Department of Veterinary Science, Viale delle Piagge 2, University of Pisa, Italy.
Department of Veterinary Science, Viale delle Piagge 2, University of Pisa, Italy; Interdepartmental Research Center Nutrafood "Nutraceuticals and Food for Health", University of Pisa, Italy.
Int J Food Microbiol. 2017 Sep 1;256:54-61. doi: 10.1016/j.ijfoodmicro.2017.05.022. Epub 2017 May 29.
Donkey milk is recently gaining attention due to its nutraceutical properties. Its low casein content does not allow caseification, so the production of a fermented milk would represent an alternative way to increase donkey milk shelf life. The aim of this study was to investigate the possibility of employing selected Streptococcus thermophilus and Lactobacillus plantarum isolates for the production of a novel donkey milk fermented beverage. Lysozyme resistance and the ability to acidify donkey milk were chosen as main selection parameters. Different fermented beverages (C1-C9) were produced, each with a specific combination of isolates, and stored at refrigerated conditions for 35days. The pH values and viability of the isolates were weekly assessed. In addition, sensory analysis was performed. Both S. thermophilus and L.plantarum showed a high degree of resistance to lysozyme with a Minimum Bactericidal Concentration>6.4mg/mL for 100% of S. thermophilus and 96% of L. plantarum. S. thermophilus and L. plantarum showed the ability to acidify donkey milk in 24h at 37°C, with an average ΔpH value of 2.91±0.16 and 1.78±0.66, respectively. Four L. plantarum and two S. thermophilus were chosen for the production of fermented milks. Those containing the association S. thermophilus/L. plantarum (C1-C4) reached a pH lower than 4.5 after 18h of fermentation and showed microbial loads higher than 7.00logcfu/mL until the end of the storage period. Moreover, comparing the microbial loads of samples containing both species and those containing S. thermophilus alone (C5), we highlighted the ability of L. plantarum to stimulate S. thermophilus replication. This boosted replication of S. thermophilus allowed to reach an appropriate pH in a time frame fitting the production schedule. This was not observed for samples containing a single species (C5-C9). Thus, L. plantarum strains seem to be good candidates in the production of a novel type of fermented milk, not only for their probiotic potential, but also for the enhancing effect on S. thermophilus growth.
驴奶由于其具有的营养特性，最近受到了关注。其低含量的酪蛋白不允许凝结，因此生产发酵乳将是延长驴奶保质期的一种替代方法。本研究的目的是研究选择的嗜热链球菌和植物乳杆菌分离株用于生产新型驴奶发酵饮料的可能性。溶菌酶抗性和酸化驴奶的能力被选为主要选择参数。不同的发酵饮料（C1-C9）分别使用特定的分离株组合生产，并在冷藏条件下储存 35 天。每周评估分离株的 pH 值和活力。此外，还进行了感官分析。嗜热链球菌和植物乳杆菌对溶菌酶均表现出高度的抗性，100%的嗜热链球菌和 96%的植物乳杆菌最小杀菌浓度（Minimum Bactericidal Concentration）>6.4mg/mL。嗜热链球菌和植物乳杆菌在 37°C 下 24 小时内能够酸化驴奶，平均ΔpH 值分别为 2.91±0.16 和 1.78±0.66。选择了四个植物乳杆菌和两个嗜热链球菌用于生产发酵乳。含有嗜热链球菌/植物乳杆菌组合（C1-C4）的发酵乳在发酵 18 小时后达到 pH 值低于 4.5，并且在整个储存期内微生物负荷高于 7.00logcfu/mL。此外，比较含有两种菌和仅含有嗜热链球菌的样品（C5）的微生物负荷，我们强调了植物乳杆菌刺激嗜热链球菌复制的能力。这种对嗜热链球菌复制的促进作用使我们能够在符合生产计划的时间范围内达到适当的 pH 值。而在仅含有单一菌种的样品（C5-C9）中则没有观察到这种情况。因此，植物乳杆菌菌株似乎是生产新型发酵乳的良好候选者，不仅因为它们具有益生菌潜力，而且还因为它们对嗜热链球菌生长的增强作用。
