Milk beverage base with lactose removed with ultrafiltration: Effect of fat and protein concentration on sensory and physical properties.

Our objectives were to determine the effect of fat (skim to whole milk) and protein (3.4%-10.5%) concentration on the sensory and physical properties of milk beverage base that had lactose and other low molecular components removed by ultrafiltration (UF). In experiment 1, a matrix of 16 treatments was produced to achieve 4 levels of lactose removal (0%, 30%, 70%, and 97%) at each of 4 fat levels (skim, 1%, 2%, and whole milk). In experiment 2, a matrix of 12 treatments was produced to achieve 4 levels of lactose removal (0%, 30%, 70%, and 97%) at each of 3 protein concentrations (3.4%, 6.5%, and 10.5% protein). Physical and sensory properties of these products were determined. Removal of >95% of milk lactose by UF required a diafiltration volume of approximately 3 times the milk volume. Lactose and low molecular weight solute removal increased whiteness across the range from skim to whole milk while decreasing viscosity and making milk flavor blander. In addition, lactose (and other low molecular weight solute) removal by UF decreased titratable acidity by more than 50% and increased milk pH at 20°C to >7.0. Future work on milk and milk-based beverages with lactose removed by UF needs to focus on interaction of the remaining milk solids with added flavorings, changing casein to whey protein ratio before removal of lactose by UF, and the effect of lactose and low molecular weight solute removal on heat stability, particularly for neutral-pH, shelf-stable milk-based beverages.

Influence of Pasteurization on Maillard Reaction in Lactose-Free Milk.

In order to improve the safety and quality of lactose-free milk (LFM) Maillard reaction products (MRPs), this study used raw cow's milk as raw material and lactase hydrolysis to prepare LFM, which was heat-treated using pasteurization and then placed in storage temperatures of 4 °C, 25 °C and 37 °C to investigate the changes in the Maillard reaction (MR). The results of the orthogonal test showed that the optimal conditions for the hydrolysis of LFM are as follows: the hydrolysis temperature was 38 °C, the addition of lactase was 0.03%, and the hydrolysis time was 2.5 h. Under these conditions, the lactose hydrolysis rate reached 97.08%, and the lactose residue was only 0.15 g/100 g as determined by high-performance liquid chromatography (HPLC), complying with the standard of LFM in GB 28050-2011. The contents of furoamic acid and 5-hydroxymethylfurfural were determined by high-performance liquid chromatography, the color difference was determined by CR-400 color difference meter, and the internal fluorescence spectrum was determined by F-320 fluorescence spectrophotometer. The test results showed that the variation range of furosine in lactose-free milk after pasteurization was 44.56~136.45 mg/100g protein, the range of 5-hydroxymethylfurfural (HMF) was 12.51~16.83 mg/kg, the color difference ranges from 88.11 to 102.53 in L*, from -0.83 to -0.10 in a*, and from 1.88 to 5.47 in b*. The furosine content of LFM during storage at 4, 25, and 37 °C ranged from 44.56 to 167.85, 44.56 to 287.13, and 44.56 to 283.72 mg/100 g protein, respectively. The average daily increase in protein content was 1.18-3.93, 6.46-18.73, and 15.7-37.66 mg/100 g, respectively. The variation range of HMF was 12.51~17.61, 12.51~23.38, and 12.51~21.1 mg/kg, and the average daily increase content was 0.03~0.07, 0.47~0.68, and 0.51~0.97 mg/kg, respectively. During storage at 4 °C, the color difference of LFM ranged from 86.82 to 103.82, a* ranged from -1.17 to -0.04, and b* ranged from 1.47 to 5.70. At 25 °C, color difference L* ranges from 72.09 to 102.35, a* ranges from -1.60 to -0.03, b* ranges from 1.27 to 6.13, and at 37 °C, color difference L* ranges from 58.84 to 102.35, a* ranges from -2.65 to 1.66, and b* ranges from 0.54 to 5.99. The maximum fluorescence intensity (FI) of LFM varies from 131.13 to 173.97, 59.46 to 173.97, and 29.83 to 173.97 at 4, 25, and 37 °C. In order to reduce the effect of the Maillard reaction on LFM, it is recommended to pasteurize it at 70 °C-15 s and drink it as soon as possible during the shelf life within 4 °C.

Consumer desires and perceptions of lactose-free milk.

