Food Science Exam 3

food safety

practices that keep food free of hazards that make people sick or hurt them, from farm to fork

hazard classes

biological, chemical, physical

biological hazards

bacteria, viruses, parasites

chemical hazards

allergens, toxins, residues

physical hazards

glass, metal, pits

microbes

cause most illnesses

gram-positive

thick wall, stain purple (listeria, staph, lactobacillus)

gram-negative

thin wall, stains pink (salmonella, E. coli, campylobacter)

spore-formers

survive cooking (C. botulinum, B. cereus)

friends

• mold makes blue cheese

• yeast raises bread

• yeast ferments sugars to make beer

foes

• mold makes aflatoxin

• pathogens make us sick

growth curve of microbes

• lag = adjusting

• log = doubling fast

• stationary = nutrients run low

• death = waste builds up

FAT TOM

• food = moist, protein rich foods

• acidity = ph below 4.6 stops C. botulinum

• temperature = danger zone 40-140 F

• time = 2 hours max in time zone

• oxygen = some need it, some die in it

• moisture = water activity below 0.85 limits pathogens

psychophile

best below 15 C

psychrotroph

grows in the fridge (cold slows but doesn’t stop)

mesophile

most pathogens, best 30-40 C

thermophile

best 55-65 C

hypertherophile

best above 80 C, not in food

infection

live cells on food → food is eaten → cells multiply in the gut → sick in hours to days

• cooking kills cells

• salmonella, listeria, norovirus

intoxication

bacteria grows in food → toxin builds up in the food → food is eaten → sick, often within hours

• reheating may kill the cells, but leave the toxin

salmonella

eggs, poultry (survives in dry foods)

E. coli 0157:H7

ground beef, produce (kidney failure in kids)

Listeria

deli meat, soft cheese, melons (grows in fridge)

C. botulinum

home-canned foods (spores survive boiling)

campylobacter

raw poultry, top cause of bacterial diarrhea

viruses

• food carries them

• never grow in food

• norovirus and hepatitis A

parasites

• live off a host

• cooking kills them

• toxoplasma, trichinella, cyclospora (fresh produce and water)

natural chemical hazards

allergens, micro toxins

added chemical hazards

colors, preservatives

contaminants

pesticides, heavy metals

allergens

milk, egg, seafood, shellfish, tree nuts, peanuts, wheat, soybeans, sesame

how plants stop physical hazards

screens, magnets, metal detectors, x-ray (to catch plastic)

4 kitchen rules

clean, separate, cook, chill

GMPs the foundation

controls the whole plant (HASCCP targets the critical steps)

8 GMP areas

• personnel

• plant and grounds

• sanitary operations

• sanitary facilities

• equipment and utensils

• processes and controls

• warehousing

• defect action levels

HACCP 7 principles

covers biological, chemical, and physical hazards

• build the plan

  • analyze hazards

  • find the CCPs (cooking steps)

  • set critical limits (165 internal temp)

  • monitor (thermometer checks)

• keep plan working

  • corrective actions

  • verify

  • keep records (cooking temp log)

emerging challenges in food safety

• clean label (less heat and fewer preservatives)

• antibiotic resistance (fewer ways to treat infections)

• climate change (more microtoxins, wider pathogen range)

• global supply chains (harder to trace and recall)

• allergen cross-contact (shared lines and mislabeling)

• novel foods (new hazards, new rules)

spores

survive normal cooking

c. botulinum

grows in sealed, low-acid food

danger zone

4 to 60 C (40-140 F)

purpose of heating food

• inactivate pathogens and enzymes

• reduce spoilage organisms

• keep food shel stable, if sealed

conduction

• solid to solid, by direct contact

• more area or a bigger temp difference = more heat

• a thicker wall means less

• foods are mostly water, they conduct heat slowly

• Fourier’s law = heat flows from hot to cold

• aluminum conducts the most

• slow, the wall gets far more heat than the center

convection

• a moving fluid carries the heat

• moving the fluid faster raises h and speeds heating

• natural = fluid moves by itself as it warms

• forces = a fan pump or stirrer moves it

• condensing steam moves heat about 2,000 times faster

• fast, agitation makes it faster

radiation

waves, no contact needed

the cold spot in conduction heating

at the geometric center

the cold spot in convection heating

below the center, on the center axis

heating process considerations

• pH

• product state

• target microbe

• cold spot

• shelf-life goal

high acid

pH 4.6 or below (fruit, juice, pickles, tomatoes with added acid)

low acid

pH above 4.6 (vegetables, meat, fish, milk, soups)

blanching

• mildest heat

• goal - quality

• heat - brief, often 1-10 min

• does = inactivate enzymes

• how = rapid heating

• before = freezing, drying or canning

• why = stop enzymes, cut surface microbes

• does not make food shelf stable

pasteurization

• goal = safety

• heat = below 100 C

• does = kills vegetative pathogens

• reduces pathogens

• keeps most flavor and nutrients

• often needs refrigeration after, for low-acid foods

• pasteurized milk still goes in the fridge → spores and some spoilers survive

• batch LTLT = 63 C for 30 min

• continuous HTST = 72 C for 15 seconds (flash method - less nutrient and flavor damage)

sterilization

• most severe heat

• goal = safety

• heat = above 100 C

• does = destroy spores

• commercial sterilization = 121 C (reference temp)

