Owing to the resistance to conventional cleaning and sanitizing agents, biofilms formed on surfaces of dairy processing equipment pose a hazard to the dairy industry. The objective of this study was to evaluate the diversity of the microflora attached to various surfaces of the processing lines of a milk powder processing factory based on 16S rRNA gene sequence analysis. The production of biofilms by the bacterial strains was evaluated on polystyrene (PS) and stainless-steel (SS) surfaces by crystal violet staining method. Especially, effects of temperatures (e.g., 37 °C and 55 °C) and growth mediums (e.g., nutrient broth, NB; tryptic soy broth, TSB) on the production of biofilms by these strains on PS surfaces were explored. Besides, the tolerance of the biofilms of the strains to CIP processes (1.5% v/v HNO₃ solution or 2.0% w/v NaOH solution at 80 °C) were analyzed. Forty-five isolates from eleven interior surfaces of the facilities were identified and the distribution of strains had high species diversity, which indicated that multiple spoilage and pathogenic microorganisms remained in milk powder processing lines after CIP processes. Bacteria showed higher biofilm-forming abilities on SS compared to PS surfaces under the same condition. Moreover, effects of the incubation temperature and growth medium on biofilm formation varied between genera, species, and strains. One strain of each species with biofilm-forming abilities on SS surfaces was selected to check the resistance of their biofilms formed on SS coupons to the CIP processes. Biofilms of all of the nine strains were highly or moderately alkali and acid resistant, posing a threat to the milk powder production. These results suggested that organisms within the biofilm might withstand temperature and pH changes better than planktonic organisms. More research is needed to investigate different species isolated from different facilities of the processing lines and to improve the key controlling points in the CIP processes.

由于对常规清洁和消毒剂的抵抗力，在乳品加工设备表面形成的生物膜对乳品行业构成了危害。这项研究的目的是基于16S rRNA基因序列分析来评估附着在奶粉加工厂的生产线各个表面上的菌群的多样性。通过结晶紫染色法评估了细菌菌株在聚苯乙烯（PS）和不锈钢（SS）表面上生物膜的产生。特别地，探索了温度（例如37℃和55℃）和生长培养基（例如营养肉汤，NB；胰蛋白酶大豆肉汤，TSB）对这些菌株在PS表面上产生生物膜的影响。此外，菌株的生物膜对CIP过程的耐受性（1.5％v / v HNO ₃在80°C下分析溶液或2.0％w / v NaOH溶液）。从设施的11个内表面分离出45个分离株，并且菌株的分布具有较高的物种多样性，这表明CIP处理后奶粉生产线中仍然存在多种变质和致病微生物。与相同条件下的PS表面相比，细菌在SS上显示出更高的生物膜形成能力。此外，温育温度和生长培养基对生物膜形成的影响在属，种和菌株之间变化。选择在SS表面具有生物膜形成能力的每个物种的一个菌株，以检查其在SS试样上形成的生物膜对CIP工艺的抵抗力。所有这九个菌株的生物膜都具有高度或中等的耐碱和耐酸能力，对奶粉生产构成威胁。这些结果表明，生物膜中的生物可能比浮游生物更好地承受温度和pH值变化。需要进行更多的研究来调查从生产线的不同设施中分离出来的不同物种，并改善CIP过程中的关键控制点。