There is provided an emulsifier composition comprising a diacetyl tartaric acid ester of mono- and diglycerides ; free acetic acid in an amount of less than 0. The variable power optical system comprises a plurality of lens groups for forming an optical image on an image surface of an image pickup device. According to a preferred embodiment, a transgenic milk feedstream is stabilized and particulate matter such as fat, casein miscelles and bacteria are removed.