  • stores at room temp

  • needs a hermetic seal

  • not absolute sterility

  • kills what could cause illness or spoil the food on the shelf

• canning/retorting and aseptic/UHT

canning or retorting

• package first, then heat, often solids and chunky foods

• 116-121 C for 50-90 minutes

• pressure = sealed vessels let steam pass 100 C

• media = steam, hot water or steam air

• still or agitating (agitating heats faster and keeps quality)

• the cold spot las the retort, hold time is set by the cold spot

aseptic or UHT

• heat first, then package in a sterile zone (jumpable liquids)

• 140-150 C for a few seconds, then cooled at once

• all four sterile = equipment, product, package, fill environment

• product must be plumbable

• seconds instead of an hour so flavor and color survive

why steam

• latent heat: huge energy in each gram

• condensation = releases it right on the container

• hot air = h near 5 vs. 10,000 for steam

what limits heating

• product = solid, liquid or particle (thermal properties)

• container = metal, glass or plastic = its size and shape

• loading = how containers are stacked = starting temp

• medium and setting = steam, water or steam-air (still or agitated)

three pressures on food processors

• less time and energy = long retort cycles cost energy and floor space

• better quality = consumers expect color, texture and vitamins kept

• same safety targets = the pathogen kill required does not change

novel thermal process

moves heat generation inside the product, and trade speed from tighter control

faster heating means

less quality loss if heating is even

conventional heating

heat applied at the surface

• conduction and convection carry it inwards, slow for thick, wet foods

volumetric

energy couples directly with the food and becomes heat throughout

• fast, but uneven hearting is the main risk

• volumetric methods cut times, but demand better control to avoid cold spots

lower frequency means

longer waves, which reach deeper into food

radio frequency

1-300 MHz

microwave frequency

300 MHz - 300 GHz

how microwaves heat

• dipolar rotation = water molecules flip with the field, 2.45 billion times a second (friction makes heat)

• ionic conduction = dissolved ions such as Na and Cl race back and forth and collide (dominant in salty foods)

• water and salt turn microwave energy into heat

inside a microwave oven

• magnetron = generates the microwaves

• waveguide = carries them to the cavity

• metal cavity = reflects them around the food

• turntable = moves food through hot and cold zones

• industrial = scaled up to tunnels

915 MHz

industrial use, deeper penetration → wavelength about 33 cm

2450 MHz

home ovens shallower penetration → wavelength of 12 cm

ISM

industrial, scientific, and medical

dielectric properties

control how much microwave energy it absorbs, and how fast

• dielectric constant = how well the food stores electric energy

• loss factor = how much of the energy becomes heat (sets the heating rate)

• tan = loss tangent = overall heating efficiency (higher heats faster)

• property changes:

  • moisture

  • temperature

  • salt

  • frequency

  • frozen or thawed

• water and salt raise the loss factor, so wet, sultry foods heat fastest

penetration depth

• low frequency = deeper penetration

• saltier, hotter = shallower penetration

  • cheese sauce absorbs more heat near the surface

• Lower frequency means deeper heating, large foods need RF ir 915 MHz

uneven heating

happens because corners take energy from several sides

• standing waves make hot and cold zones

• thawed water absorbs far more than ice

to fix → turntables or mode stirrers, lower power with rest time, even shapes 915 MHz for depth

• a microwave cold spot is a food safety risk

microwave advantages

• heats from within

• much shorter process times

• instant on and off control

• clean, no combustion

• selective heating, for example in drying

• combines with other methods

microwave problems

• limited depth in large items

• uneven heating

• little browning or crisping

• weak flavor, few maillard reactions

• moist, soggy surface

• product and field vary

microwave in industry

use microwaves where speed protects quality

• sterilization, MATS = sealed pouches at 121 C with 915 MHz, minutes instead of a long retort cycle

• pasteurization and drying = juices, milk, meats, microwave-vacuum drying of fruits and herbs

• tempering and thawing = frozen meats, fish and dough form about -20 to -4 C, ready to slice

radio frequency heating

• 1-300 MHz (dipolar rotation and ionic conduction)

• ISM bands (wavelength about 22, 11, and 7 m)

