Lactose Systems Research Articles

Viability, Storage Stability and In Vitro Gastrointestinal Tolerance of Lactiplantibacillus plantarum Grown in Model Sugar Systems with Inulin and Fructooligosaccharide Supplementation

This study aims to investigate the effects of inulin and fructooligosaccharides (FOS) supplementation on the viability, storage stability, and in vitro gastrointestinal tolerance of Lactiplantibacillus plantarum in different sugar systems using 24 h growth and 10 days survival studies at 37 °C, inulin, and FOS (0%, 0.5%, 1%, 2%, 3% and 4%) supplementation in 2%, 3%, and 4% glucose, fructose, lactose, and sucrose systems. Based on the highest percentage increase in growth index, sucrose and lactose were more suitable sugar substrates for inulin and FOS supplementation. In survival studies, based on cell viability, inulin supplementation showed a better protective effect than FOS in 3% and 4% sucrose and lactose systems. Four selected sucrose and lactose systems supplemented with inulin and FOS were used in a 12-week storage stability study at 4 °C. Inulin (3%, 4%) and FOS (2%, 4%) supplementation in sucrose and lactose systems greatly enhanced the refrigerated storage stability of L. plantarum. In the gastrointestinal tolerance study, an increase in the bacterial survival rate (%) showed that the supplementation of FOS in lactose and sucrose systems improved the storage viability of L. plantarum. Both inulin and FOS supplementation in sucrose and lactose systems improved the hydrophobicity, auto-aggregation, co-aggregation ability of L. plantarum with Escherichia coli and Enterococcus faecalis.

Lactose crystallization as affected by presence of lactic acid and calcium in model lactose systems

Acid whey is considered a hard to process stream mainly due to failure of lactose to crystallize, apparently attributed to the presence of lactic acid (LA) and calcium (Ca). Understanding the physical state and the thermal behaviour of lactose during crystallization in the presence of LA and Ca is important in order to develop adequate strategies to improve processability of acid whey and thus was the objective of this study. Presence of high concentration of LA (1% w/w) resulted in a decline in lactose crystal yields (∼59%). This was alleviated by lowering the LA content (0.2% w/w) which improved the yield (∼77%). At high LA content, small amounts of Ca (0.072% w/w) appeared to diminish the negative impact of LA presence by increasing the yield. Pure L solution yielded lactose particles of ∼84 μm. Crystal size slightly increased to ∼91 μm in the system containing high concentrations of LA along with low Ca concentration and although the presence of low concentrations of both LA (0.2% w/w) and Ca (0.072% w/w) resulted ∼ 163 μm sized crystals. Water molecules in the hydration layer around lactose molecules appeared to play a significant role governing the crystallisation behaviour and characteristics of lactose crystals in the presence of LA and Ca and/or in combination. Hence, the removal of some Ca to concentrations ≤0.072% w/w from acid whey may improve the crystallisation of lactose and thereby improve the processability of acid whey.

Structural relaxations of amorphous lactose and lactose-whey protein mixtures

Structural relaxations and relaxation times, τ, of lactose in freeze-dried amorphous lactose and lactose-WPI mixture systems were studied with glass transition data. The results indicated that Tg, enthalpy relaxation and α-relaxation temperature, Tα, of amorphous lactose was affected by the presence of lactose crystals and WPI at 0.33 aw (25 °C) due to water migration. The τ and Tα−Tg relationship of the materials was successfully modeled by the WLF equation with the material-special constants (−C1 and C2). A strength parameter, S, indicating decrease of τ from 102 to 10−2 s, could be used to measure the structural stability of lactose systems above their glass transition. The strength of amorphous lactose decreased with aw increasing up to 0.44 and enhanced by α lactose crystals and WPI in storage at 0.33 aw. Hence, the strength parameter provided a simple and convenient means to measure compositional effects on structure formation in food processing.

