Lactose recovery from Panela cheese whey: Effect of whey acidification on spontaneous and stirring-induced crystallisation

This work aimed to investigate the kinetics, yield, size and composition changes in lactose crystals when Panela cheese whey was acidified (pH 3.80) or slightly alkalinised (pH 6.89) before being subjected to spontaneous or stirring-induced crystallisation. At pH 3.8, the crystallisation was accelerated, and the incorporation of salts and proteins in lactose crystals decreased. Nevertheless, these conditions induced the formation of amorphous lactose. In contrast, at pH 6.89 and under stirring conditions, the amorphous lactose was not formed and gave a high crystallisation yield (∼25 g of lactose per Kg of whey) with ∼80% of lactose recovery.     

Amorphous lactose crystallisation kinetics

Amorphous lactose crystallisation kinetics were investigated at different relative humidity and temperature combinations. Amorphous lactose was equilibrated to a water activity of 33%, then placed in sealed pans with a saturated magnesium chloride solution to maintain a constant relative humidity (33%). The temperature was raised to 10–40 °C above the glass transition temperature (T_g). The degree of crystallisation was measured using isothermal microcalorimetry. Crystallisation was shown to be an all-or-nothing event, such that direct measurement of the kinetics was not possible. This was not expected from the Avrami model. The rapid crystallisation could be an autocatalytic effect, as moisture is released during crystallisation, or a showering event as seen in highly supersaturated lactose solutions. Experiments using a blend of crystalline and amorphous lactose, produced by spray drying a lactose crystal slurry, showed crystallisation occurring at lower T_g conditions than was required for the crystallisation of 100% amorphous lactose.     

Proposal of a new reference method to determine the water content of dried dairy products

The water content of milk powders is “officially” determined by drying. The result of drying techniques is, however, the mass loss the sample undergoes under the conditions applied. No differentiation between water and other volatile substances is made. A particular problem is the lactose that is present in all dried dairy products. The α-form contains one mole of water of crystallisation per mole. This water fraction is not determined completely by ordinary drying methods. How much of the crystallised water is detected depends very much on the conditions applied. The entity determined by drying is not defined. It is only a tradition to regard the mass loss thus detected as water content. More and more, however, the expression moisture content is used for the result of drying techniques, although this term is also unsatisfactory and misleading. The discrepancy between mass loss on drying and water content becomes more pronounced when the product has high crystalline lactose content, such as whey powders or lactose itself. In these cases the difference between mass loss and water content can be quite significant. The existing reference method for moisture determination in dried milk is therefore not reasonably applicable on dairy products with high crystalline lactose content. It could be shown that the water content of dried dairy products can be determined using the Karl Fischer titration independently of the level of crystallisation water. The results are not only more accurate but also more precise than those obtained by the reference drying method. It is therefore proposed to introduce the Karl Fischer titration as reference method for dried dairy products.     

Influence of temperature on accelerated lactose crystallization in dulce de leche

The aims of the present work were to study the crystallization of lactose in dulce de leche and to evaluate the influence of temperature on this process. Samples of approximately 1 g were placed in plastic containers and stored at –5, 5, 20 and 35°C for 25 days. Lactose crystal and lactose crystal agglomerate numbers and size were measured by using an optical microscope. Results suggested that stirring and placing a small sample of dulce de leche in a small container induced lactose crystallization. Lower storage temperatures resulted in an increase of crystal and agglomerate number but in a decrease of crystal and agglomerate size. The effect of temperature on crystal and agglomerate growth rates could be attributed to the effect of temperature on viscosity, as lower temperatures resulted in decreased crystal mobility in dulce de leche and therefore reduced crystal and agglomerate growth rate.     

Optimization of conditions for galactooligosaccharide synthesis during lactose hydrolysis by β-galactosidase from Kluyveromyces lactis (Lactozym 3000 L HP G)

A study on optimisation of the conditions for galactooligosaccharide (GOS) formation during lactose hydrolysis, produced by Lactozym 3000 L HP G, was carried out. The synthesis was performed during times up to 300 min at 40, 50 and 60 °C, pH 5.5, 6.5 and 7.5, lactose concentration 150, 250 and 350 mg/mL and enzyme concentration 3, 6 and 9 U/mL. The product mixtures were analysed by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). During the hydrolysis of lactose, besides glucose and galactose, galactobiose, allolactose and 6′ galactosyl lactose were also formed as a result of transgalactosylation catalysed by the enzyme. The effect of the reaction conditions was different in the formation of di- and the trisaccharide. Thus, the optimal conditions for galactobiose and allolactose synthesis were 50 °C, pH 6.5, 250 mg/mL of lactose, 3 U/mL of enzyme and 300 min, whereas the best reaction conditions for 6′ galactosyl lactose production were 40 °C, pH 7.5, 250 mg/mL of lactose, 3 U/mL of enzyme and 120 min. These results show the possibility to obtain reaction mixtures with Lactozym 3000 L HP G, with different composition, depending on the assayed conditions.     

