Foaming properties of milk samples collected at various processing stages in a dairy processing factory across two seasons.

BACKGROUND: A foam layer makes an essential contribution to the quality of cappuccino-style drinks. Poor foaming of milk occurs quite often, however, especially in summer. The reasons for this are still unknown. Although a substantial number of studies on the foaming process of milk have been reported, these studies have been laboratory based and have used laboratory or pilot-scale equipment to simulate the processing conditions of a dairy processing factory. This study collected about 40 different samples across different processing stages in a dairy factory over two seasons (two batches per season) and investigated their composition and physical and foaming properties by mechanical mixing and steam injection. RESULTS: The results showed that milk samples collected in summer had a significantly higher content of fat, free fatty acids, and Ca2+ ions, and larger particle sizes but a markedly lower concentration of protein and solid non-fat, and surface tension than the samples collected in spring. These differences provided spring milk with a higher steam injection foamability than summer milk. However, steam injection foam stability, and mechanical mixing foamability and foam stability were not affected by seasonal factors. Milk samples collected in different batches within a season were almost identical with regard to the properties that were investigated. CONCLUSION: The variations in composition and physical properties of milk collected between two seasons could be the reasons for their difference in foamability but not for foam stability. Processes such as standardization, homogenization, and pasteurization improved markedly the foaming properties of milk. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of shearing-induced lipolysis on foaming properties of milk.

BACKGROUND: The attraction of cappuccino-style beverages is attributed to the foam layer, as it greatly improves the texture, appearance, and taste of these products. Typical milk has a low concentration of free fatty acids (FFAs), but their concentration can increase due to lipolysis during processing and storage, which is detrimental to the foamability and foam stability of milk. There are contradictory results in reported studies concerning the effects of FFAs on the foaming properties of milk due to differences in milk sources, methods inducing lipolysis, and methods of creating foam. In this study, the foaming properties and foam structure of milk samples whose lipolysis was induced by ultra-turraxing, homogenisation, and microfluidisation (1.5-3.5 µ-equiv. mL-1 FFAs) were investigated. RESULTS: Compared with others, microfluidised milk samples had the smallest particle size, lowest absolute zeta potential, and highest surface tension; thus exhibited high foamability and foam stability, and very small and homogeneous air bubbles in foam structure. For all shearing methods, increasing FFA content from 1.5 to 3.5 µ-equiv. mL-1 markedly decreased the surface tension, foamability, and foam stability of milk samples. The FFA level that led to undesirable foam structure was 1.5 µ-equiv. mL-1 for ultra-turraxed milk samples and 2.5 µ-equiv. mL-1 for homogenised and microfluidised ones. CONCLUSION: Shearing-induced lipolysis greatly affected the physical properties of milk samples and subsequently their foaming properties and foam structure. At the same FFA level, lipolysis induced by microfluidisation was much less detrimental to the foaming properties of milk than lipolysis induced by ultra-turraxing and homogenisation. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Functionality of bovine milk proteins and other factors in foaming properties of milk: a review.

For many dairy products such as cappuccino-style beverages, the top foam layer determines the overall product quality (e.g. their appearance, texture, mouthfeel and coffee aroma release rate) and the consumer acceptance. Proteins in milk are excellent foaming agents, but the foaming properties of milk are greatly affected by several factors such as the protein content, ratio of caseins to whey proteins, casein micelle size, pH, minerals, proteolysis, presence of low molecular weight compounds (lipids and their hydrolyzed products) and high molecular weight compounds (polysaccharides); milk processing conditions (e.g. homogenization, heat treatment and aging); and foaming method and temperature. These factors either induce changes in the molecular structure, charge and surface activity of the milk proteins; or interfere and/or compete with milk proteins in the formation of highly viscoelastic film to stabilize the foam. Some factors affect the foamability while others determine the foam stability. In this review, functionality of milk proteins in the production and stabilization of liquid foam, under effects of these factors is comprehensively discussed. This will help to control the foaming process of milk on demand for a particular application, which still is difficult and challenging for researchers and the dairy industry.

Crystallisation properties of amorphous cyclodextrin powders and their complexation with fish oil.

