Published On Oct 27, 2012 | Issue 1 | Volume 17 2011

PROTEASE ACTIVITIES OF SEMIPURIFIED Pseudomonas fluorescensIN PROTEIN DEGRADATION OF PASTEURIZED MILK AT STORAGE

Tatik Khusniati
Microbiology Division, Research Center for Biology, Indonesian Institute of Sciences Cibinong Science Center, Jl Raya Jakarta-Bogor Km 46, Cibinong 16911, Phone: (62-21-8765067); Facs: (62-21-8765062)
Irma Normalia
Chemistry Department, Bogor Agricultural University
Abstract

Protein on stored milks spoiled due to protease activities of Pseudomonas fluorescens. To know protease effect on milks, protease  activities of semi-purified P. fluorescens on protein degradation in stored pasteurized milks were detected. Protease was semi-purified  by ethanol 70%. Protease activities were detected by modified Lowry method, protein degradation by formol titration, and protein  content by Kjeldahl method. Milk storage' times were conducted on 0 day (4 days before expired date) up to 12 days (8 days after expired  date). The results show that the longer the storage times the higher protease activities and protein degradation of milks. At storage  12 days, protease activities on control were 0.2556 Unit/mL (skim) and 0.2116 Unit/mL (whole), and on inoculated milk (crude) was  2.2044 Unit/mL (skim) and 1.5378 Unit/mL (whole); while on inoculated milk (semi-purified) was 3.5355 Unit/mL (skim) and 1.6778  Unit/mL (whole), respectively. The decrease of inoculated milk' homogeneous were faster than that of control. Protein degradation on  control, inoculated skim milks (crude and semi-purified) on 12 days were 4.48%, 7.28% and 7.62%, while that on whole milks were  3.81%, 7.28% and 6.04%, respectively. Based on protease, protein degradation and homogeneous, it can be concluded that skim milk  spoiled faster than whole milk.

Key words: pasteurized milk, protease, Pseudomonas fluorescens, skim, storage

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