Papers by Marianne Hammershøj
Journal of Texture Studies, Jul 1, 2001
ABSTRACT
International Journal of Dairy Technology, Sep 24, 2015
The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment o... more The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment of milk and continues during subsequent storage. We compared the initial lactosylation as well as the rate of lactosylation of milk proteins during storage in UHT milk subjected to direct or indirect heat treatment using liquid chromatography (LC) coupled with electrospray injection mass spectrometry (ESI‐MS). Furosine content was used as an overall marker to allow for a quantitative correlation of lactosylation measured by LC‐ESI‐MS in the UHT milks. Protein lactosylation increased during the storage period of 6 months at 20 °C. Both the initial extent and the rate of lactosylation positively correlated with the number of lysine residues in the different proteins. An exponential or linear correlation with furosine concentration could be established for major and minor lactosylated proteins, respectively.
Journal of Dairy Science, 2016
Previous standards in the area of effect of heat treatment processes on milk protein denaturation... more Previous standards in the area of effect of heat treatment processes on milk protein denaturation were based primarily on laboratory-scale analysis and determination of denaturation degrees by, for example, electrophoresis. In this study, whey protein denaturation was revisited by pilot-scale heating strategies and liquid chromatography quadrupole time-of-flight mass spectrometer (LC/MC Q-TOF) analysis. Skim milk was heat treated by the use of 3 heating strategies, namely plate heat exchanger (PHE), tubular heat exchanger (THE), and direct steam injection (DSI), under various heating temperatures (T) and holding times. The effect of heating strategy on the degree of denaturation of β-lactoglobulin and α-lactalbumin was determined using LC/MC Q-TOF of pH 4.5-soluble whey proteins. Furthermore, effect of heating strategy on the rennet-induced coagulation properties was studied by oscillatory rheometry. In addition, rennet-induced coagulation of heat-treated micellar casein concentrate subjected to PHE was studied. For skim milk, the whey protein denaturation increased significantly as T and holding time increased, regardless of heating method. High denaturation degrees were obtained for T >100°C using PHE and THE, whereas DSI resulted in significantly lower denaturation degrees, compared with PHE and THE. Rennet coagulation properties were impaired by increased T and holding time regardless of heating method, although DSI resulted in less impairment compared with PHE and THE. No significant difference was found between THE and PHE for effect on rennet coagulation time, whereas the curd firming rate was significantly larger for THE compared with PHE. Micellar casein concentrate possessed improved rennet coagulation properties compared with skim milk receiving equal heat treatment.
Journal of dairy science, 2011
The aim of the present investigation was to study the underlying causes of noncoagulating (NC) mi... more The aim of the present investigation was to study the underlying causes of noncoagulating (NC) milk. Based on an initial screening in a herd of 53 Danish Holstein-Friesians, 20 individual Holstein-Friesian cows were selected for good and poor chymosin-induced coagulation properties; that is, the 10 cows producing milk with the poorest and best coagulating properties, respectively. These 20 selected cows were followed and resampled on several occasions to evaluate possible changes in coagulation properties. In the follow-up study, we found that among the 10 cows with the poorest coagulating properties, 4 cows consistently produced poorly coagulating (PC) or NC milk, corresponding to a frequency of 7%. Noncoagulating milk was defined as milk that failed to form a coagulum, defined as increase in the storage modulus (G') in oscillatory rheometry, within 45min after addition of chymosin. Poorly coagulating milk was characterized by forming a weak coagulum of low G'. Milk proteom...
