Composition and relative humidity (RH) can have a profound impact on the physical (flowability, stickiness) and functional (reconstitution) properties of milk powder (MP) and therefore its quality, storage stability and shelf-life. Conventional microscopic techniques are not capable of dynamically imaging the effect of RH on MP at high magnification. The aim of this study was to develop a novel method to characterise in-situ and in real time the hydration and reconstitution of five spray-dried milk protein concentrates (MPCs) using an Environmental Scanning Electron Microscope (ESEM). ESEM was employed to observe the surface microstructure of MPC powders with varying protein content (38.63%–80.94%, w/w), at various RH values ranging from 35% to over 100%. MPC powders were imaged by an ESEM without any prior preparation, and with minimal physical sample alteration, thus providing fundamental insights into MPC hydration and reconstitution. ESEM surface analysis showed particle swelling in all MPCs, and that with increasing protein content, hydration and reconstitution efficiency decreased. For the first time, dynamic particle surface fusion was observed. Such fusion can result in stickiness and caking over time. ESEM methods developed here may provide mechanistic insights into the effects of RH during storage. Surface re-arrangement was also observed in all MPCs, but was impeded in MPC70 and MPC80 thus indicating that this is the rate limiting step for MPC reconstitution. This work validates the use of an ESEM to dynamically characterise MPC powder hydration and reconstitution in-situ and in real-time, at both high magnification and spatial resolution.

The objective of this study was to assess the ability of producing laminated edible films manufactured using the following proteins; gelatin (G), whey protein isolate (WPI) and polysaccharide sodium alginate (SA), and to evaluate their physical properties. Additionally, films’ preparation employing these ingredients was optimized through the addition of corn oil (O). Overall, 8-types of laminated films (G-SA, G-WPI, SA-WPI, SA-G-WPI, GO-SAO, GO-WPIO, SAO-WPIO and SAO-GO-WPIO) were developed in this study. The properties of the prepared films were characterized through the measurement of tensile strength (TS), elongation at break point (EB), puncture resistance (PR), tear strength (TT), water vapour permeability (WVP) and oxygen permeability (OP). The microstructure of cross-sections of laminated films was investigated by scanning electron microscopy (SEM). Mechanical properties of films were dramatically enhanced through the addition of film layers. GO-SAO laminate showed the best barrier properties to water vapour (22.6 ± 4.04 g mm/kPa d m2) and oxygen (18.2 ± 8.70 cm3 mm/kPa d m2). SAO-GO-WPIO laminate film was the strongest of all laminated films tested, having the highest TS of 55.77 MPa, PR of 41.36 N and TT of 27.32 N. SA-G-WPI film possessed the highest elasticity with an EB value of 17.4%.

Red meat has a tougher texture compared with many other food products, therefore consumption is often reduced among older adults. Acidic treatments had a positive effect on WBSF values (reduced the WBSF values from 23.35 N for control to 14.83 N), and texture parameters and a combination with apple fiber and rice starch may improve the health profile of a meat product with benefits for consumers, particularly for older population. A novel meat product with a softer texture (apple fiber 0.15%, rice starch 0.30% and citric acid 0.16 M) was optimized and successfully validated in this study. The results obtained for the objective measurements of tenderness were confirmed by consumers' tenderness results (p < .05) moreover texture-optimized beef samples were found to be more acceptable by older consumers compared with control. Meat processors have an important role in increasing the availability of suitable meat products for older consumers, by developing products that will meet their nutritional and textural needs. In this study, a novel meat product with a softer texture was developed, successfully validated and the product was found to be acceptable by older consumers. Meat processors could consider using rice starch, apple fiber, and citric acid as feasible alternative to traditional ingredients used for beef injection, in order to obtain a softer product, that appeal to older consumers with difficulties in mastication.

Journal Article Microscopy Techniques for Characterization of Hydration in Dairy Powders Get access Valentyn Maidannyk, Valentyn Maidannyk Food Chemistry & Technology department, Teagasc Food Research Centre, Moorepark, Ireland Search for other works by this author on: Oxford Academic Google Scholar Noel McCarthy, Noel McCarthy Food Chemistry & Technology department, Teagasc Food Research Centre, Moorepark, Ireland Corresponding author: noel.mccarthy@teagasc.ie Search for other works by this author on: Oxford Academic Google Scholar Mark Auty Mark Auty Food Chemistry & Technology department, Teagasc Food Research Centre, Moorepark, IrelandReading Scientific Services Ltd., Reading Science Centre, Reading, UK Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 720–721, https://doi.org/10.1017/S1431927619004331 Published: 01 August 2019

