Chinese Journal of Animal Nutrition >

2024 , Vol. 36 >Issue 6: 4003 - 4013

DOI: https://doi.org/10.12418/CJAN2024.343

RESEARCH PAPER

Effects of Steam Explosion and Steam Explosion+Fermentation on Nutritional Components, in Vitro Rumen Fermentation Characteristics and Methane Production of Bagasse

  • QU Jiajing , 1, 2 ,
  • PU Xuanxuan 2 ,
  • HUO Jiabin 2 ,
  • WANG Wenxing 2 ,
  • WANG Rong 2 ,
  • WANG Min 2 ,
  • NIU Huaxin , 1, * ,
  • ZHANG Xiumin , 2, *
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  • 1 College of Animal Science and Technology, Inner Mongolia Minzu University, Tongliao 028000, China
  • 2 Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China
*professor, E-mail: ;
associate professor, E-mail:

Received date: 2023-12-22

  Online published: 2024-06-07

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Abstract

This study was conducted to investigate the effects of steam explosion and steam explosion+fermentation on nutritional components, in vitro rumen fermentation characteristics and methane (CH4) production of bagasse. Bagasse was treated with steam explosion and steam explosion+fermentation, and 3 groups were designed: control group (CK group, untreated bagasse), steam explosion group (SE group, steam explosion treated bagasse) and steam explosion+fermentation group (SE+F group, steam explosion+fermentation treated bagasse), each group contained 3 replicates. The conventional nutritional components and carbohydrate composition of bagasse in the 3 groups were analyzed, and the Xiangdong black goat was selected as rumen fluid donor animal for 72 h in vitro rumen fermentation trial. The results show that compared with CK group, the contents of neutral detergent soluble, water soluble carbohydrate and total sugar in bagasse of SE group were significantly increased (P<0.05); the in vitro rumen fermentation dry matter degradation rate, neutral detergent fiber (NDF) degradation rate, total volatile fatty acid concentration and acetate to propionate ratio were significantly increased (P<0.05), and the gas production and CH4 production during 8 to 72 h were obvious improved. Compared with SE group, the contents of crude protein, true protein and neutral detergent soluble in bagasse of SE+F group were significantly increased (P<0.05), and the contents of hemicellulose, NDF and acid detergent fiber were significantly decreased (P<0.05); the in vitro rumen fermentation total volatile fatty acid concentration and acetate to propionate ratio were significantly decreased (P<0.05), the gas production and CH4 production during 8 to 72 h were obvious decreased, and the ammonia nitrogen content was significantly increased (P<0.05). In summary, the steam explosion treatment can increase water soluble carbohydrate content of bagasse, and release more monosaccharide, promote the degradation of bagasse and improve the total volatile fatty acids concentration during in vitro rumen fermentation. Microbial fermentation of bagasse after steam explosion can promote the rumen microbial protein synthesis and reduce the CH4 production.

Key words： bagasse; steam explosion; fermentation; in vitro; methane; volatile fatty acids

Cite this article

QU Jiajing , PU Xuanxuan , HUO Jiabin , WANG Wenxing , WANG Rong , WANG Min , NIU Huaxin , ZHANG Xiumin . Effects of Steam Explosion and Steam Explosion+Fermentation on Nutritional Components, in Vitro Rumen Fermentation Characteristics and Methane Production of Bagasse[J]. Chinese Journal of Animal Nutrition, 2024 , 36(6) : 4003 -4013 . DOI: 10.12418/CJAN2024.343