Journal of the Science of Food and Agriculture, 1999
The surface properties of aqueous egg albumen protein solutions (0.1 g litre−1) were studied at p... more The surface properties of aqueous egg albumen protein solutions (0.1 g litre−1) were studied at pH values of 4.8, 7.0, 9.2 and 10.7 and related to foaming behaviour such as bubble size distribution, overrun and drainage. By measurements far from equilibrium of dynamic steady state surface dilation using the overflowing cylinder technique, egg albumen showed ability to slow down surface expansion and to lower the dynamic surface tension. The pH-effect was small, but at pH 4.8 the film length, at which a motionless surface was created, was longer than at higher pH indicating a somewhat more rigid surface at low pH. Near equilibrium sinusoidal surface area deformation resulted in relatively high moduli of egg albumen, with a significant effect of pH. The surface modulus E showed at pH 4.8 an increase in the course of time, but at higher pH it was constant. Large deformation of egg albumen surface was not destructive, and for all pH values the surface behaved viscoelastic, with highest loss modulus E″ and tan θ values at pH 4.8. Surface deformation frequency sweeps revealed the relaxation processes to be relatively slow at pH 4.8 and faster at pH 7.0–10.7. Foamability measured as overrun of foam as a result of shaking and stirring was highest at pH 4.8 and lowest at pH 10.7. Foam stability against drainage was best at pH 7.0 after 30 min, but at a long-term scale foam at pH 4.8 was most resistant to drainage. Foam samples were subjected to microscopy and image analysis. The smallest bubbles were found at pH 4.8 (mean diameter 142 µm) and the largest at pH 7.0 (mean diameter 328 µm). In conclusion, the foaming behaviour of an aqueous egg albumen solution at pH 4.8 can be related to dynamic surface properties as follows: the more rigid behaviour of the surface at this pH favours a small bubble size and slow drainage of liquid from the foam. The high overrun at this pH can be explained by a lower dynamic surface tension, but also here film stability during foam making can be promoted by a more rigid liquid surface. © 1999 Society of Chemical Industry
International Dairy Journal, 2014
A spectrophotometric assay for plasmin and plasminogen-derived activity in dairy products was opt... more A spectrophotometric assay for plasmin and plasminogen-derived activity in dairy products was optimised and extended to determine plasmin and plasminogen-derived activity in turbid samples of dairy products. The method was validated by assessing reproducibility, repeatability, level of detection and recovery of plasmin activity in different sample matrices. Plasmin activity in raw milk was not affected by skimming, but decreased by 30% in pasteurised and homogenised whole milk, leading to an underestimation of plasmin activity. The effects of dissociation of plasmin and caseins by ε-aminocaproic acid (EACA) plus NaCl on the plasmin activity were investigated. Comparison of pasteurised milk with a micellar casein solution showed that the dissociation of plasmin and caseins on adding EACA and NaCl decreases interference by caseins, but increases inhibition of plasmin with serum-based inhibitory components. The level of detection and repeatability of this method for plasmin activity analysis were improved compared with previous spectrophotometric assays.
International Dairy Journal, 2014
ABSTRACT The effect of enzymatic activity in direct steam infusion heat treated milk with ultra-s... more ABSTRACT The effect of enzymatic activity in direct steam infusion heat treated milk with ultra-short holding times (>150 °C for <0.2 s) on age gelation during storage was investigated. Preheating at either 72 or 95 °C for 180 s was performed. Milk pre-heated at 72 °C showed extensive proteolysis and exhibited bitter off flavour and contained <40% intact αS- and β-caseins after 6 weeks storage at 20 °C. No proteolysis of κ-casein was detected. Plasmin was identified as active protease and activation of plasminogen was observed as an increase in the rate of casein hydrolysis. Proteolysis in the stored samples correlated with a decrease in pH and with changes in colour. Gelation occurred after 10 weeks along with an increase in viscosity and extensive proteolysis of αS- and β-caseins. In conclusion, plasmin activity was involved in age gelation and bitterness caused by proteolysis was the shelf-life limiting factor.
Dairy Science & Technology, 2011
The paper describes a study on the variation of coagulation properties in individual cow's milk m... more The paper describes a study on the variation of coagulation properties in individual cow's milk measured by a novel free oscillation rheometry-based method. The work is part of a study on the occurrence and underlying causes of poorly and even non-coagulating (NC) milk in Denmark, and based on that, the paper reports on the frequency of non-and poorly coagulating milk in a herd of the three main Danish dairy breeds, Jersey, Danish red (RDM), and Danish Holstein-Friesian (SDM). The cows were milked by automatic milking. The rennet coagulation time, the coagulum firmness by storage modulus G′, and the curd firming rate of fresh skimmed milk were determined. More than 20% of the milk samples exhibited poor coagulation properties by the criteria set. Of these, the 17% resulted in a weak coagulum after addition of rennet, while another 3% were due to NC milk that did not aggregate to form a curd within the 40 min of measurement. Milk from Jersey cows exhibited superior coagulation properties when compared to milk from SDM and RDM cows. The dependence of curd firming rate on protein concentration was investigated, and found to depend on milk protein concentration to the power of three, emphasizing the importance of protein interactions, and not just the protein concentration itself. The paper gives a basis for the subsequent selection of NC milk samples with the
Journal of Texture Studies, 2001
ABSTRACT
Organic eggs make out >15% of the Danish shell egg market. Consumers buy organic eggs based on en... more Organic eggs make out >15% of the Danish shell egg market. Consumers buy organic eggs based on environmental and animal welfare arguments. However, there is a need for high product quality and diversity of organic eggs to increase the market share further. The overall objective was to investigate different strategies for production of organic eggs of high and differentiable quality regarding appearance (yolk colour and carotenoid composition), sensory quality, shell strength and egg albumen protein content providing more diversi ed eggs compared with conventional eggs. Speci c objectives were to study the effect of hen genotype (layer-type versus "dual purpose"-type), identify new protein feed sources for organic laying hens in order to improve the supply of amino acids, when using 100% organic feed in diets, and investigate how foraging material interacts with egg avour and appearance. The method was a complete block design with 2 genotypes, 3 standard diets, 2 forage material types in 4 replicates of each 25 hens. In total 1200 hens during 22 weeks were distributed in 48 outdoor pens with housing facilities and area following the regulations on organic egg production. A number of selected egg quality parameters analysed during the experiment are presented.
