)，生长猪畜体重和屠宰率下降[7, 64, 66]；保持回肠可消化氨基酸一致时，20%的DDGS就会降低屠宰率[20]；与对照组相比，饲粮添加30% DDGS平均减轻了5.1 kg胴体重[75-76]。屠宰率降低的原因可能与DDGS蛋白质不平衡，内脏代谢活动增强，内脏重量增加相关[77]，也可能与DDGS粗纤维含量高，导致饲料通过速率增加，使得小肠生长增加相关[78-79]。在净能和可消化赖氨酸一致时，生长猪采食含30%DDGS的饲粮将显著降低眼肌面积和无脂瘦肉率[72]。饲粮中的DDGS从10%增加到30%，背肌大理石花纹会下降[66]。DDGS对肉质最大的影响是增加了肌肉中PUFA含量，增加其碘价，导致猪肉不易加工和储存。给100 kg公猪用20%或30% DDGS替代基础饲粮中的玉米和豆粕会降低其屠宰时(130 kg)腹部脂肪硬度[65-67, 70]，增加腹部脂肪的碘价[80]。40%的DDGS降低了肥猪的眼肌面积，背脂的不饱和程度也更高[73]。随着DDGS在生长肥育猪饲粮中从0增加到15%、30%和45%，猪的背膘厚线性下降，皮下脂肪的饱和脂肪酸和单不饱和脂肪酸浓度线性下降，PUFA浓度线性增加，背脂内外碘价线性增加[69]。Stein[24]总结了8个试验报道的DDGS对碘值的影响，7个试验表明碘值增加，1个不变。高碘值的猪肉十分柔软，不利于加工，容易氧化变质。饲粮中DDGS比例太高(30%)会影响储存期肉品的脂质过氧化值(TBARS)，降低肉货架寿命[81]。造成腹脂硬度降低和碘值增加的原因为DDGS高的不饱和脂肪酸含量导致脂肪及肌肉组织中不饱和脂肪酸增加[7, 66]。所以，当DDGS的脂肪含量从16.0%降低到5.6%时，导致猪肉PUFA浓度以及碘价降低[82]。同时添加30%的DDGS和5%的牛油能降低腹部脂肪的碘价[70]，只是改善幅度小[83]。LS-DDG[20]和10%的玉米胚芽[65]能在一定程度上缓解DDGS对猪肉的负面影响。维生素E能降低TBARS和肉的挥发性盐基氮(TVB-N)浓度，部分缓解DDGS比例太高引起肉货架寿命降低的负面影响[81]。在100 kg公猪的20% DDGS饲粮中添加0.6%的共轭亚油酸(CLA)能降低碘价，增加瘦肉率，但CLA对新鲜、冷藏或冷冻储存方式下的肉品质影响非常小[84]。Xu等[67]证实15%和30% DDGS饲粮组屠宰时和屠宰前3、6、9周去除DDGS会线性降低C18：2及碘价，所以要避免DDGS对猪肉品质的影响，最好在屠宰前3周停止饲喂DDGS饲粮，这与Hill等[85]的建议非常一致。
2.3 DDGS在母猪饲粮中的应用早期研究表明妊娠母猪饲粮中添加40%~80%的DDGS对母猪的体重、采食量、产仔数和仔猪体重无影响[86-87]。Hill等[85]研究表明仅在哺乳期添加15% DDGS和5%甜菜渣时，饲粮对仔猪增重和死亡率及母猪哺乳期失重无显著影响。将代谢能和赖氨酸配平后，在第2或3胎母猪的妊娠晚期及哺乳期饲粮中同时添加20%或40%饲粮的cDDGS，母猪繁殖性能没有受影响[88]。Wilson等[89]研究表明，妊娠期添加50% DDGS的同时在哺乳期添加20% DDGS，断奶仔猪的死亡率高，但是第2个产仔期这种现象消失，而且第1胎饲粮中添加DDGS缩短了第2胎母猪的发情间隔，所以哺乳母猪饲粮中DDGS的添加量可以达到20%。
综上所述，我们可看到，在一定范围内，让猪有个适应的过程，能用DDGS替代配方中的玉米、豆粕用于猪生产。但为了解决其PUFA引起的高碘价肉的问题，建议添加CLA和维生素E等添加剂，同时在屠宰前21 d停用DDGS。DDGS在母猪上的应用的相关报道还比较少，其实怀孕母猪能耐受粗纤维饲粮，理论上来说，富含NDF的DDGS应该是妊娠母猪的适宜原料。因此，有必要在母猪上加大DDGS的研发力度，观察其使用效果。此外，DDGS在养猪生产上的应用研究集中于生产性能和肉品质两方面，但有限的资料表明，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还富含其他矿物质和酚酸等，这些物质可能对猪的免疫、抗氧化等方面产生效果，因此，有必要对此进行研究。