我国优质粗饲料资源缺乏,每年进口约200万t优质干草,这严重限制了反刍家畜养殖业的发展。此外,饲喂低质粗饲料会增加反刍家畜的甲烷(CH4)排放,促进全球温室效应[1]。因此,对本土粗饲料资源进行提质加工利用变得越来越重要。甘蔗渣是制糖过程中的副产物,我国每年甘蔗总产量为7 000多万t,每吨生甘蔗大约产生300 kg甘蔗渣[2],每年产生2 000多万t甘蔗渣。甘蔗渣可用作反刍家畜的粗饲料,但是其木质纤维素含量高、粗蛋白质含量低、适口性差,饲喂反刍家畜时消化率低,营养价值有待提升[3]。因此,研究人员应用物理处理(蒸汽爆破)[4]、化学处理(利用尿素和氢氧化钙处理)[5]和生物处理(微生物发酵)[6]等方法对甘蔗渣进行加工,以提高甘蔗渣作为反刍动物饲料的饲用价值。Chen等[4]采用蒸汽爆破处理甘蔗渣,发现可溶性碳水化合物含量增加,体外瘤胃发酵的纤维降解率和产气量提高。Chaji等[7]报道,采用蒸汽爆破处理显著增加了甘蔗渣的可溶性碳水化合物含量和体外瘤胃发酵的干物质降解率,体外总产气量和CH4产量也有所增加。此外,对粗饲料进行微生物发酵处理也是提升其营养价值的有效手段,在对纤维素进行裂解的同时,可以增加粗饲料中粗蛋白质和真蛋白质的含量[8-9]。通过微生物发酵技术可以降低甘蔗渣中纤维素和半纤维素的含量,促进瘤胃微生物对营养物质的降解[10]。在瘤胃尼龙袋发酵过程中,利用微生物发酵饲料可增加挥发性脂肪酸(VFA)、氨态氮(NH3-N)、微生物蛋白(MCP)浓度,提高营养物质消化率[11]。饲喂微生物发酵饲料还可以显著降低反刍动物CH4产量[12]。Zhao等[13]利用微生物发酵玉米秸秆,发现可以显著降低体外瘤胃发酵的CH4产量。
目前,还缺乏关于对甘蔗渣进行蒸汽爆破和发酵双重处理后进行体外瘤胃发酵的研究。因此,本研究对甘蔗渣进行蒸汽爆破处理,并在蒸汽爆破处理后进行微生物发酵处理,研究蒸汽爆破和发酵对甘蔗渣营养成分和碳水化合物组分的影响,并结合体外瘤胃发酵试验,探究蒸汽爆破和蒸汽爆破+发酵对甘蔗渣营养成分及其体外瘤胃发酵特征和CH4产量的影响,旨在为提升甘蔗渣的饲用价值和减少反刍家畜CH4排放提供理论参考和技术支撑。

1 材料与方法

1.1 试验材料及处理

甘蔗渣的蒸汽爆破(QBS-80B蒸汽爆破试验台,正道启宝环保科技有限公司)及发酵处理均在安琪酵母股份有限公司进行。
蒸汽爆破处理:在甘蔗渣表面均匀喷洒相应雾化的蒸馏水,装入自封袋浸润12 h。蒸汽爆破前将气缸预热至100 ℃以上,加入适量甘蔗渣后,设置温度为200 ℃,压力为2.0 MPa,维压时间2~3 min,瞬间释压,甘蔗渣在自然压差条件下快速膨化后进入收集装置,由冷却器进行冷却,随后将蒸汽爆破后的甘蔗渣放入烘箱(65 ℃)中烘干备用。
发酵处理:对需要发酵的甘蔗渣按比例喷洒含发酵剂(菌种为酿酒酵母菌及乳酸杆菌,由安琪酵母股份有限公司生产)的水,发酵剂∶水=1 g∶300 kg,随后将适量尿素溶于蒸馏水后均匀喷洒在甘蔗渣上,调节甘蔗渣含水量至60%,随后装入厌氧发酵袋,将发酵袋中空气排空后密封,发酵环境温度保持在25 ℃,28 d后取出,烘干(65 ℃)粉碎后备用。

1.2 试验动物和饲粮

试验动物的处理和护理均按照中国科学院亚热带农业生态研究所动物护理专业委员会的规定进行(ISA TAN202205)。试验所用的3只瘤胃液供体动物为装有瘤胃瘘管的湘东黑山羊,饲粮精粗比为1∶1,粗饲料为玉米秸秆,精饲料组成为玉米47.00%、豆粕24.00%、麦麸22.00%、食盐0.77%、石粉2.23%和预混料4.00%。每天08:00和18:00各饲喂1次,单笼饲养,自由饮水。