Water-induced crystallisation of amorphous core-cyclodextrin (CD) complex is an essential step in a solid encapsulation process and removal of added water is a challenging. Ethanol addition is expected to shorten the complex dehydration time. This study investigated crystallisation of amorphous spray-dried α-, ß- and γ-CD powders by direct mixing 15% (w/w) of ethanol:water mixture (0:100, 20:80, 40:60, 60:40, 80:20 and 100:0) over 72 h period. The results showed α- and ß-CD powders crystallised at all concentrations of ethanol solutions. Especially mixed with 0:100 and 20:80 ethanol:water solutions, the crystallisation behaviour of α- and ß-CD powders was similar to that of commercial crystalline counterparts. γ-CD powders exhibited a crystallisation sign as mixed with 0:100 and 20:80 ethanol:water solutions only. In the study of fish oil encapsulation using the mixture of water and ethanol to induce the complex crystallisation, only γ-CD powder was able to form complex with fish oil.

Methods to characterize the structure of food powders - a review.

Food powders can exist in amorphous, crystalline or mixed structure depending on the order of molecular arrangement in the powder particle matrices. In food production, the structure of powders has a greatly effect on their stability, functionality, and applicability. The undesirable structure of powders can be accidentally formed during production. Therefore, characterization of powder structure as well as quantification of amorphous-crystalline proportions presenting in the powders are essential to control the quality of products during storage and further processing. For these purposes, many analytical techniques with large differences in the degree of selectivity and sensitivity have been developed. In this review, differences in the structure of food powders are described with a focus being placed on applications of amorphous powders. Essentially, applicability of common analytical techniques including X-ray, microscopic, vapor adsorption, thermal, and spectroscopic approaches for quantitative and qualitative structural characterization of food powders is also discussed.

Dehydration of CO2-α-cyclodextrin complex powder by desiccant adsorption method and its release properties.

Stability and release properties of CO2-α-cyclodextrin complex powder prepared by solid encapsulation (water activity, aw ≈ 0.95) followed by moisture removal using silica gel and CaCl2 desiccants during post-dehydration were investigated. The results showed that CaCl2 reduced aw much faster than silica gel did under the same conditions. After approximately 60 h, aw of complex powders reduced using silica gel was almost constant at 0.247 (±0.012), while those treated with CaCl2, aw was 0.225 (±0.005) and had not yet reached their lowest value. Moisture adsorption by silica gel and CaCl2 also led to a decrease in the CO2 concentration of complex powder (higher decrease for silica gel adsorption) without affecting the structure and morphology of complex powder. The CO2 release properties of CaCl2-aw-reduced complex powder at different relative humidities (32.73, 52.86, 75.32 and 97.30% RH), liquid environments (water and oil) and packaging methods (normal and vacuum) were also studied.

Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility.

Kinetics of enthalpy relaxation of milk protein concentrate (MPC) powder upon short-term (up to 67 h) storage at 25 °C and aw 0.85, and long-term (up to 48 days) storage at 25 °C and a range of aw values (0-0.85) were studied by differential scanning calorimetry (DSC). The short-term study showed a rapid recovery of enthalpy for the first 48 h, followed by a slower steady increase with time. The non-exponential ß parameter was calculated using the Kohlrausch-Williams-Watts function and found to be 0.39. Long-term storage showed that enthalpy relaxation depends on both storage period and water activity. The enthalpy value was much less for lower moisture content (mc) (aw ≤ 0.23, mc ≤ 5.5%) than for higher mc (aw ≥ 0.45, mc ≥ 8%) samples for a particular storage period. The results suggest that the presence of more water molecules, in close proximity to the protein surface facilitates kinetic unfreezing and subsequent motion of molecular segments of protein molecules towards thermodynamic equilibrium. Although de-ageing of stored samples did not reverse storage-induced solubility losses, the timescale of enthalpy relaxation was similar to that of solubility loss. It is suggested that enthalpy relaxation within stored samples allows structural rearrangements that are responsible for subsequent solubility decreases.

Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water.

