I have been using a nonfat dry milk solution (100 g/L) for Salmonella pre-enrichment on samples of cocoa products. This solution is recommend by ISO 6887-4, instead of Buffered Peptone Water, since cocoa has antimicrobial compounds, and milk casein can avoid this activity. The ISO standard recommends, but does not explain the preparation instructions:
- The sterilization procedure is the main issue because the 10% skim milk solution always caramelizes when trying to sterilizate it on autoclave (already tried: 121°C for 5 min; 115°C for 10 min; 110°C for 15 min). Considering that I only have this equipment for sterilization, how can I avoid the caramelization? Does the caramelization affects Salmonella growth??).
Notes:
- Also tried a sterilization cycle of 20 min at 106°C. These were the only conditions that do not caramelized the solution.
- I don't have 0.22 µm filters.
- I have tried many diferent autoclavation cycles based on this question: https://www.researchgate.net/post/How-can-I-sterilize-skim-milk-and-avoid-caramelization
- A 1% (w/v) Brilliant Green solution was prepared. Is it safe to aplly on the milk solution without inhibiting Salmonella growth? The reason that I have not been using Brilliant Green is because our cocoa samples don't usually have high bacterial counts (100-1000 x 10³ CFU/g).
You might try to find some chemical that will kill possible microorganisms in the milk solution and decompose at temperatures below the caramelization temperature. This is the first thought.
Kindly read this sir.
https://www.finecooking.com/article/the-science-of-caramel
Dear Luis Felipe Buso Bortolotto
You could try non-thermal processing method, like as, pulsed electric field (PEF). Maybe you could read usefully: Article Application of pulsed electric field in non-thermal processing of milk
The brown color which appear during conventional sterilization in autoclave (121°C for 15 min) is attributed to Maillard reaction but not to caramelization. you can use it in your experiment.