Volatile component profiles of conventional and lactose-hydrolyzed UHT milk—a dynamic headspace gas chromatography-mass spectrometry study

Factors influencing on the formation of dimethyl disulfide and dimethyl trisulfide in model systems

The generations of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) in a binary or ternary model system including lipids, free amino acids and Maillard reaction products (MRPs) were studied. Various factors affecting the formation of DMDS and DMTS indicated that cysteine (Cys) and Cys MRPs could effectively decrease not only the concentrations of methionine (Met), DMDS and DMTS, but also the pH level. Rapid drops in pH limited the formation of DMDS and DMTS during Met thermal degradation. Quantitative analyses of DMDS and DMTS at acidic aqueous solutions revealed that the mixtures of MRPs derived from Cys and xylose (Xyl) had the best inhibition effect on the formation of DMDS and DMTS. The low level of DMDS and DMTS and the increasing level of furfuryl methyl sulfide and 2-thiophenecarboxaldehyde during storage indicated that MRPs derived from Cys and Xyl could effectively not only decrease the concertation of DMDS and DMTS, but also promote the development of thiophene and sulfur substituted furan. Thus, this study implied that MRPs derived from Cys/Xyl could be applied as effective substances to control the formation of DMDS and DMTS and improve the production of volatile compounds with meat-like aroma.

Determination and Risk Assessment of Flavor Components in Flavored Milk

This study aimed to determine chemical composition and assess exposure in flavored milk among Chinese residents, based on risk assessment methodologies of acceptable daily intake (ADI) and toxicological concern threshold (TTC). Esters (32.17%), alcohols (11.19%), olefins (9.09%), aldehydes (8.39%), and ketones (7.34%) comprised the majority of the flavoring samples. Methyl palmitate (90.91%), ethyl butyrate (81.82%), and dipentene (81.82%) had the highest detection rates in flavor samples. This study screened fifteen flavor components of concern and discovered that 2,3,5-trimethylpyrazine, furfural, benzaldehyde, and benzenemethanol were detected in 100% of flavored milk samples. Benzenemethanol was found in the highest concentration (14,995.44 μg kg^-1). The risk assessment results revealed that there was no risk for Chinese residents in consuming flavored milk, and the maximum per capita daily consumption of 2,3,5-trimethylpyrazine, furfural, and benzenemethanol were 226.208 g, 140.610 g, and 120.036 g, respectively. This study could provide guidelines for amounts of flavor additive ingredients in milk.

Comparison of Automated Extraction Techniques for Volatile Analysis of Whole Milk Powder

Volatile profiling of whole milk powder is valuable for obtaining information on product quality, adulteration, legislation, shelf life, and aroma. For routine analysis, automated solventless volatile extraction techniques are favored due their simplicity and versatility, however no single extraction technique can provide a complete volatile profile due to inherent chemical bias. This study was undertaken to compare and contrast the performance of headspace solid phase microextraction, thermal desorption, and HiSorb (a sorptive extraction technique in both headspace and direct immersion modes) for the volatile analysis of whole milk powder by gas chromatography mass spectrometry. Overall, 85 unique volatiles were recovered and identified, with 80 extracted and identified using a non-polar gas chromatography column, compared to 54 extracted, and identified using a polar gas chromatography column. The impact of salting out was minimal in comparison to gas chromatography column polarity and the differences between the extraction techniques. HiSorb extracted the most and greatest abundance of volatiles, but was heavily influenced by the number and volume of lactones extracted in comparison to the other techniques. HiSorb extracted significantly more volatiles by direct immersion than by headspace. The differences in volatile selectivity was evident between the techniques and highlights the importance of using multiple extraction techniques in order to obtain a more complete volatile profile. This study provides valuable information on the volatile composition of whole milk powder and on differences between extraction techniques under different conditions, which can be extrapolated to other food and beverages.

Application of PTR-TOF-MS for the quality assessment of lactose-free milk: Effect of storage time and employment of different lactase preparations

Lactose-free dairy products undergo several chemical modifications during shelf life because of the reactivity of glucose and galactose produced by the lactose enzymatic hydrolysis. In this study, proton transfer reaction-mass spectrometry (PTR-MS), coupled with a time-of-flight (TOF) mass analyzer, was applied to get an insight on the phenomena occurring during the shelf life of ultrahigh-temperature (UHT) lactose-free milk (LFM). UHT LFMs produced by three different commercial lactase preparations were evaluated during storage at 20°C over a 150 days period, sampling the milk every 30 days. Production was repeated three times, on three consecutive weeks, in order to take milk variability into consideration. Principal component analysis applied to the whole "volatilome" data demonstrated the capability of PTR-TOF-MS in detecting the milk batch-to-batch variability: Freshly produced milk samples were distinguished based on the week of production at the beginning of shelf life. Additionally, a clear evolution of the volatiles organic compounds (VOCs) profiling during storage was highlighted. Further statistical analysis confirmed VOCs temporal evolution, mostly because of changes in methyl ketones concentration. Differences caused by the commercial lactases did not emerged, except for benzaldehyde. Altogether, data demonstrated PTR-TOF-MS analysis as a valuable and rapid method for the detection of changes in the VOCs profiling of UHT LFM.

