RHEOLOGY AND TEXTURE OF COMMERCIAL QUESO FRESCO CHEESES MADE FROM RAW AND PASTEURIZED MILK

Thermal aggregation and gelation behaviors of glucono-δ-lactone-induced soy protein hydrolysate gels: Effects of protein and coagulant concentrations

In this study, a novel acid-induced heat-set soy protein hydrolysate (SPH) gel was successfully developed. The effects of protein (7 and 8 wt%) and glucono-δ-lactone (GDL, 4, 6, 8, and 10 wt%) concentrations on its aggregation and gelation behaviors were investigated by evaluating the structural, rheological, textural, and physical properties of the SPH gel. The structural properties revealed that GDL promoted the formation of SPH aggregates and gels, primarily via disulfide bonds and hydrophobic interactions, which were closely related to the unfolding of the protein structure, exposed hydrophobic groups, decreased protein solubility, and increased particle size and turbidity during the heating process. Subsequently, the gelling properties demonstrated that acidification with GDL (4-8 wt%) significantly improved the viscosity, viscoelasticity, water-holding capacity, and stiffness of the network structures, decreased their hardness and springiness, and facilitated the formation of well-supported, soft-stiff gels, particularly for those made with 8 wt% protein. In addition, the changes in relaxation time measured via low-field nuclear magnetic resonance and magnetic resonance imaging confirmed that the SPH gels effectively retained water that was trapped in the gel network by strengthening the binding between water and protein molecules. The research could provide useful gelling technique for the protein hydrolysate products.

Physicochemical, Rheology, and Mid-Infrared Spectroscopy Techniques for the Characterization of Artisanal and Industrial Maroilles Cheeses

The investigation of the central and external zones of ten industrial and artisanal Maroilles cheeses showed differences in their physicochemical parameters, namely fat, pH, moisture content, ash, and color. This difference significantly impacted the rheological properties of the investigated cheeses, which depended on the protein network englobing lipid and water and its interaction with the other components. Overall, Maroilles cheeses had an elastic-like behavior, with the central zones exhibiting the greatest viscoelastic modules (G' and G″). The mid-infrared (MIR) spectra highlighted the presence of lipids, proteins, and sugars. A significant difference in α-helix and β-sheet levels in the central zones was noted between artisanal and industrial Maroilles cheeses. It is suggested that the difference between artisanal and industrial Maroilles cheeses observed at the macroscopic level, due to the cheese-making procedure and ripening stage, affects the structure at the molecular level, which can be determined by MIR spectroscopy. This trend was confirmed by the FDA when applied to the MIR spectra, since 96.67% correct classification was noted between artisanal and industrial cheeses. The present study indicates that MIR spectroscopy can be used successfully to study Maroilles cheese samples belonging to different production chains.

Low-moisture part-skim mozzarella cheese made from blends of camel and bovine milk: Gross composition, proteolysis, functionality, microstructure, and rheological properties

Camel (CM) milk is used in variety of ways; however, it has inferior gelling properties compared with bovine milk (BM). In this study, we aimed to investigate the physicochemical, functional, microstructural, and rheological properties of low-moisture part-skim (LMPS) mozzarella cheese, made from BM, or BM mixed with 15% CM (CM15%) or 30% CM (CM30%), at various time points (up to 60 d) of storage at 4°C after manufacture. Low-moisture part-skim mozzarella cheeses using CM15% and CM30% had high moisture and total Ca contents, but lower soluble Ca content. Compared with BM cheese, CM15% and CM30% LMPS mozzarella cheese exhibited higher proteolysis rates during storage. Adding CM affected the color properties of LMPS mozzarella cheese manufactured from mixed milk. Scanning electron microscopy images showed that the microstructure of CM15% and CM30% cheeses had smooth surfaces, whereas the BM cheese microstructures were rough with granulated surfaces. Low-moisture part-skim mozzarella cheeses using CM15% and CM30% showed significantly lower hardness and chewiness, but higher stringiness than BM cheese. Compared with BM cheese, CM15% and CM30% cheeses showed lower tan δ levels during temperature surges, suggesting that the addition of CM increased the meltability of LMPS mozzarella cheese during temperature increases. Camel milk addition affected the physicochemical, microstructural, and rheological properties of LMPS mozzarella cheese.

