对禾草源同型发酵和/或异型发酵乳酸菌发酵无芒雀麦青贮有氧稳定性的评价

本研究旨在评价禾草源同型发酵和/或异型发酵乳酸菌发酵对无芒雀麦青贮有氧稳定性的作用效果。将从禾本科牧草上分离筛选出的2株同型发酵植物乳杆菌(Lactobacillus plantarum)和蒙氏肠球菌(Enterococcus mundtti)及1株异型发酵布氏乳杆菌(Lactobacillus buchneri)制成发酵剂。选用开花期无芒雀麦,刈割切段至2~3 cm,根据所喷发酵剂菌株的不同,分为4个处理:1)对照处理(con处理),喷洒无菌去离子水;2)异型发酵处理(he处理),喷洒布氏乳杆菌液;3)同型发酵处理(ho处理),喷洒植物乳杆菌和蒙氏肠球菌混合液(2种菌1∶1混合);4)同型发酵+异型发酵处理(he+ho处理),喷洒布氏乳杆菌、植物乳杆菌和蒙氏肠球菌混合液(3种菌1∶1∶1混合)。各处理喷洒量均为10 m L/kg鲜牧草,喷洒总菌数约为5×105CFU/g鲜牧草,每个处理设5个重复。实验室常温发酵60 d后开封,通过测定无芒雀麦青贮营养成分、菌群数量及中心温度变化评价其有氧稳定性。结果显示:经60 d青贮发酵后,4个处理的p H均较青贮前显著降低(P0.05),所有处理发酵效果均较好(p H≤4.3),尤以ho处理效果最优。而在有氧暴露试验期间,con和ho处理的p H迅速增加,至第8天时达到7以上;he+ho处理p H增加幅度略低于con和ho处理,其p H至第8天时为6.3,显著低于con和ho处理(P0.05);he处理p H增加非常缓慢,至第8天时仅为4.4,显著低于其他处理(P0.05)。经60 d青贮发酵后,可溶性碳水化合物(WSC)含量以ho处理最高,显著高于其他处理(P0.05);con处理最低,显著低于其他处理(P0.05)。而在有氧暴露试验期间,WSC含量在ho处理中迅速降低,在he处理中缓慢降低;至第8天时,WSC含量以he处理最高,he+ho处理显著低于前者(P0.05),而con和ho处理则显著低于he和he+ho处理(P0.05)。青贮发酵后霉菌数量明显受到抑制,且以单独添加异型发酵乳酸菌和混合添加同型发酵和异型发酵乳酸菌时抑制效果较优,这2个处理均未检出霉菌,且he+ho处理在有氧暴露至第5天时仍未检出霉菌,he处理在有氧暴露至第8天时仍未检出霉菌。在有氧暴露第3和5天时,he和he+ho处理酵母菌数量显著低于con、ho处理(P0.05)。在有氧暴露第8天时,he+ho与he处理的乳酸、乙酸浓度均显著高于另2个处理(P0.05)。he、he+ho、con和ho处理的有氧稳定性依次降低,分别为194、126、62和58 h。综合评价结果得出:布氏乳杆菌单独或与同型发酵乳酸菌蒙氏肠球菌和植物乳杆菌联合接种可有效抑制无芒雀麦青贮的有氧腐败,保证无芒雀麦青贮有氧暴露期间品质的稳定,且前者更有效;接种同型发酵乳酸菌蒙氏肠球菌和植物乳杆菌未能在提高无芒雀麦青贮有氧稳定性方面表现出积极的作用。

Evaluation of Aerobic Stability of Bromus inermis Leyss.Silage Fermented by Homofermentative and/or Heterofermentative Lactic Acid Bacteria from Grass

