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Week 6 Food processing technologies High pressure processing Questions to check your understanding of the work: 1) Understand the basic principle of HPP 2) Understand the principle of how HPP works and the mechanics of how it is done 3) Understand what the applications of HPP are 4) Understand...

Week 6 Food processing technologies High pressure processing Questions to check your understanding of the work: 1) Understand the basic principle of HPP 2) Understand the principle of how HPP works and the mechanics of how it is done 3) Understand what the applications of HPP are 4) Understand how HPP affects bacteria to ensure food safety 5) Understand the basic principle of PEF 6) Understand the principle of how PEF works and the mechanics of how it is done 7) Understand what the applications of PFF are 8) Understand how PEF affects bacteria to ensure food safety Basic background: At pressures of up to 600MPa (6 000 bar or 600 000kPa) to treat a variety of foods Sufficient to destroy many microorganisms in foods: improved safety and shelf-life with minimal losses of sensory and nutritional quality Bacterial spores not inactivated Referred to as “cold pasteurization”, not sterilization Non thermal in nature Applied to pre-packaged foods- avoid recontamination Generally, HPP systems can be: Batch process for both solid and liquid food products Dry-cured or cooked meat products Ready-to-eat meals/ fruit and vegetables Semi-continuous for liquids Fruit juices Milk products Principle: how does it work Pressure vessel and pressure generator Food packages in vessel, usually water pumped into vessel until desired pressure reached to 6000 bar, then held for desired time Isostatic principle – Pressure is uniformly distributed throughout the entire sample, either in direct contact with the pressurizing medium or insulated from it in a flexible container Le Chateliers principle – When a system at equilibrium is disturbed the system responds in a way that tends to minimizing the disturbance Mechanism of action Lethal effect of HPP is due to several simultaneous processes: damage to cell membranes – pressure leads to increased ionization of water molecules leading to destruction/damage inactivation of key enzymes – ionization and precipitation of protein complexes (incl. transcription & replication enzymes) cell wall damage and sub-cellular structural damage in yeasts at > 200 MPa At the pressure > 400–600 MPa, mitochondria and cytoplasm can be altered Stationary phase cells more pressure-resistant than exponential phase cells (cytoplasmic membrane composition differs) Spores are proven to be pressure resistant – proteins are protected against ionization and precipitation by dipicolinic acid HPP can affect tertiary and quaternary structure of proteins- protein denaturation can lead to physical damage of cell membranes (pressure dependent) Changes cell membrane permeability Lead to enhanced or decreased enzyme activity In contrast – covalent bonds are not affected by pressure – many compounds pertaining to sensory and nutritional quality not affected (vitamins, flavor, color, etc.) Factors affecting microbiological safety of HPP treated foods: Level of pressure applied Holding time Process temperature Life cycle phase (vegetative vs spores) Species pressure resistance gram-positive bacteria are more resistant than gram-negative the larger and more complex the organism, the easier it is to inactivate Composition of substrate pH and water activity Applications: Cooked and Ready-to-eat (RTE) meats Fish and seafood Fruit and vegetable products Dairy products Raw meats, fish & poultry Advantages and disadvantages: Major advantage: Food safety and shelf-life enhancement, without negative effects on sensory and nutritional Disadvantage: batch process – lower throughput, therefore mainly for high value products Videos and references Literature https://doi.org/10.1016/j.aaspro.2016.09.077 https://www.routledgehandbooks.com/doi/10.1201/9780429326400-16  https://doi.org/10.1016/B978-0-12-411479-1.00001-2 https://doi.org/10.1016/B978-012676757-5/50003-7 Videos JBT Avure https://www.youtube.com/watch?v=IRfTB4gaztg https://www.youtube.com/watch?v=Gw-yQjoA_cM Multivac https://www.youtube.com/watch?v=CKHmLXbZTlw Hiperbaric https://www.youtube.com/watch?v=XpbcRaxrsi8 ThyssenKrupp https://www.youtube.com/watch?v=4VLSmvuwYXI Food Processing Technologies Pulsed Electric Field (PEF) Basic background Pulsed electric field (PEF) Nonthermal alternative to pasteurization of liquids Disintegration of plant and animal raw materials Induce stress responses in biological cells Quality of PEF pasteurized products- closer to that of fresh product than heat-pasteurized product safety is enhanced by inactivation of vegetative pathogens Principle: how does it work PEF technology is used to induce nonthermal permeabilization (electroporation) Electric pulse enlarges existing pores or shoots holes through the cell membrane Depending on treatment field intensity and cell properties - pore formation temporary (pore resealing) or