Two Gene Clusters Coordinate Galactose and Lactose Metabolism in Streptococcus gordonii

Streptococcus gordonii is an early colonizer of the human oral cavity and an abundant constituent of oral biofilms. Two tandemly arranged gene clusters, designated lac and gal, were identified in the S. gordonii DL1 genome, which encode genes of the tagatose pathway (lacABCD) and sugar phosphotransferase system (PTS) enzyme II permeases. Genes encoding a predicted phospho-β-galactosidase (LacG), a DeoR family transcriptional regulator (LacR), and a transcriptional antiterminator (LacT) were also present in the clusters. Growth and PTS assays supported that the permease designated EII(Lac) transports lactose and galactose, whereas EII(Gal) transports galactose. The expression of the gene for EII(Gal) was markedly upregulated in cells growing on galactose. Using promoter-cat fusions, a role for LacR in the regulation of the expressions of both gene clusters was demonstrated, and the gal cluster was also shown to be sensitive to repression by CcpA. The deletion of lacT caused an inability to grow on lactose, apparently because of its role in the regulation of the expression of the genes for EII(Lac), but had little effect on galactose utilization. S. gordonii maintained a selective advantage over Streptococcus mutans in a mixed-species competition assay, associated with its possession of a high-affinity galactose PTS, although S. mutans could persist better at low pHs. Collectively, these results support the concept that the galactose and lactose systems of S. gordonii are subject to complex regulation and that a high-affinity galactose PTS may be advantageous when S. gordonii is competing against the caries pathogen S. mutans in oral biofilms.

Effect of drying methods on the reactivity of chitosan towards Maillard reaction

The effect of drying methods on chitosan reactivity towards Maillard reaction during storage of dried chitosan–lactose systems was investigated. Two different structural forms of chitosan, scaffold and microspheres, were prepared. Then they were dried by lyophilization or using supercritical fluid technology (SF-CO2) and stored with lactose under controlled temperature conditions (60 °C) and water activity (aw = 0.65). The drying method produced slight modifications on the chitosan structure especially in samples submitted to SF-CO2 treatment. Differences were more evident in the reactivity of chitosan–lactose systems during storage. Maillard reaction development was assessed by quantification of a new compound which originated from the acid hydrolysis of Amadori compounds (NFMD) resulting from chitosan–lactose interactions, and not detected in the acid hydrolysates of freshly prepared chitosan-lactose systems. Maillard reaction was influenced by different factors such as the manner of lactose addition, structure of chitosan (microspheres and scaffolds) and drying method. Lyophilized chitosan in the form of microspheres with lactose, presented the highest values of NFMD (428.45 mg/100 g of sample). The determination of this compound could be used as an index of the progress of Maillard reaction.

Application of thermal analysis in study of binary mixtures with metformin

Thermal analysis is an essential analytical tool in development of new formulations as well as to study the interaction between drugs and excipients. This work aims to investigate the possible interactions between metformin and excipients as microcrystalline cellulose (Microcel MC101®), starch sodium glycolate (Explosol®), sodium croscarmellose (Explosel®), PVP K30, magnesium stearate, starch and lactose, usually employed in pharmaceutical products. TG, DSC and DTA techniques were used for the thermal characterization to track if the thermal properties of the drug substance were modified in the mixture. Disregard of the starch and lactose systems, no changes in thermal behavior of mixtures were found. Thermogravimetric studies (TG) of metformin and its binary mixtures showed different thermal behavior.

Prediction of Dry Powder Inhaler Formulation Performance From Surface Energetics and Blending Dynamics

The purpose of these studies was to investigate the ability of surface energy measurements and rates of mixing in dry powder inhaler (DPI) formulations to predict aerosol dispersion performance. Two lactose carrier systems comprising either spray-dried or milled particles were developed such that they had identical physical characteristics except for surface morphology and surface energies avoiding confounding variables common in other studies. Surface energy measurements confirmed significant differences between the powder systems. Spray-dried lactose had a higher surface entropy (0.20 vs. 0.13 mJ/m2K) and surface enthalpy (103.2 vs. 79.2 mJ/m2) compared with milled lactose. Mixing rates of budesonide or fluorescein were assessed dynamically, and significant differences in blending were observed between lactose systems for both drugs. Surface energies of the lactose carriers were inversely proportional to dispersion performance. In addition, the root mean square (RMS) of blending rates correlated positively with aerosol dispersion performance. Both techniques have potential utility in routine screening of DPI formulations.

