Microstructure and Fracture Properties of Semi-Hard Cheese: Differentiating the Effects of Primary Proteolysis and Calcium Solubilization

The individual roles of hydrolysis of αS1- and β-caseins, and calcium solubilization on the fracture properties of semi-hard cheeses, such as Maasdam and other eye-type cheeses, remain unclear. In this study, the hydrolysis patterns of casein were selectively altered by adding a chymosin inhibitor to the curd/whey mixture during cheese manufacture, by substituting fermentation-produced bovine chymosin (FPBC) with fermentation-produced camel chymosin (FPCC), or by modulating ripening temperature. Moreover, the level of insoluble calcium during ripening was quantified in all cheeses. Addition of a chymosin inhibitor, substitution of FPBC with FPCC, or ripening of cheeses at a consistent low temperature (8 °C) decreased the hydrolysis of αS1-casein by ~95%, ~45%, or ~30%, respectively, after 90 d of ripening, whereas ~35% of β-casein was hydrolysed in that time for all cheeses, except for those ripened at a lower temperature (~17%). The proportion of insoluble calcium as a percentage of total calcium decreased significantly from ~75% to ~60% between 1 and 90 d. The rigidity or strength of the cheese matrix was found to be higher (as indicated by higher fracture stress) in cheeses with lower levels of proteolysis or higher levels of intact caseins, primarily αS1-casein. However, contrary to the expectation that shortness of cheese texture is associated with αS1-casein hydrolysis, fracture strain was significantly positively correlated with the level of intact β-casein and insoluble calcium content, indicating that the cheeses with low levels of intact β-casein or insoluble calcium content were more likely to be shorter in texture (i.e., lower fracture strain). Overall, this study suggests that the fracture properties of cheese can be modified by selective hydrolysis of caseins, altering the level of insoluble calcium or both. Such approaches could be applied to design cheese with specific properties

Effect of milk centrifugation and incorporation of high-heat-treated centrifugate on the composition, texture, and ripening characteristics of Maasdam cheese

peer-reviewedThis study investigated the effect of centrifugation (9,000 × g, 50°C, flow rate = 1,000 L/h), as well as the incorporation of high-heat-treated (HHT) centrifugate into cheese milk on the composition, texture, and ripening characteristics of Maasdam cheese. Neither centrifugation nor incorporation of HHT centrifugate into cheese milk had a pronounced effect on the compositional parameters of any experimental cheeses, except for moisture and moisture in nonfat substance (MNFS) levels. Incorporation of HHT centrifugate at a rate of 6 to 10% of the total milk weight into centrifuged milk increased the level of denatured whey protein in the cheese milk and also increased the level of MNFS in the resultant cheese compared with cheeses made from centrifuged milk and control cheeses; moreover, cheese made from centrifuged milk had ∼3% higher moisture content on average than control cheeses. Centrifugation of cheese milk reduced the somatic cell count by ∼95% relative to the somatic cell count in raw milk. Neither centrifugation nor incorporation of HHT centrifugate into cheese milk had a significant effect on age-related changes in pH, lactate content, and levels of primary and secondary proteolysis. However, the value for hardness was significantly lower for cheeses made from milk containing HHT centrifugate than for other experimental cheese types. Overall, centrifugation appeared to have little effect on composition, texture, and ripening characteristics of Maasdam cheese. However, care should be taken when incorporating HHT centrifugate into cheese milk, because such practices can influence the level of moisture, MNFS, and texture (particularly hardness) of resultant cheeses. Such differences may have the potential to influence subsequent eye development characteristic, although no definitive trends were observed in the present study and further research on this is recommended

SURFACE MORPHOLOGY AND MICROHARDNESS BEHAVIOR OF 316L IN HAP-PMEDM

The development of biomaterials for implants nowadays requires materials with superior mechanical and physical properties for enhanced osseointegration and sustained longevity. This research work was conducted to investigate the influence of nano hydroxyapatite (HAp) powder mixed electrical discharge machining (PMEDM) on surface morphology and microhardness of modified 316L stainless steel surface. The chosen process parameters were discharge current, pulse on/off duration and gap voltage in order to analyze the selected output responses. HAp concentration (15 g/l) along with reverse polarity was kept constant for current experimentation. The experimental results testified that surface morphology of PMEDM surface was significantly improved along with augmentation of 79% in microhardness (HV) of HAp modified surface of medical grade stainless steel. Furthermore, XRD and SEM characterization confirmed the deposition of calcium, phosphorous and inter-metallic compounds on HA-PMEDMed surface. The surface thus produced is expected to facilitate better bone-implant adhesion and bioactivity