BACKGROUND: Protein conformational modifications and water-protein interactions are two major factors believed to induce instability of protein and eventually affect the solubility of milk protein concentrate (MPC) powder. To test these hypotheses, MPC was stored at different water activities (a(w) 0.0-0.85) and temperatures (25 and 45 °C) for up to 12 weeks. Samples were examined periodically to determine solubility, change in protein conformation by Fourier transform infrared (FTIR) spectroscopy and water status (interaction of water with the protein molecule/surface) by measuring the transverse relaxation time (T(2) ) with proton nuclear magnetic resonance ((1) H NMR). RESULTS: The solubility of MPC decreased significantly with ageing and this process was enhanced by increasing water activity (a(w) ) and temperature. Minor changes in protein secondary structure were observed with FTIR which indicated some degree of unfolding of protein molecules. The NMR T(2) results indicated the presence of three distinct populations of water molecules and the proton signal intensity and T(2) values of proton fractions varied with storage condition (humidity) and ageing. CONCLUSION: Results suggest that protein/protein interactions may be initiated by unfolding of protein molecules that eventually affects solubility.

Changes in surface chemical composition relating to rehydration properties of spray-dried camel milk powder during accelerated storage.

Alterations in surface chemical composition relating to rehydration properties of spray-dried camel milk powders during accelerated storage (11-33% RH, 37 °C) over 18 weeks were investigated. The results showed that the surface of the fresh spray-dried camel milk powder (t = 0) was dominated by lipids (78%), followed by proteins (16%) and lactose (6%). During storage, the surface protein and lactose content decreased while the surface lipid content increased, resulting in an increase in surface hydrophobicity and slight agglomeration of the powder, especially for powder kept at 33% RH. Although fresh camel milk powder had very poor wettability, it displayed very high dispersibility and solubility (99%). During storage, dispersibility and solubility declined with increasing storage time and increasing RH levels, which correlated with an increase in surface lipid content. However, at the end of the storage period, camel milk powder still retained very high solubility (>93%).

Foaming properties and foam structure of milk during storage.

Changes in foaming properties and foam structure of raw whole, raw skim, pasteurised whole, and pasteurised skim milk during storage at 4 °C, evaluated by mechanical mixing, air and steam injection, were investigated. The results showed that storage of milk until the end of their shelf-life (day 3 for raw milk and day 21 for pasteurised milk) did not induce any significant change in pH, particle size, viscosity and their foaming properties (foaming capacity, foam stability and size of air bubbles) although there was a slight increase in free fatty acid content. Regarding foaming methods, the air injection method produced much less foam volume than mechanical mixing and steam injection, except for raw milk where mechanical mixing showed the least foamability. However, an opposite trend was observed for foam stability. Although air injection induced the largest size of air bubbles, it produced the most stable foam, which was much more stable than foam produced by mechanical mixing and steam injection.

Changes in physicochemical properties of spray-dried camel milk powder over accelerated storage.

Changes in physiochemical properties of spray-dried camel milk powders during storage at 11-32% RH and 37 °C over 18 weeks were investigated. The results showed that fresh camel milk powders had amorphous structure, clumsy spherical shape particles and almost 100% solubility in water. During storage at controlled low RH levels (<32% RH), reduction in moisture content and aw of the powders caused glass transition signals of lactose to evolve, although the powders exhibited a slight development of crystallinity. True density, colour (L*, a* and whiteness), and morphology were almost unchanged during storage while b* values associated with non-enzymatic browning, and fat oxidation into volatile compounds increased steadily. Over storage period, solubility of the powder declined just slightly and secondary structure of proteins unfolded from α-helices to ß-sheets, loops and ß-turns. These changes were more profound for the powders stored at 32% RH than those kept at 11 and 22% RH.

Encapsulation of tea tree oil by amorphous beta-cyclodextrin powder.

An innovative method to encapsulate tea tree oil (TTO) by direct complexation with solid amorphous beta-cyclodextrin (ß-CD) was investigated. A ß-CD to TTO ratio of 90.5:9.5 (104.9mg TTO/g ß-CD) was used in all complexation methods. The encapsulation was performed by direct mixing, and direct mixing was followed by the addition of water (13-17% moisture content, MC) or absolute ethanol (1:1, 1:2, 1:3 and 1:4 TTO:ethanol). The direct mixing method complexed the lowest amount of TTO (60.77mg TTO/g ß-CD). Powder recrystallized using 17% MC included 99.63mg of TTO/g ß-CD. The addition of ethanol at 1:2 and 1:3 TTO:ethanol ratios resulted in the inclusion of 94.3 and 98.45mg of TTO/g ß-CD respectively, which was similar to that of TTO encapsulated in the conventional paste method (95.56mg TTO/g ß-CD), suggesting an effective solid encapsulation method. The XRD and DSC results indicated that the amorphous TTO-ß-CD complex was crystallized by the addition of water and ethanol.

