Protective effect of hop β-acids on microbial degradation of thick juice during storage

Abstract

Storing sugar extracts as thick juice, a form of sucrose syrup, is common practice in the sugar industry. However, thick juice storage commonly faces problems due to microbial degradation. In this study the value of a commercial alkaline solution of hop β-acids (HBA) was assessed for prevention of microbial degradation of thick juice. The antimicrobial effect of different concentrations of HBA against juice degradation was tested in a pilot-scale thick juice storage experiment. Thick juice degradation, indicated as a decrease in pH, was generally accompanied by an increase in the count of fastidious bacteria (FB) on Columbia Agar with Sheep Blood (CAwSB), which were mainly identified as Tetragenococcus halophilus. Addition of HBA delayed juice acidification and the development of T. halophilus in a concentration-dependent manner. The susceptibility of T. halophilus to HBA was determined by plating degraded thick juice (> 105 CFU/ml) on CAwSB plates with different concentrations of HBA (0–160 ppm). None of the HBA concentrations tested reduced the number of FB colonies formed, but increasing HBA concentrations extended the lag time of colony formation. In conclusion, HBA can prolong the storage life of thick juice in the sugar industry, although degradation cannot be eliminated.status: publishe