Dynamic in situ imaging of semi-hard cheese microstructure under large-strain tensile deformation: Understanding structure-fracture relationships

peer-reviewedChanges 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.Dairy Levy Trust Fun

Effect of milk centrifugation and incorporation of high heat-treated centrifugate on the microbial composition and levels of volatile organic compounds of Maasdam cheese

peer-reviewedCentrifugation is a common milk pretreatment method for removal of Clostridium spores which, on germination, can produce high levels of butyric acid and gas, resulting in rancid, gassy cheese. The aim of this study was to determine the effect of centrifugation of milk, as well as incorporation of high heat-treated centrifugate into cheese milk, on the microbial and volatile profile of Maasdam cheese. To facilitate this, 16S rRNA amplicon sequencing in combination with a selective media-based approach were used to study the microbial composition of cheese during maturation, and volatile organic compounds within the cheese matrix were analyzed by HPLC and solid-phase microextraction coupled with gas chromatography–mass spectrometry. Both culture-based and molecular approaches revealed major differences in microbial populations within the cheese matrix before and after warm room ripening. During warm room ripening, an increase in counts of propionic acid bacteria (by ∼101.5 cfu) and nonstarter lactic acid bacteria (by ∼108 cfu) and a decrease in the counts of Lactobacillus helveticus (by ∼102.5 cfu) were observed. Lactococcus species dominated the curd population throughout ripening, followed by Lactobacillus, Propionibacterium, and Leuconostoc, and the relative abundance of these accounted for more than 99% of the total genera, as revealed by high-throughput sequencing. Among subdominant microflora, the overall relative abundance of Clostridium sensu stricto was lower in cheeses made from centrifuged milk than control cheeses, which coincided with lower levels of butyric acid. Centrifugation as well as incorporation of high heat-treated centrifugate into cheese milk seemed to have little effect on the volatile profile of Maasdam cheese, except for butyric acid levels. Overall, this study suggests that centrifugation of milk before cheesemaking is a suitable method for controlling undesirable butyric acid fermentation without significantly altering the levels of other volatile organic compounds of Maasdam cheese

Solubility of carbon dioxide in renneted casein matrices: effect of pH, salt, temperature, partial pressure, and moisture to protein ratio

The solubility of carbon dioxide (CO2) in the moisture and protein components of cheese matrices and the influence of changing pH, salt and temperature levels remains unclear. In this study, model casein matrices were prepared, by renneting of micellar casein concentrate (MCC), with modulation of salt and pH levels by adding salt and glucono delta-lactone, respectively, to the MCC solutions prior to renneting. Different moisture-to-protein levels were achieved by freeze-drying, incubation of samples at different relative humidities, or by applying varying pressures during gel manufacture. The CO2 solubility of samples decreased linearly with both increasing temperature and salt-in-moisture content, whereas solubility of CO2 increased with increasing pH. A non-linear relationship was observed between CO2 solubility and the moisture-to-protein ratio of experimental samples. Overall, such knowledge may be applied to improve the quality and consistency of eye-type cheese, and in particular to avoid development of undesirable slits and cracks

Solubility of carbon dioxide in renneted casein matrices: Effect of pH, salt, temperature, partial pressure, and moisture to protein ratio

peer-reviewedThe solubility of carbon dioxide (CO2) in the moisture and protein components of cheese matrices and the influence of changing pH, salt and temperature levels remains unclear. In this study, model casein matrices were prepared, by renneting of micellar casein concentrate (MCC), with modulation of salt and pH levels by adding salt and glucono delta-lactone, respectively, to the MCC solutions prior to renneting. Different moisture-to-protein levels were achieved by freeze-drying, incubation of samples at different relative humidities, or by applying varying pressures during gel manufacture. The CO2 solubility of samples decreased linearly with both increasing temperature and salt-in-moisture content, whereas solubility of CO2 increased with increasing pH. A non-linear relationship was observed between CO2 solubility and the moisture-to-protein ratio of experimental samples. Overall, such knowledge may be applied to improve the quality and consistency of eye-type cheese, and in particular to avoid development of undesirable slits and cracks

Influence of milk pre-treatment, and changes in cheese structure and carbon dioxide solubility on the development of split defects in cheese