1.3 试验设计与体外发酵

体外瘤胃发酵试验设置对照组(CK组,未处理的甘蔗渣)、蒸汽爆破组(SE组,蒸汽爆破处理的甘蔗渣)、蒸汽爆破+发酵组(SE+F组,蒸汽爆破+发酵处理的甘蔗渣)3组,每批次试验每组3个重复,共3批次。根据Menke等[14]的方法配制800 mL人工瘤胃缓冲液,配制好后持续通入二氧化碳(CO2),以确保厌氧环境,并置于39.5 ℃水浴锅中预热1 h。在晨饲前选取3只山羊,采集瘤胃内容物至预热过的保温桶内,使用4层纱布分别过滤出瘤胃液100 mL。将滤出的200 mL瘤胃液与人工瘤胃缓冲溶液混合,配制成1 000 mL体外瘤胃培养液,期间持续通入CO2。每个发酵瓶加入0.6 g底物,在39.5 ℃条件下预热1 h,使用瓶口分液器迅速向每个发酵瓶中加入60 mL体外瘤胃培养液,在加入瘤胃液前将发酵瓶通入CO2,加入培养液后立即盖严瓶塞。随后将发酵瓶放入全自动体外分批培养系统[15],排气压力设置为10 kPa,排出的气体自动进入气相色谱仪,测定每个发酵瓶的CH4和氢气(H2)浓度,根据Wang等[16]所述的公式计算总产气量及CH4和H2产量。

1.4 样品采集与测定

体外瘤胃发酵72 h后终止发酵,使用便捷式pH计(上海奥塞斯仪器有限公司)测定发酵液pH;随后将发酵液混匀后取8 mL,于-20 ℃冰箱保存,用于测定MCP浓度。待发酵液静置分层后,取2份2 mL上清液进行离心(4 ℃、12 000×g、10 min),取2份1.5 mL上清液,转移至预先加入0.15 mL偏磷酸(25%,质量体积比)的2 mL离心管中,置于-20 ℃保存,用于测定发酵液VFA和NH3-N浓度。
参考田旭等[17]报道的方法,每个发酵瓶中剩余的发酵液和固体使用300目尼龙布过滤,至发酵瓶中无残留后,将尼龙布及未滤出物置于105 ℃恒温烘干箱中烘干至恒重,计算干物质降解率。MCP浓度参考Wang等[18]报道的方法,使用核酸(RNA)法进行测定。VFA浓度参考Wang等[19]报道的方法,将样品解冻再次离心(4 ℃、12 000×g、10 min),使用液体进样气相色谱仪(7890A,安捷伦科技有限公司,美国)分析。NH3-N浓度测定流程参考Weatherburn[20]报道的方法。
干物质含量使用烘箱(105 ℃,24 h)测定[21];粗蛋白质和粗灰分含量参考(AOAC,2005)的方法测定[21];真蛋白质含量参考辛欣[22]报道的凯氏定氮法测定;有机物含量通过干物质和粗灰分含量的差值计算;中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)含量参考Van Soest等[23]的方法测定,中性洗涤可溶物(NDS)含量通过NDF含量计算(NDS=100-NDF),半纤维素含量通过NDF和ADF含量的差值计算;可溶性碳水化合物(WSC)含量采用蒽酮比色法测定;单糖含量使用高效液相色谱仪(LC1290,安捷伦科技有限公司,美国)测定。

1.5 统计分析

试验数据利用SPSS 27.0软件的混合线性模型进行线性分析。每批次每组中3个重复样品取平均值后用于统计,将分组(n=3)作为固定因子,试验批次(n=3)作为随机因子。结果用平均值和均值标准误(SEM)表示,P<0.05表示差异显著。

