Volker Heinz

Deutsches Institut für Lebensmitteltechnik, Quakenbrück, Lower Saxony, Germany

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Publications (115)158.36 Total impact

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    ABSTRACT: HPP benefits have led to increasing commercial production of HP preserved foods.•Microorganism inactivation by HPP in complex food matrices is reviewed.•Emphasis is set on inactivation mechanisms in low or non-uniform aw products.•aw alone is not sufficient to explain disparities in inactivation.•Matrix specificities must be considered in addition to aw protection effect.
    Innovative Food Science & Emerging Technologies 11/2014; · 2.53 Impact Factor
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    ABSTRACT: The comparison between technologies was performed based on microbial equivalence•Industrial scale HPP and pilot scale PEF and thermal units were used•The effect of storage on the fingerprint of tomato juice was taken into account•All pasteurisation technologies caused loss of several volatiles compared to control•All technologies caused the increase of Z-citral and 6-methyl-5-hepten-2-one•Fatty acids, carotenoids and amino acids degradation were observed
    Innovative Food Science & Emerging Technologies 10/2014; 26:431-444. · 2.53 Impact Factor
  • Conference Paper: 1
    1; 10/2014
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    ABSTRACT: Bacterial endospores through their strong resistance to both chemical and physical hurdles constitute a risk for food industry. Inactivation strategies are based on thermal and/or chemical treatments but rely on incomplete knowledge of the mechanisms of inactivation. Alternative strategies were suggested to achieve food safety while improving product quality. One of them relies on the successive germination and inactivation by pasteurization of bacterial spores. However, to date, a gap of knowledge on bacterial spore germination remains and hinders such an application for food sterilization. Geobacillus stearothermophilus ATCC 7953 spore germination mechanisms were investigated by in situ fluorometry combined with plate counts. G. stearothermophilus spores' inner membrane was stained with Laurdan fluorescent dye. While nutrient pathways showed no strong germination with the combinations tested, successful germination up to 3 log10 could be achieved using 60 mmol l−1 calcium-dipicolinic acid (CaDPA) at 55 °C for 2 h. A model for the CaDPA germination mechanism in two phases could be derived which suggested a potential key role of cortex fragments in the germination path, before completion of the cortex degradation. Additionally, it was confirmed that the germination potential of CaDPA, which does not rely on nutrient receptors, is a widespread germination trigger across spore formers. Understanding germination mechanisms and the limitations of different germination paths is important for the development of multi-hurdle approaches to achieve commercial sterility with reduced thermal load.
    Food Control 09/2014; · 2.74 Impact Factor
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    ABSTRACT: A new generation of high pressure homogenizers reaching up to 400 MPa offers opportunities for spore inactivation and high pressure sterilization of foods. A Stansted Fluid Power ultra-high pressure homogenization (UHPH) unit was tested to inactivate bacterial spores in a model buffer system. Bacillus subtilis PS832 and Geobacillus stearothermophilus ATCC7953 spores’ thermal resistances were assessed (D, z-value and Ea). The pressure and valve temperature were monitored during UHPH. Residence times under pressure and high temperature were estimated and enabled comparison with thermal inactivation, indicating the estimated thermal contribution to inactivation. Spore germination was also assessed but no germination was observed. Up to five log10B. subtilis and two log10G. stearothermophilus spores were inactivated by the harshest treatments (> 300 MPa –Tvalve > 145 °C for ~ 0.24 s). The inactivation profiles were similar to the predicted thermal inactivation suggesting that the valve temperature might be a dominant parameter leading to bacterial spore inactivation.
    Innovative Food Science & Emerging Technologies 08/2014; 26:116-123. · 2.53 Impact Factor
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    ABSTRACT: Bacterial spores have a strong resistance to both chemical and physical hurdles and create a risk for food industry which has been tackled by applying high thermal intensity treatments to sterilize food. These strong thermal treatments lead to reduction of the organoleptic and nutritional properties of food and alternative are actively searched for. Innovative hurdles offer an alternative to inactivate bacterial spores. In particular, recent technological developments have enabled a new generation of high pressure homogenizer working at pressures up to 400 MPa and thus opening new opportunities for high pressure sterilization of foods. In this short review, we summarize the work conducted on (ultra)-high pressure homogenization (U)HPH to inactivate endospores in model and food systems. Specific attention is given to process parameters (pressure, inlet and valve temperatures). This review gathers the current state of the art and underlines the potential of UHPH sterilization of pumpable foods while highlighting the needs for future work. http://journal.frontiersin.org/Journal/104283/abstract
    Frontiers in Nutrition. 08/2014; 1(15).
