Feys et al., 1994
Disulfides are cleaved reductively by -mercaptoethanol, dithiothreitol, or TCEP, or oxidatively by performic acid reagents widely used in protein structure analysis
But all of these improvements are highly individual, strongly influenced by nutrition, movement, sleep, stress, and existing medications, and dependent on correct use, appropriate dose, and adequate monitoring
Your best insurance to protect yourself against such cases is to only accept injecting pure B12, mixed only with pure, preservative-free, sterile saline
Safety-wise, handle the powder using gloves and in a clean environment
If you have a known medical condition, are taking prescription medications, or have allergies, disclose this during your intake