a) Optimum temperature and relative humidity
The best cold storage temperature is 0? c to 1.7?c with ? 95 percent RH is required to optimize cabbage storage life. Early round cabbage cultivars can be stored for 3-6 weeks. While late cabbage cultivars can be stored up to 6 months (Dhall, R.K.2012). For later storage cabbage can be stored at -0.5 ?c is sometimes recommended. During storage spoilage of cabbage is observed on stem or seed stalk growth (bolting), root growth, internal breakdown, discoloration, decay and black speck. Long term storage usually results in extensive trimming of heads to remove spoiled leaves.
b) Freezing injury
During storage freezing injury appears as dark translucent or water soaked areas that will deteriorate rapidly after thawing (Dhall, R.K.2012). It can occur if round cabbages are stored below -0.9?c.
c) Response of cabbage heads to ethylene during storage
Cabbages are sensitive to ethylene which causes leaf abscission and leaf yellowing (Dhall, R.K.2012). During storage is important to maintain very low ethylene levels by providing adequate ventilation.
d) Responses to controlled atmospheres (CA)
Some benefits to shelf life can be obtained with low oxygen (2.5-5 percent) and high carbon dioxide (2.5-6 percent). During storage due to controlled conditions color, flavor of cabbage heads is maintained and it also retards roots, stems growth and reduces leaf abscission.
Treatments with chemicals to extend storage life of cabbage
Cabbage is very perishable vegetable crop and it is spoiled due to various factors like microbial infections and post harvest disorders during storage. Bacterial soft rot during storage and marketing is the most serious problem in cabbage. Storage life or shelf life of cabbage can be prolonged by applying lime paste (lime in water at a ratio of 1:1) or alum paste (15 g of potassium aluminum sulphate in 100 L of water) to the stem end immediately after harvesting and sealing in polythene bags with 0.5% perforations. Storage life of the treated cabbage heads was significantly extended for 14-15 days over untreated cabbage heads 6-7 days.
POST HARVEST LOSSES OF CABBAGE HEADS DUE TO WEIGHT LOSS, DISORDERS, DISEASES AND THEIR CONTROL
During normal storage conditions cabbage head losses weight very slowly. Loss can be reduced by using proper packaging materials and keeping the temperature constant during storage. Cabbage can be marketable even its loses its weight up to 5%, if it exceeds 7% or more will be wilted and unacceptable.
1. BLACK LEAF SPECK ( also called as pepper spot and petiole spot)
This disorder is begins with the development of specks individually and distributed randomly over the leaves of cabbage head. In the beginning, (Dhall, R.K.2012) specks are small in size, further in storage they may unite and develop into spots as large as 2mm in diameter. Symptoms often seen well into the center of the head. During storage low temperature followed by warm temperature enhance the development of injury.
2. CHILLING INJURY / COLD STORAGE INJURY
It occurs in some of the varieties of cabbage during storage at 0?c for 3 months or longer. Major symptom of chilling injury is observed on midrib discoloration on outer leaves.
3. PHYSICAL INJURY
During field packing of cabbage heads, damage occurs to the midrib and causes browning and increases susceptibility to decay and often most noticeable symptoms observed on the leaf edge. In over mature heads outer midribs of cabbage head will crack easily. This injury can be reduced by leaving a few outer leaves intact to the cabbage heads.
4. YELLOWING / ETHYLENE DAMAGE
Cabbage heads stored at ambient temperature will result in a gradual loss of green chlorophyll pigment and outer leaves become yellow. Cabbage heads are very much sensitive to ethylene, which causes both leaf yellowing and leaf shedding is an inevitable symptom of senescence. During storage adequate ventilation must be provided to maintain very low ethylene levels in the holding area. In addition, cabbage heads should not stored in close proximity with fruits that emit high amounts of ethylene.
POST HARVEST DISEASES
1. WHITE MOULD /WATERY SOFT ROT caused by Sclerotinia sclerotiorum
White mould appears first as a watery light brown rot that spreads rapidly. When cabbage heads are stored in humid conditions white cottony mould growth is developed and is followed by hard black fruiting bodies (sclerotia) on heads
2. ALTERNARIA ROT / ALTERNARIA LEAF SPOT caused by Alternaia brassicola
Dark grey to black colour spots spread over the leaves. These spots are developed into sunken centre with distinct margins, more often surrounded by a yellow halo. The spot growth is favored by warm, wet and weather conditions along with spores.
3. BACTERIAL SOFT ROT caused by Erwinia carotovora
A wet slimy rot often starts at the cut base. The infected tissue becomes water soaked and disintegrates, often developed with unpleasant smell. Symptoms developed soon after harvest on storage.
4. BLACK ROT caused by Xanthomonas campestris
It appears on the outer edges of leaves with yellow to brown v-shaped areas and gradually progress inwards. This problem is developed in cabbages grown in warm and humid climates.
Trimming outer leaves, rapid cooling of cabbage head and maintaining low temperature during storage reduces the development of these rots.
a) Optimum temperature and relative humidity