Fluid milk consumption has declined in the United States, but lactose-free dairy milk (LFM) sales have steadily increased. It is important to understand how consumers perceive LFM and what consumers value when purchasing LFM. This study characterized consumer perceptions and preferences for LFM. Three 1.5-h focus groups (n = 25), an online survey (n = 331), trained panel descriptive analysis, and a consumer acceptance taste test (n = 160) were conducted with LFM consumers. Focus groups were evaluated by frequency of responses. From the focus group findings, we found that price was a primary choice driver of LFM. Habit and flavor familiarity with cow milk were a major driver of selection of LFM over plant-based alternatives for consumers. Higher sweetness and lower viscosity were the primary sensory differences between LFM and traditional milk, and were viewed negatively in general. The online survey included Kano questions, maximum difference scaling, and an adaptive choice-based conjoint. The data gathered from these techniques provided insight into the perceptions and purchase habits of consumers. Kano data demonstrated consumer attitudes toward the presence or absence of product attributes. The maximum difference scaling scaled the importance of product attributes to consumers. An adaptive choice-based conjoint provided insight into consumer purchase habits by simulating a purchase decision through an online interface. The attributes evaluated included price, packaging material, package size, lactose removal method, shelf life, sweetness, texture, nutrition claims, and label claims. Survey responses were analyzed by univariate and multivariate statistics. Survey results quantitatively confirmed many focus group observations. Price, texture, sweetness, shelf life, and package size were the most important attributes to LFM consumers. A low price, ultrapasteurized LFM in a half-gallon cardboard package was the ideal LFM. Descriptive analysis of 9 commercial LFM followed by consumer acceptance testing was conducted. External preference mapping was conducted with trained panel and consumer acceptance results. Consumer acceptance testing of commercial LFM revealed 3 consumer clusters with distinct preferences for LFM flavor and texture. High sweet taste was a driver of liking for the overall population, and eggy flavor and viscosity were drivers of disliking. Knowledge of consumer preferences for LFM will provide actionable insights for new product development within the dairy industry for this market segment.

Cloning, Expression and Characterization of a Novel Cold-adapted ß-galactosidase from the Deep-sea Bacterium Alteromonas sp. ML52.

The bacterium Alteromonas sp. ML52, isolated from deep-sea water, was found to synthesize an intracellular cold-adapted ß-galactosidase. A novel ß-galactosidase gene from strain ML52, encoding 1058 amino acids residues, was cloned and expressed in Escherichia coli. The enzyme belongs to glycoside hydrolase family 2 and is active as a homotetrameric protein. The recombinant enzyme had maximum activity at 35 °C and pH 8 with a low thermal stability over 30 °C. The enzyme also exhibited a Km of 0.14 mM, a Vmax of 464.7 U/mg and a kcat of 3688.1 S-1 at 35 °C with 2-nitrophenyl-ß-d-galactopyranoside as a substrate. Hydrolysis of lactose assay, performed using milk, indicated that over 90% lactose in milk was hydrolyzed after incubation for 5 h at 25 °C or 24 h at 4 °C and 10 °C, respectively. These properties suggest that recombinant Alteromonas sp. ML52 ß-galactosidase is a potential biocatalyst for the lactose-reduced dairy industry.

The effects of milk intake and whole-body vibration exercise on bone mineral density in elderly women in nursing homes.

[Purpose] This study was designed to investigate the effects of lactose-free milk intake and whole-body vibration exercises on bone density in elderly female nursing home residents who had difficulty exercising outdoors and had not consumed milk. [Subjects and Methods] Twenty seven elderly women aged 70 or older from 3 nursing homes located in Incheon, Korea participated in the study. The experimental group (n=13) carried out whole-body vibration exercises and drank lactose-free milk, while the control group (n=14) continued to live their ordinary nursing home lives. Weight, BMI, T-scores, and Z-scores were compared between the experimental and control groups after 12 weeks. [Results] The comparison of changes in weight and BMI in the control group before and after the 12-week experiment found no statistically significant differences. However, bone mineral density was significantly different, with the T-score significantly decreasing from -2.99 to -3.48 and the Z-score decreasing from -1.87 to -2.58. The other comparisons of physical changes in the control group before and after the 12-week experiment found no statistical significance. [Conclusion] The results indicate that regular consumption of lactose-free milk and performing whole-body vibration exercises can delay the progression of bone density loss in older adults in nursing homes; adequate exercise and calcium intake could eventually help prevent fractures.

