▁and ▁cas p ases , ▁which ▁eng age ▁in ▁prote ol ysis ▁in ▁the ▁apo pt otic ▁cycle . ▁ ▁In te ins ▁often ▁function ▁with ▁the ▁help ▁of ▁a ▁catal yt ic ▁c yst e ine . ▁ ▁These ▁roles ▁are ▁typically ▁limited ▁to ▁the ▁int rac ell ular ▁milieu , ▁where ▁the ▁environment ▁is ▁reducing , ▁and ▁c yst e ine ▁is ▁not ▁ox id ized ▁to ▁c yst ine . ▁ ▁App lications ▁C yst e ine , ▁mainly ▁the ▁- en anti omer , ▁is ▁a ▁prec ursor ▁in ▁the ▁food , ▁ph arma ce ut ical ▁and ▁personal - care ▁indust ries . ▁One ▁of ▁the ▁largest ▁applications ▁is ▁the ▁production ▁of ▁flav ors . ▁For ▁example , ▁the ▁reaction ▁of ▁c yst e ine ▁with ▁sug ars ▁in ▁a ▁Ma ill ard ▁reaction ▁yields ▁meat ▁flav ors . ▁- C yst e ine ▁is ▁also ▁used ▁as ▁a ▁processing ▁aid ▁for ▁b aking . ▁ ▁In ▁the ▁field ▁of ▁personal ▁care , ▁c yst e ine ▁is ▁used ▁for ▁permanent - wave ▁applications , ▁pre domin antly ▁in ▁Asia . ▁Again , ▁the ▁c yst e ine ▁is ▁used ▁for ▁breaking ▁up ▁the ▁dis ulf ide ▁b onds ▁in ▁the ▁hair ' s ▁ker atin . ▁ ▁C yst e ine ▁is ▁a ▁very ▁popular ▁target ▁for ▁site - direct ed ▁label ing ▁experiments ▁to ▁investigate ▁bi om ole cular ▁structure ▁and ▁dynamics . ▁Male im ides ▁select ively ▁attach ▁to ▁c yst e ine ▁using ▁a