Novel Solid Encapsulation of Ethylene Gas Using Amorphous α-Cyclodextrin and the Release Characteristics.

This research investigated the encapsulation of ethylene gas into amorphous α-cyclodextrins (α-CDs) at low (LM) and high (HM) moisture contents at 1.0-1.5 MPa for 24-120 h and its controlled release characteristics at 11.2-52.9% relative humidity (RH) for 1-168 h. The inclusion complexes (ICs) were characterized using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP-MAS (13)C NMR), and scanning electron microscopy (SEM). Ethylene concentrations in the ICs were from 0.45 to 0.87 mol of ethylene/mol CD and from 0.42 to 0.54 mol of ethylene/mol CD for LM and HM α-CDs, respectively. Ethylene gas released from the encapsulated powder at higher rates with increasing RH. An analysis of release kinetics using Avrami's equation showed that the LM and HM amorphous α-CDs were not associated with significant differences in release constant k and parameter n for any given RH condition. NMR spectra showed the presence of the characteristic carbon-carbon double bond of ethylene gas in the encapsulated α-CD powder.

Encapsulation of CO2 into amorphous alpha-cyclodextrin powder at different moisture contents - Part 1: Encapsulation capacity and stability of inclusion complexes.

This study investigated the effects of water-induced crystallization of amorphous alpha-cyclodextrin (α-CD) powder on CO2 encapsulation at 0.4-1.6 MPa pressure for 1-72 h through the addition of water (to reach to 13, 15 and 17% wet basis, w.b.) into amorphous α-CD powder prior to the encapsulation. The results showed that the α-CD encapsulation capacity was over 1 mol CO2/mol α-CD after pressurizing for longer than 48 h. The encapsulated CO2 concentration by the addition of water was considerably higher (p<0.05) than that of amorphous α-CD powder (5.51% MC, w.b.) without an addition of water and that of crystalline α-CD powders under the same MC and encapsulation conditions. A comparison of CO2 release properties (75% relative humidity, 25 °C) from complexed powders prepared from amorphous and crystalline α-CD powders under the same conditions is also presented.

Encapsulation of CO2 into amorphous alpha-cyclodextrin powder at different moisture contents - Part 2: Characterization of complexed powders and determination of crystalline structure.

This study aims to characterize CO2-α-cyclodextrin (α-CD) inclusion complexes produced from amorphous α-CD powder at moisture contents (MC) close to or higher than the critical level of crystallization (e.g. 13, 15 and 17% MC on wet basis, w.b.) at 0.4 and 1.6MPa pressure for 72h. The results of (13)C NMR, SEM, DSC and X-ray analyses showed that these MC levels were high enough to induce crystallization of CO2-α-CD complexed powders during encapsulation, by which amount of CO2 encapsulated by amorphous α-CD powder was significantly increased. The formation of inclusion complexes were well confirmed by results of FTIR and (13)C NMR analyses through an appearance of a peak associated with CO2 on the FTIR (2334cm(-1)) and NMR (125.3ppm) spectra. Determination of crystal packing patterns of CO2-α-CD complexed powders showed that during crystallization, α-CD molecules were arranged in cage-type structure in which CO2 molecules were entrapped in isolated cavities.

Encapsulation of CO2 into amorphous and crystalline α-cyclodextrin powders and the characterization of the complexes formed.

Carbon dioxide complexation was undertaken into solid matrices of amorphous and crystalline α-cyclodextrin (α-CD) powders, under various pressures (0.4-1.6 MPa) and time periods (4-96 h). The results show that the encapsulation capacity of crystalline α-CD was significantly lower than that of amorphous α-CD at low pressure and short time (0.4-0.8 MPa and 4-24 h), but was markedly enhanced with an increase of pressure and prolongation of encapsulation time. For each pressure level tested, the time required to reach a near equilibrium encapsulation capacity of the crystalline powder was around 48 h, which was much longer than that of the amorphous one, which only required about 8h. The inclusion complex formation of both types of α-CD powders was confirmed by the appearance of a CO2 peak on the FTIR and NMR spectra. Moreover, inclusion complexes were also characterized by DSC, TGA, SEM and X-ray analyses.

