Different Quality Changes Seen in Canning

Quality changes in canning

2. Physical and chemical changes
◦Sensory properties
◦Nutritional properties
Changes influenced by
◦Time and temp of the process
◦Composition and properties of food
◦Canning medium

3. Flavour, Colour and Texture changes
Changes in the form of
◦Direct effects of heat on food constituents
Starch gelatinization
Protein denaturation
Cell separation
◦Heat induced reactions
Maillard reactions
◦Oxidative reactions
During processing
During storage

4. Lipid oxidation
Maillard reaction
Taints

5. SFA –stable at standard canning process
UFA –degrades –heat and oxygen –
volatile compounds
◦I –Uptake of O
2-Catalysts (metals,
heamoproteins) –Initiators (heat, light)
◦II –Hydroperoxides –Low MW compounds
(aldehydes, ketones, alcohols, acids, alkanes,
alkenes, alkynes)
Volatile compounds –rancid, stale off
odour

6. Reducing sugars and amino acids/ proteins
Increase with temp, water (30%), pH (alkaline),
phosphate-citrate buffer
Three stages
◦I –Condensation reaction –carbonyl gp. of a
reducing CHO and free amino gp. of a.a/ protein –
glycosylamines –rearrangements to Amadori
compounds -loss of protein quality but no flavours
◦II –Flavour and off-flavour compounds –Four gps.
–Nitrogen heterocyles, cyclid enolenes (flavour of
heated foods)-monocarbonyls, polycarbonyls
(suppl. flavours)
◦III-Polymerization of highly reactive products –
brown melanoidin pigments

7. Off-flavour -contamination of product with taint
Catty taint –heat dependent reaction between
natural sulfur containing compounds and
unstaurated ketones (mesityl oxide) (solvents) –
processed meat products
Cold store painted with MO
Side seam lacquer dissolved with impure solvent
Dye in rice sack printing contain MO
Hooks coated with protective oils

8. Starch gelatinization
Pectin changes
Protein denaturation

9. Vegetable cans
Dependent upon type of starch
Proportions of amylose / amylopectin and water
Amylose –opaque solution –sets to a firm gel on
cooling
Amylopectin –translucent paste –remains fluid
on cooling
Swelling of starch (cellular disruption) + starch
gelatinization
◦Softening of texture
◦Increase in palatability

10. Canned fruits and vegetables
Loss of semi permeability of cell membranes
–solubilization –breakdown of pectic
substances in cellwalls and middle lamellae
Loss of crispness and softening of product
Over processing leads to excessive softening
High temp processing –intentional firmness –
cross-linking of pectins (apples, cherries)

11. Changes in tertiary structure of proteins
Hydrogen bond rupture –random coil
configuration
Affects solubility, elasticity, fexibility
Sarcoplasmic and myofibrillar proteins –
coagulate during HP –firm texture
Collagen –more soluble –softening due to
uptake of water

12. Breakdown of natural pigments
Oxidation reactions
Maillard reactions
Interactions between product and
constituents

13. Canned vegetables
Breakdown chlorophyll –bright green to olive
green or brown
Chlorophyll –pheophytin due to loss of Mg
2+
with heat and low pH
To reduce chlorophyll degradation
◦Addition of alkaline salts to maintain pH 6.2-7.0
◦HTST processing

14. Red coloration of meat –haemoglobin and
myoglobin
Oxidation of myoglobin –
ferrihaemochromogen –cooked red meat
colour
Canning of dark fleshed fish (tuna and
mackerel)
Overheating causes green discoloration
Green discoloration -reaction of myoglobin
with hydrogen sulfide (protein denaturation)

15. Fat soluble, highly unsaturated red orange/
yellow pigments
Susceptible for oxidation and isomerization –
heat and low pH
Carotenoids complex with proteins or fatty
acids –these complex breakdown during
canning
Crustaceans –denaturation of
cartenoproteins-release carotenoid
astaxanthin –change natural blue-grey
colour to pinky red
Two isomers –cis-trans and epoxide –gives
slight lightening of colour

16. Canned red fruits -Water soluble red violet
pigments
Heat and oxygen –hydrolysis of glycosidic bonds –
loss of color –yellow or brown precipitates
Aldehydes (sugar breakdown), ascorbic acid
accelerates
Low pH gives color stability
Production of anthocyanin from
leucoanthocyanidins –red gosseberries/ dark
broad beans
Leucoanthocyanin and Leucoanthocyanidins –
metal complexes (tin, iron) –pink discoloration
(pears, peaches) –blueing (red fruits)

17. Browning of beans in tomato sauce –
melanoidins
Canned apricots –melanoidins partly
Canned mackerel and tuna –little
consequence
Canned white flesh fish –major problem

18. Betalains –water soluble –split into two
groups
Red coloured betacyanins and yellow
betaxanthins
Betanin-important pigment –beetroot-
oxidation –loss of colour

19. Water
Proteins
Carbohydrates
Dietary fibre
Lipids
Water-soluble vitamins
Fat-soluble vitamins
Minerals

20. Consume complete can content
If canning liquor discarded
◦Dilution/ Dehydration –affect relative
proportion of other constituents
◦Loss of total solids –soluble nutrients

21. Enzyme inactivation
◦Rupture of hydrogen bond and non-covalent
bonds -Protein denaturation –Heat, oxidation
and reaction with constituents
◦Decrease solubility
Loss of EAA
◦40% loss of available lysine and sulfur
containing aminoacids
Loss of digestability
Improved digestability and protein
availability
◦Denaturation of antidigestive factors

22. Conversion of cis FA to trans FA by
oxidation
Loss of essential FA activity

23. Starch gelatinization
Increased digestibility
No effect on dietary fibre

24. No change in total mineral content
Enhance bioavailability of iron
Losses resulting from leaching –
potassium prone for leaching (15-50%) –
Zn, Mn, Co
Possible increase in sodium and calcium
levels by uptake of canning liquor

25. Water soluble vitamins
◦Large losses of vitamin C (80%) and B1 (10-40%)
due to leaching and heat degradation
Vitamin C-oxidation, chemical degradation, leaching
Vitamin B1 –alkaline condition
Folic acid –oxidation and heat degradation (30%)
Pyridoxine –heat degradation and leaching (80%)
◦Increased bioavailability of biotin, riboflavin and
nicotinic acid as a result of enzyme inactivation
Fat soluble vitamins
◦Mainly heat-stable
◦Losses due to oxidation of lipids