Changes in the microstructure of semi-hard cheeses were observed in situ under tensile deformation by placing a microtensile stage directly under a confocal scanning laser microscope, and recording force/displacement data simultaneously. On tensile deformation, detachment of fat globules and their subsequent release from the cheese matrix were observed, suggesting that they are weakly bonded to or entrapped within the cheese matrix. Moreover, an inherent micro-defect was observed at a curd granule junction within the cheese matrix, which fractured along the curd granule junction under tensile deformation, suggesting that such micro-defects could be a key to the formation of undesirable slits or cracks. Furthermore, the fracture behaviour of semi-hard cheese varied with ripening temperature, coagulant type, and inhibition of residual chymosin activity. Overall, this study demonstrated the potential of dynamic in situ imaging of cheese microstructure for developing a greater understanding of the breakdown behaviour of cheese matrices.

A new method for the visualisation and determination of local diffusion coefficients in dairy powders is described based on real-time visualisation of penetration of fluorescent dyes into individual particles of spray-dried dairy powders including skim milk powder, milk protein concentrate and whey protein isolate. The rehydration process was controlled by adding polyethylene glycol (PEG) as a viscosity modifier to the aqueous phase in ratios of 1:0, 1:1, 1:3 and 1:4 aqueous rhodamine to PEG, respectively. Real-time effective diffusivity values were obtained from analysis of confocal laser scanning microscope images. Particle size was measured optically. Results indicated that for all dairy powders, rehydration rates were highly dependent on particle size. Effective diffusivity increased linearly with increasing particle size and average effective diffusivity of the liquid phase was calculated for all particle size distributions using this dependence. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used to model water sorption isotherms over a broad range of water activities. Vapour phase systems had significantly higher effective diffusivity than liquid phase systems. The results obtained by this new method is broadly in agreement with previously published works, suggesting this new method may be used to measure the hydration of individual powder particles.

The effect of plant protein inclusion in cooked meat upon in vitro gastro-intestinal (GI) digestion was investigated. Pea protein isolate, rice protein and lentil flour were used to increase the protein content in a meat model system restructured using two transglutaminase enzymes [Activa (R) EB (TG) and Transgluseen (TM)-M (TS)]. Restructured beef steaks were subjected to simulated GI digestion using the static INFOGEST method. Samples taken at different digestion times were analysed using SDS-PAGE, size exclusion-HPLC, free amino acid analysis and microscopy. SDS-PAGE analysis revealed significant protein hydrolysis during GI digestion. Most soluble peptides had a molecular weight smaller than 500 Da, corresponding to peptides of < 5 amino acids, regardless of food treatment. The amounts of released, free amino acids isoleucine, lysine, phenylalanine and valine were higher (P < 0.05) in lentil-enriched restructured beef steaks following GI digestion. Confocal laser scanning microscopy (CSLM) revealed pronounced aggregation in digested samples. In vitro digestates of protein-enriched restructured beef steaks showed lower production of small molecular weight peptides. This study demonstrated how the bioaccessibility of protein-enriched restructured beef steaks are influenced by formulation and processing.

Phytosterols possess the ability to significantly lower low-density lipoprotein (LDL) cholesterol levels in the blood, but their bioaccessibility is highly dependent upon the solubility of the phytosterol within the carrier matrix. Currently, there is a limited amount of knowledge on how phytosterols interact at oil-water interfaces, despite research indicating that these interfaces could promote the crystallization of phytosterols and thus decrease bioaccessibility. In order to fill this knowledge gap, this work expands upon a previously studied emulsion system for encapsulating phytosterols and addresses whether phytosterols can crystalize at an oil-in-water emulsion interface. Images from multiple microscopic techniques suggest interfacial phytosterol crystallization in 0.6% phytosterol-enriched emulsions, while interfacial tension results and calculated models showed that whey protein and phytosterols had a synergistic effect on interfacial tension. A deeper understanding of the interfacial behavior of phytosterols in emulsions can provide the functional food and pharmaceutical industry with the knowledge needed to design more bioaccessible phytosterol-enriched products.

