Grete Bertelsen

University of Copenhagen, Copenhagen, Capital Region, Denmark

Are you Grete Bertelsen?

Claim your profile

Publications (80)119.2 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Broiler chickens were fed diets containing 0, 210, 420 or 840 mg vitamin C kg−1 feed from 10 to 42 days of age. The diets contained 13.6% fat and 87.7% unsaturated fatty acids.
    10/2008; 47(3):187-196.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The technological, microbiological, and sensory storage characteristics of low temperature sous vide cooked roast beef were investigated. the effect of two heat treatments, 59°C (P7010in core 8.4) and 62°C (P7010 in core 15.9) on the stability of spiced roast beef made from Musculus semitendinosus with a high initial microbial load were compared as well as storage temperatures of 2 and 10°C. Although chilling baths with circulating water were used, recommended chilling rates for sous vide products could not be attained. Yield was significantly higher at 59°C and at a storage temperature of 2°C but decreased during storage. At 62°C the meat became significantly more tender than at 59°C as measured by shear force. No differences in microbiology were observed between heating regimes. At low storage temperature products were microbiologically stable over a 35-day period. At 10°C, however, a rise in psychrotrophic aerobic counts and occasional pack swelling was observed. In a commercial scale experiment conducted with sous vide cooked (62°C) beef with low initial counts, no increase in aerobic counts was observed at 2, 5 and 10°C while swelling occurred in 28% of the packages stored at 10°C and in none at 2 and 5°C. the swelling was due to different types of gas-producing clostridia. Warmed-over flavour (as TBARS) showed no development during storage in intact packages, while slicing and serving the roast beef under commercial conditions resulted in a marked increase to < 100 μmole kg−1. In spiced roast beef only minor changes in off-odour and off-flavour of the product were observed during 23 days of storage at 2°C.
    International Journal of Food Science & Technology 06/2007; 30(3):365 - 378. · 1.24 Impact Factor
  • M. JAKOBSEN, G. BERTELSEN
    [Show abstract] [Hide abstract]
    ABSTRACT: The antimicrobial effect of carbon dioxide (CO2) is well documented but comparison of the large number of often contradictory studies investigating the effect of CO2 on chemical quality changes is lacking. The amount of absorbed CO2 varies from 0 - 1.79 L CO2/kg meat depending on the applied packaging and storage conditions, which clearly demonstrates the necessity of optimizing these conditions with respect to the required amount of CO2. Absorption of large amounts of CO2 in meat tissue can cause a minor decrease in pH due to the dissociation of the produced carbonic acid to bicarbonate and hydrogen ions. A decrease in pH might affect other chemical quality parameters but this is not observed to be the case in the reviewed studies and general detrimental effects of CO2 cannot be found for color, weight loss or lipid oxidation. However, elevated CO2 levels can cause pore formation in cooked meat.
    Journal of Muscle Foods 05/2007; 13(2):143 - 168. · 0.50 Impact Factor
  • MARIANNE JAKOBSEN, GRETE BERTELSEN
    [Show abstract] [Hide abstract]
    ABSTRACT: When meat is packed in atmospheres containing elevated carbon dioxide (CO2) levels, substantial amounts of CO2 are absorbed into the meat. Knowledge of CO2 absorption into the meat is important to ensure optimal microbial protection of the meat and package design, preventing package collapse when the headspace is reduced because of CO2 absorption. However, knowledge on fatty products is lacking. This study shows that there is a significant difference between the amounts of CO2 that can be absorbed in meat with different fat content. The CO2 absorption in fats has a rather complex temperature dependence that varies with fatty acid composition. The CO2 absorption increases along with the increasing content of unsaturated fat, the effect growing larger as the temperature rises. In conclusion, the CO2 solubility in meat samples varies with fat content, fatty acid composition as well as temperature. In this study CO2 absorptions between 0.55 and 0.85 L CO2/kg meat were observed when varying these factors.
