Hello all,
I had prepared xylitol crystals by yeast fermentation. The white crystals on storage at room temperature turns to light brown in color. I would like to know the reason of this browning. The crystals were air dried and had less than 5% moisture content. The image of brown crystals have been attached.
Kindly tell me the possible cause and method to prevent this browning.
Thank you in advance.
Dr. Sidana
It seems like a kind of impurity adhered to the surface that has oxidized. A question: have you washed the crystals? Try to redissolve and recrystallize again. or thy to wash a part of then in a buchner filter.
Since xylitol itself shouldn't undergo maillard reaction (which can happen at room temperature) I assume like Silas that your crystals are impure. Are you sure the xylitol is pure and no other sugars as xylose/glucose/fructose are apparent?
Also important could your method of crystallization. Which one do you use?
Hello Arushdeep,
It is likely that the culture medium you use for yeast culture contains glucose. It would be advisable to check if the crystallized xylitol you obtained is indeed free of this sugar.
Jacques
I think it is the caramelisation which is the oxidaton of sugar in the presence of heat to produce caramelans (C24H36O18), caramelens (C36H50O25), and caramelins(C125H188O80) ....but it usually occurs during dry heating , I am not sure if the same phenomena may occur during the drying by air. I think sample Fehling test will help to investigate the presence of other reduced sugars like glucose and fructose which could be oxidized.
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