Raulio Mari, Wilhelmson Annika, Salkinoja-Salonen Mirja, Laitila Arja
Department of Applied Chemistry and Microbiology, University of Helsinki, P.O. Box 56, FI-00014 University of Helsinki, Finland.
Food Microbiol. 2009 Jun;26(4):437-43. doi: 10.1016/j.fm.2009.02.004. Epub 2009 Feb 28.
Malted barley is a major raw material of beer, as well as distilled spirits and several food products. In the malting process, dry barley kernels are steeped in water which initiates germination and invigorates microbial growth on the kernels. In the present study, field emission scanning electron microscopy (FESEM) was used to visualize the microbial community within the tissues of barley kernels before and after the steeping, with and without Lactobacillus plantarum E76 added as a starter culture. The results show that the community of 10(8)cfu g(-1) on dry, stored barley kernels increased 5-10 fold during the steeping forming a dense biofilm of bacteria and fungi with slimy exopolymeric matrix. FESEM revealed that crevices between the outer epidermis and the testa of sound barley kernels were heavily colonized with microbes, whereas there were only few microbes on the outer surface of the husks, in the aleurone layer or in the endosperm underneath an intact testa layer. The microbes frequently possessed appendages forming bridging them to the kernel and the individual microbial cells to each other. The L. plantarum added to the steeping water reduced the amount of exopolymeric matrix in the biofilm and improved the wort filterability.
麦芽大麦是啤酒、蒸馏酒和多种食品的主要原料。在麦芽制造过程中，干燥的大麦粒浸泡在水中，这会引发发芽并促进麦粒上微生物的生长。在本研究中，使用场发射扫描电子显微镜（FESEM）观察浸泡前后大麦粒组织内的微生物群落，浸泡过程中添加或不添加植物乳杆菌E76作为起始培养物。结果表明，干燥、储存的大麦粒上10(8)cfu g(-1)的微生物群落在浸泡过程中增加了5至10倍，形成了由细菌和真菌组成的密集生物膜，并带有粘性的胞外聚合物基质。FESEM显示，完好大麦粒的外表皮与种皮之间的缝隙被微生物大量占据，而在种皮、糊粉层或完整种皮层下胚乳的外表面只有少量微生物。这些微生物常常具有附属物，将它们与麦粒以及彼此的单个微生物细胞连接起来。添加到浸泡水中的植物乳杆菌减少了生物膜中胞外聚合物基质的量，并改善了麦芽汁的过滤性能。
