Dairy Microbiology Division, Indian Council of Agricultural Research (ICAR)-National Dairy Research Institute, Karnal-132001, Haryana, India.
Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, P61 C996 Ireland.
J Dairy Sci. 2020 Dec;103(12):11138-11151. doi: 10.3168/jds.2020-19120. Epub 2020 Oct 1.
Mannitol is a sugar alcohol, or polyol, widely used in the food industry because of its low-calorie properties. Industrial production of mannitol is difficult and expensive. However, certain bacterial species are known to produce mannitol naturally, including certain lactic acid bacteria and fructophilic lactic acid bacteria (LAB). In this study, bacterial strains isolated from fructose-rich sources, including flowers, leaves, and honey, were identified by 16S rRNA sequence analysis as Leuconostoc, Fructobacillus, Lactococcus, and Lactobacillus species and 4 non-LAB species. DNA profiles generated by pulsed-field gel electrophoresis discriminated 32 strains of Leuconostoc mesenteroides and 6 Fructobacillus strains. Out of 41 LAB strains isolated, 32 were shown to harbor the mdh gene, which encodes the mannitol dehydrogenase enzyme, and several showed remarkable fructose tolerance even at 50% fructose concentrations, indicating their fructophilic nature. Several of the strains isolated, including Leuconostoc mesenteroides strains DPC 7232 and DPC 7261, Fructobacillus fructosus DPC 7237, and Fructobacillus fructosus DPC 7238, produced higher mannitol concentrations than did the positive control strain Limosilactobacillus reuteri DSM 20016 during an enzymatic screening assay. Mannitol concentrations were also examined via HPLC in 1% fructose de Man, Rogosa, and Sharpe medium (FMRS) or 1% fructose milk (FM). Among the strains, Fructobacillus fructosus DPC 7238 displayed high fructose utilization (9.27 g/L), high mannitol yield (0.99 g of mannitol/g of fructose), and greatest volumetric productivities (0.46 g/L per h) in FMRS. However, Leuconostoc mesenteroides DPC 7261 demonstrated the highest fructose utilization (8.99 g/L), mannitol yield (0.72 g of mannitol/g of fructose), and volumetric productivities (0.04 g/L per h) in FM. Storage modulus G' (>0.1 Pa) indicated a shorter gelation time for Limosilactobacillus reuteri DSM 20016 (8.73 h), followed by F. fructosus DPC 7238 (11.57 h) and L. mesenteroides DPC 7261 (14.52 h). Our results show that fructose-rich niches can be considered important sources of fructophilic LAB strains, with the potential to be used as starter cultures or adjunct cultures for the manufacture of mannitol-enriched fermented dairy products and beverages.
甘露醇是一种糖醇，又称多元醇，由于其低卡路里的特性，在食品工业中广泛使用。甘露醇的工业生产既困难又昂贵。然而，某些细菌物种自然会产生甘露醇，包括某些乳酸菌和果糖偏好性乳酸菌（LAB）。在这项研究中，通过 16S rRNA 序列分析，从富含果糖的来源（如花、叶和蜂蜜）中分离出的细菌菌株被鉴定为肠膜明串珠菌、果糖乳杆菌、乳球菌和乳杆菌属以及 4 种非-LAB 物种。脉冲场凝胶电泳生成的 DNA 图谱区分了 32 株肠膜明串珠菌和 6 株果糖乳杆菌。在分离出的 41 株 LAB 菌株中，有 32 株携带 mdh 基因，该基因编码甘露醇脱氢酶，其中一些菌株甚至在 50%果糖浓度下表现出显著的果糖耐受性，表明它们具有果糖偏好性。从分离出的菌株中，包括肠膜明串珠菌菌株 DPC 7232 和 DPC 7261、果糖乳杆菌 DPC 7237 和果糖乳杆菌 DPC 7238，在酶筛选试验中产生的甘露醇浓度高于阳性对照菌株罗伊氏乳杆菌 DSM 20016。在 1%果糖 de Man、Rogosa 和 Sharpe 培养基（FMRS）或 1%果糖牛奶（FM）中，通过 HPLC 也检测了甘露醇浓度。在这些菌株中，果糖乳杆菌 DPC 7238 在 FMRS 中表现出高果糖利用率（9.27 g/L）、高甘露醇产量（0.99 g 甘露醇/g 果糖）和最大的体积产率（0.46 g/L/h）。然而，肠膜明串珠菌 DPC 7261 在 FM 中表现出最高的果糖利用率（8.99 g/L）、甘露醇产量（0.72 g 甘露醇/g 果糖）和体积产率（0.04 g/L/h）。存储模量 G'（>0.1 Pa）表明罗伊氏乳杆菌 DSM 20016（8.73 h）的凝胶时间较短，其次是果糖乳杆菌 DPC 7238（11.57 h）和肠膜明串珠菌 DPC 7261（14.52 h）。我们的结果表明，富含果糖的小生境可以被认为是果糖偏好性 LAB 菌株的重要来源，具有作为发酵乳制品和饮料制造中甘露醇富集发酵的起始培养物或辅助培养物的潜力。