WATER PLASTICIZATION EFFECTS ON CRYSTALLIZATION BEHAVIOR OF LACTOSE IN A CO-LYOPHILIZED AMORPHOUS POLYSACCHARIDE MATRIX AND ITS RELEVANCE TO THE GLASS TRANSITION

ABSTRACT

Crystallization of lactose in a co-lyophilized amorphous polysaccharide matrix was investigated under various hydration conditions to test the possible relation between the ability of the polymer to raise the glass transition temperature (T_g) of the lactose-pullulan blend, relative to pure lactose, and the crystallization kinetics. Both calorimetric (DSC) non-isothermal measurements and x-ray diffraction analysis of samples stored at a constant temperature revealed a marked retardation in lactose crystallization in the presence of pullulan; i.e., the rate constant values, as determined by the Avrami analysis, declined and the ‘half-time’ (t_1/2c) for lactose crystallization increased with decreasing ratio of lactose/pullulan. The inhibitory action of pullulan on crystallization of lactose could not be solely attributed to T_g-related effects on molecular mobility of the composite systems. At a pullulan weight fraction range of 0.25–0.33 (w/w of total solids) the influence of the polymeric additive on T_g was marginal over the entire water content range examined, although crystallization was delayed as compared with pure lactose. Modeling of the temperature-dependence of t_1/2c for the combined lactose-pullulan systems with the Williams-Landel-Ferry (WLF) equation was feasible only when the coefficients C₁ and C₂ were allowed to vary instead of assuming their ‘universal’ values.     

The effects of operating conditions on lactose crystallization in a pilot-scale spray dryer

The effects of operating conditions on the rate of drying and degree of crystallinity of lactose have been explored in a pilot-scale spray dryer. Temperature, moisture content, feed flow rate, atomizing air-flow rate, main air-flow rate and particle size have been varied to estimate the range of crystallinity of lactose obtainable in a pilot-scale spray dryer. Modulated differential scanning calorimetry (MDSC) and sorption tests (water-induced crystallization) have been used to assess the degree of crystallinity for freshly spray-dried samples. The degree of crystallinity could be varied from 18% to 72% by varying the operating conditions while allowing reasonable drying of the material. The study suggested that the use of a lower inlet temperature increased the crystallinity of the product from 25% (at 230 °C) to 60% (at 170 °C). A decrease in product crystallinity was also noted when using a lower atomizing air-flow rate. Statistical analysis with t-tests confirmed these differences to be significant with 95% confidence. The results suggest differences between small and pilot-scale spray dryers due to differences in particle sizes and drying rates.     

Production of lactose-hydrolyzed milk using ethanol permeabilized yeast cells

To overcome the problem of enzyme extraction and poor permeability of cell membrane to lactose, experimentation was carried to permeabilize Kluyveromyces marxianus NCIM 3465 cells for their subsequent use for the production of lactose-hydrolyzed milk. Different process parameters, such as biomass load, temperature, agitation and treatment time, were optimized for maximum lactose hydrolysis in skim milk using these cells. The ethanol-permeabilized yeast cells gave 89% hydrolysis of milk lactose under optimized conditions.     

Optimisation of process conditions for lactose hydrolysis in paneer whey with cold‐active β‐galactosidase from psychrophilic Thalassospira frigidphilosprofundus

The present study was conducted to analyse the physiochemical properties of Indian paneer whey. High concentration of minerals such as potassium, calcium, zinc and sodium, as NaCl, were observed which indicates the suitability of paneer whey in the preparation of beverages. A central composite rotatable design (CCRD) of response surface methodology (RSM) was employed to optimise the hydrolysis of lactose from whey using cold‐active β‐galactosidase of Thalassospira frigidphilosprofundus. Results indicated that 80% of lactose was hydrolysed at pH of 6.5 at 20 °C in 40 min in comparison with 40% at 30 °C. This emphasises the potential use of cold‐active β‐galactosidase in dairy industry.     

Laminar flow continuous settling crystalliser. Part 1. Initial exploration

Conventional lactose crystallisations give large spans that are not suitable for direct use in inhaler grade lactose. The factors causing large spans are successive nucleation events and growth rate dispersion. This paper (Part 1 of 2) explores a novel lactose crystallisation technique, laminar flow continuous settling crystallisation, proposed as a method for directly producing a narrow particle size distribution with a span of less than 1. A theoretical model was developed that modelled the growth and settling of individual crystals with growth rate dispersion within a column full of lactose solution flowing upwards in laminar flow. The model predicted a d₅₀ of 73.2 ± 0.9 μm and a span of 0.47 ± 0.01. In an experimental crystalliser crystals obtained had a d₅₀ between 50 and 90 μm but the span was greater than 1. The difference has been attributed to agglomeration and flow variations from true laminar flow, which is reported in Part 2.     

