It’s impossible to answer to this question. Each case is specific. The change of color may come from of the reaction between the flavours and ingredients in finished products. The pH of finished product may have an influence too. The color of the flavor may also change itself during the shelf-life.
Sure, because if there is too much flavours, off-notes of solvents astringency of chemical molecules, natural substances and natural preparations may affect the balance of organoleptic perception of finished products during consumption. You also have sometimes reactions between compounds of flavor and ingredients of finished products.
Of course not, provided people do not ingest flavours as they are, respecting the recommended dosages given by the flavours manufacturer in the corresponding finished products. Regarding specifically staff working in the flavours industry, strict rules have to be respected, the high concentration of the substances used being a critical point. Staff should wear glasses, gloves, lab coats, mobcaps, overshoes or even security shoes, masks (from simple ones to cartridge masks). Some substances have to be weighed under fume cupboard depending on their possible toxicity.
Check the technical data sheet.
Our flavor are stable from microbiological point of view if they are stored in a dark-cool and ventilated area and in sealed drum.
If the drum is abnormally inflated (due to bacteria/moulds/yeast growth)
Globally speaking, as far as the taste itself is concerned, we do recommend to compare an incriminated lot with on one hand the last lot received before that one and on the other hand a freshly weighed formulation. Loss of strength, appearance of off-notes (such as oxidized ones or any unpleasant ones) could lead you to consider that the profile of your flavor significantly changed for some reasons. As far its bacteriological stability is concerned, an inflated drum could be as a matter of fact a critical sign.
It depends of the flavor. For oil sobluble flavours, you may have acid note because of oxidation of triglycerides. Flavour with lot of furaneol can have a burned note with oxidation of this molecules during the time. Roasted notes of coffee flavor can decrease because of oxidation of furfuryl mercaptan. Fruits flavours with high level of lactones change during the time, a “cardboard” note may appear. We could also speak about oxidation of terpens….