2 结果

2.1 蒸汽爆破和蒸汽爆破+发酵处理对甘蔗渣营养成分和单糖组成的影响

由表1可见,与CK组相比,SE组甘蔗渣的粗蛋白质、真蛋白质、中性洗涤可溶物、有机物、可溶性碳水化合物、阿拉伯糖、半乳糖、葡萄糖、木糖、鼠李糖、甘露糖和总糖含量显著提高(P<0.05),NDF、ADF、半纤维素含量显著降低(P<0.05);与CK组相比,SE+F组甘蔗渣的粗蛋白质、真蛋白质、中性洗涤可溶物、可溶性碳水化合物、阿拉伯糖、半乳糖、葡萄糖、木糖、鼠李糖、甘露糖和总糖含量显著提高(P<0.05),中性洗涤纤维、酸性洗涤纤维、半纤维素和核糖含量显著降低(P<0.05);与SE组相比,SE+F组甘蔗渣的粗蛋白质、真蛋白质、中性洗涤可溶物、阿拉伯糖、葡萄糖和甘露糖含量显著提高(P<0.05),NDF、ADF、半纤维素、可溶性碳水化合物、半乳糖、木糖、核糖、鼠李糖和总糖含量显著降低(P<0.05)。
表1 蒸汽爆破和蒸汽爆破+发酵处理对甘蔗渣营养成分和单糖组成的影响(干物质基础)

Table 1 Effects of steam explosion and steam explosion+fermentation treatment on nutrient composition and monosaccharide composition of bagasse (DM basis)

项目
Items		 组别 Groups SEM P值
P-value
CK SE SE+F
营养成分 Nutrient composition/%
粗蛋白质 CP 2.42c 3.29b 16.80a 0.241 <0.01
真蛋白质 TP 1.69c 1.97b 13.33a 0.211 <0.01
中性洗涤纤维 NDF 85.12a 74.00b 62.11c 0.731 <0.01
酸性洗涤纤维 ADF 50.44a 47.41b 41.67c 0.600 <0.01
半纤维素 HC 34.71a 26.64b 20.41c 0.734 <0.01
中性洗涤可溶物 NDS 14.92c 26.33b 38.02a 0.735 <0.01
有机物 OM 94.70b 95.40a 92.21b 0.581 <0.01
可溶性碳水化合物 WSC 11.44c 39.89a 16.71b 1.056 <0.01
单糖组成 Monosaccharide composition/(g/kg)
阿拉伯糖 Arabinose 0.23c 0.54b 0.86a 0.034 <0.01
半乳糖 Galacose 0.13c 0.38a 0.31b 0.018 <0.01
葡萄糖 Glucose 0.43c 0.76b 1.20a 0.037 <0.01
木糖 Xylose 0.32c 2.29a 1.30b 0.094 <0.01
核糖 Ribose 0.12a 0.12a 0.09b 0.010 0.04
鼠李糖 Rhamnose 0.10c 3.20a 1.34b 0.119 <0.01
甘露糖 Mannose 0.27c 0.12b 0.49a 0.011 <0.01
总糖 Total 1.34c 7.27a 5.59b 0.340 <0.01

同行数据肩标不同小写字母表示差异显著(P<0.05),相同或无字母表示差异不显著(P>0.05)。下表同。

In the same row, values with different small letter superscripts mean significant difference (P<0.05), while with the same or no letter superscripts mean no significant difference (P>0.05). The same as below.