Efficacy of Lactose-Free Milk in Treating Acute Gastroenteritis in Vietnamese Children: A Randomized Controlled Trial.

BACKGROUND: Low lactase levels in Asian children appear to be genetically determined or rotavirus-induced gastroenteritis. Consuming lactose-free formula in children with acute gastroenteritis may shorten diarrhea's duration and increase weight gain. This study aims to determine whether lactose-free milk will change the duration of diarrhea and weight gain in Vietnamese children aged 2-24 months with acute gastroenteritis. MATERIALS AND METHODS: A randomized control trial was performed on 66 children under 24 months of age with acute gastroenteritis at the Gastroenterology Department of Can Tho Children's Hospital. In adjunction to oral rehydration solution, they received either a lactose-free formula (n=33) or a lactose-containing formula (n=33). OUTCOME MEASURES: Diarrhea duration, weight gain, treatment failure, and days of hospitalization were all studied. RESULTS: A total of 66 children participated in this trial, with a mean age of 13.4 ± 5.1 months, and 38 participants (57.6%) were male. There were no significant differences between the lactose-free formula group and the lactose-containing formula group in the duration of diarrhea (2.2±0.8 days versus 2.4±0.9 days; P=0.321), percentage of weight gain (1.96 [IQR:1.35-2.36] percent vs. 2.29 [IQR:1.81-2.40] percent; P=0.131), treatment failure rate (33.3% vs. 36.4%; P= 0.796), and days of hospitalization (5.8±1.7 vs. 6.5±2.5 days; P=0.158). CONCLUSIONS: It may not be necessary to use lactose-free milk routinely in Vietnamese children under 24 months with acute gastroenteritis as the duration of diarrhea, weight change, treatment failure rates, and hospital stay are similar to those of children fed lactose-containing milk.

Effect of Agave Fructans on Changes in Chemistry, Morphology and Composition in the Biomass Growth of Milk Kefir Grains.

Prebiotic effects have been attributed to agave fructans through bacterial and yeast fermentations, but there are few reports on their use as raw materials of a carbon source. Kefir milk is a fermented drink with lactic acid bacteria and yeast that coexist in a symbiotic association. During fermentation, these microorganisms mainly consume lactose and produce a polymeric matrix called kefiran, which is an exopolysaccharide composed mainly of water-soluble glucogalactan, suitable for the development of bio-degradable films. Using the biomass of microorganisms and proteins together can be a sustainable and innovative source of biopolymers. In this investigation, the effects of lactose-free milk as a culture medium and the addition of other carbon sources (dextrose, fructose, galactose, lactose, inulin and fructans) in concentrations of 2, 4 and 6% w/w, coupled with initial parameters such as temperature (20, 25 and 30 °C), % of starter inoculum (2, 5 and 10% w/w) was evaluated. The method of response surface analysis was performed to determine the optimum biomass production conditions at the start of the experiment. The response surface method showed that a 2% inoculum and a temperature of 25 °C were the best parameters for fermentation. The addition of 6% w/w agave fructans in the culture medium favored the growth of biomass (75.94%) with respect to the lactose-free culture medium. An increase in fat (3.76%), ash (5.57%) and protein (7.12%) content was observed when adding agave fructans. There was an important change in the diversity of microorganisms with an absence of lactose. These compounds have the potential to be used as a carbon source in a medium culture to increase kefir granule biomass. There was an important change in the diversity of microorganisms with an absence of lactose, where the applied image digital analysis led to the identification of the morphological changes in the kefir granules through modification of the profile of such microorganisms.

Critical Parameters in an Enzymatic Way to Obtain the Unsweet Lactose-Free Milk Using Catalase and Glucose Oxidase Co-Encapsulated into Hydrogel with Chemical Cross-Linking.