permanent (cell death) Very short electric pulses (1- 100𝜇m) at intensities: 0.1-1 kV.cm-1 – reversible poration for stress induction 0.5-3 kV.cm-1 – irreversible poration plant & animal tissues 15-40 kV.cm-1 – irreversible poration of microbial cells Mechanism of action: Biological membranes are dielectric material of low permittivity, and they maintain an electrochemical gradient at both membrane sides Accumulation of equal number of negative ions, at the inner surface of the membrane and positive ions outside the cell is called the “resting potential” After exposure to high external electric field, membrane ions migrate toward the membrane walls, which results in accumulation of the free charges on opposite sides Accumulation of charges lead to an increase of the potential difference across the membrane. Higher electric field intensity induces an additional transmembrane potential, larger than the membrane’s natural potential, which is unevenly distributed over the surface of membrane Field intensities lead to formation of critical transmembrane potential (TMP) – precondition for cell membrane breakdown and electroporation Reversible electroporation – formation of conductive channels, but electrically insulating properties recovered in seconds Irreversible electroporation – loss of turgor, leakage of cytoplasmic content and lysis Process factors affecting microbial inactivation: Electric field intensity (E) Intensity of E influences degree of cell membrane electroporation – is determined by the amount of voltage discharged into the chamber (where the substrate is placed) The E is not homogeneous – strongly depends on the insulator geometry, modification of insulators geometry and the distance between the two electrodes results in different E distributions What is the implication of increasing the gap between the two electrodes? Pulse width and shape Treatment time Temperature Biological factors affecting inactivation Type of microorganisms gram-(+) bacteria are more resistant than gram-(-) bacteria Shape & Size of microorganisms the inactivation of larger microbial cells (e.g., yeast) needs less intense field strengths to suffer a similar inactivation than smaller cells (e.g., bacteria) electric field induction of the transmembrane potential is cell size-dependent Concentration initial microbial load, mixed microbial cultures, etc. Growth stage cells in their exponential growth phase are more susceptible than those in lag or stationary phase Media characteristic / Food matrix pH, antimicrobials, ionic compounds, electrical conductivity, and medium ionic strength Impact on protein High-intensity electrical fields – unlikely to affect covalent bonds Hence, minimal impact to pigments, flavor compounds or vitamins degradation of some sensory attributes and nutritional content could be perceived Electric field application and related side-effects may cause changes in protein structure and enzyme activity Applications Pasteurization of liquid foods Softening of plant tissues Electroporation of tissues to aid extraction efficiency Videos and references References https://doi.org/10.1111/jam.12558 https://doi.org/10.3390/foods11111556 Videos ELEA Technology http://elea-technology.de/how-pef-works/ https://www.youtube.com/watch?v=IvHfNGCqU0s Otago Univ – French Fries https://www.youtube.com/watch?v=-doPfIKimNY Summary https://www.youtube.com/watch?v=2z0uLS8oQ_I Pulsemaster https://vimeo.com/267023911 Week 7 UV radiation 1) Understand the basic principle of UV 2) Understand the principle of how UV works and the mechanics of how it is done 3) Understand what the applications of UV are 4) Understand how UV affects bacteria to ensure food safety What is ultraviolet light Electromagnetic radiation rather than “light” – specific form of wave energy (photon) Shorter wavelength than visible light, but longer than X-rays UV photons belong to wavelength range 10 to 400 nm ( 1 nm = 10−9 m) Optimal UV Disinfection/Germicidal Range = UVC (200-280) Basic background- UV radiation Form of wave energy (photon) It belongs specific portion of electromagnetic radiation spectrum (ERS) Photon energy expressed in Joules (J) or electron volts (eV) 1 J = 1.609 X 10−19 eV Photon energy (E) is a function of waves properties frequency and wavelength UV region = 10 - 400 nm shorter than visible (400-800 nm), but less than X-ray (< 10nm) UV- applications Basic background- general UVC has special affinity for some proteins and enzymes particularly – nucleic acids, ability to disrupt the DNA/RNA Established effectiveness in: controlling growth of single-cell organisms (fungi, bacteria) and viruses (not considered MO’s) against complex and multicellular organisms such as nematodes and arthropod (insects and mites) pests UVC has limited depth of penetration in most materials – absorbing chemicals penetrates air and optically clear water – 1000’s of meters inactivation usually restricted to surface of solids or a narrow depth in liquids History of ultraviolet germicidal irradiation Mechanism of action UV induced DNA changes are critical and responsible for the disinfection