Potato Processing

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Potato Processing
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
• Semi-perishable, contains approx 80% water
• Under tropical and sub-tropical conditions 40-50 % losses occur due
to poor handling and storage.
• Processing of potatoes is advantageous, because it reduce bulkiness
and increase shelf-life.
• Potatoes are processed into-
1. fried products such as wafers/chips etc.;
2. dehydrated products such as dice etc.
3. Frozen products such as French fries, patties, puffs, dice etc.
4. Canned.

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Consideration in potato processing
1. Specific gravity:
 High: chips, French fries. Due to higher yield, low uptake of fat/oil, low
mc need to be removed.
 Low: Canning. Cause firm piece is desirable.
 But!!! too high (1.106) is not suitable for French fries, chips because of
biscuit like hardness and hard chips.
 Measured by-
a) brine solution of known sp. Gravity
b) Hydrometer
c) Archimedes principle
d) Variable load hydrometer
e) Ordinary scale
2. Dry matter:
 Important because of its high yield of potato chips or wafers, and
texture of chips and reconstituted dried products.
 Measured by-
a) Oven drying but non-destructive method

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3. Sugar content
 Sugar content influences the color of the processed products.
 High glucose, fructose containing potatoes are not suitable for chips and
French fries because of the reaction between reducing sugar and amino
acid and causes discoloration
 Generally, freshly harvested mature potatoes contain acceptable level of
reducing sugar but when stored at low temperature (-5 oC) sugar content
increase.
 On the other hand, when stored at ambient temperature then sugar
content are not increased that much but sprouting and weight loss are
excessive.
3. Sugar content
 Sugar content influences the color of the processed products.
 High glucose, fructose containing potatoes are not suitable for chips and
French fries because of the reaction between reducing sugar and amino acid
and causes discoloration
 Generally, freshly harvested mature potatoes contain acceptable level of
reducing sugar but when stored at low temperature (-5 oC) sugar content
increase.
 On the other hand, when stored at ambient temperature then sugar content
are not increased that much but sprouting and weight loss are excessive.
 Evaporative cooled storage system has still similar change in sugar content
and problems with lower weight loss but still sprouting problem remained.

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3. Sugar content
 To overcome these problems potatoes are often treated with CIPC
(Isopropyl-N-chlorophenyl carbamate) and stored at low temperature.
But under this condition potatoes are unfit for processing within short
period.
 Reconditioning: cold stored potatoes are stored at 15-20 oC for 2-3 weeks
and reduction in sugar content take place.
 To overcome unacceptable color problem, chips often fried at lower
temperature but it contain 30 % more oil than normal condition.
 Discoloration due to sugar content is cope up by selection of right variety
which accumulates less sugar content.
4. Discoloration
 Problems affecting appearance and acceptability.
 Potatoes and potato products are prone to 3 types of discoloration-
a. Enzymatic discoloration: PPO enzyme acts on polyphenol content in
presence of air and oxygen.
 Exclusion of oxygen and air: inactivating enzyme with heat or lowering
the pH; treat the whole potato with SO2 gas and stored; high conc. of
CO2 also can be used.
 Potash fertilizer often used on field to overcome enzymatic discoloration
but still low dry mater content problem may occur.
 Chemicals like sulfite often use though it has health hazard problems esp.
for asthmatic patient.

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4. Discoloration
b. After cooking discoloration: Non enzymatic browning reaction take place at high
temperatures.
 It happen due to the formation of dark colored complex of ferric iron and
phenolic compound.
 Factors such as iron content, organic acid, phenolic compounds and pH is less in
immature than mature tubers.
 Darkening can be prevented if the potato in solution is acidic than normal
condition.
 Organic acid such as aspartic acid affects discoloration after cooking attributed to
pH or ability to chelate iron. The more citric acid lesser content of darkening.
 This problems with different varieties can be overcome by storing at high
temeprature or by reconditioning at 3035 oC for two weeks.
4. Discoloration
b. Discoloration of fried and dehydrated products: high sugar
content and discolored during dehydration and to turn dark during
storage.
i. Fermentation: excess quantity of sugars can be fermented to lactic
acid by Lactobacillus plantarum.
ii. Washing raw slices in water: 50% of the RS and 40% of free AA are
removed.

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5. Peeling
 Ideal peeling operation should only remove a very thin outer layer
of the potato, leaving no eyes, blemishes, or other material for
later removal by hand trimming. It should not significantly change
the physical or chemical characteristics of the remaining tissue.
 The effectiveness of peeling determine the yield of finished
product, the amount of waste, and cost of waste disposal.
5. Peeling
A. Abrasive peeler: designed to uniformly contact the surface of
tubers with abrasive discs or rollers so that, while peeling, the
losses are minimum.
 The peel fragments are flushed out by water sprays.
 Works best with uniform size of tubers.
 Suitable for chips/wafers, since other peeling processes which use
heat, give a coated layer of tissue, or a visible heat ring.

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5. Peeling
B. Lye peeling: NaOH solution is used at a high temperature, i.e. 160 oF or
lower temperature, i.e. 120-160 oF.
 Potaoes may be preheated for a short period of time in water at
temperature ranging from 140-190 oF. This minimize cooling effect and
help to maintain uniform temperature.
 Use of low temperature reduces the heat ring or cooked surface layer on
peeled potato.
 Lye peeling softens the surface of the potato and the color changes to
deep yellow due to reaction of the lye with potato constituents.
 After lye peeling, potatoes are washed to remove lye solution.
5. Peeling
C. Brine peeling: Brine solution maintained near boiling or saturation
points.
 However, evaporation of water happen continuously hence it is necessary
to prevent over saturation and crystallization.
 Immersion time: 3-10 minutes.
D. Steam peeling: High pressure steam for short time.
 Hydrates potatoes and soften surface tissue and loosen the peel. The
softened tissue removed by brushes or water sprays.
 This method leaves heat ring on outer surface which is not objectionable
for many products exception in chips/wafers.

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5. Peeling
C. Brine peeling: Brine solution maintained near boiling or saturation
points.
 However, evaporation of water happen continuously hence it is necessary
to prevent over saturation and crystallization.
 Immersion time: 3-10 minutes.
D. Steam peeling: High pressure steam for short time.
 Hydrates potatoes and soften surface tissue and loosen the peel. The
softened tissue removed by brushes or water sprays.
 This method leaves heat ring on outer surface which is not objectionable
for many products exception in chips/wafers.
The potato verities criteria for processing
1) High degree of maturity, round or oval shape, medium to large
with fleet eyes, and free from diseases.
2) Long dormancy
3) High sp. Gravity and dry matter content.
4) Low sugar content
5) Free from after cooking discoloration
6) Low peeling losses.

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Processing of potato chips/wafers
Potatoes (fully mature)
Washing
Sorting
(Removal of defective and small tubers)
Peeling (abrasive)
Trimming
(Removal of residual skin, discolored
area, green portion)
Slicing
(1/5 to 1/25 inch thick slices by rotary
slicer)
Drying
(Optional process may be done by drum
dryer)
Frying
(In continuous or batch type fryers using
refined oil)
Salting and addition of flavoring
(immediate after frying)
Cooling and inspection
Packaging and storage
• Also look for processing of French fries.

Potato Processing

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