Design of a Prediction Model for the Differentiation of Pasteurized Milk from Heated ESL Milk by Peptide Profiling.

This study designs a prediction model to differentiate pasteurized milk from heated extended shelf life (ESL) milk based on milk peptides. For this purpose, quantitative peptide profiles of a training set of commercial samples including pasteurized (n = 20), pasteurized-ESL (n = 13), and heated-ESL (n = 16) milk are recorded by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Seven peptides are selected as putative markers, and cutoff levels and performance measures of each marker are defined by receiver operating characteristic (ROC) analysis. The accuracy of these peptides in the training set range between 71% and 90%. A prediction model is established based on the combined cutoff levels and evaluated by an independent blind test set. The processing method of 19 out of 20 unknown milk samples is predicted correctly achieving 95% accuracy. Five peptides of the prediction model are identified as αS1 -casein182-199 (m/z 2014.0), αS1 -casein180-199 (m/z 2216.1), αS1 -casein1-24 (m/z 2910.6), ß-casein108-125 (m/z 2126.0), and ß-casein106-125 (m/z 2391.2) indicating thermal release and the action of plasmin and cathepsins. Thus, the present study demonstrates that the milk peptide profile reflects even minor differences in production parameters.

Short communication: Source tracking Bacillus cereus in an extended-shelf-life milk processing plant using partial sequencing of rpoB and multilocus sequence typing.

We used rpoB partial sequencing and multilocus sequence typing (MLST) to characterize 7 Bacillus cereus strains obtained at the following points: ESL milk during shelf life, pasteurized milk, raw milk, and filler nozzles after cleaning in place. The objective of the study was to determine relatedness among B. cereus isolates from several sampling points along an ESL processing plant with the aim of source tracking. The study revealed that isolates from filler nozzles shared 100% similarity with isolates from ESL milk and raw milk using rpoB sequencing. It also revealed that isolates from pasteurized milk shared 100% similarities with isolates from filler nozzles and ESL milk using MLST. We suggest 3 routes of B. cereus contamination in ESL milk. We showed that B. cereus contamination of ESL milk might be through raw milk and biofilms from filler nozzles. In addition, rpoB partial sequencing and MLST can be used as tools for source tracking in ESL milk processing.

Inhibitory activity of propolis against Listeria monocytogenes in milk stored under refrigeration.

Propolis is a natural bee-product with documented antimicrobial properties in vitro. The objective of this study was to develop a protocol for adding propolis into milk and to determine whether the addition of propolis can confer anti-listerial activity during the storage of milk under optimal or improper refrigeration conditions. Upon dissolving propolis ethanolic extract (PEE) into glycerol, the PEE-glycerol mixture contained no visible insoluble particles and could be dispersed evenly into milk, without leaving any insoluble material. PEE, with or without glycerol, was added into extended shelf-life milk, artificially contaminated with Listeria monocytogenes. The addition of PEE dissolved into glycerol resulted in a pronounced and dose-dependent anti-listerial effect in milk stored at 4 °C, with the higher concentration tested (4 mg of dry PEE per mL of milk) resulting in complete inhibition of L. monocytogenes growth throughout 30 days of storage. The combination of PEE with glycerol was also effective in significantly reducing the growth rate of the pathogen in milk stored under improper refrigeration (10 °C). Based on a patented PEE-deodorization protocol, the addition of deodorized PEE into milk resulted in a product with average consumer acceptability. However, the PEE deodorization process resulted in reduction or even complete removal of propolis constituents with known antibacterial activity, with a concomitant significant reduction in its anti-listerial effect. Nonetheless, the data presented in this manuscript highlight the strong anti-listerial potential of propolis in milk and suggest that, upon further research on its deodorization and standardization, there may be room for the application of propolis as a natural preservative in dairy beverages.

Packaging modifications for protecting flavor of extended-shelf-life milk from light.

The effectiveness of titanium dioxide (TiO2)-loaded high-density polyethylene (HDPE) to reduce light-induced oxidation of extended-shelf-life milk (2% total fat) was studied. The objective was to determine differences over time in sensory quality, vitamin retention, and oxidative chemistry as a function of packaging and retail light exposure duration. Effectiveness of packaging for protecting milk quality was assessed by sensory evaluation (triangle tests, untrained panel), changes in volatile compounds, thiobarbituric reactive substances (TBARS), and riboflavin concentration. Milk (2%) was stored in HDPE packages consisting of TiO2 at 3 levels (low: 0.6%; medium: 1.3%; high: 4.3%) at 3 °C for up to 43 d. Light-protected (translucent, foil-wrapped) and light-exposed (translucent) HDPE packages served as controls. The high TiO2-HDPE package provided protection similar to light-protected control package through d 22 of light exposure, with less consistent performance by the medium TiO2 package. The TBARS increased in all treatments during storage. Under the experimental conditions used, a TBARS value of 1.3mg/L could be considered the limiting sensory threshold for differentiating oxidized milk from light-protected milk. Riboflavin concentration decreased 10.5% in the light-protected control and 28.5% in the high TiO2 packaged milk past 29 d of light exposure, but losses were greater than 40% for all other packages. The high TiO2 package protected riboflavin concentration from degradation and controlled aldehyde concentration throughout the test period.

Similarities and differences among fluid milk products: traditionally produced, extended shelf life and ultrahigh-temperature processed.

Extended shelf life milk is a relatively new kind of fluid milk, generally manufactured by high-temperature treatment and/or micro-filtration. Being advertised as 'pasteurized milk with an extended shelf life', its flavour, compositional quality and labelling was questioned. Extended shelf life (high-temperature treatment), pasteurized ('traditionally produced') and ultrahigh-temperature milk were, therefore, compared at the beginning and end of shelf life. In triangle tests, panellists distinguished clearly between all products. High-temperature treatment milk's flavour was closer to ultrahigh-temperature and traditionally produced milk in the beginning and at the end of shelf life, respectively. Physicochemically and bacteriologically, all three types could be distinguished. Since 'extended shelf life' comprises many process varieties (each affecting flavour differently), consumer information and appropriate package labelling beyond 'long-lasting' is necessary, e.g. by mentioning the heat treatment applied.