    Journal of Muscle Foods 12/2005; 17(1):9 - 19. · 0.50 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A sensor array (electronic nose) was successfully applied for predicting the content of hexanal and other volatiles in different dry fat-containing products, showing the potential of replacing time-consuming traditional laboratory analysis by faster in-process monitoring methods. Unfortunately, prediction of free radical content was not successful, making early prediction of oxidation by sensor array infeasible. Owing to the non-specificity of the sensors, a generic model could not be generated even though a series of standards was shown to have a high correlation between hexanal concentration and individual or multiple sensor responses. PCA models of sensor array responses of eg pork scratchings revealed a clear separation of samples stored in the experimental factor light versus darkness. Copyright © 2004 Society of Chemical Industry
    Journal of the Science of Food and Agriculture 01/2005; 85(2):206 - 212. · 1.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Peanuts, pork scratchings, oatmeal and two types of muesli were stored in two experiments, where external factors (light, oxygen concentrations, product-headspace ratios) were varied, and where packaging materials with different properties (light transmission and oxygen permeability) were used. The oxidative changes in the products were followed by the formation of hexanal as detected by headspace gas chromatography (headspace-GC), free radicals as detected by electron spin resonance (ESR) spectroscopy and sensory evaluations. Generally, increased oxygen availability and exposure to light resulted in increased lipid oxidation. Statistical analysis of the results revealed that light accounted for the greatest systematic variation of the relative levels of free radicals in peanuts, oatmeal and muesli, whereas the oxygen availability had the largest influence on the formation of hexanal. The opposite was observed for pork scratchings, where oxygen had the most significant effect on the formation of radicals. It is concluded that ESR and headspace-GC complement each other in detecting the oxidative changes.
    Food Chemistry. 01/2005;
  • Marianne Jakobsen, Grete Bertelsen
    [Show abstract] [Hide abstract]
    ABSTRACT: Carbon dioxide is commonly used in modified atmosphere packaging of meat and the gas is highly soluble in meat. Both intrinsic (pH, water and fat content) and extrinsic (CO(2) partial pressure, headspace to meat volume ratio and storage temperature) factors affect the amount of CO(2) absorbed in meat. A multi factorial packaging experiment using minced pork was carried out in order to evaluate the effect of such factors under realistic conditions and to develop models for prediction of the amount of absorbed CO(2). For most practical applications CO(2) partial pressure and headspace to meat volume ratio are the key factors determining CO(2) absorption in meat. For volume ratios of more than 2 L gas/kg meat, knowledge of the partial pressure of CO(2) was sufficient to predict the amount of absorbed CO(2).
    Meat Science 12/2004; 68(4):603-10. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To study the influence of different packaging and storage parameters on the colour stability of modified atmosphere packed, cured, cooked ham, a multiplicative analysis of variance model (GEMANOVA) was developed. The critical parameters investigated were % residual-O(2), product to headspace volume ratio (P/H volume ratio), temperature, light intensity and oxygen transmission rate (OTR). The model illustrated that all the investigated parameters interacted, but especially % residual-O(2) and P/H volume ratio - i.e., the absolute O(2) content, influenced the degree of discoloration. The complex interactions of the parameters justified the selected model, as it emphasised the necessity of evaluating the parameters simultaneously instead of considering them individually. The importance of absolute O(2) content was further validated through an industrial experiment including three different kinds of sliced meat products.
    Meat Science 12/2004; 68(4):577-85. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Colour stability and development of lipid oxidation were followed during chill storage for 6 days of chops from M. Longissimus dorsi produced from pigs with high (6.3) and low (5.5) ultimate pH (pH(u)). The chops from the same individual pigs were either chill stored at 2 days post-mortem or after frozen storage for 30 months (pre-frozen). Initial redness, measured as tristimulus parameter a(*), was lower for pre-frozen chops than for fresh chops. Chops with the high pH(u) had a stable a(*)-value during chill storage, while chops with the low pH(u) showed a rapidly decreasing a(*)-value both for fresh and pre-frozen chops. In contrast, initial lipid oxidation, measured as TBARS, was similar for pre-frozen and fresh chops prior to chill storage for both the high and the low pH(u) meat but developed most significantly in pre-frozen, low pH(u) meat. Individual differences in colour stability and development of lipid oxidation between pigs were notable for pre-frozen low pH(u) meat and need to be considered in quality control since meat from single pigs otherwise might give problems.
