Doctoral Dissertations

Date of Award

8-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science and Technology

Major Professor

Marjorie P. Penfield

Committee Members

Arnold Saxton, John Mount, Sharon Melton

Abstract

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.

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