Maillard reaction products and amino acid cross-links in liquid infant formula: Effects of UHT treatment and storage

The formation of Maillard reaction products, including Amadori compounds (determined as furosine), advanced glycation end products (AGEs), α-dicarbonyl and furfural compounds, as well as amino acid cross-links (lysinoalanine and lanthionine) was investigated in direct (DI) and indirect (IN) UHT-treated experimental liquid infant formula (IF) during storage at 40 °C. IN-IF had higher concentrations of all investigated compounds compared to DI-IF and low pasteurized IF. IN UHT treatment induced significantly higher concentrations of α-dicarbonyl compounds (glyoxal, methylglyoxal, 3-deoxyglucosone and 3-deoxygalactosone) compared to DI, which facilitated increased formation of AGEs (N-Ɛ-(carboxymethyl)lysine, methylglyoxal- and glyoxal-derived hydroimidazolones) in unstored IFs. During storage for 6 months, concentrations of furosine and AGEs increased while α-dicarbonyl compounds decreased. Principal component analysis indicated that differences between IN-IF and DI-IF disappeared after 2 months of storage. IN-IF had higher concentrations of lysinoalanine and lanthionine and lower concentrations of available lysine and arginine than DI-IF indicating higher loss of protein quality in IN-IF.

Short communication: Decrease of lipid profiles in cow milk by ultra-high-temperature treatment but not by pasteurization

Triglyceride (TG) and fatty acid profiles of raw (RM), pasteurized (PM, 85°C for 15 s), and indirect UHT-treated (UM, 135°C for 15 s) cow milk were investigated by a lipidomics approach. Ninety-four TG were identified and all were present at significantly lower concentrations in UM than in RM or PM, and free fatty acid contents were significantly higher in UM than in RM and PM, indicating that TG lipolysis occurred to a greater degree in UM than in RM and PM. In addition, UM contained significantly fewer unsaturated fatty acids (14 types) than those in RM and PM, including C14:1n-5, C15:1n-5, C16:1n-7, C17:1n-7, C18:1n9 cis, C18:2n-6 cis, C18:3n-3, C18:3n-6, C20:1, C20:2, C20:3n-6, C20:3n-3, C20:4n-6, and C20:5n-3. However, we detected no significant differences between RM and PM in these fatty acids. In conclusion, UHT treatment, but not pasteurization, caused loss of the nutritional quality and bioactivity of cow milk lipid profiles.

Coagulation behaviour of milk under gastric digestion: Effect of pasteurization and ultra-high temperature treatment

The digestion behaviours of pasteurized and UHT homogenized milks were investigated in in vivo rat stomach and in an in vitro dynamic human gastric simulator. The formation of coagulum under gastric conditions and the protein digestion profiles were similar in both systems. UHT milk formed curds with fragmented and crumbled structures, compared with the more cohesive curds formed from unheated or pasteurized milk. UHT milk had faster rates of protein hydrolysis and of the release of fat globules during digestion. These results are attributed to the differences in the structures of the curds formed from the samples with different treatments. The fragmented and crumbled structure of the curds obtained from UHT milk was probably the result of β-lactoglobulin binding with casein micelles during processing, which sterically hindered aggregation of the casein micelles under gastric conditions. This study provides knowledge for understanding the gastric emptying and digestion of processed consumer milk.

Effect of different homogenisation methods and UHT processing on the stability of pea protein emulsion

Pea protein is a very popular source of edible plant-based protein among legumes. In this study, the stability of ultra high temperature (UHT) processed pea protein emulsion prepared from 0.5 and 1.0% (w/v) pea protein concentrate (PPC) by two different homogenisation methods of microfluidisation (500 Bar) and ultrasonication (ultrasonicated for 1, 3 and 5 min) was investigated. In addition, the emulsion properties (particle and droplet size, flocculation, coalescence, zeta potential, hydrophobicity and creaming index) of PPC emulsions before and after UHT treatment were measured. The overall heat transfer coefficient (OHTC) versus time graphs were stable during UHT processing for both microfluidised and ultrasonicated PPC emulsions that indicates no fouling and good stability under the thermal treatment condition. Freshly prepared emulsion using 0.5 and 1.0% PPC and ultrasonicated for 5 min showed creaming index of 5.73 and 8.39%, particle size of 0.96 and 1.53 μm respectively. In addition, the fat droplet size for the above samples measured 1.05 and 1.85 μm for larger fat droplets and 0.51 and 0.72 μm for smaller fat droplets, respectively. However, after UHT treatment this emulsion destabilised due to protein aggregation as indicated by the high flocculation index (13.22 and 103.35%), particle size (1.59 and 3.23 μm) and droplet size (1.30 and 2.53 μm, for large fat droplets and 0.90 and 1.22 μm, for small fat droplets). After UHT treatment the microfluidised PPC emulsion using 0.5 and 1.0% PPC were the most stable with small particle size (2.85 and 0.36 μm), high zeta potential (-56.36 and - 27.30) and low creaming index (3.87% and 4.97%), respectively as compared to ultrasonicated samples. Overall, this study revealed that UHT treatment improved emulsion properties of the microfluidised PPC emulsion compared to the ultrasonicated PPC emulsion.

Ser2 from Serratia liquefaciens L53: A new heat stable protease able to destabilize UHT milk during its storage

The heat-stable protease Ser2 is secreted by the species Serratia liquefaciens, a psychrotrophic bacteria frequently found in raw milk. To understand the physicochemical modifications of casein micelles induced by Ser2 and to confirm its implication in UHT milk destabilization, the enzyme was purified and added to microfiltered raw milk before UHT treatment. UHT milk destabilization was investigated during 90days of storage. A visual destabilization appeared after 8days of storage with the presence of sediment. Zeta potential increase and formation of aggregates were observed during the storage. Using tandem mass spectrometry, numerous released peptides from the four caseins were identified at the end of storage. Caseins were hydrolyzed in the preferential order β->α_s1->κ->α_s2. No specific peptidic hydrolysed bond was detected. The present study confirmed that the presence of the protease Ser2 in raw milk can be one of the main causes of UHT milk destabilization.