Setup of a procedure for cider proteins recovery and quantification

Cider contains low amount of proteins that, nonetheless, can affect its stability, foam formation and potential allergenicity. At present, scarce information is available on cider proteins, probably due to the lack of methods for their recovery and analysis. The aim of the present study was to set up a method for recovering and quantifying cider proteins. To this purpose, the proteins from 13 Italian commercial ciders were recovered by dialy- sis, gel filtration, trichloroacetic acid/acetone (TCA/ace- tone) and potassium dodecyl sulfate (KDS) precipitation. The protein content of the samples was then determined by bicinchoninic acid (BCA), Bradford and o-phthaldi- aldehyde (OPA) assays. The results were compared to quantitative data obtained by densitometry of electropho- retic gels. The most reliable protocol resulted in the KDS method followed by OPA assay. KDS, in addition, allowed also to separate proteins from glycocompounds. KDS/OPA is the method of choice for cider proteins precipitation and quantification.