Fundamental research enables process optimization in the sugar Industry

Abstract

Storing sugar extracts as thick juice, a form of sucrose syrup, is common practice in the sugar industry. However, this thick juice storage commonly faces problems due to juice degradation. The precise cause for this problem was ill defined but believed to be of microbial origin. In this research, the microbial population dynamics during thick juice storage was described and we identified the causative degradation flora. Finally, optimal good storage practices were defined with the ultimate goal of preventing thick juice degradation. The thick juice microflora has been thoroughly studied with both culture-based and culture-independent techniques, encompassing the application of 16S rRNA gene clone libraries and T-RFLP analysis, providing a more comprehensive representation of the thick juice microflora than the previous studies. The initial, heterogeneous microflora in freshly produced thick juice evolved to the dominance (>99%) of Tetragenococcus halophilus during storage. Based on its high population density (106–107 cfu/ml), the ability to consume sucrose and the similar acidification pattern of experimentally infested thick juice, T. halophilus is proposed to be the key player in thick juice degradation. Remarkably, T. halophilus has thus far been associated only with high salt food products and our work is the first to associate it with high sugar matrices. In addition to T. halophilus, other bacteria such as Staphylococcus and Bacillus species were consistently present, though in lower steady concentrations of 103 cfu/ml. In order to be able to detect the different bacteria that may occur in thick juice, a DNA array was developed containing detector oligonucleotides for the genera Bacillus, Kocuria, Staphylococccus and Tetragenococcus, and the species Aerococcus viridans, Leuconostoc mesenteroides and T. halophilus. The developed macroarray was shown reliable and sensitive (up to 102 cfu/ml) and has potential for monitoring the thick juice microflora during storage as an early warning system. Finally, best available storage practices were defined based on laboratory and pilot scale storage experiments using the independent variables solids content, pH, storage temperature and biocide concentration. In conclusion, this work has contributed to a better description of the microbial population dynamics during thick juice storage and degradation, and to the definition of improved storage practices that will be useful for the sugar industry.status: publishe