Isolation, identification, and technological characterization of wild leuconostocs and lactococci for traditional Raib type milk fermentation
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- Bendimerad, N., Kihal, M. & Berthier, F. Dairy Sci. & Technol. (2012) 92: 249. doi:10.1007/s13594-012-0063-8
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Raib (Rayeb) is a spontaneously fermented milk primarily acidified and flavored by strains of lactococci and leuconostocs. Raib and its by-products are traditionally consumed in many Mediterranean and sub-Saharan countries. Dedicated ready-to-use starter strains are currently missing. The aim of this study was to isolate and characterize wild strains of lactococci and leuconostocs that could be used to produce these dairy products while preserving their traditional characteristics. Dominant lactic acid cocci were isolated on M17 and MRS-vancomycin plates from Algerian cow's, ewe's, goat's, mare's, and camel's milks, either raw and/or fermented under laboratory conditions. The DNA of the isolates was fingerprinted by Rep-PCR. Strain identification was performed by Rep-PCR combined with specific PCR for genus Enterococcus and subspecies lactis/hordniae and cremoris of Lactococcus lactis. Isolates were characterized for three phenotypes essential for Raib manufacture: (a) high acidifying activity over the normal associated temperature range, (b) presence of protease, and (c) ability to metabolize citrate. Eighty-four isolates were characterized including four different strains of lactococci and four different strains of leuconostocs. Vancomycin-resistant enterococci were often coisolated. One strain of Leuconostoc mesenteroides exhibited an atypical genotype compared to the subspecies-type strains and to other wild Leuconostoc strains. Two protease-positive strains of Lactococcus lactis subsp. lactis biovar diacetylactis isolated from camel's fermented milks and the strain Leuconostoc mesenteroides subsp. mesenteroides isolated from mare's fermented milks had high acidifying potential in milk. These three strains were considered as suitable candidates as acidifying starters to preserve the typical sensory characteristics of traditional Raib while improving its safety and shelf life.
KeywordsLeuconostocs Lactococci Enterococci Raib type milk fermentation Rep-PCR
摘要 Raib(Rayeb)是由乳球菌和明串珠菌发酵产酸进而酸化和产生风味的一种自然发酵乳。Raib以及其副产品是许多地中海和撒哈拉以南非洲国家的传统食品。当前尚未有用于发酵Raib的专门发酵剂。本研究目的是分离和鉴定可用于Raib及其副产品的生产,并能保持自身传统特性的天然乳球菌和明串珠菌菌株。在实验室中,采用M17和MRS(含万古霉素)培养基,从新鲜阿尔及利亚牛乳、绵羊乳、山羊乳、马乳、骆驼乳等原料乳或者其发酵乳中,分离了优势乳酸球菌。提取这些菌株的DNA,并且采用Rep-PCR技术对上述菌株指纹图谱分析。采用Rep-PCR技术结合Enterococcus属特异性引物、lactis/hordniae 和cremoris of Lactococcus lactis.亚属特异性引物,对菌株进行鉴定。分离获得菌株的三个与Raib生产相关的特性被确定,其中包括a)在正常的相关温度范围内体现的高酸化能力;b)蛋白酶活性;c)柠檬酸代谢能力。 84株菌被定性,其中包括4株乳球菌和4株明串珠菌。具有抗万古霉素的肠球菌,常常被共分离。一株Leuconostoc mesenteroides菌与亚种模式菌株以及其他天然明串珠菌相比,显示了非典型的表型特征。两株分离自骆驼发酵乳,并具有蛋白酶活性的Lactococcus lactis subsp. lactis biovar diacetylactis 和分离自马发酵乳的Leuconostoc mesenteroides subsp. mesenteroides 在乳中显示高的酸化潜力。以上三株菌适合用作酸化发酵剂,它们既可保留传统Raib的传统的感官特性,同时可以改善Raib的安全性和延长货架期。