Non-Thermal Food Processing Quiz

Non-Thermal Processing

• Food preservation methods that do not involve heating
• Aims to preserve food quality and natural freshness while inactivating microorganisms
• Alternative to conventional thermal processing methods, which can lead to loss of colour, flavour and functionality

Topics Covered

• Fundamental concepts
• High-pressure processing techniques (HPP)
• Pulsed electric field (PEF) technology
• Pulse light
• Irradiation
• Ozone and cold plasma technology
• Hurdle technology

Introduction

• Food can be preserved via thermal or non-thermal processes
• Thermal processes (heating/cooking) affect food quality and inactivate microorganisms
• Conventional thermal processing methods lead to undesirable changes in food
• Alternative minimal processing strategies (non-thermal) avoid these issues
• Minimally processed foods retain better nutrient retention, higher quality and "fresh-like" characteristics

Novel Technologies

• Advantages:
  • Retention of nutritional and sensory attributes
  • Desired textures
  • Improved functional properties
• Categorization:
  • Electrotechnologies (PEF, radio frequency heating, ohmic heating)
  • Non-thermal technologies (HPP, membrane filtration, pulse light, dense phase carbon dioxide)

High-Pressure Processing (HPP)

• A non-thermal food preservation method based on Pascal's law
• Also known as hyperbaric pressure processing, ultra-high pressure processing, high hydrostatic pressure processing, pascalization
• Retains food quality and natural freshness, extends shelf life
• Capital intensive
• Process steps: product loading, vessel pre-filling, pressurizing, product unloading

Pascal's Law

• When external pressure is applied at a point in a fluid contained in a vessel, it is transmitted undiminished and equally in all directions.
• West Virginia Agricultural Experimental Station chemist investigated the law's potential for food preservation

Features of HPP in Food

• Sterilization
• Tissue destruction
• Allergen extraction
• Control of enzyme function
• Maintaining original flavor and taste
• Safety and high nutritious value

High-Pressure Processing-Food Industry

• Applications: jams, jellies, fish, meat products, sliced ham, salad dressings, rice cakes, juices, yogurt, guacamole, oysters (commercially available in the US)

High Pressure Range

• Pressures used range from 100 to 900 MPa
• Processes typically involve 3-4 minutes to build up pressure and a 5+ minute holding time
• At pressures of 4000-9000 atm, enzymes and bacteria are inactivated, but taste and flavor remain unchanged

Main Components of HPP

• Pressure vessel and its closure
• Pressure generation system
• Temperature control device
• Material handling system

Pressure Generation in HPP (Types)

• Direct Compression
• Indirect Compression
• Heating of the pressure medium
• High Pressure Generation

Isostatic Pressing System

• Cold isostatic pressing system
• Warm isostatic pressing system
• Hot isostatic pressing system

Modes of Operation of HPP

• Batch processing mode
• Semi-continuous mode
• Continuous mode

Schematic Flow Diagram of HPP

• Package food
• Load into HPP chamber
• Fill chamber with water
• Pressurize the chamber
• Hold under pressure
• Depressurize the chamber
• Remove processed food

Effect of HPP on Microorganisms

• Due to changes in the microbial cell

First Order Kinetics

• Mathematical equation relating the process rate to the time taken
• Constants Z and Ea are determined by the experimental data

Weibull Distribution Model

• Equation for modeling the reliability of a product over time.
• α and β are mathematical properties of the process

Pulse Electric Field (PEF)

• A non-thermal method of food preservation that uses short pulses of electricity for microbial inactivation
• High-intensity PEF involves applying high-voltage pulses (20-80 kV/cm)
• Food is placed between two electrodes
• Treatment time is short, typically milliseconds to microseconds
• Minimize energy loss due to heating in the food

Application of PEF for products

• Fruit juices
• Apple sauce
• Milk
• Liquid egg products
• Yogurt drink
• Tomato juice
• Liquid whole egg

Components of PEF

• High-voltage power source (converts low voltage to high voltage DC)
• Capacitor bank (energy storage)
• Treatment chamber (holds food during processing and has electrodes to generate the electric field)
• Electrical switch (discharges energy from capacitor)
• Oscilloscope (observes pulse waveform)

Pulse Electric Field - Working Principle

• Electroporation is the key concept
• Generating temporary or permanent pores on the cell membrane
• Dielectric breakdown theory
• Electroporation increases cell membrane permeability