Low and high protein dairy powders are prone to caking and sticking and can also be highly insoluble; with powder storage conditions an important factor responsible for such issues. The aim of this study focused on the bulk and surface properties of anhydrous and humidified spray-dried milk protein concentrate (MPC) powders (protein content ~40, 50, 60, 70 or 80%, w/w). Water sorption isotherms, polarized light and scanning electron micrographs showed crystallized lactose in low protein powders at high water activities. High protein systems demonstrated increased bulk diffusion coefficients compared to low protein systems. Glass transition temperatures, α-relaxation temperatures and structural strength significantly decreased with water uptake. CLSM measurements showed that humidified systems have slower real time water diffusion compared to anhydrous systems. Overall, the rate of water diffusion was higher for low protein powders but high protein powders absorbed higher levels of water under high humidity conditions.

The aim of this study was to investigate the aggregation behaviour of a pure beta-casein (beta-CNpure) and a beta-casein concentrate (beta-CNconc) as a function of temperature, buffer type (pH 6.8) and the presence of CaCl2. The particle size distribution and turbidity of beta-casein (beta-CN) dispersions were measured by dynamic light-scattering (DLS) and UV/vis spectroscopy between 4 and 55 degrees C. Upon heating (4-55 degrees C), the particle size of both beta-CN samples increased, indicating self-association via hydrophobic interactions. It was shown that the self-association of beta-CN increased with increasing beta-CN concentration and that beta-CNpure self-associated at significantly lower concentration than beta-CNconc. Both turbidity and particle size measurements showed that the beta-CN samples had similar aggregation behaviour in water and imidazole buffer (pH 6.8) but differed in sodium phosphate buffer (pH 6.8), especially at higher ionic calcium concentrations. Fourier Transform Infrared (FTIR) spectroscopy revealed very little change in the secondary structure of beta-CN during heating (4-55 degrees C). The microstructure of beta-CN aggregates was monitored during heating from 10 to 55 degrees C, followed by cooling to 10 degrees C, using polarised light microscopy. Spherical and heterogeneous aggregates were observed when heated at temperatures above 37 degrees C, which were reversible upon cooling. This study confirmed that beta-CN undergoes self-association on heating that reverses upon cooling, with the aggregation process being highly dependent on the purity of beta-CN, the solvent type and the presence of ionic calcium.

The microstructure of dairy products and ingredients has a significant impact on their processing, texture, flavor release, storage stability and overall quality. Compositional and process factors combine to produce a complex structure at the molecular, nano-, micro- and macro-scales. There is a growing need to characterize microstructure to characterize complex structure–function relationships in dairy products. There is now a large and growing toolbox of imaging techniques available for dairy research and technology, mostly based on various forms of microscopy. This chapter reviews the various types of microscopy used to study various dairy products including optical, electron, atomic force and dynamic microscopy techniques, together with a synopsis of applications and examples. The advantages and disadvantages of each technique are summarized, but a correlative approach should be used when trying to understand the complex structures of dairy products at the nano- and micro-length scales. There is a focus in this chapter on confocal microscopy, as this is probably the most useful single imaging technique of practical benefit to both researchers and food industry technologists; however, relevant emerging techniques such as confocal Raman microscopy and X-ray tomography are also discussed.

With the goal of optimising a protein-enriched restructured beef steak targeted at the nutritional and chemosensory requirements of older adults, technological performance of thirty formulations, containing plant-based ingredients, pea protein isolate (PPI), rice protein (RP) and lentil flour (LF) with transglutaminase (TG) to enhance binding of meat pieces, were analysed. Maximal protein content of 28% in cooked product was achieved with PPI, RP and LF. Binding strength was primarily affected by TG, while textural parameters were improved with LF inclusion. Optimal formulation (F) to obtain a protein-enriched steak with lowest hardness values was achieved with TG (2%), PPI (8%), RP (9.35%) and LF (4%). F, F1S (optimal formulation 1 with added seasoning) and control restructured products (not containing plant proteins or seasonings) were scored by 120 consumers' aged over-65 years. Controls were most preferred (P <.05), while F1S were least liked by the older consumers. Consumer testing suggests further refinement and optimisation of restructured products with plant proteins should be undertaken.

Encapsulant systems are gaining wide practical interest due to their functional and nutritional properties. This paper was focusing on understanding structural relaxations in that systems near glass transition temperature. Freeze-dried trehalose-whey protein isolate-sunflower oil systems with various ratios of the last were used as a carbohydrate-protein-lipid food model. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used as a tool to model water sorption isotherms. The glass transition temperature was obtained by differential scanning calorimetry (DSC). Structural α-relaxation temperatures were measured by dynamical mechanical analyses (DMA), dielectric analysis (DEA) and combined to cover a broad range for strength assessment. The microstructure was characterized by optical light microscopy, confocal laser scanning microscopy and scanning electron microscopy. The C1 and C2 constants for Williams-Landel-Ferry (WLF) equation and structural strength parameter were calculated for each system. The effect of sunflower oil and water contents on strength of carbohydrate-protein system was analyzed. Strength shows decreasing with increasing of lipid concentration in the mixtures and more complex dependence on the water content in a system.