• trades some speed for depth and evenness

RF heating advantages

• deep penetration

• more uniform in large items

• high efficiency

• short times

• no hot surfaces

RF heating limitation

higher upfront equipment cost

RF in industry

• pest control in nuts and grains (insects heat faster)

• post-bake drying

• thawing blocks (even)

• pasteurizing packaged foods

• shines with bulky, dry or packaged products

ohmic heating

direct resistance or electroconductive heating (joule)

• food is the resistor → current flows through the food and its own resistance turns electricity into heat

• food must conduct electricity, which takes water and dissolved salts (pure fat or oil will not heat)

• no waves at all, the current itself heats the food

• suits liquids with chunks that conventional heating overcooks

ohmic vs a water bath

• more voltage = faster heating

• water bath = slows as it nears 70 C because surface heating depend son change in temp

• ohmic heating rate is set by the current, not by a temperature difference

ohmic strengths

• very rapid heating

• no hot surface to scorch food

• gentle on particles

• no moving parts, quiet

• better energy use than microwave

ohmic limits

• electrodes corrode at 50 to 60 Hz

• titanium electrodes are costly

• above 1 kHz, steel can be used

• food must conduct

• particles and liquid must conduct alike

reasons for non-thermal heating

• sensory = fresh flavor, color and texture

• nutritional = heat-sensitive vitamins kept

• functional = proteins and starches keep their behavior

compression

warms water about 3 C per 100 MPs, and pulses and sound waves add a little heat, too

goal of non-thermal heating

safe food that still tastes fresh

high pressure processing (HPP)

uses high pressure to inactivate pathogens and spoilage microbes, extending shelf life without high temp

• reaches up to 10,000 times the pressure at sea level and up to 10 times that at deepest point of the ocean

• an emerging technology that preserves with pressure instead of heat

• HPP pushes from every side at once (nothing is squeezed out of shape)

water resists compression

fresh foods are mostly water, which barely shrink under pressure

principles of HPP

• isostatic principle (physical): pressure is applied instantly and uniformly throughout the sample, whatever its size or shape

• Le Chatelier’s principle (chemical) = pressure speeds reactions that shrink volume, and suppress reactions that expand it

how high pressure is made

• direct = a piston squeezes the fluid in the vessel

• indirect = a pump forces extra fluid into the vessel

• food goes in flexible, water-tight packs, and water carries the pressure

where HPP is used

most = pasteurized, chilled products

• pasteurization = juices, milk, meat products

• sterilization = high and low acid foods, with heat

• texture change = fish, egg, proteins, starches

• functional change = cheese, yogurt, surimi, rice

• specialty = freezing, thawing, faster reactions

HPP pasteurization

• 300-600 MPa

• seconds to minutes

• low temp, under about 45-50 C

• kills vegetative pathogens and spoilage microbes

• for acid foods, pH below 4.6 or chilled storage

HP sterilization

• 600-800 MPs

• plus high temp, 90 -121 C

• can inactivate clostridium botulinum spores

• for low-acid foods, pH above 4.6

how pressure kills microbes

• higher pressure kills faster (membranes = first target)

• membrane damage = membranes break and cell contents leak out

• manage juice, below = L monocytogenes falls faster at 400 MPa than at 250 MPa

HPP and food quality

• kept = small molecules such as vitamins, amino acids, and flavor compounds are largely unaffected

• changed = proteins unfold, which lowers the activity of quality enzymes such as oxidases (protein rich foods look cooked)

• reason = high pressure only break non-covalent bonds (hydrogen, ionic, and hydrophobic)

  • covalent bonds stay intact

• big, folded molecules change (small stay the same)

what affects HPP

• process = pressure level, temp, come-up and come-down times, pulses and cycles

• product = composition (carbs, fat, protein), pH, initial temperature

• equipment = vessel size and insulation, heaters, pressure medium, carriers

• low pH and high pressure work together

• fat and sugar can protect microbes

food irradiation

a controlled dose of radiant energy makes food safer and longer-lasting

• non-ionizing = excited molecules, microwave, IR, RF

• ionizing = knocks electrons out, leaving ions and free radicals

• opposite end of spectrum

how irradiation kills microbes

• direct DNA damage = radiation strikes microbial DNA, breaking strands the cell cannot replicate

• indirect, radiolysis = water splits, the radicals attack DNA, proteins and membranes

• enzyme inactivation = key enzymes and denatures, so metabolism stops

• the source never touches the food and leaves no radioactivity

• DNA is the main target, and large cells are easier targets than viruses

approved radiation types (Codes Alimentarius)

• gamma rays

• electron beam

• x-rays

gamma rays

• source = cobalt-60

• penetration = deep, whole pallets

• speed = slow, hours

• it is a radioactive source

• main use = spices, grains, meat, produce