    Meat Science 11/2004; 68(3):479-84. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Antioxidative efficiency of extracts of rosemary, green tea, coffee and grape skin in precooked pork patties was investigated during storage under retail conditions (10 days, 4 °C, atmospheric air), using descriptive sensory profiling following reheating and quantitative measurements of hexanal, thiobarbituric acid reactive substances (TBARS) and vitamin E as indicators of lipid oxidation. The initial oxidative status of pork patties (evaluated by ANOVA) showed a significant lower level of secondary oxidation products and higher levels of vitamin E in patties with extracts incorporated, indicating that the extracts retarded lipid oxidation during processing of the meat. Data analysis for the storage study was based on qualitative overview of sensory/chemical variation by principal component analysis (PCA) and quantitative ANOVA-PLSR for determination of the relationship between design variables (days of chill-storage, extract treatment) versus sensory-chemical variables and PLSR for elucidating the predictive ability of the chemical methods for sensory terms. Lipid oxidation was seen to involve a decrease in perception of meat flavour/odour and a concomitant increase in the off-flavour/odours linseed, rancid. TBARS, hexanal and vitamin E were all significant predictive indices (P<0.05) for the majority of the sensory terms, while vitamin E through negative correlation with TBARS and hexanal displayed its antioxidative effect and thus, its ability to preserve sensory fresh meat flavour/odour. The effect of the various extracts incorporated in the product was clearly related to the degree of lipid oxidation and an overall ranking of the antioxidative efficiency of extracts in declining order became apparent: Rosemary>Grape skin>Tea>Coffee>Reference. Furthermore, the relation between extracts and vitamin E indicated that the extracts, to some extent, interacted with the vitamin and prevented it from degrading. In conclusion, the rosemary extract displayed potential for maintaining sensory eating quality in processed pork products.
    Meat Science 11/2004; 68(3):485-95. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This review presents current knowledge on light-induced effects on packaged cheeses. As research in this area is somewhat limited and involves highly non-standardized light exposure conditions, the review includes, if deemed necessary, effects observed in other dairy products. Most of these effects may be explained by general lipid oxidation mechanisms combined with knowledge on the spectral balance between the singlet oxygen quencher, β-carotene, and the sensitizer, riboflavin. As determined by Lambert-Beer's law, β-Carotene absorbs light in a concentration-dependent manner, which would otherwise be absorbed by riboflavin, thereby inducing quality changes. Consequently, these processes may be prevented by total exclusion of light and by storage in an oxygen-free atmosphere. Unfortunately, quality changes are apparent at residual oxygen levels even as low as 0.5% in headspace, which is often considered an acceptable residual oxygen level in industry. For a given product composition, spectral distribution and photon flux of the light source determine the extent of quality changes, since photochemical processes have limited temperature dependence, in contrast to the consecutive lipid autoxidation process. Hence, precautionary measures include changes of light source and targeted prevention of photon flux relative to the cheese by use of creative packaging. In order to optimize packaging and display conditions, a substantial need exists for analytical methods, which reflect the sensory perception of the consumer. Once established, optimization to include marketing and consumer aspects will harbor no major obstacles.
    International Dairy Journal. 01/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Storage of nuts at a high oxygen concentration results in rancid nuts whereas storage at a low oxygen concentration results in fine-tasting nuts. During a 13 month experiment, packaging of walnuts with an oxygen absorber was compared to packaging in nitrogen or atmospheric air. At the same time, the effects of oxygen permeability of the packaging material and storage temperature (11 and 21 degrees C) were investigated by determination of hexanal and rancid taste of the walnuts. The optimal storage condition for walnuts is at 11 degrees C or lower, eventually combined with an oxygen absorber. However, without chilled storage and use of an oxygen absorber, it is possible to obtain an acceptable quality of walnuts with a packaging material having a very low oxygen permeability (e.g., laminate with EVOH) combined with nitrogen flushing. The results also revealed that the development of hexanal during time can be described by a second-order polynomial regression model.
