Evaluation of a new method for production of lipolyzed milk reference samples

Rancid flavor can be a defect in milk. Using the current standard method, obtaining a lipolyzed reference sample consistent in flavor and intensity for training panelists to evaluate lipolyzed flavor is difficult. The objectives of this research were to develop a reproducible method for preparation of lipolyzed milk reference samples and to test the shelf-life of lipolyzed cream used to prepare the reference sample. In Phase 1, pasteurized cream was hydrolyzed using 3 lipases, Penicillium roqueforti, porcine pancreatic and Rhizomucor miehei, at 4 incubation temperatures. Free fatty acids (FFA) released during hydrolysis were quantitated using extraction-titration and gas chromatography. Pancreatic lipase released greater concentrations of total, short- and long-chain fatty acids (P<0.05) than the other 2 lipases at all temperatures. Recombined lipolyzed milk samples were evaluated by a dairy flavor expert. Pancreatic lipase gave the most characteristic lipolyzed flavor to milk. Paired con^arison tests indicated that lipolyzed milk prepared from cream hydrolyzed with pancreatic lipase did not differ (P > 0.05) in flavor from milk prepared by 2 variations of the current standard method. Recombining hydrolyzed cream and skim milk to produce lipolyzed milk was found to be a reproducible method as determined through sensory evaluation. For Phase 2, cream hydrolyzed with pancreatic lipase was freeze-dried and stored at 3 temperatures (-18, 4 and 25°C) for 32 wk. Milk flavor, fat percentage and FFA content were evaluated every 4 wk on recombined milk samples. Moisture, color and water activity were evaluated on the dehydrated cream at the same 4-wk intervals; no changes were found. All dehydrated cream samples increased more rapidly in lipolyzed flavor intensity with high storage temperatures. Samples stored at 4 and -18°C become more rancid than freshly-prepared lipolyzed samples in 20 and 24 wk, respectively. Samples stored at 25°C developed a "fruity" off-flavor in 8 wk, but did not increase in rancidity (P>0.05). Cream can be successfully hydrolyzed with pancreatic lipase to give a characteristic lipolyzed flavor to milk and can be successfully dehydrated and stored at -18°C in darkness for 20 wk without changes in flavor.