Short communication: Short-time freezing does not alter the sensory properties or the physical stability of ultra-high-temperature hydrolyzed-lactose milk

In this study, the effect of milk freezing was studied, focusing on the changes in 1% and 3% fat UHT hydrolyzed-lactose milk after slow- (-20°C) and fast-rate freezing (-80°C) for 72 h. Changes on the sensory properties were first assessed by discriminant analysis (triangle test), and then by volatile organic compounds and color analysis. The milk emulsion stability was characterized by optical centrifugation, particle size analysis, and confocal microscopy. The sensory panel was not able to distinguish the milk subjected to freezing from the control (72 h at 20°C). The volatile organic compounds and color analysis demonstrated that both freezing rates did not cause any significant changes in the milk aroma or color characteristics. The results of physical properties confirmed that short-time freezing did not lead to a distinct destabilization, except for a slight increase in the mean particle diameter at -80°C. Taking all the results together, UHT hydrolyzed-lactose milk was not significantly altered during the operation of freezing and thawing and, therefore, short-time freezing at both -20°C and -80°C can be used for milk storage without altering the product.

Chemical and sensory changes during shelf-life of UHT hydrolyzed-lactose milk produced by "in batch" system employing different commercial lactase preparations

Manufacturing shelf-stable Ultra-high temperature hydrolyzed-lactose milk (UHLM) is a challenge for dairy producers, as the product undergoes chemical changes during storage due to both reducing sugars reactivity and proteolysis arising from the impurity of the lactase preparations. In the present study, the "in batch" production system, which includes the addition of the lactase before the thermal treatment, was demonstrated a valuable alternative to the more popular "in pack" system, where lactase is added directly into each milk package after thermal sterilization. The features of the technology were investigated by monitoring the changes in free amino acids, volatile organic compounds, color and sensory properties of UHLMs produced with three different lactase preparations (LPs), up to 120 days at 20 °C. Upon UHT processing, the proteolytic side activity of lactases was minimized, so minimum breakdown of milk protein was achieved. The release of free amino acids was dependent on the lactase purity only in the early production phases, whereas it did not change over time. The Strecker aldehydes benzaldehyde and 2-methylbutanal resulted as effective markers to correlate with the initial lactase purity during storage. Color and sensory slightly changed during storage but were poorly correlated with the different lactases, resembling to phenomena typical of milk aging. This latter result suggested that production costs might be lowered by opting for less-purified lactases when considering the "in batch" technology, supporting the application of this production system for the design of UHLM with high-quality standards and low risk of alterations during shelf-life.

Changes in fatty acids composition, antioxidant potential and induction period of UHT-treated tea whitener, milk and dairy drink

Background

In developing and developed countries, several versions of safe and shelf-stable Ultra High Temperature, UHT-treated products are manufactured. Terminologies and formulations of UHT-treated tea whitener, milk and dairy drink considerably vary. Comprehensive studies have been performed on UHT-treated milk; however, fatty acids compositional changes and oxidation status of UHT-treated tea whitener and dairy drink at different storage intervals have not been reported in literature.

Methods

UHT-treated tea whitener, milk and dairy drink samples (450 each) of the same manufacturing date were purchased from the market and stored at ambient temperature (25-30 °C) for 90 days. At the time of collection, all the samples were only one week old. Samples of UHT-treated tea whitener, milk and dairy drink were regarded as treatments and every treatment was replicated five times. Chemical composition, fatty acid profile, 2, 2-Diphenyl-1-picrylhydrazyle (DPPH) radical scavenging activity, total antioxidant activity, reducing power, antioxidant activity in linoleic acid system and induction period were determined at 0, 45 and 90 days of storage.