action of UV photons Photochemical reactions UV is effective in altering chemical structure of biological molecules (incl. nucleic acids) DNA is most likely target – nucleotide bases, purine (adenine; guanine) and pyrimidine (thymine; cytosine) are highly UV-absorbent chromophores DNA has maximum absorption band at 265 nm Proteins absorb mainly at ≈280 nm and at equal concentrations are lower absorbents than nucleic acid Structural alteration of DNA based on the formation of cyclobutane pyrimidine dimers (CPD), known as thymine dimers Results in: deformation of DNA’s helix structure, restricting its effective coupling and the transcription and replication process Videos Campden BRI https://www.campdenbri.co.uk/research/uv-light-treatment.php Water purification system https://www.youtube.com/watch?v=G0jRb5jM2n8 UV’s mode of action in disinfection Called UV radiation because you can’t see the rays CPDs are usually formed between thymines (TT), cytosines (CC), or cytosine/thymine (CT) bases These molecules interfere with normal RNA transcription and DNA replication, limiting reproduction, leading to mutagenesis and ultimately to cell death Mechanism of action UVC induced cellular lesions UV-induced lesion mechanisms in cells form CPD’s and/or Pyrimidine-pyrimidone (6-4) photoproducts (6-4 PPs) and their valence isomers these are the principal lesions leading to mutagenesis other lesions initiated by either: alkylating agents hydrolytic processes formation of free radicals Any UVC source is effective in inducing critical lesions Any UVC source is effective in inducing critical lesions that inactivate vital cell processes All UVC potentially useful for food safety applications UV-induced dark repair mechanisms and/or enzymatic so-called recA system, regulated by the expression of the recA gene Applications Temperature sensitive commodities (fresh produce) Processed foods (i.e., fruit juices & milk) Air and water (irrigation, processing, recycling, wastewater) Microorganisms can get used to the UV level, the default then is to use chlorine Different amounts and types of microorganisms in the water Initial microbial load is a determining factor that affects the performance of UV Different UV lamps give different results Advantages of UV-C disinfection Effective against algae, bacteria, fungi, moulds, nematode eggs, viruses, yeasts and protozoa (Cryptosporidium and Giardia) No chemicals added to food or water – also no handling and storage No disinfectant by-products (DBPs) formed Very short contact/treatment time Small space requirements – often very easy to retrofit User-friendly and easy to adjust dose (not linear) Energy efficient Disadvantages of UV-C disinfection Low doses can be ineffective UV leaves no residual* (chemical) may have organic waste Microorganisms can sometimes repair DNA damage (UV-A induced or dark repair) Food surfaces can deflect UV or suspended material in water can shield microorganisms Lamp breakage – mercury hazard Factors that affect the UV-light processing of food Literature https://doi.org/10.1016/j.cej.2020.128084 https://doi.org/10.1016/j.tifs.2020.06.001 https://doi.org/10.1177/003335491012500105 https://doi.org/10.1016/j.dnarep.2007.09.002 Effect of UV radiation technology on quality parameters of dairy products Protein precipitation UV-C lamp dependent Treatments < 4.2 J/cm2 did not increase protein oxidation  Thiobarbituric acid reactive substance were UV dose dependent. Week 8 Cold plasma: A sustainable non-thermal technology for food processing application What is plasma Plasma is considered as the fourth state of matter (ionized gas) Like gas, plasma consist of particles that can pulled apart or dissociated Unlike gas, plasma can respond to magnetic field and conduct electricity It consist of electrically charges particles (ions) Plasma can be generated via the partial or full ionization of gas, It consists of charged and neutral: particles and electrons Positive and negative charged: ions Free radicals in balanced proportions Highly charged/energetic ionized gas Why is it called cold plasma? Non-thermal plasma exists at a non-equilibrium state Electron temperature (Te) is higher than the global gas temperature (Tg) and the temperature of constituting ions (Ti) Most of the energy in cold plasma is stored in the free electrons Temperature can be further reduced at low pressure Cold plasma generation Cold plasmas could be generated continuously via electric discharge in a gas under atmospheric- or low-pressure or vacuum conditions System is fitted with an electrode(s), radiofrequency generator, a regulating unit (for voltage and pressure control) For plasma vacuum chamber the pressure could be reduced to about 0.1 – 0.5 mbar Electron energy (dissociation energy) generated can separate covalent bonds in organic molecules Dissociation energy required for single, double, and triple bonds is within the range of about 1.5 – 6.2 eV, 4.4 – 7.4 eV, and 8.5 – 11.2 eV, respectively Methods of cold plasma generation Glow discharge Electric current is passed through gas mixture, between two electrodes Glow