The presented work involves obtaining and characterising a two-enzymatic one-pot bioreactor, including encapsulated (co-immobilised) glucose oxidase and catalase. The enzymatic capsules were applied to produce unsweet, lactose-free milk during low-temperature catalysis. Furthermore, operational conditions, like pH and aeration, were selected in the paper, which sorts out discrepancies in literature reports. All experiments were carried out at 12 °C, corresponding to milk storage and transportation temperature. Preliminary studies (for reasons of analytical accuracy) were carried out in a buffer (pH, concentration of sugars mimicking conditions in the lactose-free milk, the initial glucose concentration 27.5 g/L) verified by processes carried out in milk in the final stage of the study. The presented results showed the need for regulating pH and the aeration of the reaction mixture in the continuous mode during the process. The procedure of co-immobilisation was performed in an alginate matrix with the cross-linking of glutaraldehyde or carbodiimide while carbodiimide showed better enzymes retention inside alginate capsules. Co-encapsulated enzymes could be used for nine cycles, preserving finally about 40% of the initial activity.

Is Ultra-High Temperature Processed Milk Safe in Terms of Heterocyclic Aromatic Amines?

Herein, the presence of heterocyclic aromatic amines (HAAs) in 24 different commercial ultra-high temperature processed (UHT) milk types was investigated. The dry matter and pH values of the samples were also determined. The milk types showed significant differences (p < 0.01) regarding the dry matter, pH values, and individual HAAs and total HAAs. The milk sample dry matter and pH values were in the range of 8.56-13.92% and 6.66-6.91, respectively. The growing up milk samples had the highest dry matter and pH values. While no significant correlation between the total HAAs and dry matter was found, a negative correlation (p < 0.01) between the total HAAs and pH value was determined. Among the tested HAAs, five compounds, (IQx (up to 0.06 ng), IQ (up to 0.10 ng), MeIQx (up to 0.55 ng), MeIQ (up to 1.97 ng), and PhIP (up to 0.39 ng)) were quantified in the samples. The average total HAAs of the samples ranged from 0.13 to 0.67 ng; however, one milk sample (200 mL) contained between 10.10 and 53.35 ng total HAAs. Therefore, it was shown that protein fortification and lactose hydrolysis substantially increased the formation of HAAs in UHT milk.

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.

Evaluation of 5-hydroxymethylfurfural content in market milk products.

5-Hydroxymethylfurfural (5-HMF) is a cyclic aldehyde formed during non-enzymatic browning reactions. In milk, it is, on the one hand, a contaminant, on the other, a quality indicator. The objective of this study was to evaluate the content and selected factors affecting the concentration of 5-HMF in cows' milk and first infant milk. The content of 5-HMF in market milk varied widely, the average was 54.8 µg L-1 (3.3-136.8). There was no significant difference in the concentration of this contaminant between UHT, HTST pasteurised and micro-filtered milk. It was also shown that the content of lipid components did not affect the concentration and kinetics of the 5-HMF formation in milk subjected to thermal treatment. Lactose-free milk was characterised by a level of this compound much higher than regular products. The 5-HMF average contents in powder cows' milk and first infant milk were respectively 642 and 2315 µg kg-1.

Coeliac disease: no difference in milk and dairy products consumption in comparison with controls.

BACKGROUND: Nutritional deficiencies are common in patients with coeliac disease and they can cause osteopenia among other associated diseases. Reduced consumption of milk and dairy products may play a major role in determining low bone mass in patients with coeliac disease. AIM: We aimed to investigate milk and dairy products consumption in patients with coeliac disease compared with the general population. METHODS: We examined the average consumption of milk and dairy products and the reasons for not consuming them. An online survey was sent by email to patients with coeliac disease on a gluten-free diet and aged 18-75. Matched controls were selected among volunteers who responded to the survey posted on the public access sites. Differences in frequencies and means between the two groups were calculated using the χ2 test and t-test, respectively. All tests were two-tailed with a significance level set at p<0.05. RESULTS: 176 patients with coeliac disease and 528 controls participated in the study. We found that 22.2% of the patients with coeliac disease and 19.9% of controls did not drink fluid milk on a regular basis; lactose-free milk was preferred by 20.4% of the patients with coeliac disease and by 19% of controls (p=0.69). Only a minority of patients with coeliac disease contacted a doctor before having lactose-free milk, despite this being led by the presence of gastrointestinal symptoms. More patients with coeliac disease than the general population reported a breath test before avoiding milk and dairy products. CONCLUSIONS: There is no significant difference between patients with coeliac disease and controls in regular milk consumption. Follow-up visits for patients with coeliac disease could avoid unnecessary dietary restrictions.

Retention of Microbiota Diversity by Lactose-Free Milk in a Mouse Model of Elderly Gut Microbiota.