2.2 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵营养物质降解率和产气参数的影响

由图1可见,与CK组相比,SE组和SE+F组甘蔗渣体外瘤胃发酵的8~72 h产气量均明显提高;与SE组相比,SE+F组甘蔗渣体外瘤胃发酵的8~72 h产气量均明显降低。
图1 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵72 h产气量影响

Fig.1 Effects of stem explosion and stem explosion+fermentation treatment of bagasse on gas production during 72 h in vitro rumen fermentation

由表2可见,与CK组相比,SE组甘蔗渣的体外瘤胃发酵干物质降解率、NDF降解率、每克底物的产气量、降解每克底物的产气量、潜在最大产气量、产气速率和起始底物降解速率显著提高(P<0.05);与CK组相比,SE+F组甘蔗渣的体外瘤胃发酵干物质降解率、产气速率和起始底物降解速率显著提高(P<0.05),NDF降解率、ADF降解率、降解每克底物的产气量显著降低(P<0.05);与SE组相比,SE+F组甘蔗渣的体外瘤胃发酵NDF降解率、ADF降解率、每克底物的产气量、降解每克底物的产气量、潜在最大产气量显著降低(P<0.05)。
表2 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵营养物质降解率和产气参数的影响

Table 2 Effects of steam explosion and steam explosion+fermentation treatments of bagasse on nutrient degradation rates and gas production parameters in vitro rumen fermentation

项目
Items		 组别 Groups SEM P值
P-value
CK SE SE+F
营养物质降解率 Nutrient degradation rate/%
干物质 Dry matter 36.71b 50.00a 48.02a 0.872 <0.01
中性洗涤纤维 NDF 37.72b 42.71a 30.22c 1.112 <0.01
酸性洗涤纤维 ADF 35.70a 39.71a 28.44b 1.141 <0.01
产气量 Gas production
每克底物的产气量
Gas production per gram of substrate/(mL/g)		 255.04b 449.73a 282.87b 9.370 <0.01
降解每克底物的产气量
Gas production per gram of degraded substrate/(mL/g)		 695.06b 899.64a 593.00c 21.544 <0.01
潜在最大产气量
Potential maximum gas production/(mL/g)		 258.11b 457.52a 288.38b 8.740 <0.01
产气速率
Gas production rate/×10-2 h-1		 5.24b 6.70a 7.00a 0.009 <0.01
起始底物降解速率
Initial substrate degradation rate/×10-2 h-1		 1.93b 6.74a 7.05a 0.200 <0.01

2.3 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵CH4和H2生成的影响

由图2可见,与CK组相比,SE组甘蔗渣体外瘤胃发酵的8~72 h CH4产量均明显提高,SE+F组甘蔗渣体外瘤胃发酵的8~72 h CH4产量均明显降低;与SE组相比,SE+F组甘蔗渣体外瘤胃发酵的8~72 h CH4产量均明显降低。
图2 蒸汽爆破与蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵72 h CH4产量的影响

Fig.2 Effects of stem explosion and stem explosion+fermentation treatments of bagasse on CH4 production during 72 h in vitro ruminal fermentation

由表3可见,与CK组相比,SE组甘蔗渣的体外瘤胃发酵CH4每克底物的产量、潜在最大产量、降解每克底物的产量和产生速率显著提高(P<0.05),H2降解每克底物的产量显著降低(P<0.05);与CK组相比,SE+F组甘蔗渣的体外瘤胃发酵CH4潜在最大产量、产生速率显著提高(P<0.05),CH4降解每克底物的产量、产生速率及H2降解每克底物的产量显著降低(P<0.05);与SE组相比,SE+F组甘蔗渣的体外瘤胃发酵CH4潜在最大产量、降解每克底物的产量和产生速率显著降低(P<0.05)。
表3 蒸汽爆破与蒸汽爆破+发酵处理甘蔗渣对体外发酵72 h CH4和氢气生成的影响

Table 3 Effects of steam explosion and steam explosion+fermentation treatment of bagasse on CH4 and H2 productions during 72 h in vitro rumen fermentation