FT-NIR Microspectroscopy: A Method for Quantitatively Mapping One-Dimensional Moisture Penetration Into Sugar Glasses

In this methods paper, one-dimensional moisture penetration into thin films of sugar glass exposed to different relative humidity was measured by use of FT-near infrared microspectroscopy working in a spectrum range of wavelength from 1.35 to 2.50 μm. The peak height ratio of characteristic peaks for H—OH (primarily water) and O— H (primarily sugar) bands, respectively, were highly correlated to moisture content for both sucrose and lactose systems and were used for calibration of moisture content. Moisture content along one-dimensional locations was accurately measured using microscopic mapping. Sorption penetration profiles of moisture content vs. penetration depth were obtained. Depending on the sorption time and storage conditions, moisture penetration profiles typically showed a fairly sharp boundary between intact glass in the interior and a high moisture content surface layer, which slowly moved into the sample interior over time. Crystal- lization was observed to occur at the surface under certain conditions when insufficient inhibitors were present. In these cases, a moisture peak was seen to penetrate into the glass. Microspectroscopic mapping proved to be an excellent technique for studying moisture penetration behavior and kinetics, providing quantitative data for future diffusion modeling.

Water–solids interactions, matrix structural properties and the rate of non-enzymatic browning

The kinetics of non-enzymatic browning (NEB) was studied in freeze-dried model and food systems in a wide range of relative humidity (R.H.) values. PVP, lactose, lactose–starch solutions and food (milk, cabbage, apple, potato, and chicken meat) systems were freeze-dried, equilibrated at 11–85% of R.H. and incubated at 70 °C. Thermal transitions were determined by DSC. The kinetics of NEB development was analyzed. In PVP systems the maximum rate occurred at 33% R.H., at which T g was close to the storage temperature. Above 33% R.H. the samples presented a fluid aspect at 70 °C and the NEB rate decreased when increasing R.H. In tissues containing structuring water insoluble biopolymers and presenting an intermediate degree of collapse, the maximum rate of NEB occurred at relative humidities in a range of 50–80%, when the samples were well above T g at the storage temperature. In the lactose systems the maximum rate occurred at R.H. close to 40%, at conditions at which lactose was highly crystalline.

FTIR study of state and phase transitions of low moisture sucrose and lactose

Mid-infrared spectra of freeze-dried sucrose and lactose systems were acquired over a range of temperatures (30–200 °C) and water contents (0–6.3%). Starting from the glassy state, the experimental conditions were selected to cover the main thermal transitions: the glass–rubber transition, the crystallisation and, for some samples, the subsequent melting. The FTIR spectra were very sensitive to the physical state. While subtle but systematic spectral differences between the glassy and rubbery states were detectable throughout the spectrum, a very pronounced increase in spectral resolution was observed as crystallisation occurred and was followed by the expected spectral broadening during melting. The temperatures at which these changes occurred were in satisfactory agreement with the transition temperatures measured by differential scanning calorimetry (DSC). The increase in molecular mobility as a result of increasing temperature or plasticisation by water led to a significant shift of the OH stretching band to higher wavenumbers indicating a weakening of hydrogen bonding. This shift reached a maximum as the DSC measured crystallisation temperature range was approached. As expected, the crystallisation led to a highly effective hydrogen bonding network. This was more significant for lactose than for sucrose. No significant step change in hydrogen bonding was observed at Tg. As anticipated, the temperature at which these transitions occurred decreased with increasing water content but overlapped when observed in the context of the shifted temperature ( T−Tg).

Thermal resistance of β-galactosidase in dehydrated dairy model systems as affected by physical and chemical changes

Abstract The objective was to study the remaining activity of the enzyme β-galactosidase in dehydrated dairy systems and its relationship with simultaneous chemical (i.e. non-enzymatic browning, NEB) and physical changes (structural collapse) at temperatures from 70 to 105 °C. The presence of milk proteins had a structure-stabilizing effect, which was not reflected by enzymic stabilization or NEB prevention. Although the remaining enzyme activity was correlated with physical and chemical changes in some of the systems exposed at 22% R.H., these changes were not parallel to the macroscopic changes in some of the anhydrous systems. The single lactose systems were highly collapsed at all the temperatures analyzed, but enzymic inactivation and NEB were dependent on the storage temperature rather than on the degree of collapse. Chemical and physical changes were not correlated to the remaining activity. Changes which occur at a molecular level may not be related to the changes at a supramolecular level (such as those derived from glass transition or collapse).

