抗冻融乳酸菌的筛选及其对燕麦青贮品质和有氧稳定性的影响

Screening of antifreeze-thawed lactic acid bacteria and their effects on oat silage fermentation quality and aerobic stability

为提高冻融条件下燕麦青贮的发酵品质和有氧稳定性,利用传统的平板培养法,从青藏高原地区分离到437株乳酸菌,从中筛选出4株在反复冻融条件下(20℃/-5℃)能快速生长、高效产酸的抗冻融乳酸菌。经生理、生化特性检测和16S rRNA基因序列比对鉴定,4株菌分别是植物乳杆菌157(LP157)、植物乳杆菌160(LP160)、短乳杆菌248(LB248)和戊糖乳杆菌260(LPE260)。为进一步评价其在冻融条件下对燕麦青贮发酵品质、营养成分、微生物数量及有氧稳定性的影响,试验设7个处理,分别为:1)LP157;2)LP160;3)LB248;4)LPE260;5)LP160+鼠李糖乳杆菌753混合(MIX);6)商业菌(COM);7)等量灭菌蒸馏水(CK),在20℃恒温和20℃/-5℃每12 h交替条件(冻融)下分别青贮60 d。结果表明,无论在20℃恒温条件还是在冻融条件下,LP157、LP160、LB248和LPE260处理组青贮后的pH和干物质损失显著低于CK(P<0。05),乳酸、乙酸含量均显著高于CK(P<0。05),肠杆菌、酵母菌和霉菌等不良微生物的生长得到抑制,提高了燕麦青贮品质。有氧暴露5 d后,LP157、LP160、LB248和LPE260处理组pH和NH3-N显著(P<0。05)低于CK、MIX和COM处理组,提高了燕麦青贮的有氧稳定性,尤其LP160作用最显著(70 h VS。对照11 h)。结果表明,筛选出的4株乳酸菌均具有作为青藏高原地区冻融环境下青贮调制用乳酸菌添加剂的潜质。

The effects of freeze-thaw conditions on the fermentation quality and aerobic stability of oat silage were investigated.Four strains of freeze-thaw-resistant lactic acid bacteria(LAB)with rapid growth and efficient acid production were screened from 437 strains,which had been isolated from the Qinghai-Tibetan Plateau.Based on physiological and biochemical characteristics and 16S rRNA gene sequence alignment,the four strains were identified as Lactobacillus plantarum 157(LP157),L.plantarum 160(LP160),Lactobacillus brevis 248(LB248),and Lactobacillus pentosus 260(LPE260).In order to investigate their effects on the fermentation quality,nutrient composition,microbial counts and aerobic stability of oat silage under freeze-thaw conditions,seven treatments were tested as follows:1)LP157;2)LP160;3)LB248;4)LPE260;5)LP160+Lactobacillus rhamnosus 753 mixture(MIX);6)A commercial bacterial silage additive(COM);7)The same amount of sterilized distilled water(CK).All treatments were ensiled for 60 days at a constant temperature of 20℃and under a 20℃/-5℃regime alternating every 12 h(freeze-thaw).LP inoculation improved silage quality:The pH and dry matter loss in silages inoculated with LP157,LP160,LB248 and LPE260 were significantly lower than CK(P<0.05)and lactic acid and acetic acid contents were significantly higher than CK(P<0.05),and the growth of spoilage micro-organisms such as coliform bacteria,yeast and mold were inhibited,both with fermentation at constant 20℃and under freeze-thaw conditions.After aerobic exposure for 5 days,the pH and NH3-N of silages treated with LP157,LP160,LB248 and LPE260 were significantly(P<0.05)lower than CK,MIX and COM.The aerobic stability of oat silage was improved,especially when inoculated with LP160(70 h vs.CK 11 h).The results show that the four screened strains can be used as effective LAB inoculants for silage preparation in the freeze-thaw environment of the QinghaiTibetan Plateau.