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BY5502-40 Feb 2015 Nutrition and food processing

Covers effects of processing on macro- and micronutrients, anti-nutritional components.

Richard Marshall

on 9 February 2015

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Transcript of BY5502-40 Feb 2015 Nutrition and food processing

Nutrition & Food Processing 1
Effects of treatments on macro- and micronutrients
Effects of example processes
Advantages/disadvantages of processing
What do you think?
What is/are the overall effects of the following processes on nutritional content of food?
Home cooking?
Mass canning?
Mass freezing?
NO evidence that factory-produced food is nutritionally inferior to home cooking
Mass production
Reduces the cost of food preparation
Reduces the time for food preparation
Destruction of pathogens
Destruction of toxins (lectins, enzyme inhibitors - legumes, eggs
Increased bioavailability of niacin (cereals)
Increased biological value of proteins (legumes)
Inactivation of degradative enzymes
Benficial effects of processing
Highly refined foods containing high levels of saturated fats, simple sugars and salt, artificial colours etc, can have negative effects on health.
Losses during processing 1
Removal of unwanted parts, such as:
Skins, oil residues, whey, bones etc
Losses during processing 2
Heat labile nutrients destroyed/partly destroyed
eg Vit C > Thiamine > Riboflavin
Water soluble nutrients dissolve into cooking water
eg Vit C
Vitamin C losses from green vegetables
Vitamin C losses in frozen vegetables
Greatest effect from blanching stage
Why blanch?
To inactivate enzymic browning
To inhibit spoilage organisms, not kill
Most losses occur in blanching
Very little in freezing & storage
Up to half original Vit C lost from
Peas, sliced beans, sliced carrots etc
large surface area
Less than 30% lost from
Whole beans, sprouts etc - smaller surface area
Vitamin C losses in frozen vegetables
Losses of Thiamine (vitamin B )
Damaged/lost in wet and dry heating
Losses not as great as Vit C
Losses occur in boiling,
Baking & toasting of cereals/flours - 15 - 30 % loss
0.1 % (pH ~6) - up to 90% lost
0.04 % - up to 55 % lost
Effects of canning on nutrient content
Denatured, allergenicity reduced, free SH produced

Possible changes include
reduction of enzymic hydrolysis
acceleration of oxidative rancidity
but absence of oxygen enhances stability
So no change in canning

Degradation of starch, Maillard reaction (browning)

Water soluble vitamins
Vitamin A
stable in absence of oxygen
major losses when oxygen present
Vitamins D & E
Moderately heat stable but HEAT + oxygen cause rapid destruction
Losses of nutrients in factory milling of flour
Advantages and disadvantages of processing
Preservation of food, longer availability
Safety - destruction of pathogens, poisons

Adverse changes in colour, texture, flavour
Loss of vitamins
Changes in protein quality
Modern food processing has improved food safety
Stabilised sensory properties
Stabilised nutrient content
Extended availability
Addition of nutrients permitted to make up losses or improve value
Nutrition & Food Processing 2
Natural food toxins
Effects of processing
Origins of risk
Microbiological, chemical
Added or natural

Macronutrient imbalance
Excess sugar - diabetes
Excess fat, salt - circulatory disorders
Excess fat, sugar - CHD

Vitamin deficiencies/excesses
Scurvy (Vit C), anaemia (Iron)
Kidney stones (Vit D)
Skin colour ( carotene, Vit A)
Potential antinutrient hazards
Natural - pyrrolizidine alkaloids
(plant poisons, weed seeds) (liver toxins)
Microbiological - Salmonella, Clostridia, E. coli (infective)
Toxins - lectins, aflatoxins (microbiological),
Staph. aureus toxin
Contaminants - pesticide residues, heavy metals
Deliberate additives - colours (coal tar derivatives),
flavours, preservatives
Products of cooking - nitrosamines, amino acid pyrolysates, acrylamide
Natural Food Toxins
Glycoalkaloids ( solanin) - anticholinesterase
Glucosinolate - goitrogens
Oxalate - oxaluria, kidney damage/stones
Phenylethylamine - migraine
Red Kidney Beans
Lectin - phytohaemagglutinin
Glycyrrhizic acid - hypokalaemia, cardiac arrythmas
Apple, pear seeds, apricot stones
amygdalin - cyanogenic glycoside
Some fungi, eg death cap
amotoxins, phallotoxins - liver poisoning
furocoumarin - stomach ache, skin rashes

Risk due to consumption of toxins
Short-term poisoning
Diarrhoea, vomiting, nausea, etc
Liver damage
Kidney damage