The effect of agitation on the nucleation of α-lactose monohydrate

Nucleation in an industrial crystallisation process determines how many crystals are formed and defines the final particle size distribution. This parameter plays a critical role in determining the success of an industrial lactose crystallisation, impacting yield, throughput and product quality. Previous studies on lactose crystallisation have reported that mixing can influence the nucleation kinetics of α-lactose monohydrate. This work looked to authenticate this by measuring the induction time required for nucleation of supersaturated lactose solutions across a range of agitation rates. Increasing agitation increased the rate of nucleation at a given supersaturation. The results show that this is a result of an increase in the frequency of activated molecular collisions and not a change in the critical nucleus size, which remains constant at a defined supersaturation.     

Optimisation of rancidity stability in long‐chain PUFA concentrates obtained from a rainbow trout (Oncorhynchus mykiss) by‐product

This research was focused on the production of polyunsaturated fatty acid concentrates from a farmed rainbow trout (Oncorhynchus mykiss) by‐product (i.e. belly muscle). The effect of different process variables (urea/fatty acids (FA) contents ratio, crystallisation time and temperature and stirring speed of the urea/FA mixture) on the lipid oxidation development during the urea complexation process was investigated. For this purpose, an experimental design (26 runs) following the response‐surface methodology was developed. As a result, peroxide value and TOTOX index showed to be dependent on the crystallisation time and temperature and the urea/FA ratio, while no influence of the crystallisation stirring speed was detected on both indices; additionally, polyene index was affected by the urea/FA ratio and its interaction with the crystallisation time. An optimised desirability score near 1.0 was attained provided values of 2.8 °C, 3.05 h and 3.57 were applied for crystallisation temperature, crystallisation time and urea/FA ratio, respectively.     

The effects of probiotics in lactose intolerance: A systematic review

Over 60 percent of the human population has a reduced ability to digest lactose due to low levels of lactase enzyme activity. Probiotics are live bacteria or yeast that supplements the gastrointestinal flora. Studies have shown that probiotics exhibit various health beneficial properties such as improvement of intestinal health, enhancement of the immune responses, and reduction of serum cholesterol. Accumulating evidence has shown that probiotic bacteria in fermented and unfermented milk products can be used to alleviate the clinical symptoms of lactose intolerance (LI). In this systematic review, the effectiveness of probiotics in the treatment of LI was evaluated using 15 randomized double-blind studies. Eight probiotic strains with the greatest number of proven benefits were studied. Results showed varying degrees of efficacy but an overall positive relationship between probiotics and lactose intolerance.     

Glass transition and crystallization behaviour of freeze-dried lactose-salt mixtures

Glass transition temperatures were determined for dehydrated lactose/salt mixtures with various water contents and water activities, and state diagrams were established. Crystallization behaviour was studied for pure amorphous lactose stored at various relative water vapour pressures (RVP). Furthermore, glass transitions temperatures and time-dependent lactose crystallization of freeze-dried lactose and lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂ and lactose/KCl mixtures in molar ratios of 9:1 were determined. Glass transition temperatures (T_g) of lactose powder as determined by differential scanning calorimetry (DSC) was lower than that of lactose/CaCl₂ (9:1)_, and lactose/MgCl₂ (9:1), but it was slightly higher than the T_g of lactose/NaCl (9:1), and lactose/KCl (9:1). Lactose/KCl had the lowest glass transition temperature, but it had about the same crystallization temperature as lactose/NaCl, and lactose/MgCl₂. The glass transition temperatures decreased as water contents increased. The critical water contents and water activities at 23 °C were predicted using data on glass transition temperature and water sorption. Pure lactose had a different critical water activity and water content from lactose/salt mixtures. The critical values of lactose/CaCl₂ (9:1) were the highest. Loss of sorbed water, indicating lactose crystallization, was observed in lactose and lactose/salt mixtures stored above the critical RVP.     

Egg shell as catalyst of lactose isomerisation to lactulose

A feasible way to produce lactulose, employing milk ultrafiltrate as source of lactose and egg shell as catalyst, is proposed as an alternative means for utilising these industrial wastes. Influences of catalyst loadings, lactose concentration and pH on lactose isomerisation were studied. Optimal production of lactulose was reached at 98 °C, employing 6 mg/ml of catalyst loading within 60 min of reaction. Quantities of lactulose of 1.18 g/100 ml and low levels of secondary products (epi-lactose, galactose and organic acids) were produced under these conditions of reaction. Methodology to remove coloured by-products from lactulose syrup in a range of 65–92% was established.     

