Effect Of Milk Fat Decomposition And Oxidation On Mijiunai Flavor And Quality

Mijiunai,also called the Imperial Cheese,Buckle Bowl Cheese is Chinese traditional dairy products.It is made by the milk and glutinous rice wine contained curd enzyme according to a certain mixing ratio.It is milk-white,holding concurrently milk and rice wine fragrance flvor and delicate taste.Milk coagulant prepared from glutinous rice wine was used to produce Mijiunai.Coagulation time between 10 to 20 min showed a better effect.Using titration method the lipolytic activity of glutinous rice wine used in Mijiunai was 1.0^-1.5 LU/mL.The accumulating of fatty acids was mainly happened in milk-clotting period.The free fatty acids contents in Mijiunai were analyzed by GC-MS.Palmitic,oleic,myristic and stearic acids were found in higher concentration.Experiments show that Mijiunai in storage period will go on oxidation to some degree.ADV from 0.79 ?mol·g^-1increased to 3.1 ?mol·g^-1 for Mijiunai,which provided the possibility of oxidation.POV and TBA value have obviously changed,which POV value changes faster in prophase than later period;TBA value changes the quickly later.Meanwhile it is also observed that oxidation happens through the color difference.Through changes of pH,acidity,WHC?water hold capacity?,as well as quality decay is determined.The quality of Mijiunai aroma was evaluated by inspecting the headspace fingerprint of the same set of samples using the electronic nose.The results showed that electronic nose was better to identify the above products by LDA method than PCA.Changes of flavor during storing period were analyzed by solid-phase microextraction?SPME?method and found that alcohols,ketones,acids,esters etc were the main flavor contents.