Main Electrical Parameters of PEF Treatment

• Processing time: calculated as t = nτ, where τ is pulse duration and n is number of pulses
• Average electric field strength: calculated as E = V/d, where V is voltage across food sample and d is distance between electrodes

Main Electrical Parameters of PEF Treatment (Capacity)

• Energy stored (W) = (1/2)CU² where C is capacitance and U is voltage
• Monopolar decaying pulse: The voltage increases rapidly to a set point (Vo) and slows down with time according to the equation V(t)= Vo e-t/τ
• Time constant (τ)= RC where R is resistance and C is total capacitance

Factors Affecting the Outcome of Pulse Electric Field

• Biological factors
• Technological factors
• Media factors

Function of PEF

• Inactivation of microorganisms, enzymes, spores, and vegetative cells

Inactivation of Microorganisms (PEF process)

• Pore initiation through electric field
• Water influx
• Swelling
• Membrane rupture
• Cell lysis

Difference between PEF and Thermal Processing

• PEF: Maintains color, flavor, and aroma of food; can kill all microbes and spores
• Thermal: Loses color, flavor, and aroma; may not kill all spores

Pulse Light Technology

• A non-thermal method of food preservation that uses intense and short duration pulses of broad-spectrum white light
• Sterilizes microbial populations on packaging materials, equipment, and foods
• Reduces the need for chemical disinfectants and preservatives
• Inactivates select resistant microorganisms with the full spectrum, and others with a filtered spectrum
• Flashes typically applied at 1 to 20 flashes per second; duration from 1 µs to 0.1 s

Design of Pulse Light System

• High-voltage power supply
• Storage capacitor
• Pulse-forming network
• Gas discharge flash lamp
• Trigger signal

Technical Terms (Pulse Light)

• Fluence rate: Energy received per unit area per second
• Fluence/dose: Energy received per unit area during treatment
• Pulse width: Time interval of energy delivery
• Exposure time: Period during which treatment is applied
• Peak power: Pulse energy divided by pulse duration
• Pulse repetition rate: Number of pulses per second

Theory of Pulse Light

• Light penetrates materials according to the equation I = (1-R)I₀e⁻ˣ
• I is energy intensity, R is reflection coefficient, I₀ is incident intensity, and x is extinction coefficient

Theory of Pulse Light (Heat)

• Heat dissipated per unit area (E_d) = (1 – R)I₀(1 – e⁻^d)
• Heat transferred by conduction (Ex) = AkdT/dx*t

Factors Affecting Inactivation of Microorganisms (Pulse Light)

• Types of microorganisms
• Interaction between light and substrate
• Distance from the light source

Application of Pulse Light in Food Industry

• Kills bacteria and spores
• Used for transparent and coloured food materials (refraction)
• Used for sterilization of utensils, packaging, and surfaces; for decontamination of fruits and vegetables
• Used in hurdle treatments, for inactivation of microorganisms on fluid foods

Food Irradiation

• Irradiating food with high-energy ionizing radiation (like gamma rays, x-rays, or electrons) to preserve, sterilize, or eliminate pests, spoilage, or disease organisms
• Used to preserve food, reduce foodborne illness, delay or prevent sprouting/ripening

Food Irradiation-Advantages

• One process for multiple uses
• Extended shelf life (of some food products)
• Reduced risk of disease (in certain conditions)
• Removal of pests/parasites in products

Sources of Radiation Used in Food Irradiation

• Gamma rays from radioactive cobalt-60 or cesium-137
• X-rays from electron beams
• Electron beams from electron accelerators directed into the food item.

How Does Irradiation Work

• Destroys/deactivates microorganisms/microorganisms by damaging/creating instability in the DNA molecules.
• Higher doses (e.g., with frozen foods) are required to eradicate microbes
• Effectiveness varies depending on the microorganism's sensitivity to irradiation

How Foods are Irradiated

• Specific processes and handling methods to ensure consistent and controlled irradiation.
• Typically includes loading, radiation, and unloading steps.