项目
Items		 组别 Groups SEM P值
P-value
CK SE SE+F
甲烷 CH4
每克底物的产量 Production per gram of substrate/(mL/g) 21.20b 42.60a 21.30b 0.960 <0.01
潜在最大产量 Potential maximum production/(mL/g) 19.88c 47.63a 23.34b 0.744 <0.01
降解每克底物的产量
Production per gram of degraded substrate/(mL/g)		 57.82b 85.16a 44.51c 1.871 <0.01
产生速率 Production rate/h-1 0.26c 0.80a 0.62b 0.023 <0.01
氢气 H2
每克底物的产量 Production per gram of substrate/(mL/g) 0.45 0.38 0.36 0.034 0.18
潜在最大产气量 Potential maximum production/(mL/g) 0.42 0.37 0.36 0.030 0.40
降解每克底物的产量
Production per gram of degraded substrate/(mL/g)		 1.24a 0.77b 0.75b 0.085 0.01
产生速率 Production rate/h-1 0.57 1.10 0.73 0.220 0.31
消耗速率 Consumption rate/h-1 0.36b 1.22a 0.97ab 0.164 0.01

2.4 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵VFA和MCP生成的影响

由表4可知,与CK组相比,SE组甘蔗渣的体外瘤胃发酵NH3-N、总挥发性脂肪酸(TVFA)浓度及乙酸/丙酸、乙酸比例显著提高(P<0.05);与CK组相比,SE+F组甘蔗渣的体外瘤胃发酵NH3-N、MCP浓度及丁酸、异丁酸、戊酸、异戊酸比例显著提高(P<0.05);与SE组相比,SE+F组甘蔗渣的体外瘤胃发酵NH3-N、MCP浓度及丁酸、异丁酸、戊酸、异戊酸比例显著提高(P<0.05),TVFA浓度、乙酸/丙酸和乙酸比例显著降低(P<0.05)。
表4 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵VFA和MCP生成的影响

Table 4 Effects of steam explosion and steam explosion+fermentation treatment of bagasse on VFA and MCP production during 72 h in vitro rumen fermentation

项目
Items		 组别 Groups SEM P值
P-value
CK SE SE+F
pH 6.79 6.69 6.73 0.023 0.12
氨态氮 NH3-N/(mmol/L) 8.61c 9.75b 20.85a 0.330 <0.01
微生物蛋白 MCP/(mg/mL) 0.32b 0.34ab 0.36a 0.007 <0.01
总挥发性脂肪酸 TVFA/(mmol/L) 41.69b 63.70a 42.16b 1.730 <0.01
乙酸/丙酸 Acetate/propionate 2.30b 2.51a 2.32b 0.082 0.02
挥发性脂肪酸比例 VFA proportion/%
乙酸 Acetate 60.62b 63.60a 59.62b 1.051 0.04
丙酸 Propionate 26.66 25.30 25.68 0.422 0.09
丁酸 Butyrate 8.73b 9.99b 11.61a 0.360 <0.01
异丁酸 Isobutyrate 0.98b 0.90b 1.24a 0.053 <0.01
戊酸 Valerate 0.78b 0.87b 1.30a 0.039 <0.01
异戊酸 Isovalerate 1.49b 1.32b 2.19a 0.070 <0.01

3 讨论

3.1 蒸汽爆破和蒸汽爆破+发酵处理对甘蔗渣营养成分的影响

甘蔗渣的细胞壁主要成分为难降解的木质纤维素,难以被瘤胃微生物利用,并影响其他营养物质的降解。蒸汽爆破是将底物在高温高压状态下瞬时爆破,断裂木质素与半纤维素之间的化学键,大量的纤维素和半纤维素被释放[24]。在本试验中,SE组甘蔗渣的NDF、ADF和半纤维素含量显著下降,与蒸汽爆破处理玉米秸秆研究结果[25]一致。蒸汽爆破过程还能够水解生成更多的可溶性碳水化合物和单糖[26]。Jiang等[27]研究发现,蒸汽爆破后麦麸的可溶性碳水化合物含量显著提高。本试验中,蒸汽爆破处理后甘蔗渣的可溶性碳水化合物含量也显著提高。崔潇文等[28]对番茄皮渣进行蒸汽爆破处理,发现增加了单糖含量。Chang等[29]也研究发现,蒸汽爆破处理可增加玉米秸秆中各类单糖含量。本研究发现相似结果,蒸汽爆破处理显著增加了甘蔗渣的阿拉伯糖、半乳糖、葡萄糖、木糖和鼠李糖含量。
发酵处理可以通过微生物将低质粗饲料中难以消化的纤维素进行降解,而蒸汽爆破处理可以增大微生物对纤维的可及性,在对甘蔗渣蒸汽爆破后进行发酵处理则可以进一步促进纤维素的降解。本试验中,SE+F组甘蔗渣的NDF和ADF含量低于SE组。可溶性碳水化合物作为碳源供发酵微生物生长和繁殖[30],在发酵过程中会被消耗,所以其含量存在降低的现象。SE+F组的阿拉伯糖、葡萄糖含量高于SE组,是由于纤维素和半纤维素通过蒸汽爆破后,更有利于微生物的附着和发酵,使一部分多糖被降解为单糖。由于发酵处理时加入了无机氮源,因此SE+F组甘蔗渣的粗蛋白质含量要高于SE组,且发酵过程中微生物可将无机氮转化为MCP[30-31],导致SE+F组甘蔗渣的真蛋白质含量显著提高。

