Volker Heinz

Deutsches Institut für Lebensmitteltechnik, Quakenbrück, Lower Saxony, Germany

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Publications (102)101.46 Total impact

  • Source
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    ABSTRACT: Eight different types of Bologna type cooked sausages apart from the control were produced in order to reduce the fat content (15%, 30%, 45%), replace the animal fat by olive oil (3%, 6.5% and 10%) as well as concomitant reduction and replacement of animal fat (30% of fat reduction with 2% of olive oil as an animal fat replacer). Quality attributes such as texture, water binding and color were monitored. Texture and water binding of fat reduced and fat replaced samples were quite similar to the control while color was strongly affected by the fat reduction and replacement. Fat reduction led to a redder cooked sausage and the addition of olive oil to a more yellow product. Chemical analysis revealed no major changes among samples apart from protein and fat content and fatty acid profile. Noteworthy, cooked sausage with more than 6.5% of olive oil achieved the World Health Organization’s recommendation on the nutritional fat index ((polyunsaturated + monounsaturated)/saturated fatty acid ≥ 2) which is very relevant to the development of healthier formulations. Cooked sausages with 45% of fat reduction and 30% fat reduced with 2% of olive oil were considered as the best by the panelists, which in addition had a balanced nutritional content by a lower caloric content. We concluded that fat reduction (up to 45%) and replacement (up to 10%) are possible with acceptable sensory quality and improved nutritional composition. When replacing animal fats by plant oils, the color of the product, which has a strong influence in the sensory acceptability of Bologna type cooked sausages, is affected. Therefore it must be controlled for a proper product development of meat products containing vegetable oils.
    Food and Nutrition Sciences 03/2014; 5(7):645-657.
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    ABSTRACT: Bacterial spores are a major concern for food safety due to their high resistance to conventional preservation hurdles. Innovative hurdles can trigger bacterial spore germination or inactivate them. In this work, Geobacillus stearothermophilus spore high pressure (HP) germination and inactivation mechanisms were investigated by in situ infrared spectroscopy (FT-IR) and fluorometry. G. stearothermophilus spores’ inner membrane (IM) was stained with Laurdan fluorescent dye. Time-dependent FT-IR and fluorescence spectra were recorded in situ under pressure at different temperatures. The Laurdan spectrum is affected by the lipid packing and level of hydration, and provided information on the IM state through the Laurdan generalized polarization. Changes in the –CH2 and –CH3 asymmetric stretching bands, characteristic of lipids, and in the amide I´ band region, characteristic of proteins’ secondary structure elements, enabled evaluation of the impact of HP on endospores lipid and protein structures. These studies were complemented by ex situ analyses (plate counts and microscopy). The methods applied showed high potential to identify germination mechanisms, particularly associated to the IM. Germination up to 3 log10 was achieved at 200 MPa and 55 °C. A molecular-level understanding of these mechanisms is important for the development and validation of multi-hurdle approaches to achieve commercial sterility. http://www.sciencedirect.com/science/article/pii/S0740002014000100
    Food Microbiology 01/2014; 41:8-18. · 3.41 Impact Factor
  • Claudia Siemer, Stefan Toepfl, Volker Heinz
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    ABSTRACT: The application of pulsed electric fields (PEF) can be used to inactivate bacterial endospores if combined with thermal energy. A model was developed in the second part of the study aiming to separate thermal and PEF induced spore inactivation. Therefore thermal inactivation data of B. subtilis spores was obtained by glass capillary method and combined with temperature time profile of the PEF process. The PEF process can be separated in pre heating, PEF treatment and cooling phase. The temperature development in pre heating and cooling phase was simulated based on a theoretical numerical approach, the temperatures in the PEF unit were measured by fiber optic sensors. To evaluate the effect of pH on the inactivation the PEF treatment was performed in Ringer solution (4 mS/cm) at pH 4 and 7. The results of the developed model indicate a thermal and a PEF induced inactivation, where the temperature induced inactivation is slightly higher in acid Ringer solution. The impact of specific energy inputs up to 195 kJ/kg was evaluated, showing an increasing total inactivation of the spores, but also shift towards PEF induced inactivation. Applying an energy input of 195 kJ/kg an inactivation of 4.4 log was obtained in Ringer solution at pH 7, which could be separated in 1.15 log of thermal and 3.25 log of PEF related inactivation. The F-value, typically used to describe thermal spore inactivation processes was calculated for the combined PEF process based on the temperature time profile. The highest F-value determined for the maximum applied energy was 2.43 s, which confirms the low product heat load.
    Food Control. 01/2014; 39:244–250.