Rheological properties of transglutaminase-treated concentrated pea protein under conditions relevant to high-moisture extrusion processing

At present, the structural changes of extruded materials under thermal-mechanical stress during high-moisture extrusion are still unclear. In this study, the transglutaminase (TG) treatments on the structure of pea protein isolate (PPI) under conditions relevant to high-moisture extrusion processing (50 wt% PPI at 30°C, 120°C and heated to 120°C and subsequently cooled to 30°C) was studied by using a closed cavity rheometer. Strain and frequency sweeping were carried out under various temperature conditions, and the information obtained was drawn into a texture map. Lissajous curves combined with energy dissipation ratio were introduced to characterize the nonlinear response of the samples. The results showed that the storage modulus of PPI increased with the increase of TG concentration during heat treatment. After cooling to 30°C, PPI with 0.25-1%TG could enhance the elasticity, but treating by 2% TG could inhibit the formation of disulfide bonds, the uniform development of the protein network, thus showing the "tough" character. These findings can help to better understand the relationships of material-structure during the extrusion process, and also provide help for further optimization of the quality of meat substitutes.

Low-fat akawi cheese made from bovine-camel milk blends: Rheological properties and microstructural characteristics

Camel milk (CM) can be used as an ingredient to produce various dairy products but it forms weak rennet-induced and acid-induced gels compared with bovine milk (BM). Therefore, in this study, we aimed to investigate the effect of blending bovine milk with camel milk on the physicochemical, rheological (amplitude sweep and frequency sweep), and microstructural properties of low-fat akawi (LFA) cheese. The cheeses were made of BM only or BM blended with 15% (CM15%) or 30% (CM30%) camel milk and stored at 4°C for 28 d. The viscoelastic properties as a function of temperature were assessed. The LFA cheeses made from blended milks had higher moisture, total Ca, and soluble Ca contents, and had higher pH 4.6-water-soluble nitrogen compared with those made from BM. Analysis by scanning electron microscopy demonstrated that the microstructures formed in BM cheese were rough with granular surfaces, whereas those in blended milk cheeses had smooth surfaces. Hardness was lower for LFA cheeses made from blended milk than for those made from BM only. The LFA cheeses demonstrated viscoelastic behavior in a linear viscoelastic range from 0.1 to 1.0% strain. The storage modulus (G') was lower in LFA cheese made from BM over a range of frequencies. Adding CM reduced the resistance of LFA cheeses to flow as temperature increased. Blended cheeses exhibited lower complex viscosity values than BM cheeses during temperature increases. Thus, the addition of camel milk improved the rheological properties of LFA cheese.

Non-linear rheology reveals the importance of elasticity in meat and meat analogues

The interest in plant-based meat analogues as an alternative to meat is currently growing. Rheological benchmarking is used to reveal how closely meat analogues resemble the original meat products. Texture maps and dissipation colour schemes were used to reveal similarities in and differences between rheological responses of meat and meat analogues (especially chicken analogues). Under heating, meat analogues differ in terms of their lower elasticity compared with heated meat. The changes caused by heating meat and meat analogues were different as well. Heating of meat resulted in a tougher and more elastic material, while heating has a minor effect on meat analogues. Future developments should therefore focus on routes to create more elasticity and possibly allow heating effects on texture to mimic meat characteristics even better.

Prevalence and characterization of Listeria monocytogenes, Salmonella and Shiga toxin-producing Escherichia coli isolated from small Mexican retail markets of queso fresco

Queso fresco (QF) is a handmade cheese consumed and produced in Latin America. In Mexico, QF production is associated with a microbiological risk. The aim of the study was to determine the incidence and characterization of Listeria monocytogenes, Salmonella spp., and Shiga toxin-producing Escherichia coli (STEC) in QF from retail markets of the north-western State of Sinaloa, Mexico, and to assess the effect of physicochemical parameters on Listeria presence. A total of 75 QF samples were obtained. L. monocytogenes, E. coli, and coliforms were detected in 9.3, 94, and 100%, respectively. Salmonella was not detected. STEC isolates showed virulence genes. Microbial loads were above the maximum values recommended by the Official Mexican Standards. Physicochemical parameters such as water activity (aw), moisture content, pH, and salinity played a role in Listeria prevalence in QF. Rigorous control in QF made in Culiacan, Mexico is needed to reduce the risk of foodborne pathogens.

Comparison of the milk-clotting properties of three plant extracts

Several proteases from plant sources have been proposed as milk coagulants, however, limited research has been done on their milk-clotting properties. The effect of temperature on the milk-clotting activity of kiwi fruit, melon and ginger extracts was evaluated, as well as the effects of the different extracts on curd properties. Melon extracts showed high milk-clotting activity over a broad temperature range (45-75 °C) while kiwi fruit and ginger extracts showed high activity over a narrower temperature range, with a maximum at 40 and 63 °C, respectively. Curds produced using kiwi extracts had textural properties comparable with those obtained using commercial rennet, while melon extracts produced a fragile gel and low curd yield. The milk-clotting behavior of the three plant extracts was related to the protease specificity present in these extracts. The kiwi proteases displayed chymosin-like properties and thus hold the best potential for use as a milk coagulant in cheese production.