    Journal of Agricultural and Food Chemistry 09/2003; 51(17):4941-7. · 3.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A multifactorial design, including (1) percent residual oxygen, (2) oxygen transmission rate of packaging film (OTR), (3) product to headspace volume ratio, (4) illuminance level and (5) nitrite level during curing, was established to investigate factors affecting light-induced oxidative discoloration of cured ham (packaged in modified atmosphere of 20% carbon dioxide and balanced with nitrogen) during 14 days of chill storage. Univariate statistical analysis found significant effects of all main factors on the redness (tristimulus a-value) of the ham. Subsequently, Response Surface Modelling of the data further proved that the interactions between packaging and storage conditions are important when optimising colour stability. The measured content of oxygen in the headspace was incorporated in the model and the interaction between measured oxygen content in the headspace and the product to headspace volume ratio was found to be crucial. Thus, it is not enough to keep the headspace oxygen level low, if the headspace volume at the same time is large, there will still be sufficient oxygen for colour deteriorating processes to take place.
    Meat Science 02/2003; 63(2):169-75. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Pre-slaughter physiological conditions (A serving as control, B subjected to treadmill exercise immediately prior to stunning, C epinephrine injection 15 h prior to slaughter, and D epinephrine injection 15 h prior to slaughter and subjected to treadmill exercise immediately before stunning) were found to significantly affect colour and lipid oxidation of sliced, retail packed roast ham, produced from nitrite-cured (78 ppm nitrite) M. Longissimus dorsi. The pre-slaughter treatment resulted in variations in the level of glycogen, lactate, ATP and IMP and pH development as monitored in Longissimus dorsi muscles, with the lowest ultimate pH (pH(u)) in muscles from non-epinephrine treated pigs (treatments A and B). The initial tristimulus L(∗)-value and the L(∗)-value during chill storage of sliced roast ham packed in laminates with low or with very low oxygen transmission rate (OTR=40 and <0.5 cm(3)/m(2)/atm/24 h, respectively) were significantly affected by treatment, although the effect of the treatments was different during storage for 28 days (interaction between treatment and storage time). Roast ham from treatments A and B generally had a paler appearance (higher L(∗)-values) than from treatments C and D. No differences in the initial tristimulus a(∗)-values (redness) were found. During chill storage, a pronounced colour fading (decrease in a(∗)-values) was seen for laminate with low OTR, with a tendency of better colour stability for treatment C than A, but with no differences for the other treatments. For laminates with very low OTR, the cured meat pigment was stable with no decreases in a(∗)-values during storage. Lipid oxidation (thiobarbituric acid reactive substances, TBARS) in products in laminates with low OTR increased during storage and was significantly higher for roast ham from non-epinephrine treated pigs (A and B) than for ham from epinephrine-treated pigs (C and D). Statistical analysis relating pH and the level of glycogen, lactate, creatine phosphate, ATP and IMP in the individual pigs to the product quality parameters revealed that the ultimate level of lactate was the most important single parameter affecting product quality. After 28 days of chill storage, roast ham from pigs subjected to treatments C and D were more likely to support bacterial growth than from treatments A and B. In conclusion, the results show that pre-slaughter physiological conditions are of importance for chemical as well as for microbiological changes in retail stored roast ham.
    Meat Science 02/2003; 63(2):151-9. · 2.75 Impact Factor
  • V. K. Haugaard, B. Danielsen, G. Bertelsen
    [Show abstract] [Hide abstract]
    ABSTRACT: Cups based on polylactate (PLA) and poly(hydroxybutyrate) (PHB) were found to be as effective as high-density polyethylene (HDPE) cups in protecting an orange juice simulant and a dressing from quality changes during storage. The orange juice simulant and the dressing were stored in PLA, PHB and HDPE for 10 weeks at 4 C under fluorescent light or in darkness. The suitability of PLA and PHB compared to HDPE was investigated by determination of colour changes and loss of ascorbic acid of the juice simulant and by determination of colour changes, primary (peroxide value) and secondary lipid oxidation (volatiles determined by static headspace) products and reduction of &#102-tocopherols of the dressing. The study also revealed that the quality changes were primarily induced by light, since the quality of samples stored in light changed considerably compared to the quality of samples stored in darkness.
