Curing in horticultural crops

1. Curing of horticultural
commodities
Postharvest Physiology of Horticulture crops

2. Objectives of the session
To make aware about the process
of curing of horticultural
commodities

3. Curing
 Process of toughening and self–healing of bruises and
skinned areas
 Common in root, bulb and tuber crops
 Also practiced in citrus
Why curing ?
 Healing of wounds in tuber crops
 Minimize water loss
 Lessen the microbial attack
 Rapid closing of neck of bulb crops

4. Curing
 Wound healing process in root and tuber: development and
suberization of new epidermal tissues or wound periderm
 Drying in bulb crops: drying of neck tissues and drying out
leaves to form dry scales,
 Reduce metabolic process along with drying
 Closing necks hinders the pathogen entry
 Low moisture level slower down the microorganisms growth, if
already entered
 More darker skin in some varieties

5. Curing stage – root and tuber
Deposition of suberin in tubers or lignin in root crops or
both in carrot along the wall of cell adjacent to the
wounded cells
Suberized or lignified layers act as temporary barrier to
water loss and microbial infection
 Sweet/potato – cells in a layer just below the suberized
layer lose their starch and vacuoles leads to cork cambium
formation in layers
Form the cork cells outsides after development of such 6-8
layers
New parenchyma cells are formed inside along the layers

6. Curing stage – root and tuber
The dead surface cells are pushed out after corky cell
formation
The corky cells becomes the new skin or wound periderm
Subsequent lignification of new cells occurs and the
process completes
The process takes 7-15 in potato and 3-12 in sweet potato
The exact day varies and need to verify
Generally 7-14 is recommended

7. Curing stage – onion and garlic
Neck and outer scales start drying internally
Outer scales become crips
Neck bends and flatten and completely dries up
Curing completes after losing 12-14% moisture from the
scales
Total weight loss after curing is about 3-5%
Onion: take care of sun scalding
Garlic and shallot: Spread under sun for 4-6 days

8. Curing stage – Citrus
Citrus has capacity to lignify after minor wounds
Curing lignify the cells with minor injuries
Lemon: inhibit the decline of Citral (antifungal compound)

9. Bulbs curing methods
1. Solar drying or sun drying
Don’t directly expose with intense sunlight
Direct exposure results sun-scalding (discoloration of the
exposed parts)
Bulbs need to arranged in rows with the leavers of the crop
in one row protecting the bulbs in the next row
Can also be cured after packing in jute and net sacs
Packed sacs can be left in field 5-10 days till outer skin and
neck tissues are properly dried

10. Bulbs curing methods
2. Air or cold curing
Common in onion
Root and top trimmed bulbs are kept on ambient
conditions at 25-30DC for 3 day or longer
Bamboo, wood and steel racks is used for large quantity
Fan can be used for small quantity
3. Forced heated-air curing
Uses special dryer to cure shortly in 48-60 hrs
Has high significance in rainy season production
Slatted floor and circulating fan is necessary
Generally maintained 37 to 40DC
Bulb crops requires 60-70% RH; 65% for good coloration

11. Citrus curing
Allowing citrus fruit to dry out for some time, results
superficial wounds healing by lignification
Mandarin: Mandarin cured at 30DC for 3-5 days before
storage showed reduce puffiness
Pumelo: Pumelo are stored for 1-2 wk in ambient condition
for curing

12. Root and tuber crops curing
Root and tuber crops like yam, taro are cured
Stalked or heaped and covered by canvas, woven grass
mats or straw or dried grasses for covering
Covering help confine self-generated heat and moisture
Left for 4-5 days

13. Factor affecting curing
1. Temperature
Normally higher temperature for curing than growing
Wound healing is faster at higher temperature, but very
high is deleterious
Effect of temp on wound healing process of potato
Temperature DC No of days
For suberin formation For periderm formation
25 1 2
15 2 3
10 3 6
5 5-8 10
2 7-8 Not formed

14. Factor affecting curing
Optimum temp, RH and duration for curing
Crop Temp DC RH (%) Duration
Onion 35-38 60-70 48-60 hr
Potato 12-15 80-95 10-14 day
Sweet potato 33 95-97 4-7 day
Yam 29-32 90-95 4 day
Taro 34-36 95-100 3-5 day

15. Factor affecting curing
2. Relative humidity
80-95% RH is optimum for wound healing
Very lower RH leads to drying up outer cells and forming a
crust
In >95% RH, too many cells are formed on surface of the
wound and, which leads delaying the curing process

16. Factor affecting curing
3. Gases
CO2 level >10% and O2 level <5% inhibit wound healing in
root/tuber crops, because of
respiration slow down
As a development process, need synthesis of DNA and
protein
4. Type of damage
Smooth cuts heals faster
If possible, rugged should be cut smoothly

17. Factor affecting curing
5. Length of period after harvest
Faster rate of healing at immediately after harvest
Gradually decreasing during storage due to fast pace of
metabolic processes
Wounds incurred after storage heals less quickly

18. Any question?

19. Thank you for
your
cooperation