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    ABSTRACT: Nitrate is a natural constituent of the human diet and an approved food additive. It can be partially converted to nitrogen monoxide, which induces vasodilation and thereby decreases blood pressure. This effect is associated with a reduced risk regarding cardiovascular disease, myocardial infarction and stroke. Moreover, dietary nitrate has been associated with beneficial effects in patients with gastric ulcer, renal failure or metabolic syndrome. Recent studies indicate that such beneficial health effects due to dietary nitrate may be achievable at intake levels resulting from the daily consumption of nitrate-rich vegetables. N-nitroso compounds are endogenously formed in humans. However, their relevance for human health has not been adequately explored up to now. Nitrate and nitrite are per se not carcinogenic, but under conditions that result in endogenous nitrosation it cannot be excluded that ingested nitrate and nitrite may lead to an increased cancer risk probably be carcinogenic to humans. In this review the known beneficial and detrimental health effects related to dietary nitrate/nitrite intake are described and the identified gaps in knowledge as well as the research needs required to perform a reliable benefit/risk assessment in terms of long-term human health consequences due to dietary nitrate/nitrite intake are presented.This article is protected by copyright. All rights reserved
    Molecular Nutrition & Food Research 08/2014; · 4.31 Impact Factor
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    ABSTRACT: Hydrodynamic pressure processing (HDP) or shockwave treatment improved tenderness (18% reduction in Warner-Bratzler shear force (WBSF) of beef loin steaks. Endogenous muscle proteolyic activities (cathepsins and peptidases) and protein fragmentation of sarcoplasmic and myofibrillar proteins detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were not influenced by HDP. However, microstructure changes were clearly detected using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Specifically a disruption of the structure at the muscle fiber bundles and an increased endomysium space were observed. The present paper supports the evidence of physical disruption of the muscle fibers as a cause behind the tenderness improvement. The paper discusses the possible mechanisms responsible for the meat tenderisation induced by HDP treatment.
    Meat Science 07/2014; 98(4):759-765. · 2.75 Impact Factor
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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 06/2014; · 2.53 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 05/2014; 39:244–250. · 2.74 Impact Factor
  • 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 05/2014; 39:163–171. · 2.74 Impact Factor
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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
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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: The combination of pulsed electric fields (PEF) and texturizing and antifreeze agents on quality retention of defrosted potato strips were studied. Potato strips (10 mm thickness, 100 g) were placed in different solutions (1% w/v) of CaCl2, glycerol, trehalose as well as NaCl and sucrose, treated with PEF (0.5 kV cm−1, 100 pulses, 4 Hz). Then, all the samples were soaked in the same solutions for 10 min. After draining, samples were packed into polypropylene pouches and stored at −18 °C for 12 h. Samples were thawed out at room temperature (20 °C) in 3 h. Untreated controls and PEF treated control samples were also frozen and thawed in similar conditions. To assess the potato strip quality, the thawed samples were analysed for moisture content, weight loss, firmness and colour attributes. The results indicate that PEF treatment by itself is not a suitable pre‐treatment method for frozen potato strips and should be assisted by CaCl2 and trehalose treatment to prevent softening after defrosting. Firmness analyses determined that application of PEF alone results in 2.38 N. However, PEF in combination with CaCl2 and trehalose result in 2.97 N and 2.99 N, respectively, which are both significantly firmer than the samples solely treated with PEF. CaCl2 and trehalose were effective in not only maintaining the structural integrity of the cells, but also retaining colour attributes. The L* value was found to be higher (P 2 and trehalose treated samples (58.95 and 57.21, respectively), as compared to PEF treated samples (53.97) denoting a darker colour. Application of CaCl2 and trehalsoe in combination with PEF also resulted in significantly less weight loss after thawing.
    International Journal of Food Science & Technology 06/2013; 48(6). · 1.24 Impact Factor
  • Shima Shayanfar, Volker Heinz
    I.C. FABE, Skiathos, Greece; 05/2013
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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 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

Publication Stats

1k Citations
158.36 Total Impact Points

Institutions

  • 2005–2014
    • Deutsches Institut für Lebensmitteltechnik
      Quakenbrück, Lower Saxony, Germany
  • 1996–2013
    • Technische Universität Berlin
      • • Department of Chemistry
      • • Institut für Lebensmitteltechnologie und Lebensmittelchemie
      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
  • 2000
    • Georg-August-Universität Göttingen
      • Institute for X-Ray Physics
      Göttingen, Lower Saxony, Germany