International Journal of Dairy Technology, 2011
ABSTRACT
Journal of dairy science, 2011
Lipoprotein lipase (LPL) activity and free fatty acid levels were studied in freshly milked, unco... more Lipoprotein lipase (LPL) activity and free fatty acid levels were studied in freshly milked, uncooled milk from individual Danish Holstein or Jersey cows, or after storage for up to 24h at either a cooling temperature (4°C) or at the milking temperature (31°C). Upon cooling for up to 24h, LPL activity increased in the cream phase, whereas the activity in the skim milk was steady, as observed for Jersey cows, or increased, as seen for the Holsteins. Storage at 31°C decreased the LPL activity in both the cream phase and the skim milk phase. The increase in free fatty acid levels was found to depend on LPL activity, incubation temperature, substrate availability, and incubation time. Furthermore, the migration of milk proteins between the skim milk phase and the cream phase upon cooling of milk from Jersey cows or from Danish Holstein cows was studied using proteomic methods involving 2-dimensional gel electrophoresis and mass spectrometry. Proteins associated with the milk fat globule...
Journal of dairy science, 2012
The objective of this study was to examine variation in overall milk, protein, and mineral compos... more The objective of this study was to examine variation in overall milk, protein, and mineral composition of bovine milk in relation to rennet-induced coagulation, with the aim of elucidating the underlying causes of milk with impaired coagulation abilities. On the basis of an initial screening of 892 milk samples from 42 herds with Danish Jersey and Holstein-Friesian cows, a subset of 102 samples was selected to represent milk with good, poor, or noncoagulating properties (i.e., samples that within each breed represented the most extremes in regard to coagulation properties). Milk with good coagulation characteristics was defined as milk forming a strong coagulum based on oscillatory rheology, as indicated by high values for maximum coagulum strength (G'(max)) and curd firming rate (CFR) and a short rennet coagulation time. Poorly coagulating milk formed a weak coagulum, with a low G'(max) and CFR and a long rennet coagulation time. Noncoagulating milk was defined as milk that...
Journal of dairy science, 2011
The aim of the present investigation was to study the underlying causes of noncoagulating (NC) mi... more The aim of the present investigation was to study the underlying causes of noncoagulating (NC) milk. Based on an initial screening in a herd of 53 Danish Holstein-Friesians, 20 individual Holstein-Friesian cows were selected for good and poor chymosin-induced coagulation properties; that is, the 10 cows producing milk with the poorest and best coagulating properties, respectively. These 20 selected cows were followed and resampled on several occasions to evaluate possible changes in coagulation properties. In the follow-up study, we found that among the 10 cows with the poorest coagulating properties, 4 cows consistently produced poorly coagulating (PC) or NC milk, corresponding to a frequency of 7%. Noncoagulating milk was defined as milk that failed to form a coagulum, defined as increase in the storage modulus (G') in oscillatory rheometry, within 45min after addition of chymosin. Poorly coagulating milk was characterized by forming a weak coagulum of low G'. Milk proteom...
Journal of Agricultural and Food Chemistry, 2014
Plasmin, the major indigenous protease in milk, is linked to quality defects in dairy products. T... more Plasmin, the major indigenous protease in milk, is linked to quality defects in dairy products. The specificity of plasmin on caseins has previously been studied using purified caseins and in the indigenous peptide profile of milk. We investigated the specificity and proteolytic pathway of plasmin in directly heated UHT milk (>150 °C for <0.2 s) during 14 weeks of storage at 20 °C in relation to age gelation and bitter peptides. Sixty-six peptides from αS- and β-caseins could be attributed to plasmin activity during the storage period, of which 23 were potentially bitter. Plasmin exhibited the highest affinity for the hydrophilic regions in the caseins that most probably were exposed to the serum phase and the least affinity for hydrophobic or phosphorylated regions. The proteolytic pattern observed suggests that plasmin destabilizes the casein micelle by hydrolyzing casein-casein and casein-calcium phosphate interaction sites, which may subsequently cause age gelation in UHT milk.