Dissolution of sucrose crystals in the anhydrous sorbitol melt.

The dissolution of a sugar (sucrose as a model) with higher melting point was studied in a molten food polyol (sorbitol as a model) with lower melting point, both in anhydrous state. A DSC and optical examination revealed the dissolution of anhydrous sucrose crystals (mp 192 degrees C) in anhydrous sorbitol (mp 99 degrees C) liquid melt. The sucrose-sorbitol crystal mixtures at the proportions of 10, 30, 60, 100 and 150 g of sucrose per 100 g of sorbitol were heat scanned in a DSC to above melting endotherm of sorbitol but well below the onset temperature of melting of sucrose at three different temperatures 110, 130 and 150 degrees C. The heat scanning modes used were with or without isothermal holding. The dissolution of sucrose in the sorbitol liquid melt was manifested by an increase in the glass transition temperature of the melt and corresponding decrease in endothermic melting enthalpy of sucrose. At given experimental conditions, as high as 25 and 85% of sucrose dissolved in the sorbitol melt during 1 h of isothermal holding at 110 and 150 degrees C, respectively. Optical microscopic observation also clearly showed the reduction in the size of sucrose crystals in sorbitol melt during the isothermal holding at those temperatures.

Encapsulation of ethylene gas into α-cyclodextrin and characterisation of the inclusion complexes.

Molecular encapsulation of various apolar compounds with α-cyclodextrin (α-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an α-CD under 0.2-1.5MPa for 12-120h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-α-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP-MAS (13)C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C(4), C(3) and C(5) in NMR spectra, intensity changes of C-H bending and CC stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans.

Release kinetics of ethylene gas from ethylene-α-cyclodextrin inclusion complexes.

Ethylene was included into α-cyclodextrin (α-CD) by molecular encapsulation. Characterisation of the ethylene-α-CD inclusion complexes (ICs) using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) confirmed their crystalline structures. Release kinetics of ethylene gas from the ICs was investigated. Release characteristics experiments were carried out at various relative humidities (RH) (52.9%, 75.5%, and 93.6%) and temperatures (45, 65, 85, and 105°C). The Power Law and Avrami's equations were used to analyse release kinetics. The latter showed better fit for ethylene release. Kinetics analysis based on Avrami's equation showed that the release of ethylene was accelerated by increases in RH and temperature. For humidity treatments, the release parameter n represented a diffusive mechanism at 52.9% and 75.5% RH and a first-order mode at 93.6% RH. However, a diffusive mechanism was found in all temperature experiments. Release rate constants increased as a function of increasing temperature. Temperature coefficient (Q10), activation energy (Ea) and half-life release of ethylene gas were also analysed.

Protein conformational modifications and kinetics of water-protein interactions in milk protein concentrate powder upon aging: effect on solubility.

Protein conformational modifications and water-protein interactions are two major factors believed to induce instability of protein and eventually affect the solubility of milk protein concentrate (MPC) powder. To test these hypotheses, MPC was stored at different water activities (a(w) 0.0-0.85) and temperatures (25 and 45 degrees C) for up to 12 weeks. Samples were examined periodically to determine solubility, change in protein conformation by Fourier transform infrared (FTIR) spectroscopy and principal component analysis (PCA), and water status (interaction of water with the protein molecule/surface) by measuring the transverse relaxation time (T(2)) with proton nuclear magnetic resonance ((1)H NMR). The solubility of MPC decreased significantly with aging, and this process was enhanced by increasing water activity (a(w)) and storage temperature. Minor changes in protein secondary structure were observed with FTIR, which indicated some degree of unfolding of protein molecules. PCA of the FTIR data was able to discriminate samples according to moisture content and storage period. Partial least-squares (PLS) analysis showed some correlation between FTIR spectral feature and solubility. The NMR T(2) results indicated the presence of three distinct populations of water molecules, and the proton signal intensity and T(2) values of proton fractions varied with storage conditions (humidity, temperature) and aging. Results suggest that protein/protein interactions may be initiated by unfolding of protein molecules that eventually affects solubility.