Prebiotics may improve aging-related dysbiosis. Milk is a source of nutrients including oligosaccharides whose prebiotic potential remains largely unexplored. We used a murine model to explore the effect of milk products on high diversity and lower diversity faecal microbiota from healthy and frail elderly subjects, respectively. Mice were treated with antibiotics and subsequently "humanized" with human faecal microbiota. The mice received lactose-free or whole milk, glycomacropeptide, or soy protein (control) supplemented diets for one month. The faecal microbiota was analyzed by 16S rRNA gene amplicon sequencing. Lactose-free milk diet was as efficient as the control diet in retaining faecal microbiota diversity in mice. Both milk diets had a significant effect on the relative abundance of health-relevant taxa (e.g., Ruminococcaceae, Lachnospiraceae). The glycomacropeptide prebiotic activity previously observed in vitro was not replicated in vivo. However, these data indicate the novel prebiotic potential of bovine milk for human nutrition.

Assessment of Lactose-Free Diet on the Phalangeal Bone Mineral Status in Italian Adolescents Affected by Adult-Type Hypolactasia.

Adult-type hypolactasia (ATH) is a clinical syndrome of primary lactase deficiency. A lactose-free diet is advisable to avoid the symptoms linked to the condition, but this potentially creates problems for optimal bone mineralization due to reduced calcium intake. To evaluate the effect of the lactose-free diet on the bone mineral status (BMS), we compared the phalangeal BMS of adolescents with ATH to that of peers on a normal diet. Also, we analyzed the correlations between BMS and dietary behavior, physical exercise, and calcium and vitamin D intake. A total of 102 cases and 102 healthy controls filled out a diet record and underwent phalangeal Quantitative Ultrasound (QUS). No difference in BMS was observed. The time spent on lactose-free diet (4.8 ± 3.1 years) was inversely correlated to the BMS. More than 98% of cases consumed lactose-free milk, but calcium and vitamin D intake were significantly lower. Calcium intake was correlated to physical exercise but not to BMS. Our results suggest that a lactose-free diet does not affect the phalangeal BMS of adolescents with primary lactase deficiency when their diet includes lactose-free cow’s milk. However, there is still a significantly lower calcium intake than in the population reference. The inverse correlation observed between the BMS and the time spent on a lactose-free diet suggests that a long-term follow-up is advisable.

Biochemical characterization of a novel ß-galactosidase from Paenibacillus barengoltzii suitable for lactose hydrolysis and galactooligosaccharides synthesis.

A ß-galactosidase gene (PbBGal2A) was cloned from Paenibacillus barengoltzii and expressed in Escherichia coli. The in silico analysis of the deduced amino acid sequences revealed that PbBGal2A shared the highest identity of 40% with the characterized glycoside hydrolase (GH) family 2 ß-galactosidase from Actinobacillus pleuropneumoniae. The recombinant ß-galactosidase (PbBGal2A) was purified with a molecular mass of 124.2kDa on SDS-PAGE. The optimal pH and temperature of PbBGal2A were determined to be pH 7.5 and 45°C, respectively. PbBGal2A was stable within pH 6.0-8.0 and up to 45°C. It completely hydrolyzed the lactose in milk and whey powder solution. In addition, PbBGal2A exhibited high transglycosylation activity and a maximum yield of 47.9% (w/w) for galactooligosaccharides (GOS) production was obtained in 8h at a lactose concentration of 350g/L. These properties make PbBGal2A an ideal candidate for commercial use in the production of lactose-free milk and GOS.

Hexose-derived glycation sites in processed bovine milk.