3 DDGS应用过程中存在的问题及改进思路 3.1 过筛DDGS最大问题是质量变异大，蛋白质品质低，粗纤维含量太高。对采用POET (Sioux Fals，SD)系统的27个乙醇工厂进行DDGS采样分析，干物质含量的变异25.6%来自于时间，7.1%的变异源于不同生产地点，生产地点的不同解释了粗蛋白质、粗脂肪、ADF、NDF、粗纤维和硫含量变异的38.9%、12.5%、11.1%、17.2%和25.5%，而ADF和NDF含量的变异大部分是因为时间原因(43.6%和50.1%)，因此，在使用DDGS时尽可能采用同一时间段相同生产工艺厂家的原料，养分变异程度相对较小[90]。降低DDGS中粗纤维最简单而有效的方法是过筛。用1 130、869、582、389 μm的筛子对干酒糟进行过筛处理后，得到物占27.2%、22.8%、21.4%和15.0%，底盘上物料占13.5%，其NDF含量分别为38.8%、36.8%、34.6%、32.2%和27.7%[91]。过80号筛(249~177 μm)的wDDGS将粗蛋白质含量从原来的371.6 g/kg增加到底盘中的432.4 g/kg，同时显著降低了NDF和ADF含量[92]。过筛后再对各筛上物进行空气流分级能进一步降低DDGS的粗纤维含量。对869~1 130 μm筛上部分的片段进行空气分级，风力从1.75到1.92 ms-1增加，轻片段含量从7.2%增加到13.6%，其中的NDF含量从63.1%降低到59.0%，NDF分离系数从2.7下降到2.2[91]。这也在试验工厂得到验证，效果不错[93]。在降低NDF方面低速率扬风3次的效果与中速率扬风1次效果相当，把整个DDGS一次性扬风效率不及过筛后再分别对筛上筛下物扬风[94]。木聚糖酶的添加(24 000 U/kg)能增加液态DDGS饲粮的NDF的AID[95]。只是，酶的作用具有针对性，所以要有效降解DDGS中的纤维，还需要多酶混合。
3.2 发酵对发酵过程进行改良也能改善DDGS的质量。对生淀粉进行发酵能增加Pronghorn黑小麦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，发酵前对原料进行预处理能增加DDGS营养价值[97]。对DDGS进行酸碱或热水预处理能分解纤维素释放出糖，预处理后的DDGS还能继续加纤维素酶等进行酶解产糖[98]，由此产生的发酵副产物DDGS营养价值也得到提升。用含有α-淀粉酶和葡糖淀粉酶的复合酶制剂STARGEN 001在50 ℃处理生淀粉后再用酿酒酵母发酵谷物产乙醇所产生的DDGS营养价值更高[96]。
3.3 不同组分组合试验证实将去壳大麦和谷物DDGS混合后能显著改变营养组分的结构。检测发现谷物和谷物副产物混合后与脂肪相关的分子光谱强度[99]以及与蛋白质分子结构相关的光谱特征都发生了改变[100]，最终饲料的组合改变了饲料化学和营养结构，营养物质的消化率和可利用率得到改变。在混合浓缩蒸馏可溶物(CDS)和湿蒸馏谷物(WDG)时，随着CDS的减少，cDDGS的颜色变得更亮，样品的不溶纤维含量以及氨基酸增加，而脂肪、总可溶性糖含量下降[101]。与混合饱和及不饱和脂肪相比，通过化学方法对脂肪进行部分加氢更能有效的提高消化率，但需注意，饲粮碘价太低(20)时，消化率反倒会降低[102]。研究一般认为是热损伤导致了DDGS中氨基酸的消化率低下，但糖浆块的氨基酸AID和SID与DDGS一致或更高，只是冷凝液可溶物和酒精废液蒸发物的大部分氨基酸消化率低于DDGS，尤其是蛋氨酸。可如果是热损伤导致冷凝液可溶物的氨基酸消化率下降，下降最严重的应该是赖氨酸而不是蛋氨酸，所以导致DDGS氨基酸消化率下降的原因可能还是因为饲粮纤维浓度太高或赖氨酸浓度太低等其他原因[103]。
3.4 生产活性物质DDGS可用于生产生物活性物质，如通过红发夫酵母(Phaffia rhodozyma，ATCC 24202)和红掷孢酵母(Sporobolomyces roseus，ATCC 28988)共发酵或单发酵DDGS生产278 μg/g β-胡萝卜素[104]；通过白腐菌发酵产生木质素降解酶[105]；通过裂褶菌(Schizophyllum commune，ATCC 20165)发酵麦芽提取物和DDGS生产裂褶多糖[106]。此外，也能从cDDGS和高粱DDGS中提取植物甾醇和二十八烷醇[107]。
4 小结虽然DDGS能生产生物活性物质，但其大量的使用还是在动物生产中。养殖者需要了解原料的营养组分及其变异程度才能更好地选择和利用这种原料。乙醇生产厂家应调控生产工艺，使DDGS质量更稳定。同时，对DDGS营养价值的关注不应仅仅在其氨基酸和粗纤维以及植酸磷方面，DDGS还富含有其他矿物质以及维生素，也许能在免疫和抗氧化方面改善其在动物上的饲养效果。DDGS在母猪上的使用也有必要投入更多的研究。最终，通过乙醇生产企业的工艺改良以及动物营养专家的努力，全方面探究DDGS的营养价值，扩大DDGS的利用率，将为缓解饲料行业能量饲料缺乏提供有效解决路径。
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