Longer term effects
Risk due to consumption of toxins
Perceived risk Measured risk
Products of processing
Environmental contamination
Natural toxicants
Pesticide residues
Deliberate additives
Deliberate additives
Pesticide residues
Environmental contamination
Natural toxicants
Hazards associated with moulds
Aflatoxin (peanuts, Brazil nuts) - carcinogens
Palmotoxins (grapes, apples etc) - carcinogens, anticoagulants
Penicillic acid (liver-bile poisoning)
Ergot alkaloids (St Anthony's Fire) (rye and other grains) - CV system, related to LSD
The pain and deformity caused by convulsive ergotism. Detail from 17th C painting.
See: http://www.angelfire.com/wizard/kimbrough/Textbook/Ergotism_blue.htm
For more details see:
Processing & Toxic Hazards
Natural is NOT always safe
Processing may remove a hazard

Example - cooking
Red Kidney Beans - lectin
Cassava - cyanide

Preservatives make food safer
Microorganisms, oxidative changes
Red Kidney Beans
Phaseolus vulgaris

Raw beans contain high levels of toxin
Phytohaemagglutinin (lectin)
Two components
erythroagglutinin affects erythrocytes
leucoagglutinin affects leucocytes
Causes blood cells to agglutinate
Also stimulates T lymphocytes
Kidney Bean lectin
Raw beans contain 20,000 - 70,000 units
1 unit sufficient to agglutinate 1 mg rbc in 1 minute

Extreme nausea in 1 - 2 h
Severe vomiting
Possible pain
Recovery in 3 - 4 h

All groups of population susceptible
KB Lectins - details
Lectins are glycoproteins
Can be denatured by sufficient cooking
Beans must be cooked to at least 70 C
Problem may occur with slow cookers - temperature too low

Soak dry beans for at least 5 h
Pour water away
Boil in fresh water for at least 10 min.
Undercooked beans can be more toxic than raw
Canned beans - already well cooked
Processing of cassava
Manihot esculenta

Staple food for >500M people
Grown in many tropical countries
Hardy, drought-resistant, grows in low-fertility soils
Edible part is roots
Very starchy, low in protein
From: http://www.bath.ac.uk/bio-sci/cassava-project/taxonomy.html
From: http://www.peacecorps.gov/index.cfm?shell=learn.whatvol.foodsecurity.volstories
Antinutritional properties
Older varieties of cassava contain cyanogenic glucosides
Must be processed before eating to remove them
Amount varies with variety - low: 1ppm HCN, very high: 1000ppm
Processing starts with breaking cells
Endogenous enzymes and/or fermentation by lactic acid bacteria
Traditional processing of cassava
Fully-grown roots harvested
Skin peeled by hand, roots cut up
Left in small heap 3 - 5 days
Fermentation helps liberate HCN
Sun dried until brittle
Pounded in wooden pestle and mortar
Sieved to remove fibrous material
Flour used for cooking
Detoxification (1)
Main cyanogens are linmarin and lotaustralin
Breakdown catalysed by enzymes from lactic acid bacteria and plant - linamarase

Linamarin =
1-cyano-1-methylethyl- -glucopyranoside

Lotaustralin =
1-cyano-1-1methylpropyl- -glucopyranoside
Different processing methods
Fermentation & cooking
West Africa - gari, fufu, various versions
Stored wet 2 - 3 days
Allows time for bacterial fermentation by LAB
Then squeezed, dried, roasted, cooked
Removes almost all of the cyanide
Other similar processes not involving roasting/frying also detoxify the cassava

Video clip on introduction of new virus-resistant strains (Guardian.co.uk)
Planning a barbecue in the holidays?
What happens to food when we barbecue it?
Depends on type of food and whether
we over cook it or not!
Barbecuing of meats and other fatty foods can form
heterocyclic amines (HCAs) and
polyaromatic hydrocarbons (PACs)
HCAs formed from meat juices

Can affect DNA
Have been implicated in some cancers
Formed when fat starts to burn
Are components in smoke
End up coating outside of food
dibenzo[a, h]anthracene
Possible link with cancer formation
How to barbecue safely
All food, especially meat, must be properly cooked
Avoid fatty cuts of meat, burgers, sausages
Marinading before cooking can reduce formation of HCAs
Don't over-heat/over-cook
Damp flames quickly
Acrylamide in foods
Formed when high CHO, protein foods fried or baked
Formed from Maillard reaction between reducing sugars and asparagine
Acrylamide is neurotoxin, may be carcinogen
Found in crisps, fries, bread etc
Avoid eating large amounts of these
Considerable research underway to find ways of reducing its formation
Overall conclusions
Toxic hazards grouped by origin
Microbiological, processing products, contaminants, natural toxicants, deliberate additives
Thermal treatment/cold storage essential for safe food
Not all natural products are safe
Are unprocessed foods safer?
Does processing always make foods safe?
Many factors involved
Vitamins retained after processing
Full transcript