Milk products are consumed by many people on a daily basis, which demands sophisticated technical processes to guarantee the microbiological safety and to retain the nutritional value. The heating during pasteurization and ultra high temperature (UHT) treatment triggers diverse chemical reactions, such as the reaction of sugars and amino groups of proteins typically termed protein glycation. The glycation by lactose as dominant sugar in milk has been recently investigated, whereas the contribution of hexoses remains open. We identified first hexose-derived glycation sites in raw milk, colostrum, three brands of pasteurized milk, three brands of UHT milk, five brands of infant formula, and one brand of lactose-free pasteurized and UHT milk using tandem mass spectrometry and electron transfer dissociation. In total, we could identify 124 hexosylated tryptic peptides in a bottom-up proteomics approach after enriching glycated peptides by boronate affinity chromatography, which corresponded to 86 glycation sites in 17 bovine milk proteins. In quantitative terms glycation increased from raw milk to pasteurized milk to UHT milk and infant formula. Lactose-free milk contained significantly higher hexosylation degrees than the corresponding regular milk product. Interestingly, the glycation degrees varied considerably among different brands with lactose-free UHT milk and infant formula showing the highest levels. BIOLOGICAL SIGNIFICANCE: The established proteomics strategy enables the identification and relative quantification of different protein glycation types in diverse milk products ranging from raw milk to milk powders. This will allow detailed in vitro studies to judge positive or negative aspects when consuming differently processed milk products including lactose-free milk that is obligatory for people with lactose intolerance but is increasingly consumed by the general population assuming health benefits. The established analytics will also permit studying the influence of each technical processing step on the glycation degrees and thus offers the possibility to reduce glycation early during production, as obvious from the variation among different brands. Special attention should be given to the high hexose- and lactose-derived glycation levels found in infant formula, although it is still controversially discussed if protein glycation has a negative biological impact.

Novel high-performance metagenome ß-galactosidases for lactose hydrolysis in the dairy industry.

The industrially utilised ß-galactosidases from Kluyveromyces spp. and Aspergillus spp. feature undesirable kinetic properties in praxis, such as an unsatisfactory lactose affinity (KM) and product inhibition (KI) by galactose. In this study, a metagenome library of about 1.3 million clones was investigated with a three-step activity-based screening strategy in order to find new ß-galactosidases with more favourable kinetic properties. Six novel metagenome ß-galactosidases (M1-M6) were found with an improved lactose hydrolysis performance in original milk when directly compared to the commercial ß-galactosidase from Kluyveromyces lactis (GODO-YNL2). The best metagenome candidate, called "M1", was recombinantly produced in Escherichia coli BL21(DE3) in a bioreactor (volume 35 L), resulting in a total ß-galactosidase M1 activity of about 1100 µkatoNPGal,37 °C L(-1). Since milk is a sensitive and complex medium, it has to be processed at 5-10 °C in the dairy industry. Therefore, the ß-galactosidase M1 was tested at 8 °C in milk and possessed a good stability (t1/2=21.8 d), a desirably low apparent KM,lactose,8 °C value of 3.8±0.7 mM and a high apparent KI,galactose,8 °C value of 196.6±55.5 mM. A lactose hydrolysis process (milk, 40 nkatlactose mLmilk,8 °C(-1)) was conducted at a scale of 0.5L to compare the performance of M1 with the commercial ß-galactosidase from K. lactis (GODO-YNL2). Lactose was completely (>99.99%) hydrolysed by M1 and to 99.6% (w/v) by K. lactis ß-galactosidase after 25 h process time. Thus, M1 was able to achieve the limit of <100 mg lactose per litre milk, which is recommended for dairy products labelled as "lactose-free".

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 ß-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 ß-CN and αs1-CN, which were clearly hydrolyzed after approximately 90 days of storage in the lactose-hydrolyzed milk.

Galactooligosaccharides formation during enzymatic hydrolysis of lactose: towards a prebiotic-enriched milk.

The formation of galactooligosaccharides (GOS) in skim milk during treatment with several commercial ß-galactosidases (Bacillus circulans, Kluyveromyces lactis and Aspergillus oryzae) was analysed in detail, at 4 and 40°C. The maximum GOS concentration was obtained at a lactose conversion of approximately 40-50% with B. circulans and A. oryzae ß-galactosidases, and at 95% lactose depletion for K. lactis ß-galactosidase. Using an enzyme dosage of 0.1% (v/v), the maximum GOS concentration with K. lactis ß-galactosidase was achieved in 1 and 5h at 40 and 4 °C, respectively. With this enzyme, it was possible to obtain a treated milk with 7.0 g/L GOS - the human milk oligosaccharides (HMOs) concentration is between 5 and 15 g/L--and with a low content of residual lactose (2.1g/L, compared with 44-46 g/L in the initial milk sample). The major GOS synthesised by this enzyme were 6-galactobiose [Gal-ß(1 → 6)-Gal], allolactose [Gal-ß(1 → 6)-Glc] and 6'-O-ß-galactosyl-lactose [Gal-ß(1 → 6)-Gal-ß(1 → 4)-Glc].