Date of Award:

1994

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Donald J. McMahon

Abstract

The purpose of this research was to investigate the effect of ultra-high temperature process parameters on age gelation of milk concentrate. Skim milk was concentrated to 2X (volume reduction) using reverse osmosis. The milk concentrate was preheated at 75 or 90°C for 20 or 50 s and UHT-processed at 138 or 145°C for 4 or 16 s. Sterilizing methods used were direct steam injection and indirect plate heat exchanger. The samples were aseptically collected in presterilized plastic containers and stored at 15 or 35°C. At 15°C storage temperature, the steam-injected samples gelled in 5 months when 4 s UHT time was used. When UHT time was increased to 16 s, the samples gelled in 6 months.

Of the samples that were UHT processed by indirect plate heat exchanger for 4 s and stored at 15°C, all gelled after 7 months. When UHT time was increased to 16 s, all the 138°C samples gelled after 7 months as did the samples that were preheated for 50 s and UHT-processed at 138°C. The samples preheated at 75°C for 50 sand UHT-processed at 145°C gelled after 8 months, whereas at 90°C preheat temperature the samples gelled after 9 months.

The samples stored at 35°C did not gel but showed different sedimentation levels. The sediment depth in the container was always greater for the steam-injected samples. The samples that received higher heat treatments by the two processing methods had a higher sedimentation depth.

The pH decreased during storage and the extent of reduction was higher at 35°C storage temperature . Maillard browning occurred at both storage temperatures. Browning was greater in samples stored at 35°C and processed by indirect plate heat exchanger.

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