Conditions for inactivation of thermophilic spores in NaOH solutions for reuse applications

摘要

The reuse of NaOH-based cleaning solutions is one approach that dairy factories may adopt to reduce the levels of sodium discharged in dairy waste streams. However, it is important that the introduction of such a practice does not lead to undesirable product quality issues by, for example, spreading bacterial spores to production locations where cleaning solutions are reused. In particular, the survival and spread of the spores of thermophilic bacteria may be an issue where the cleaning solution has previously been used to clean heated processing equipment. This study investigated the ability of spores of a thermophilic microorganism that was isolated from milk powder to survive within sodium hydroxide solutions (0.5-2.0% w/v NaOH) at elevated temperatures (40-70 degrees C). It was demonstrated that sporicidal activity of NaOH solutions increased with increasing NaOH concentration and treatment temperature. An investigation of an industry pasteurisation process confirmed that thermophilic bacteria are removed from equipment surfaces by NaOH cleaning solutions. The cleaning conditions (1.3% w/v NaOH at 70 degrees C) were sufficient to reduce counts of thermophilic bacteria in the cleaning solution from 4,100 cfu/mL to less than the detection limit (1 cfu/mL) within 40 min, which is consistent with inactivation data obtained in the laboratory study with the milk powder isolate. To minimise the potential for survival and spread of spores, it is recommended that cleaning solutions for reuse applications be applied to heated dairy processing equipment at concentrations of >= 1.0% w/v NaOH and temperatures of >= 60 degrees C. Cleaning solutions applied at a concentration of 1.0% w/v NaOH should be maintained at >= 60 degrees C for an additional 1 h, following cleaning, before reuse with other production equipment. Cleaning solutions applied at >= 2.0% w/v NaOH and >= 60 degrees C may be reused immediately.