Destabilization and off-flavors generated by Pseudomonas proteases during or after UHT-processing of milk

Sophie Marchand,Katleen Coudijzer,Jan De Block,Barbara Duquenne,Marc Heyndrickx

doi:10.1186/s40550-016-0047-1

Sophie Marchand, Katleen Coudijzer + Show 3 more

Open Access

https://doi.org/10.1186/s40550-016-0047-1

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Abstract

BackgroundPseudomonads play a major role in the spoilage of UHT processed dairy products, due to their growth-related protease production in raw milk.ResultsTo assess the off-flavor generating capacity of these AprX proteases in milk after UHT-processing, six major milk spoiling Pseudomonas groups were investigated. Sensory evaluation of the different processed milk samples showed large differences in the degree of proteolysis related to onset of off-flavors. Nevertheless, it was illustrated that P. fragi has the greatest spoilage potential within the tested Pseudomonas groups, when it comes to generating off-flavors.ConclusionsNo clear correlation could be obtained between protein hydrolysis and the presence of off-flavors in UHT milk.

Highlights

Pseudomonads play a major role in the spoilage of UHT processed dairy products, due to their growth-related protease production in raw milk
After pasteurization total bacterial counts were reduced to 1900 cfu/mL in the pasteurized milk
Pseudomonas counts and total bacterial counts were determined at the moment of inoculation (t0) and before UHT-processing (t3, t4) for every milk batch

Summary

Introduction

Pseudomonads play a major role in the spoilage of UHT processed dairy products, due to their growth-related protease production in raw milk. Refrigerated storage of raw milk is universally accepted for prolonging shelf life and preventing spoilage by mesophilic bacteria. Due to evolutions in the dairy market in which dairies have become more and more centralized, milk is stored longer at refrigerated temperatures (Gaafar and Ali 1995). To ensure good dairy products, the Belgian legislation foresees, that milk on farm should be collected within 72 h post-production (Anonymous 2007). Quality problems may arise if milk is stored too long at these refrigerated temperatures. This is mainly due to an outgrowth of pyschrotrophic microorganisms in the raw milk. While pseudomonads are readily eliminated by UHT heating conditions

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