  • Claudia Siemer, Stefan Toepfl, Volker Heinz
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    ABSTRACT: In addition to inactivation of vegetative microorganisms, PEF can be used to inactivate bacterial endospores when combined with thermal energy. In the first part of this study, the impact of the product parameters pH value (4 and 7), sugar level (5 and 10%) and conductivity (4 and 15 mS/cm) as well as the process parameters specific energy (up to 350 kJ/kg), electric field strength (6–11 kV/cm) and inlet temperature (56, 70 and 80 °C) on the inactivation of Bacillus subtilis spores were analyzed. The results of spore inactivation by PEF at different inlet temperatures indicated less energy requirements for sufficient inactivation at higher inlet temperatures. Comparing the inactivation at different pH values, the inactivation at acid pH value required less energy than at neutral pH value. A 1.6 log reduction using 167 kJ/kg was detected in Ringer solution at pH 4 compared to 0.6 log in neutral medium at an energy of 165 kJ/kg (inlet temperature of 80 °C and 9 kV/cm as electric field strength). Under the same process conditions (9 kV/cm and 80 °C inlet temperature), the addition of 10% sugar permitted to reduce the energy from 178 to 146 kJ/kg, require to reach a 3 log cycles inactivation of B. subtilis spores. The results showed a successful inactivation of B. subtilis spores by PEF in combination with thermal energy and represent therefore a promising process for spore inactivation with reduced heat load.
    Food Control. 01/2014; 39:163–171.
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    ABSTRACT: The effect of pulsed electric fields (PEF) on the inactivation of inoculated Pseudomonas (P.) fragi, Escherichia (E.) coli (K12) and Staphylococcus (S.) xylosus as well as on the total aerobic plate count (TPC) of porcine blood plasma was investigated. Furthermore, the impact of PEF on gel strength and solubility was analysed. Inoculated plasma samples were PEF treated at an initial temperature of 30°C, electric field strength between 9 and 13 kV/cm and a specific energy input in a range of 40 to 182 kJ/kg for total treatment times between 35 μs and 233 μs. Increased specific energy input led to increased microbial inactivation, but then decrease in soluble protein and gel strength occurred. To avoid undesired protein denaturation, energy input should not exceed 120 kJ/kg. Considering these processing conditions an inactivation of 3.0 ± 0.4 log steps for the total plate count was proven (p < 0.001). Inoculated E. coli K12 and P. fragi could be reduced below the detection limit (p < 0.0001) and for at least 3 log steps (p < 0.0001), respectively. S. xylosus was the most PEF resistant germ and for sufficient inactivation higher energy input was needed which resulted in outlet temperatures above 60 °C (p < 0.01). Industrial relevance The treatment of blood plasma with pulsed electric fields (PEF) is in principle a suitable method for reducing the total plate count, Pseudomonas fragi, Escherichia coli and Staphylococcus xylosus in porcine blood plasma. Inactivation is limited by the specific energy input which should not exceed 120 kJ/kg at start temperatures of 30°C to avoid undesired protein denaturation. Improved microbiological quality of PEF-treated blood plasma enables enhanced utilisation possibilities and allows extended storage times.
    Innovative Food Science & Emerging Technologies 01/2014; · 2.53 Impact Factor
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    ABSTRACT: The interaction of pulsed electric fields (PEF) with different cryoprotectant and texturizing agents in quality retention of carrot discs was analysed. Increasing the permeability properties by PEF may lead to better accessibility of intracellular materials to freezing and thus reducing the freezing time, leading to better maintaining the texture after thawing. Carrot discs of 5 mm thickness were immersed in different solutions of CaCl2, glycerol, trehalose and tap water, and subsequently were treated with PEF (1 kV/cm, 100 pulses, 4 Hz). Then, the samples were drained and packed along with a control group in separate prepared polypropylene pouches. All the samples were frozen at −18 °C for 24 h and thawed during 3 h at ambient temperature (20 °C) the following day. The quality of the thawed carrot discs was certified by measuring weight loss, firmness, microscopic studies and CIE colorimetric attributes. All the PEF-treated samples, no matter what solution they were soaked in, could significantly (P < 0.05) maintain the firmness as well as colour attributes. However, it was deducted that application of CaCl2 in conjunction with PEF can result in a firmer texture. Firmness analyses determined that application of PEF alone results in 5.84 N, while its combination with CaCl2 leads to higher value of 6.63 N. Firmness in control samples was found to be 3.46 N. The SEM studies supported the results of firmness analysis and depicted more integrity in the cell walls of the samples treated with CaCl2 and glycerol. The weight loss values varied among different samples, and the highest amount and lowest amount were reported in CaCl2 and solely PEF-treated samples, respectively. There was no significant difference between the colour attributes measured in different groups including control sample (P > 0.05).
