Proteolysis of casein micelles by Pseudomonas fluorescens CNRZ 798 contributes to the destabilisation of UHT milk during its storage

Abstract

International audienc

Quantitative and qualitative variability of the caseinolytic potential of different strains of Pseudomonas fluorescens: Implications for the stability of casein micelles of UHT milks during their storage

“…To follow quantitatively and qualitatively the residual caseinolytic activity and study the consequences of this potential caseinolysis, the experimental procedure described by Gaucher et al (2011) was applied. Fresh raw milk was first skimmed, microfiltered to remove somatic cells and bacteria and then inoculated with the different strains of P. fluorescens.…”

“…This protocol was described in detail by Gaucher et al (2011). Briefly, for each experiment, raw milk from a local Brittany farm was skimmed using a cream separator (Elecrem, Châtillon, France) at 50°C and then microfiltered by a TIA microfiltration unit (TIA, Bollène, France) equipped with a ceramic membrane Sterilox (reference 1P1940, membrane area = 0.24 m 2 , 1.02 m long, pore size = 0.8 lm, temperature of microfiltration = 50°C, Pall-Exekia, Bazet, France).…”

“…The protocol used was as described by Ramsdell, Johnson, and Evans (1931) and Gaucher et al (2011). Ten millilitres of milk were mixed with different volumes of KH 2 PO 4 (0.5 M) (Panreac quimica SA, Barcelona, Spain) and then heated to 100°C ± 1°C for 10 min.…”

“…Thus, the proteolysis of purified caseins appears different to that of casein associated in casein micelles (Gaucher et al, 2011). Up to now, this proteolytic variability in relation to destabilization of UHT milk has not been specifically studied.…”

Detection of Proteolysis in Milk by Pseudomonas fluorescens Using Urea PAGE Method

“…As a result, spoilage in milk may occur after pasteurisation and, more likely, after UHT heat treatment. Enzymatic spoilage without concomitant bacterial growth is of special concern in UHT milks (Gaucher et al, 2011). As these enzymes are not commercially available, one aim of this research was to extract them followed by partial purification before inoculation into UHT skim milk.…”