Dose and Dose Rate

• Measures of the energy deposited in the product during irradiation, which serve as metrics to control microbial processes.
• Different terms (radicidation, ruidization, radapperization) represent different classifications/energy values
• Ranges of doses/radiation are given based on the type of organism and the level of desired sterilization

Effects of Irradiation on Microorganisms (Indirect Effect)

• Radiations produce free radicals that react with molecules
• Cause damage to cell components and cell membranes, leading to microbial death

Effects of Irradiation on Microorganisms (Direct Effect)

• Radiation directly damages biomolecules
• Disrupts chemical bonds
• Interferes with cell metabolism and division

Factors Affecting Efficiency of Radiation

• Food temperature
• Moisture content
• Oxygen presence

Effect of Food Irradiation on Food Quality

• Food molecule compositions can change
• Radiolysis occurs (chemical breakdown of molecules due to radiation)
• Changes in food molecules are noticeable at high doses
• Sterilization levels can result in nutrient loss

Ozone in Food Processing

• Ozone (O₃) is a potent antimicrobial agent
• Useful for deodorizing air and water, replacing chlorination in some circumstances.
• Effectively kills viruses, bacteria, fungi, and parasites within food.

Concepts of Generating Ozone

• Ozone is generated through electrical discharge, which turns oxygen (O₂) into ozone (O₃)

Ozone Used in Food Industry

• Primarily used in sauce production, dairy processes, juice production, and handling fresh, produce-like, fruit and spices
• Applications also exist for water bottling plants and breweries

Case Study-Research Findings (Ozone)

• Studies (e.g., Hapmson & Fiori, 1997) have indicated ozone's effectiveness
• Ozone can be a powerful germicide in certain applications. Values of ozone concentrations are indicated, in addition to treatment times, which are often used to determine the effect of ozone on treated foods

Bactericidal Effect of Ozone

• Oxygen atoms from ozone attach to bacteria to produce a chain reaction that results in bacteria death
• Ozone is highly reactive and oxidizes various components of the cell

Equipment - Ozone

• Some example systems are provided (e.g. ozone-based produce sanitizer, ozone-based shellog sanitizer)

Ozone as a Novel Technology for CIP Systems

• Eliminates the need for traditional chemical disinfectants
• Reduces total disinfection time; High oxidation potential
• Enables reuse of disinfection volumes (in some cases)

Effective CIP System

• Typical CIP cycle stages with traditional and improved (Ozone Based) cleaning and disinfection stages

Conclusion: Ozone

• Wide acceptability in food processing today
• Effective biocide
• Requires moderate contact times for efficiency compared to other methods

What is Plasma

• A mixture of positive and negative charges and neutral particles, existing over a wide range of temperatures and densities.
• Can be important in food preservation for non-thermal procedures

Cold Plasma Technology

• A novel food processing technology
• Utilizes energetic and reactive gases to inactivate contaminating microbes in food items

Generation of Plasma

• Processes create plasma for use in food processing
• Typical equipment systems to create ionization procedures are shown

Plasma Classification

• Classified based on temperature, mode, and pressure considerations

Cold Plasma

• A type of plasma with minimal thermal motion of ions
• Eliminates the need for pressure or magnetic forces
• Temperature is relatively close to room temperature in operation

Areas of Cold Plasma Technology Used in Food

• Decontamination of products with external microbes is prevalent.
• Applicable to surfaces of cut vegetables or meat, although alternative mild surface decontamination techniques exist.
• Can disinfect surfaces before/during packaging procedures.

Case Study on Raw Chicken

• Dricks et al. (2012) research shows efficacy of cold plasma in reducing Campylobacter and Salmonella populations on raw chicken.
• Significant reduction of bacteria observed

Case Study on Eggs

• Ragni et al. (2010) indicates reduction in levels of Salmonella in eggs.

Limitations of Cold Plasma Technology

• Technology is immature
• Optimization for higher-scale treatments and commercial viability is still under development
• High capital costs

Hurdle Technology

• A food preservation method that combines several approaches to prevent microorganism survival/growth and proliferation
• Microorganisms have to overcome multiple barriers to survive in food product

Important Hurdles in Food

• High/low temperature
• Acidity
• Redox potential
• Preservatives
• Aseptic packaging

Principles of Hurdle Technology

• Disrupts homeostasis of microorganisms
• Preventing microbes from overcoming the hurdles
• Causes microbes to become inactive or die

Comparison of Different Novel Technologies

• Summary table comparing different non-thermal food processing technologies. Covers treatment name, nature of treatment, effective microorganisms, treatment parameters, and treatment range.

Test your knowledge on non-thermal food processing methods and their advantages. This quiz covers flavor alterations and various techniques used in the industry. Match processing methods with their descriptions to deepen your understanding.