3.2 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵营养物质降解率和产气参数的影响

蒸汽爆破处理对原料纤维素结构的裂解作用,能够增大瘤胃微生物对底物纤维的可及性,有利于瘤胃微生物的定植[32-33]。Zhao等[25]对玉米秸秆蒸汽爆破处理后进行体内原位培养试验(尼龙袋降解试验)发现,可以显著提高干物质降解率。蒸汽爆破处理芦苇也显著增加了体外瘤胃发酵的NDF和ADF降解率[29]。本研究中,与CK组相比,蒸汽爆破处理甘蔗渣的体外瘤胃发酵干物质和NDF降解率显著提高,可见蒸汽爆破处理后底物的纤维更容易被降解消化。瘤胃中的气体主要由瘤胃微生物降解碳水化合物产生。阳伏林等[34]报道,体外发酵总产气量与干物质降解率、饲粮中碳水化合物含量及降解率具有高度相关性,在一定程度上能够反映瘤胃微生物对饲粮的降解利用程度。本试验中,SE组的甘蔗渣体外瘤胃发酵产气量显著大于CK组,这也与其干物质降解率高于CK组一致。蒸汽爆破+发酵处理同样显著提高了甘蔗渣体外瘤胃发酵的干物质降解率,但是却降低了NDF和ADF降解率,可能是蒸汽爆破后发酵过程中微生物将易降解的纤维素进行降解,用作自身生长和繁殖所需的碳源,甘蔗渣中不易降解的纤维比例增加,导致在体外瘤胃发酵中纤维的降解率降低[35]。且由于SE+F组甘蔗渣的NDF、ADF及可溶性碳水化合物等含量低于SE组,产气潜力较低,并且SE+F组甘蔗渣的NDF和ADF的降解率低于SE组,导致SE+F组体外发酵总产气量降低。此外,SE+F组CH4产量显著低于SE组,也是导致SE+F组总产气量低于SE组的原因之一。