Ultrasonic characterization of lactose dissolution

The ultrasonic properties (at 2.25 MHz) of lactose solutions and suspension of lactose crystals (d ∼ 50 μm) were measured as a function of concentration (0–40 wt.%). Ultrasonic velocity increased linearly with concentration regardless of the state of dissolution of the lactose crystals while ultrasonic attenuation was low and concentration-independent when the lactose was dissolved and increased approximately linearly with the concentration of suspended crystals. Therefore the amount of lactose present and the state of dissolution can be determined simultaneously with single ultrasonic sensor. A sensor based on this principle was applied to a stirred tank and used to measure the time taken to mix powdered lactose into a solution and the time for the added lactose to dissolve.     

Lactose uptake rate measurements by C-labelled lactose reveals promotional activity of porous cellulose in whey fermentation by kefir yeast

Lactose uptake rate by kefir yeast, immobilized on tubular cellulose and gluten pellets during fermentation of lactose and whey, was monitored using ¹⁴C-labelled lactose. Results illustrated that, in all cases, lactose uptake rate was strongly correlated with fermentation rate and the fermentation’s kinetic parameters were improved by kefir yeast entrapped in tubular cellulose. As a result, twofold faster fermentations were achieved in comparison with kefir yeast immobilized on gluten. This is probably due to cluster and hydrogen bonds formation between cellulose and inhibitors, such as Ca⁺⁺ and generated lactic acid, by which they leave the liquid medium. The findings, regarding the promotional effect of cellulose, seem promising for application in industrial whey fermentations.     

Water sorption and time-dependent crystallization behaviour of freeze-dried lactose-salt mixtures

Water sorption properties of freeze-dried lactose, lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂, and lactose/KCl mixtures in their molar ratio of (9:1) were investigated. Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were used to model water sorption properties. Water is known to function as a plasticizer, depressing the glass transition and facilitating crystallization. Crystallization in the present study resulted in loss of sorbed water from lactose. The crystallization of pure lactose and lactose/salt mixtures was observed at RVP?44.0% within 24 h. At RVP?54.4% water contents were higher in lactose/CaCl₂ and lactose/MgCl₂ mixtures than in pure lactose, lactose/NaCl, and lactose/KCl.Water content in pure lactose after crystallization was ?5.0%, suggesting that lactose crystallized as a mixture of α-lactose monohydrate and various anhydrous forms of α/β-lactose crystals. Anhydrous lactose/CaCl₂ and lactose/MgCl₂ had higher glass transition temperatures than lactose, but other salts (NaCl and KCl) with lactose gave lower glass transition than amorphous lactose. It seems that bivalent salts in mixtures with lactose gave a higher T_g than smaller monovalent ions. Salts delayed lactose crystallization. The effect on lactose crystallization was highest with calcium chloride (CaCl₂) and lowest with potassium chloride (KCl). It seems that different salts interacted with lactose to different extents. For water sorption, GAB model gave a better fit than BET model. Water sorption and time-dependent crystallization properties of lactose/salt mixtures should be considered in manufacturing and storage of dairy-based dehydrated materials.     

Statistical Modeling of β-galactosidase Inhibition During Lactose Hydrolysis

A statistical model approach called response surface methodology was used to describe the product and substrate inhibition effect on β-galactosidase enzyme during lactose hydrolysis. The effect of independent variables, namely the initial concentrations of lactose (73 - 146 mM), galactose (44 - 122 mM) and glucose (83 - 167 mM) on the reaction rate of β-galactosidase was evaluated. The enzymatic reaction rate was influenced by both combined and individual effects of all the substrate and products. Although, glucose acted as an activator at low lactose and low galactose concentrations, glucose caused the inhibition of β-galactosidase at higher concentrations of lactose and galactose. The effect of galactose concentration on β-galactosidase enzyme was in the direction of inhibition. At low lactose concentrations and high glucose concentrations, galactose concentration became more effective on the reaction rate.     

Prediction of Lactose Crystals Present in Supersaturated Lactose and Whey Solutions by Measuring the Water Activity

Linear models based on water activity measurement were developed to predict the crystalline fraction of lactose present in the supersaturated crystal-solution mixture of lactose and whey. By this method, it was possible to measure the crystalline fraction in the mixture even if the sample is opaque or coloured, which would be difficult to measure by the conventional refractometric method. To calculate the fraction of lactose crystallized, the differential water activity of the crystallized mixture and non-crystalline supersaturated solution needs to be determined. For the pure lactose, the predictive linear equation was Δ?L = 1874.4 Δ?a_w, whereas for whey it was Δ?L = 1155.2 Δ a_w, where Δ L is the amount of α-lactose monohydrate crystals (g 100g^?1 water) that is in the crystallized solution, and Δ a_w is the differential water activity after and prior to crystallization. Other equations such as Raoult's. Norrish, and Money-Born were also tested to predict the water activity of supersaturated solutions of lactose or whey.