    International Journal of Food Science & Technology 12/2013; · 1.24 Impact Factor
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    ABSTRACT: Meat tenderness is an important quality parameter determining consumer acceptance and price. Meat tenderness is difficult to ensure in the global meat chain because the production systems are not always aiming at this purpose (ex.: cattle derived from milk production) and by the existence within the carcass of "tough" primals. Different methods can be used by the meat industry to improve meat tenderness each with its advantages and drawbacks. The application of hydrodynamic pressure or shockwaves has showed outstanding improvements by reducing the Warner Bratzler Shear Force by 25% or more. However, the technology has not penetrated into the market as first systems were based on the use of explosives and further developments seemed to lack the robustness to fulfill industrial requirements. The present paper describes the main challenges to construct a prototype for the continuous treatment of meat by shockwaves based on electrical discharges under water. Finally, improvements on the tenderness of meat by using the novel prototype are presented.
    Meat Science 04/2013; · 2.75 Impact Factor
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    ABSTRACT: It is well known that spore germination and inactivation can be achieved within a broad temperature and pressure range. The existing literature, however, reports contradictory results concerning the effectiveness of different pressure-temperature combinations and the underlying inactivation mechanism(s). Much of the published kinetic data are prone to error as a result of unstable process conditions or an incomplete investigation of the entire inactivation pathway. Here, we review this field of research, and also discuss an inactivation mechanism of at least two steps and propose an inactivation model based on current data. Further, spore resistance properties and matrix interactions are linked to spore inactivation effectiveness.
    Trends in Microbiology 03/2013; · 8.43 Impact Factor
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    ABSTRACT: The impact of high pressure/temperature treatment on structure modification and functional sensory properties of frankfurter batter was investigated. The degree of solubilization of meat proteins, particularly of myosin, was identified as a key process with significant effect on the batter's structural properties. The maximal solubilization level was at 200MPa/40°C IT for all formulations which was found to be treatment time dependent. The impact of the pressurizing gradient - PG=40MPa/s and PG=2.5MPa/s was investigated and estimated to have a significant effect on the protein network and functional properties, respectively. These were improved at low PG (2.5MPa/s) as a phenomenon of secondary network formation parallel to the main matrix. Batter secondary-structure characteristics were found to be ionic-strength dependent. According to SDS-PAGE analysis, the major role in the solubilization, aggregation and gelation processes occurring in the aqueous phase was due to the myosin S-1 and S-2, N-terminal, C-terminals, the MLC and actin during the high pressure/temperature treatment.
    Meat Science 03/2013; 94(3):376-387. · 2.75 Impact Factor
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    ABSTRACT: The shift of the dissociation equilibrium under pressure and temperature plays a decisive role in the inactivation of bacterial spores. To obtain the dissociation equilibrium shift in water and buffer systems, the thermodynamic dissociation constants in a wide range of pressure and temperature were modelled. Heat and pressure inactivation of Geobacillus stearothermophilus spores at different initial pH-values in ACES and phosphate buffer confirmed the modelled data. Thermal inactivation in both buffers at 114, 122 and 127 °C resulted in higher logarithmic reductions with ACES. Contrary, after pressure treatment at 500, 600 and 900 MPa with 80 °C phosphate buffer showed higher inactivation. These results indicated the different dissociation equilibrium shifts in buffer systems by heat and pressure.
    Food Control 02/2013; · 2.74 Impact Factor
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    ABSTRACT: The impact of agglomeration on the quantitative assessment of thermal spore inactivation was investigated. The agglomeration size distribution in suspensions of Bacillus stearothermophilus spores was determined by using a three-fold dynamic optical back-reflexion measurement (3D ORM). Thermal inactivation data have been modelled using first-order inactivation kinetics, superimposed by the agglomeration size. Since 3D ORM accurately yields the maximum length of an agglomerate, but provides no information on the packing density, two limiting cases have been discriminated in mathematical modelling: three-dimensional, spherical packing for maximum spore count and two dimensional, circular packing for minimum spore count of a particular agglomerate. Thermal inactivation studies have been carried out in thin glass capillaries, where by using numerical simulations the non-isothermal conditions were modelled and taken into account.It is shown that the lag phase often found in thermal spore inactivation (shoulder formation) can sufficiently be described by first-order inactivation kinetics when the agglomeration size is considered.