    European Food Research and Technology 01/2003; 216(3):233-240. · 1.39 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sliced Samsø cheese, stored up to 3 weeks, exposed to light (1500lx), packaged in 0% CO2 (100% N2), 20% CO2 (80% N2), or 100% CO2 showed a significant decrease in yellowness (b*) and an increase in redness (a*). Cheese packaged in atmospheres containing 100% CO2 and exposed to light was significantly darker (L*) than cheese exposed to 0% CO2, and the 100% CO2 resulted in a drying-out of the cheeses. Descriptive sensory analysis revealed that light, gas composition, and storage time significantly affected taste and odour attributes of the semi-hard Samsø cheese. Assessors characterised dark-stored cheeses packed in 20% CO2 or 0% CO2 as the most buttermilk-like. Cheeses packed in 100% CO2 and exposed to light were described as rancid and as having a dry/crumbly texture. Dynamic headspace gas chromatography–mass spectrometry was used to identify volatile compounds. Significant light exposure effects during storage were noted for the following oxidation products: 1-Pentanol, 1-octanol, 2-ethyl-1-butanol, 2-butanol, 2-heptanol, 2-pentanol, 2-nonanol, benzaldehyde, 2-butanone, 2-nonanone, dimethyl trisulfide, and tetrahydrofuran. The gas composition had no impact on the formation of volatiles.
    International Dairy Journal 01/2003; 13(2):239-249. · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The present study demonstrates that a rigid packaging material based on polylactate (PLA) was at least as effective as conventional high density polyethylene (HDPE) and polystyrene (PS) packaging materials in protecting fresh, unpasteurised orange juice against quality changes. Fresh, unpasteurised orange juice was stored in PLA, HDPE, and PS at 4 C for 14 days. Quality changes were evaluated by determination of colour stability, ascorbic acid (AA) degradation, and sorption of limonene by the polymers (scalping). Results showed a significantly greater loss of AA in orange juice stored in HDPE and PS compared to PLA, significantly less colour changes of orange juice stored in PLA and PS than in HDPE, and no detectable limonene scalping into PLA and PS, as opposed to a high degree of scalping into HDPE.
    European Food Research and Technology 04/2002; 214(5):423-428. · 1.39 Impact Factor
  • Journal of Agricultural and Food Chemistry - J AGR FOOD CHEM. 04/2002; 43(5).
  • Jens K S Møller, Grete Bertelsen, Leif H Skibsted
    [Show abstract] [Hide abstract]
    ABSTRACT: Photooxidation of the nitrite-cured meat pigment, nitrosylmyoglobin, in aqueous solution saturated with a 20% CO(2)/80% N(2) gas mixture with varying oxygen contents (0.1, 0.5 or 1.0%) was found to depend linearly on the oxygen content for both visible (436 nm) and UV-light (366 nm). Quantum yields were similar for the two wavelengths of excitation in agreement with previous findings at higher oxygen pressures. The reaction stoechiometry for photooxidation was different from that of thermal oxidation (investigated at the same oxygen pressures) with a unity MbFe(II)NO/O(2) ratio in the thermal reaction and a ratio larger than one for the photooxidation. For cured meat products packed in modified atmospheres light exposure may be even more harmful for the oxidative stability than expected from the concentration of residual oxygen.
    Meat Science 04/2002; 60(4):421-5. · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Materials based on renewable resources are being developed at an increasing rate. Today, the only biobased food-packaging materials used commercially on a major scale are based on cellulose. However, materials based on proteins, starch, polylactate and other renewable resources may be the food-packaging materials of tomorrow. The paper presents some of the different biobased materials and their potential as food-packaging materials.
    Food Additives and Contaminants 02/2002; 19 Suppl:172-7. · 2.13 Impact Factor

Publication Stats

1k Citations
119.20 Total Impact Points

Institutions

  • 2002
    • University of Copenhagen
      • Department of Food Science
      Copenhagen, Capital Region, Denmark
  • 1995–2002
    • Royal Agricultural University
      Cicester, England, United Kingdom