This experiment was conducted to evaluate the action effect of homofermentative and/or heterofer-mentative lactic acid bacteria from grass on aerobic stability of Bromus inermis Leyss. silage. Two homofer-mentative lactic acid bacteria ( LAB) ( a strain of Lactobacillus plantarum and a strain of Enterococcus mundt-ti) and a heterofermentative LAB ( a strain of Lactobacillus buchneri) from grass were selected and were used to prepare fermentation agents. Bromus inermis Leyss. was harvested at the flowering stage, chopped to 2 to 3 cm lengths and treated with fermentation agents. Based on the bacteria type, four treatments were designed:1) control treatment ( con treatment) , which was sprayed with sterile deionized water; 2) heterofermentative treatment ( he treatment) , which was sprayed with Lactobacillus buchneri liquid; 3 ) homofermentative treat-ment ( ho treatment) , which was sprayed with a mixed liquid of Lactobacillus plantarum and Enterococcus mundtti (1:1); 4) heterofermentative+homofermentative treatment (he+ho treatment), which was sprayed with a mixed liquid of Lactobacillus plantarum, Enterococcus mundtti and Lactobacillus buchneri ( 1:1:1 ) . The spraying dose of each treatment was 10 mL/kg fresh forage, and the total bacteria count was about 5 × 105 CFU/g fresh forage. Each treatment had five replicates. After ensiling 60 days under lab condition, the aer-obic stability of Bromus inermis Leyss. silage was evaluated by testing nutrient contents, microbial number and core temperature change. The results showed as follows: at the end of ensiling period ( 60 days) , the pH of four treatments was significantly decreased compared with before silage ( P<0.05) , all treatments silage had a good fermentation quality ( pH≤4.3) and especially ho treatment was the best. When exposed to air, the pH of con and ho treatments increased rapidly, and reached up to 7 on the 8th day of aerobic exposure; the in-creasing extent of pH of he+ho treatment was slightly lower than that of con and ho treatments, and the pH of he+ho treatment reached up to 6.3 on the 8th day of aerobic exposure which was significantly lower than that of con and ho treatments ( P<0.05);the pH of he treatment increased slowly, and only was 4.4 on the 8th day of aerobic exposure which was significantly lower than that of other treatments ( P<0.05) . After 60 days of ensi-ling, the water soluble carbohydrate ( WSC) content of ho treatment was the highest, and significantly higher than that of other treatments ( P<0.05); the WSC content of ho treatment was the lowest, and significantly lower than that of other treatments (P<0.05). When exposed to air, ho treatment silage showed a sharp de-cline in the WSC content while he treatment decreased slowly. On the 8th day of aerobic exposure, the WSC content of he treatment was the highest, he+ho treatment was significantly lower than the former (P<0.05),while con and he treatments was significantly lower than he and he+ho treatments ( P<0.05) . The mold activity was obviously inhibited after silage fermentation, and the inhibitory effect of he and he+ho treatments was bet-ter in which mold was not detected. Moreover, the mold was not detected in the he+ho treatment until the 5th day of aerobic exposure, and it was not detected in the he treatment until the 8th day of aerobic exposure. The yeast quantity of he and he+ho treatments was significantly lower than that of con and he treatments on the 3rd and 5th day of aerobic exposure ( P<0.05) . Lactic and acetic acid concentrations of he and he+ho treatments were significantly higher than those of other 2 treatments on the 8th day of aerobic exposure ( P<0.05) . Aero-bic stability of he, he+ho, con and ho treatments decreased systematically, which showed 194, 126, 62 and 58 h, respectively. Through synthetic analysis, the results indicate that inoculation with Lactobacillus buchneri alone or in combination with homofermentative lactic acid bacteria Lactobacillus plantarum and Enterococcus mundtti can effectively inhibit the aerobic deterioration and ensure the stable quality of Bromus inermis Leyss. silage when exposed to air, even if the former is more effective. The results also confirm that inoculation with homofermentative lactic acid bacteria Lactobacillus plantarum and Enterococcus mundtti cannot play an active role in the improvement of aerobic stability of Bromus inermis Leyss. silage.