Colin A. Ray

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.

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.

Control of Maillard Reactions in Foods: Strategies and Chemical Mechanisms

Maillard reactions lead to changes in food color, organoleptic properties, protein functionality, and protein digestibility. Numerous different strategies for controlling Maillard reactions in foods have been attempted during the past decades. In this paper, recent advances in strategies for controlling the Maillard reaction and subsequent downstream reaction products in food systems are critically reviewed. The underlying mechanisms at play are presented, strengths and weaknesses of each strategy are discussed, and reasonable reaction mechanisms are proposed to reinforce the evaluations. The review includes strategies involving addition of functional ingredients, such as plant polyphenols and vitamins, as well as enzymes. The resulting trapping or modification of Maillard targets, reactive intermediates, and advanced glycation endproducts (AGEs) are presented with their potential unwanted side effects. Finally, recent advances in processing for control of Maillard reactions are discussed.

Storage-induced changes in the sensory characteristics and volatiles of conventional and lactose-hydrolyzed UHT processed milk

Storage-induced changes are known to be more prominent in lactose-hydrolyzed (LH) milk compared to conventional milk. Therefore the present study aimed at identifying off-flavors resembling from formation of volatiles during storage of ultra-high temperature treated (UHT) LH milk and conventional UHT milk. Further, the influence of heat processing, indirect or direct, on UHT LH milk was also examined. Storage-induced changes in sensory attributes, volatiles and primary amines were investigated during a 4xa0months period. Conventional UHT milk (with 5xa0% lactose) processed using indirect heat treatment (CONVI) and two types of UHT LH milk (with less than 0.01xa0% lactose) produced using either direct heat treatment (LHD) or indirect heat treatment (LHI) were represented in the study. Sensory descriptive analysis showed that fresh samples of CONVI, LHI and LHD differed in sensory properties and the samples could be differentiated according to boiled and stale aroma as well as color saturation. Differentiation of the fresh samples based on the volatile gas chromatography–mass spectrometry profile was not achievable. During storage, samples developed differently with respect to sensory characteristics, volatiles and the amount of primary amines. Partial least squares models (PLS1) including only methyl ketones and aldehydes showed that 2-butanone, 2-pentanone, 2-heptanone, 2-nonanone, heptanal, octanal and nonanal predicted stale flavor. Bitter taste, on the other hand, correlated with the amount of primary amines (Pearson’s correlation, r2xa0=xa00.71). This finding indicates that storage-induced changes in sensory characteristics, volatiles and primary amines depend on both differences in lactose content and the applied heat processing.

Green Tea Polyphenols Decrease Strecker Aldehydes and Bind to Proteins in Lactose-Hydrolyzed UHT Milk

The effect of epigallocatechin gallate enriched green tea extract (GTE) on flavor, Maillard reactions and protein modifications in lactose-hydrolyzed (LH) ultrahigh temperature (UHT) processed milk was examined during storage at 40 °C for up to 42 days. Addition of GTE inhibited the formation of Strecker aldehydes by up to 95% compared to control milk, and the effect was similar when GTE was added either before or after UHT treatment. Release of free amino acids, caused by proteolysis, during storage was also decreased in GTE-added milk either before or after UHT treatment compared to control milk. Binding of polyphenols to milk proteins was observed in both fresh and stored milk samples. The inhibition of Strecker aldehyde formation by GTE may be explained by two different mechanisms; inhibition of proteolysis during storage by GTE or binding of amino acids and proteins to the GTE polyphenols.