The objective of this research was to understand the underlying issues leading to the development of undesirable split or crack defects within continental semi-hard cheeses made from a seasonally produced milk supply. Such defects result in poor aesthetic quality (a key retail requirement) and poor performance under high speed slicing for global food service markets, with consequential economic loss. Centrifugation (at centrifugal force of 9,000 × g) and incorporation of high heat-treated (HHT) centrifugate are common milk pre-treatment methods/practices prior to continental cheese manufacture. Centrifugation had little effect on the composition, texture, volatile profile and ripening characteristics of Maasdam cheese, except for significantly lower butyric acid levels. However, incorporating HHT centrifugate into the cheese milk significantly increased the levels of moisture in non-fat substance and decreased the hardness of the resultant cheeses. This may have the potential to influence subsequent eye formation characteristics, and possibly influence split or crack development. Primary proteolysis and levels of insoluble calcium content are considered to influence the fracture properties of cheese, including fracture stress and fracture strain. The present research found that (1) inhibition of rennet activity during ripening; (2) reduction of rennet activity during ripening; and (3) reduction of ripening temperature decreased the hydrolysis of αS1-casein by ~95%, ~45%, or ~30%, respectively, after 90 d of ripening. During the same ripening period, ~35% of β-casein was hydrolysed for all cheeses, except for those ripened at a lower temperature (~17%). The proportion of insoluble calcium as a percentage of total calcium decreased significantly from ~75% to ~60% between 1 and 90 d of ripening. Further results showed that although modulation of αS1-casein hydrolysis is an effective means to maintain the strength of the cheese matrix during ripening, maintaining higher levels of intact β-casein or insoluble calcium content (or both) within the cheese matrix results in reduced levels of shortness or brittleness of cheese texture. For the first time, dynamic microscopy was applied to understand the microstructural changes occurring in semi-hard eye-type cheeses during large-strain tensile deformation. It was observed that pre-existing micro-defects within cheese matrices led to the formation of undesirable slits or cracks. Gas behaviour, including solubility, is considered one of the critical factors for development of eyes, and also slits or cracks within cheese matrices. Therefore, CO2 solubility behaviour was studied in casein matrices, representing the protein-water phase of cheese matrices. It was observed that the CO2 solubility of casein matrices largely depends on the moisture-to-protein ratio, salt-in-moisture content, pH and temperature. Overall, this research provides a knowledge base to minimize or avoid development of splits or cracks defects and thus improves the quality and consistency of continental-type cheeses

A Quantitative Risk Analysis Model and Simulation of Enterprise Networks

In a computer network, an attacker can get access and privilege to critical assets through step by step vulnerabilities exploitation of network devices. These security problems need to be resolved to protect an enterprise network from great data loss and business interruptions. One of the ways to protect a network is to analyze network risk at given network topology and security conditions and act accordingly to secure the critical devices before an attacker takes benefit of vulnerabilities on transition devices. In this thesis, we proposed a quantitative risk analysis model to compute network risk. We consider network risk as a function of total vulnerabilities exploitation along the path and impact of exploitation. Most of the research including Topological Vulnerability Analysis (TVA) models and analyzes attacking pathway to target host through attack graph generation. They consider only vulnerabilities along the path to measure the security of the network. However, in this thesis, we compute the network security based on both vulnerability exploitation cost along the path and the impact of exploits (based on risk). We also bolster our approach with simulation results and show how risk score changes with varying parameters

Symposium review: Structure-function relationships in cheese

The quality and commercial value of cheese are primarily determined by its physico-chemical properties (e.g., melt, stretch, flow, and color), specific sensory attributes (e.g., flavor, texture, and mouthfeel), usage characteristics (e.g., convenience), and nutritional properties (e.g., nutrient profile, bioavailability, and digestibility). Many of these functionalities are determined by cheese structure, requiring an appropriate understanding of the relationships between structure and functionality to design bespoke functionalities. This review provides an overview of a broad range of functional properties of cheese and how they are influenced by the structural organization of cheese components and their interactions, as well as how they are influenced by environmental factors (e.g., pH and temperature).This review was funded by the Dairy Levy Trust, Dublin, Ireland, Teagasc Walsh Fellowship program, Oak Park, Carlow, Ireland, and in part by Ornua, Dubin, Ireland. Prabin Lamichhane is currently in receipt of a Teagasc Walsh Fellowship (RMIS6259)