Search

Aims: Thermophilic spoilage bacteria and their biofilms formed during milk powder processing posed threats to safety and quality of dairy products. This research aims to understand more about the bacterial behaviours and their social models in biofilms. Methods and Results: Interactional effects from both extracellular metabolites and co‐culture on biofilms formation of the contaminating thermophilic bacteria were determined. The results showed that strong biofilm formers always had high AI‐2 activities, including Geobacillus stearothermophilus gs1, Bacillus licheniformis bl1 and Thermoactinomyces vulgaris tv1. Metabolites from themself or other species altered their biofilm biomass detected by crystal violet staining. Dual‐species cultures observed by confocal laser scanning microscope indicated either synergistic or inhibitory effects between B. circulans bc1 and G. stearothermophilus gs1, as well as B. licheniformis bl1 and G. stearothermophilus gs1. Fourier transform infrared spectrometry results revealed the significant diversities in polysaccharides of the biofilm matrix. Conclusions: Cell communication played an important role on biofilm formation in the complex microbial community. Intraspecific and interspecific extracellular metabolites influenced collective bacterial behaviours under mixed circumstances. Significance and impact of study: This research provided evidences on cell communication and biofilm formation of thermophilic bacteria in dairy industry. [ABSTRACT FROM AUTHOR]

Thermophilic spore-forming bacteria are common contaminations in milk powder processing lines. In this study, a remarkable change of bacterial community structure was observed after heat sterilization, and thermophilic bacteria took significant advantages after high temperature treatment. Some culturable thermophilic spores survived from pasteurization and even ultra-high temperature sterilization. Feed tank before spraying drying proved to be a key point for controlling thermophilic bacteria. Benzalkonium chloride (BAC) is an effective disinfectant to remove biofilms formed by the isolated dominant species, Bacillus licheniformis. The synergistic reduction of B. licheniformis biofilm on stainless steel in skimmed milk was 3.89 log CFU/cm2 after combined treatment by 0.0625% (v/v) BAC and cleaning-in-place (CIP). This research provided meaningful proposals on determinations of critical control points in a milk powder processing line and removal strategies of B. licheniformis biofilm, which are of valuable significance on quality guarantees for dairy industry. • Thermophilic bacteria took advantages after high temperature treatment. • Feed tank before spraying drying was a key point for controlling thermophilic bacteria. • Bacillus licheniformis was the most prevailing species in this milk powder processing line. • Routine CIP regime was not efficacious enough to remove B. licheniformis biofilms. • 0.0625% of BAC conjoined with CIP reduced 3.89 log CFU/cm2 of B. licheniformis biofilms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spoilage effects on milk were superimposed from multiple thermophilic bacteria. • Competitive relationship existed between B. licheniformis and G. stearothermophilus. • Synergistic impacts were observed between B. licheniformis and A. flavithermus. • Interspecific interactions played a role in community structure of mixed-species biofilm. • The predominant strain was dynamic with development of multi-species biofilm. Thermophilic bacteria, such as Bacillus licheniformis , Geobacillus stearothermophilus , Bacillus Subtilis and Anoxybacillus flavithermus , are detected frequently in milk powder products. Biofilms of those strains act as a major contamination to milk powder manufactures and pose potential risks in food safety. In this study, we explored the developing process of multi-species biofilm formed by the four thermophilic bacteria on stainless steel immerged in skimmed milk. The results showed that the thermophilic strains possessed strong capacities to decompose proteins and lactose in skimmed milk, and the spoilage effects were superimposed from multiple strains. B. licheniformis was the most predominant species in the mixed-species biofilm after 12-h incubation. From 24 h to 48 h, G. stearothermophilus occupied the highest proportion. Within the multi-species biofilm, competitive relation existed between B. licheniformis and G. stearothermophilus , while synergistic impacts were observed between B. licheniformis and A. flavithermus. The interspecies mutual influences on biofilm development provided important evidences for understanding colonization of the predominant thermophilic bacteria during milk powder processing. [ABSTRACT FROM AUTHOR]

Bacillus licheniformis is a major source of microbial contamination to dairy industry, and biofilm formation by this spoilage bacterium aggravates the safety issues. Especially for milk powder manufactures, the evaporation process at temperatures between 50 °C and 70 °C before spray drying, is a critical control point against thermophilic bacteria multiplication. In our study, metabolomics analysis was performed to investigate dynamic changes of the metabolites and their roles during process of biofilm development of B. licheniformis at 55 °C for 24 h. Amino acid metabolism was quite active, with cooperation from lipid metabolism, carbohydrate metabolism and nucleotide metabolism. Amino acid biosynthesis provided significant contributions especially during early biofilm development from 8 to 12 h. Metabolites involved in specific pathways of arginine biosynthetic, galactose metabolism and sphingolipid metabolism played a crucial role in building biofilm. This work provided new insights into dynamic metabolic alternations and a comprehensive network during B. licheniformis biofilm development, which will extend the knowledge on the metabolic process of biofilm formation by B. licheniformis. The results are helpful in creating better environmental hygiene in dairy processing and new strategies for ensuring quality of dairy products. • Dynamic metabolic process was established during biofilm formation by Bacillus licheniformis. • The most notable metabolic alternations were detected in early biofilm development. • Arginine biosynthesis played a key role on B. licheniformis biofilm development. • Galactose metabolism and sphingolipid metabolism were crucial for B. licheniformis biofilm. • Amino acid, carbohydrate, lipid metabolism interacted and cooperated in B. licheniformis biofilm. [ABSTRACT FROM AUTHOR]