Institute of Ensiling and Processing of Grass, College of Agro-grassland Science, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China.
Department of Applied Biology and Chemical Technology, Research Institute for Future Food, Hong Kong Polytechnic University, Y807, Lee Shau Kee Building, PolyU, 999077, Hong Kong, China.
Food Res Int. 2023 Oct;172:113104. doi: 10.1016/j.foodres.2023.113104. Epub 2023 Jun 10.
The objectives of this study were to explore the β-carotene-producing bacteria and ascertain the main factors affecting β-carotene content via investigating the effects of various additives on β-carotene content, bacterial community succession, and quality of fermented alfalfa, using single-molecule real-time (SMRT) sequencing technology. Fresh alfalfa was fermented without (CON) or with squalene (SQ), the combination of Lactobacillus plantarum and cellulase (LPEN), and the combination of SQ and LPEN (SQLPEN) for 3, 45, and 90 d. The results showed that relative to the fresh alfalfa, extensive β-carotene loss in all groups occurred in the early fermentation phase (3 d) since epiphytic Pantoea agglomerans with the ability to produce β-carotene disappeared and β-carotene was oxidized by lipoxygenase and peroxidase. With the prolonged fermentation days, β-carotene content in all groups increased due to bacterial community succession in the middle and late phases of fermentation (45 and 90 d). The species L. parabuchneri, L. kunkeei, and L. kullabergensis (r = 0.591, 0.366, 0.341, orderly) had positive correlations with β-carotene content (P < 0.05). Bacterial functional potential prediction showed that species L. kunkeei, L. helsingborgensis, and L. kullabergensis had positive (r = 0.478, 0.765, 0.601) correlations with C10-C20 isoprenoid biosynthesis (P < 0.01), and L. helsingborgensis and L. kullabergensis had positive (r = 0.805, 0.522) correlations with β-carotene biosynthesis (P < 0.01). Additionally, the pH and propionic acid (r = -0.567, -0.504) had negative correlations with β-carotene content (P < 0.01). The CON group was preserved well after 90 d, LPEN and SQLPEN further improved fermentation quality. In conclusion, certain Lactobacillus had the potential for β-carotene biosynthesis, and high pH and propionic acid content were the unbenefited factors for β-carotene retention in fermented alfalfa.
本研究旨在利用单分子实时（SMRT）测序技术，通过考察不同添加剂对β-胡萝卜素含量、细菌群落演替和发酵紫花苜蓿质量的影响，探索产β-胡萝卜素细菌，并确定影响β-胡萝卜素含量的主要因素。新鲜紫花苜蓿分别在不添加（CON）或添加角鲨烯（SQ）、植物乳杆菌和纤维素酶（LPEN）组合、SQ 和 LPEN 组合（SQLPEN）条件下发酵 3、45 和 90 d。结果表明，与新鲜紫花苜蓿相比，所有组在早期发酵阶段（3 d）β-胡萝卜素大量损失，原因是具有产β-胡萝卜素能力的附生 Pantoea agglomerans 消失，且β-胡萝卜素被脂氧合酶和过氧化物酶氧化。随着发酵天数的延长，由于发酵中后期细菌群落的演替，所有组的β-胡萝卜素含量在 45 和 90 d 时增加。L. parabuchneri、L. kunkeei 和 L. kullabergensis（r=0.591、0.366、0.341，依次）与β-胡萝卜素含量呈正相关（P<0.05）。细菌功能预测表明，L. kunkeei、L. helsingborgensis 和 L. kullabergensis 与 C10-C20 异戊二烯生物合成呈正相关（r=0.478、0.765、0.601）（P<0.01），L. helsingborgensis 和 L. kullabergensis 与β-胡萝卜素生物合成呈正相关（r=0.805、0.522）（P<0.01）。此外，pH 值和丙酸（r=-0.567、-0.504）与β-胡萝卜素含量呈负相关（P<0.01）。90 d 后 CON 组保存良好，LPEN 和 SQLPEN 进一步改善了发酵质量。综上所述，某些乳杆菌具有β-胡萝卜素生物合成的潜力，高 pH 值和丙酸含量是发酵紫花苜蓿中β-胡萝卜素保留的不利因素。