A Study on Advanced Maillard Reaction in Heated Casein/Sugar Solutions: Colour Formation

The Maillard reaction in its advanced state was studied with respect to colour formation in milk-resembling model systems (lactose–caseinate or glucose–caseinate solutions), heated between 110 and 150°C. Browning was measured spectrophotometrically (420 nm) and via a tristimulus colorimeter. The pigments causing browning (measured at 420 nm) were mainly bound to caseinate (brown pigments not bound to protein amounted to 5–6% of total colour). No significant difference between glucose and lactose was found in this respect. Scans of the brown pigments showed a shift from blue-absorbing regions to the yellow/orange/brown regions. The temperature dependence for browning rate (estimated via the Arrhenius equation) was also the same for the glucose and lactose systems (activation energy ∼120 kJ mol-1). However, differences were found between glucose and lactose when colour was measured via the tristimulus colorimeter: visual colour changes (i.e. decrease in luminosity, increase in the yellow-blue component) appeared faster with the glucose system.

Movement of liquids through powder beds

The movement of hydrophilic fluids into and out of beds of two grades of lactose, microcrystalline cellulose (MCC) and mixtures of the two materials has been assessed by a pressure membrane technique. While water was an appropriate fluid to use with MCC, because of its solvent properties, it proved unsuitable for use with lactose and the binary mixtures with MCC. In these cases, a 50:50% mixture of ethanol and water proved acceptable. The method clearly illustrated the differences in the movement of fluid in the two grades of lactose, which differed in particle size, and between lactose and MCC. These differences could be quantified in terms of limiting saturation pressures, irreducible saturation and ‘apparent’ pore distributions. The MCC introduces absorptive and adsorptive influences into the binary mixtures with lactose which are absent or minimal in the lactose systems. Such effects are undoubtedly involved in ensuring that these binary mixtures can be used to produce spherical granules by extrusion/ spheronisation whereas the process is not successful for lactose alone.

Regulation of plasmid-encoded lactose genes in different gram-negative enterobacteriaceae

The expression and regulation of a variety of plasmid-encoded lactose systems have been studied in different gram-negative Enterobacteriaceae ( Escherichia coli K-12, Serratia marcescens, and Enterobacter liquefaciens). They are similarly expressed in all strains, and they are inducible and sensitive to catabolite repression. Urea, known to bring about a specific catabolite repression effect, has been chosen to study some regulatory aspects of these plasmid-encoded lactose systems. We have shown that the expression of all lactose systems is inhibited by urea but the extent of the inhibition is strain dependent. This indicates that the genetic background of the host might modify in certain instances the expression of plasmid-encoded genes.

Expression and regulation of lactose genes carried by plasmids.

A number of plasmids carrying the lactose character have been studied. All of the plasmids examined so far code for proteins essential for lactose utilization, i.e., beta-galactosidase and galactoside permease. None of them carries enzymatically or immunologically detectable thiogalactoside transacetylase. The expression of the two enzymes is both negatively and positively controlled: they are inducible by different galactosides and are sensitive to catabolite repression. Since the plasmid-coded lactose systems have many features in common with the Escherichia coli lactose operon, it is suggested that the plasmids could have acquired the lactose genes from an E. coli chromosome.

Studies of Heated Milk III. Mode of Formation of Certain Furan Compounds

Summary The mechanism by which furfuryl alcohol and hydroxymethylfurfural are heat-generated in condensed skimmilk and certain lactose systems has been studied. The importance of pH and buffer capacity in the reactions concerned has been demonstrated and discussed. Condensed skimmilk and weakly alkaline lactose systems produced both furfuryl alcohol and hydroxymethylfurfural. Acidified condensed skimmilk and neutral or acidic lactose systems yielded significant quantities of hydroxymethylfurfural but no furfuryl alcohol. The structure of the lactose molecule or that of a similar sugar, maltose, was shown to be rather specifically required in furfuryl alcohol formation. A proposed mechanism for the conversion of lactose to furfuryl alcohol has been presented schematically. In this mechanism the production of furfuryl alcohol is related to that of formic acid. It is suggested that a variation of the mechanism accounts for the conversion of lactose to hydroxymethylfurfural.