Phytosterols can lower LDL-cholesterol and are frequently used by the functional food industry. However, little is known regarding how phytosterol crystallisation can be controlled, despite solubilised phytosterols having improved bioaccessibility. This study investigates phytosterol crystallisation in bulk milk fat and in model dairy emulsion systems at two average droplet sizes, 1.0 and 0.2 mu m. The effect of lecithin and monoacylglycerol addition on phytosterol crystallisation for both emulsion and bulk systems was also evaluated. Results demonstrated that lecithin and monoacylglycerols enrichment into the bulk system minimised phytosterol crystallisation. However, in emulsions, phytosterol crystallisation was mainly influenced by decreasing the droplet size. Smaller emulsion droplets containing lecithin showed the greatest potential for decreasing phytosterol crystallisation and had improved physicochemical stability. This information can be employed by the functional food industry to minimise phytosterol crystallisation and possibly improve bioaccessibility.

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The effect of varying cook temperature (40 or 50 degrees C) and salting method (dry or brine salting) on bacterial viability, enzymatic activity and chemical composition in cheeses made using Streptococcus thermophilus and Lactobacillus helveticus were investigated. Dry salting resulted in decreased cell viability of L. helveticus, increased lactate dehydrogenase activity and increased free amino acid levels, compared with brine salted cheeses, irrespective of cook temperature. A cook temperature of 50 degrees C resulted in reduced primary proteolysis and increased pH in comparison with that in cheeses cooked to 40 degrees C. Salting method influenced moisture content with higher levels in brine salted cheeses; cook temperature was also influential with higher cook temperature resulting in lower moisture within each salting method. Variations in manufacture procedure can allow for the development of cheese varieties with novel flavour and texture profiles using existing Cheddar or Swiss-style manufacturing facilities. (C) 2017 Elsevier Ltd. All rights reserved.

Membrane separation processes used in the concentration and isolation of micellar casein-based milk proteins from skim milk rely on extensive permeation of its soluble serum constituents, especially lactose and minerals. Whereas extensive literature exists on how these processes influence the gross composition of milk proteins, we have little understanding of the effects of such ionic depletion on the core structural unit of micellar casein [i.e., the casein phosphate nanocluster (CPN)]. The 31P nuclear magnetic resonance (NMR) is an analytical technique that is capable of identifying soluble and organic forms of phosphate in milk. Thus, our objective was to investigate changes to the 31P NMR spectra of skim milk during microfiltration (MF) and diafiltration (DF) by tracking movements in different species of phosphate. In particular, we examined the peak at 1.11 ppm corresponding to inorganic phosphate in the serum, as well as the low-intensity broad signal between 1.5 and 3.0 ppm attributed to casein-associated phosphate in the retentate. The MF concentration and DF using water caused a shift in the relevant 31P NMR peak that could be minimized if orthophosphate was added to the DF water. However, this did not resolve the simultaneous change in retentate pH and increased solubilization of micellar casein protein. The addition of calcium in combination with orthophosphate prevented micellar casein solubilization and simultaneously contributed to preservation of the CPN structure, except for overcorrection of retentate pH in the acidic direction. A more complex DF solution, involving a combination of phosphate, calcium, and citrate, succeeded in both CPN and micellar casein structure preservation while maintaining retentate pH in the region of the original milk pH. The combination of 31P NMR as an analytical technique and experimental probe during MF/DF processes provided useful insights into changes occurring to CPN while retaining the micellar state of casein.

Cheese microstructure, flavor, quality, and microbial growth are intricately linked. It has been argued that cheese microstructure dictates development of enzymatic flavor reactions, appearance, texture, release of nutrients under digestive conditions, and the relative populations of microbial species. New developments in advanced physical analyses have provided new insights into cheese microstructure. Milk and cheese processing and ripening conditions have profound effects upon the textural quality of the cheese. The relative location of cheese structural components dictates digestibility and ultimately the release of key nutrients, clearly showing the importance of microstructure on cheese quality.