Results

Fat content in freshly collected samples of UHT treated-tea whitener, milk and dairy drink were 6 and 3.5%. UHT treated milk had highest total antioxidant capacity, antioxidant activity in linoleic acid and 2, 2-Diphenyl-1-picrylhydrazyle (DPPH) free radical scavenging activity followed by UHT tea whitener and dairy drink. In freshly collected samples of UHT-treated milk, concentrations vitamin A and E were 0.46 μg/100 g and 0.63 mg/100 g, respectively. UHT-treated tea whitener had the lowest concentrations of vitamin A and E. With the progression of storage period, amount of vitamin A and E decreased. In freshly collected samples, amount of short, medium and unsaturated fatty acids in UHT-treated milk were 10.54, 59.71 and 27.44%, respectively. After 45 days of storage of UHT-treated milk, the loss of short, medium and unsaturated fatty acid was 7%, 7.1 and 5.8%, respectively. After 90 days of storage of UHT-treated milk, the loss of short, medium and unsaturated fatty acid was 8.53, 13.51 and 11.88%, accordingly. After 45 days of storage of UHT-treated tea whitener, the loss of medium and unsaturated fatty acid was 1.6 and 0.99%, respectively. After 90 days of storage, the loss of medium and unsaturated fatty acids were 8.2 and 6.6%, respectively. The induction period of fresh UHT-treated tea whitener, milk and dairy drink was 15.67, .74 and 7.27 h. Strong correlations were recorded between induction period and peroxide value of UHT-treated products.

Conclusion

This investigation disclosed that UHT-treated tea whitener had 6% fat content with no short-chain fatty acids. Antioxidant capacity of UHT-treated milk was higher than dairy drink and tea whitener. Due to the presence of partially hydrogenated fat, oxidative stability of UHT-treated tea whitener was better than UHT-treated milk and dairy drink. Vitamin A and E was not found in UHT-treated tea whitener. For the anticipation of oxidative stability of UHT-treated milk, dairy drink and tea whitener, induction period/ Rancimat method can be used.

Quantitation of α-Dicarbonyls and Advanced Glycation Endproducts in Conventional and Lactose-Hydrolyzed Ultrahigh Temperature Milk during 1 Year of Storage

A comprehensive quantitative characterization of Maillard reaction products was carried out for conventional (CON) and lactose-hydrolyzed (LH) ultrahigh temperature (UHT) milk during storage at 20, 30, and 40 °C for 1 year. The accumulation of 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) in LH-UHT milk ranged from 20-fold (at 20 °C) to 44-fold (at 40 °C) higher than that in CON-UHT milk. High temperature storage (40 °C) significantly accelerated the accumulation of 3-DG, 3-DGal, and 5-hydroxymethyl furfural but not the majority of the analyzed advanced glycation endproducts (AGEs). The concentrations of major AGEs including N-ε-carboxymethyllysine (CML), N-ε-carboxyethyllysine (CEL), methylglyoxal-hydroimidazolone isomers (MG-H1/H3), glyoxal-hydroimidazolone isomers (G-H1/H3), and G-H2 detected in CON milk during storage were in the range 12-700, 1-14, 8-45, 4-13, and 1-30 μM, respectively, while they were 30-570, 2-88, 17-150, 9-20, and 5-34 μM, respectively, in LH milk. Pyrraline, S-(carboxymethyl)cysteine (CMC), and glyoxal-lysine dimer were detected in lower levels, while MG-H2, methylglyoxal-lysine dimer, argpyrimidine, glyoxal-lysine-amide, glycolic acid-lysine-amide, and pentosidine were not detected in any of the milk samples. This work demonstrates for the first time that five of the analyzed AGEs (CML, CEL, MG-H1/H3, G-H1/H3, and G-H2) could be selected as markers for evaluation of the extent of the Maillard reaction in UHT milk. These results contribute to a better understanding of how Maillard reactions progress during storage of UHT milk and can be used to develop strategies to inhibit Maillard reactions in LH milk.

Interplay between Residual Protease Activity in Commercial Lactases and the Subsequent Digestibility of β-Casein in a Model System

One of the conventional ways to produce lactose-hydrolyzed (LH) milk is via the addition of commercial lactases into heat-treated milk in which lactose is hydrolyzed throughout storage. This post-hydrolysis method can induce proteolysis in milk proteins due to protease impurities remaining in commercial lactase preparations. In this work, the interplay between lactose hydrolysis, proteolysis, and glycation was studied in a model system of purified β-casein (β-CN), lactose, and lactases using peptidomic methods. With a lactase presence, the proteolysis of β-CN was found to be increased during storage. The protease side-activities mainly acted on the hydrophobic C-terminus of β-CN at Ala, Pro, Ile, Phe, Leu, Lys, Gln, and Tyr positions, resulting in the formation of peptides, some of which were N-terminal glycated or potentially bitter. The proteolysis in β-CN incubated with a lactase was shown to act as a kind of “pre-digestion”, thus increasing the subsequent in vitro digestibility of β-CN and drastically changing the peptide profiles of the in vitro digests. This model study provides a better understanding of how the residual proteases in commercial lactase preparations affect the quality and nutritional aspects of β-CN itself and could be related to its behavior in LH milk.