International Journal of Dairy Technology, 2010
Direct heat treatment of two milk types, skimmed and nonstandardised full-fat, was performed by i... more Direct heat treatment of two milk types, skimmed and nonstandardised full-fat, was performed by instant steam infusion and compared with indirect heating. Infusion conditions were temperatures of 72-120°C combined with holding times of 100-700 ms, and indirect heat conditions were 72°C ⁄ 15 s and 85°C ⁄ 30 s. The activity of indigenous enzymes such as alkaline phosphatase, lactoperoxidase, xanthine oxidase and c-glutamyl transpeptidase was evaluated. Infusion temperature was the main determinant of inactivation. Whey protein denaturation represented by b-lactoglobulin increased significantly with infusion temperature. The nonstandardised milk had a higher denaturation rate than skimmed milk. The effect of instant infusion on pH and milk fat globule size in relation to whey protein denaturation and association is discussed.
Dairy Science & Technology, 2014
ABSTRACT The development of coagulation properties during cold storage of raw milks categorized a... more ABSTRACT The development of coagulation properties during cold storage of raw milks categorized as good or poorly coagulating is largely unknown. This was studied in the present investigation at individual cow’s milk level in addition to elucidating the impact of cheesemaking processing steps on the resulting coagulation properties of silo tank cheesemilk. Rennet coagulation time (RCT), curd firming rate (CFR) and gel firmness (G’max); Ca, P and Mg distribution; pH; and casein micelle size of raw skim milk from individual cows classified as “good” or “poor” in coagulation properties were investigated over 72 h storage at 4 °C. For the cheesemilk, the impact of overnight cold storage, thermization and standardization, pasteurization, and acidification to either pH 6.45 or 6.30 on the coagulation properties were studied. After 24 h of cold storage, RCT of both good and poorly coagulating milks was significantly prolonged though recovering somewhat after prolonged storage for good coagulating samples. In contrast, G’max was significantly reduced after 72 h of cold storage for good coagulating milk. Both total and colloidal Ca were higher in good compared with poorly coagulating milk, while mineral distribution and milk pH did not change during storage. For cheesemilk, up to 14 h, cold storage did not impair coagulation properties significantly, which was markedly improved by acidification. The study shows that rheological parameters of good and poorly coagulating milks are impacted differently by the cold storage. Conversely, cheesemilk coagulation properties were not impaired by the studied cheesemaking processing steps and, further, were enhanced by acidification steps.
Meat Science, 1999
An experiment with 96 broilers distributed across six treatments was carried out. Each treatment ... more An experiment with 96 broilers distributed across six treatments was carried out. Each treatment consisted of four cages each with four broilers. The six treatments were: the control (treatment 1), broilers placed in cages with a welded wire bottom hanging over smelling pig manure (treatment 2), or placed on a pig manure mat (treatment 3), combined with two intervals, i.e. 1 week (group a) and 2 weeks (group b) before slaughter. The content of skatole in the abdominal fat was measured, and the odour and flavour impressions after cooking were evaluated by a taste panel. The treatments were compared with two control treatments: broilers produced traditionally in cages either without (treatment 1a) or with (treatment 1b) contact with their own manure for a fortnight. A higher skatole level in abdominal fat of broilers in physical contact with pig manure (treatment 3) was measured, compared with broilers without physical contact with pig manure for at least 1 week (treatments 1 and 2) (p<0.05). The consumer taste panel evaluation was not affected by the fact that the broilers had been lying on pig manure. However, the evaluation of the odour of the cooked meat, when opening the cooking bag, was to some extent negatively affected by the experimental treatments of broilers, which had physical contact with the pig manure (p<0.05). Furthermore, physical contact with the manure, regardless of whether it was broiler or pig manure, proved to affect the odour of the meat (p<0.01). For broilers placed in cages without physical contact with the pig manure (treatments 2a and 2), the smell had no negative influence on either the odour or on the flavour of the meat, and the content of skatole was not different from that of the broilers on the control treatment. A taste panel evaluation performed on four broilers of the treatments 1a, 2b, and 3b showed no flavour differences among treatments. Whether the broilers had been exposed to a given treatment for 1 or 2 weeks made no difference, either to the skatole concentration or to the odour or flavour impression of the newly cooked chicken meat.
Uploads
Papers by Marianne Hammershøj