3.3 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣对体外瘤胃发酵CH4和H2生成的影响

反刍动物可在瘤胃微生物的协同作用下,将饲粮发酵转化为各类营养物质供机体吸收,在此过程伴随着CH4的产生,瘤胃发酵产生的CH4占反刍动物CH4生成总量的80%以上[36]。研究表明,蒸汽爆破处理会增加秸秆等粗饲料体外瘤胃发酵的CH4产量[25];芦苇在经过蒸汽爆破处理后进行体外瘤胃发酵,也会产生更多的C H 4 [33];Theuretzbacher等[37]对麦秸进行蒸汽爆破处理,发现体外瘤胃发酵CH4产生速率显著提高。在本研究中也有相似发现,可能是由于蒸汽爆破后原料中的营养物质更易被甲烷菌获取,有利于甲烷菌的增殖与活动,从而促进CH4生成。而CH4产量增加意味着大量的H2被甲烷菌利用合成CH4,H2的消耗速率也随之增加。
研究表明,饲粮中添加酵母菌[38]和乳酸菌[39]可以降低瘤胃CH4产量。利用乳酸菌发酵全混合日粮(TMR),可显著降低体外瘤胃发酵的CH4产量[40-41]。本试验也发现SE+F组的甘蔗渣体外瘤胃发酵CH4产量显著低于SE组。这可能是因为发酵饲料中酵母菌、乳酸菌和其他微生物可以利用纤维和可溶性碳水化合物等营养成分生成乳酸等有机酸,改变底物的碳水化合物的组成和降解特性,减少用于与CH4生成相关的瘤胃发酵活动所需的碳水化合物含量,导致CH4生成减少,这在上述添加乳酸菌等微生物制作发酵饲料导致CH4产量减少的研究中有相似报道[39⇓-41]。此外,饲料原料在发酵处理过程中,酵母菌和乳酸菌等微生物会产生一些次级代谢产物,也会对瘤胃CH4生成产生抑制作用[38-39]。

3.4 蒸汽爆破和蒸汽爆破+发酵处理甘蔗渣体外瘤胃发酵对发酵特征的影响

NH3-N浓度是瘤胃氮代谢的重要衡量指标,为瘤胃MCP合成提供前体物质[42]。研究表明,蒸汽爆破处理秸秆等粗饲料,可以增加瘤胃液NH3-N浓度,并且MCP浓度增加[43]。可能是由于蒸汽爆破处理破坏了甘蔗渣紧密的物理化学结构,使一部分被紧密包裹的含氮化合物得到了释放。He等[44]对多种农作物副产品蒸汽爆破后进行体外瘤胃发酵试验发现,蒸汽爆破后的瘤胃液NH3-N浓度增加,并且提高了MCP浓度。本试验中,SE组体外瘤胃发酵的NH3-N浓度也高于CK组,但未观察到SE组MCP浓度高于CK组,推测是由于NH3-N浓度增加幅度有限,未能引起MCP浓度显著增加。SE+F组体外瘤胃发酵的NH3-N浓度显著高于SE组和CK组,同时MCP浓度显著高于CK组,可能是SE+F组较高含量的真蛋白被降解为氨基酸后更易被微生物吸收利用,从而促进MCP合成。
VFA是碳水化合物经瘤胃微生物降解后的主要产物,本试验中SE组体外瘤胃发酵的TVFA浓度显著增加,这与其干物质和纤维降解率提高是一致的。瘤胃内纤维降解过程产生较多的乙酸[45],SE组甘蔗渣的NDF和ADF降解率均显著提高,更有利于乙酸生成,使得乙酸比例显著升高。SE+F组体外瘤胃发酵的TVFA浓度较SE组要低,是由于微生物发酵处理过程中对可溶性碳水化合物等易降解碳水化合物组分的消耗,导致底物中可用于瘤胃发酵的碳水化合物含量减少,进而降低TVFA浓度。SE+F组甘蔗渣的NDF和ADF降解率低于SE组,导致发酵液中乙酸比例降低。另外,SE+F组甘蔗渣的CH4产量减少,这会减少对H2的消耗,也起到抑制乙酸生成作用[45]。本研究还发现SE+F组体外瘤胃发酵的异丁酸和异戊酸比例显著增加,这可能是因为该组底物中的菌体蛋白被瘤胃微生物降解产生氨基酸,在氨基酸的发酵代谢过程中会增加异丁酸和异戊酸的产量[46]。

4 结论

蒸汽爆破处理可以降低甘蔗渣的纤维含量,增加可溶性碳水化合物和单糖含量,促进体外瘤胃发酵纤维降解和VFA生成。在蒸汽爆破处理基础上再进行微生物发酵处理,可以促进甘蔗渣的体外瘤胃发酵MCP合成并减少CH4产量。因此,蒸汽爆破+发酵处理具备提高甘蔗渣饲用价值并减少反刍家畜CH4排放的潜力,应用前景值得深入挖掘。

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