discharge is generated at low temperature and in large volume (homogeneous) under low pressure Operation parameter - applied voltage: ≥100 V and low-pressure gas: 1 – 1000 Pa Methods of cold plasma generation Dielectric barrier discharge (DBD) Plasma is generated between two electrodes separated by dielectric layer DBD is adaptable to a wide range of gases Operation parameters: It is based on DC/AC discharge; frequency range from 0.05 – 500 kHz; applied voltage: 1 – 100 kV; gas pressure: 104 – 106 Pa; distance between electrode Gliding arc discharge Composed of diverging metallic electrodes Plasma is generated with discharge gap Operation parameters: It is based on DC/AC discharge; applied voltage: 1 – 10 kV; minimum distance between electrode 2 – 3 mm Corona discharge Plasma generated is a weak luminous discharge  Operation parameters: ? Plasma jet A plasma jet consist of two concentric/coaxial electrodes that gas or mixture of gases flow between Operation parameters: The inner electrode is excited with a high voltage (100 - 250 V), at a high radio frequency (RF, 13.56 MHz) Ionization of gas particles via the acceleration of free electrons: RF + rapid collision of electrons Plasma application Direct DBD - Plasma is generated between two electrodes and samples are exposed to all elements Semi-direct DBD - Plasma is generated between two electrodes, but samples are exposed to selected elements Indirect - Plasma functionalized/activated water and in-packaged fruit Process gas and system parameters Process gases The type of gas used impacts the type of reactive species generated and the associated functional/biological activities Oxygen (O2 ) molecules generates, reactive oxygen species (ROS) Cascades into hydrogen peroxide (H2 O2 ), ozone (O3 ), superoxide anion (O2 ―), hydroperoxyl (HO2 ), alkoxyl (RO ), peroxyl (ROO ), singlet oxygen (1O2 ), Carbonate anion radical (CO3 ―), and hydroxyl radical ( OH) Hydroxyl radicals could facilitate accumulation of H2O2 and hydronium ions (H3O+) Air and/ gas rich nitrogen generates, reactive nitrogen species (RNS) plasma  Nitric oxide (NO /NOx ), nitrogen dioxide radical ( NO2 ), peroxynitrite (ONOO―), peroxynitrous acid (OONOH), and alkylperoxynitrite (ROONO) RNS and NO , including NO2 , NO3 , N2O, N2O3 , and N2O5 , comparatively more stable than ROS Increase in the input power results in increase in RNS generation and decline in O3 Process gas: A case for sustainability Plasma activated medium Nitric oxide (NO ) and other radicals ready dissolve in liquid medium, e.g., water NOx forms nitric and nitrous acid via reaction with water, decompose afterwards into nitrate and nitrite: NO + NO2 + H2O → 2HNO2 2NO2 − + 2H+ (1) 2NO2 + H2O → HNO2 + HNO3 NO2 − + NO3 − + 2H+ (2) N2O3 + H2O → 2HNO2 2NO2 − + 2H+ (3) N2O4 + H2O → HNO2 + HNO3 NO2 − + NO3 − + 2H+ (4) What role does plasma generated nitrite play in meat and meat product curing? Role of nitrite in meat production Nitrite plays a vital multifunctional role in meat and meat products curing imparting the characteristic red/pink colour to meats shift in visible spectrum of myoglobin to red is noted when treated with N2 plasma Nitrites could impact the meat red colour via action on myoglobin Nitrite reacts with myoglobin to produce nitrosomyoglobin (red in color) When heating is applied nitrosomyoglobin is converted to nitrosochemochrome (a pink component) Generation of nitrite is complemented with the production of hydrogen ions which could have significant influence on the treated solution pH Nitrite generated under alkaline conditions is found to be relatively stable Under acidic conditions nitrite is not stable it decomposes to form nitrous acid, and further broken-down into nitrate and nitrogen oxide  Nitrite concentration in plasma-treated solutions declines with the increase in treatment duration Mechanism of microbial inactivation Reactive spices – results in pore formation, diffuse into the cell membranes, alters transmembrane potential, liberate internal fluid, binds to membrane lipids leading to severe injury by reacting with macromolecules (membrane lipids, proteins, nucleic acids) UV irradiation – Intrinsic photodesorption Leading to rupture of chemical bonds, and release of volatile by-products Microbial Inactivation – ACP physically disrupts bacterial cell walls and membranes, causing cellular leakage and death Oxidative Stress – Reactive species generated by ACP induce oxidative stress in microorganisms and disrupting their metabolic processes Presence of active compounds – Induce oxidative stress in microorganisms and disrupting their metabolic processes like H2O2 , superoxide anions and hydroperoxyl radicals UV irradiation – Intrinsic photodesorption Leading to rupture of chemical bonds, and Release of volatile by-products  Plasma activated/functionalized liquid – the gas-liquid interphase as it contains a mixture with a chemical composition of O2 - , O3 , H2O2 , OH, ONOO- , NO2 - and NO3 – pH to decrease oxidation-reduction potential increase, and electrical conductivity of the liquids to increase Impact of plant or fruit tissue