    Journal of Food Engineering 02/2013; · 2.28 Impact Factor
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    ABSTRACT: The physiological response of Bacillus licheniformis spores to high pressure and thermal inactivation in sodium citrate buffer and nutrient broth was investigated using multiparameter flow cytometry. Spores were treated by heat-only at 121 °C, by high pressure at 150 MPa (37 °C), or by a combined high pressure and heat treatment at 600 MPa and 77 °C, and then dual stained with the fluorescent dyes SYTO 16 and propidium iodide (PI). For pressure treated spores, but not heat-only treated spores, four distinct sub-populations were detected by flow cytometry, and for these we suggest a three step model of inactivation involving a germination step following hydrolysis of the spore cortex, an unknown step, and finally an inactivation step with physical compromise of the spore's inner membrane.Industrial relevanceThis preliminary study offers a simple and fast flow cytometric method for the rapid assessment of the physiological state of bacterial spores following high pressure and thermal processing. An improved understanding of the mechanisms of spore inactivation will aid in the food safety assessment of pressure assisted thermal sterilisation in particular, and also assist in the commercialisation of these processes facilitating adoption by industry.
    Innovative Food Science & Emerging Technologies 02/2013; · 2.53 Impact Factor
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    ABSTRACT: Bacterial endospores constitute a hazard for food processors by their strong resistance to chemical and physical hurdles. Presence of spores in a food matrix or on processing equipment may lead to food (re)contamination following germination and jeopardize consumer safety as well as product quality. To counter this issue, inactivation strategies both for food and equipment surfaces have been developed, based, respectively, on thermal or a combination of thermal and chemical treatments. In this entry, the existing spore inactivation mechanisms that occur during food sterilization are described. Conventional techniques for sterilization used in the food industry are summarized for food as well as equipment.
    02/2013: pages 1-6; , ISBN: 0-8493-5027-1
  • 01/2013; , ISBN: 978-1-118-40632-8
  • Source
    Bajo Bajovic, Tomas Bolumar, Volker Heinz
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    ABSTRACT: Pressure can be applied by high hydrostatic pressure, better known as high pressure processing (HPP), or by hydrodynamic pressure (HDP) in the form of shockwaves to alter quality parameters, such as shelf-life and texture of meat and meat products. The aim of this review is to give an overview of the use of pressure in the meat industry and to highlight its usage as a method to inactivate microorganisms but also a novel strategy to alter the structure and the quality parameters of meat and meat products. Benefits and possibilities of the technologies are presented, as well as how to overcome undesired product changes caused by HPP. The use of hydrodynamic shockwaves is briefly described and a promising newly developed industrial prototype for the generation of shockwaves by underwater explosion is presented.
    Meat Science 04/2012; 92(3):280-9. · 2.75 Impact Factor
  • Source
    Claudia Siemer, Stefan Toepfl, Volker Heinz
    03/2012; , ISBN: 978-953-51-0428-5
  • Food Factory, Laval; 01/2012
  • Kongress Lebensmitteltechnologie GDL, Dresden; 01/2012
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    ABSTRACT: In our work, the effect of medium hydrostatic pressure on the properties of wheat flour’s main ingredients, starch and proteins, is presented and discussed. The symbiotic effect of the different constituents via size exclusion chromatography, water binding, gelatinization experiments as well as atomic force microscopy measurements and X-ray diffraction is elucidated. From results of size exclusion chromatography and protein content analysis, prolamin fractions seemed to be most sensitive to pressure. Hydrostatic pressure, however, had a significant influence on the amount of bound water and gelatinization enthalpy, especially at moderate pressures and higher temperatures. In this case, an optimal interaction between macromolecules and water occurs. This was also confirmed by atomic force microscopy images and X-ray diffraction patterns. Amorphous and crystalline regions of starch granules were modified, depending on pressure and temperature. At medium pressure (200 MPa), water was pressed into the starch cavities remaining there, whereas higher pressure (600 MPa) led to complete flattening of the surface. With X-ray diffraction, it was shown that medium pressure had nearly no effect on molecular structure, whereas higher pressure caused thermal-like molecular modifications.
    Journal of Cereal Science 01/2012; · 2.09 Impact Factor

Publication Stats

1k Citations
101.46 Total Impact Points


  • 2005–2014
    • Deutsches Institut für Lebensmitteltechnik
      Quakenbrück, Lower Saxony, Germany
  • 1998–2013
    • Technische Universität Berlin
      • Department of Chemistry
      Berlín, Berlin, Germany
  • 2012
    • Laval University
      Québec, Quebec, Canada
    • Universitätsklinikum Dresden
      Dresden, Saxony, Germany
  • 2011
    • Klinikum Osnabrück
      Osnabrück, Lower Saxony, Germany
  • 2001
    • University of Zaragoza
      Caesaraugusta, Aragon, Spain