Glycation of whey proteins: Technological and nutritional implications

Whey proteins are globular proteins that have received much attention due to their high nutritional value and characteristic functional properties. In addition to being part of the protein system in milk, they constitute the main proteins in whey and whey protein products. Interaction of whey proteins with reducing sugars and carbohydrates via Maillard reaction have been extensively studied in milk and in model systems. Glycation of individual whey proteins results in variable increases in their solubility, thermal stability, antioxidant activity, and emulsion and foam stabilization. Limited glycation of whey protein products particularly whey protein isolates (WPI) using polysaccharides has been studied with the aim to produce conjugates with modified functional properties and acceptable sensory properties. An overview is presented here on the effect of glycation on individual whey proteins and whey protein products and the potential uses of the glycated whey proteins.

Effect of Storage on Lactase-Treated β-Casein and β-Lactoglobulin with Respect to Bitter Peptide Formation and Subsequent in Vitro Digestibility

Using active lactose to hydrolyze lactose during storage is a common process to produce lactose-hydrolyzed (LH) milk. Proteolysis induced by residual proteases in commercial lactase was studied in a system using purified β-casein or β-lactoglobulin during a 60-day storage period at 22 or 38 °C. The proteolysis of β-casein by residual proteases occurred more extensively than that of β-lactoglobulin. Peptidomic analysis by LC-ESI-MS/MS revealed that Ile, Leu, Tyr, and Phe residues near the C-terminus of β-casein were the main sites of cleavage by the residual proteases, generating assumed bitter peptides. In the subsequent in vitro digestion study, proteolysis during storage was shown to greatly affect the subsequent digestibility of β-casein, leading to an elevated degree of hydrolysis and the formation of new digested peptides. This study highlights the potential influence of residual proteases in commercial lactase on the storage quality and digestibility of LH milk containing active lactase.

Chemical and proteolysis-derived changes during long-term storage of lactose-hydrolyzed ultrahigh-temperature (UHT) milk

Proteolytic activity in milk may release bitter-tasting peptides and generate free amino terminals that react with carbohydrates, which initiate Maillard reaction. Ultrahigh temperature (UHT) heat treatment inactivates the majority of proteolytic enzymes in milk. In lactose-hydrolyzed milk a β-galactosidase preparation is applied to the milk after heat treatment, which has proteolytic side activities that may induce quality deterioration of long-term-stored milk. In the present study proteolysis, glycation, and volatile compound formation were investigated in conventional (100% lactose), filtered (60% lactose), and lactose-hydrolyzed (<1% lactose) UHT milk using reverse phase high-pressure liquid chromatography-mass spectrometry, proton nuclear magnetic resonance, and gas chromatography-mass spectrometry. Proteolysis was observed in all milk types. However, the degree of proteolysis was significantly higher in the lactose-hydrolyzed milk compared to the conventional and filtered milk. The proteins most prone to proteolysis were β-CN and αs1-CN, which were clearly hydrolyzed after approximately 90 days of storage in the lactose-hydrolyzed milk.

Lactose-hydrolyzed milk is more prone to chemical changes during storage than conventional ultra-high-temperature (UHT) milk

The enzymatic hydrolysis of lactose to glucose and galactose gives rise to reactions that change the chemistry and quality of ambient-stored lactose-hydrolyzed ultra-high-temperature (UHT) milk. The aim of the present study was to investigate and compare chemical changes in lactose-hydrolyzed and conventional UHT milk during a 9 month ambient storage period. Several complementary analyses of volatiles, free amino acids, acetate, furosine, and level of free amino terminals were concluded. The analyses revealed an increased level of free amino acids and an increased formation rate of specific compounds such as furosine and 2-methylbutanal in lactose-hydrolyzed UHT milk compared to conventional UHT milk during storage. These observations indicate more favorable conditions for Maillard and subsequent reactions in lactose-hydrolyzed milk compared to conventional UHT milk stored at ambient temperature. Furthermore, it is postulated that proteolytic activity from the lactase-enzyme preparation may be responsible for the observed higher levels of free amino acids in lactose-hydrolyzed UHT milk.