Postharvest

Northern technical university\  Mosul

Technical Agricultural college                              Mosul                                 Subject :     Postharvest Physiology           

By\ Dr. Mohammad Alhadeedy

Second year students\ 2015—2016

Introduction:

Horticultural crops not only provide us with nutritional and healthy foods, but also generate a cash income to growers. Appropriate production practices, careful harvesting and proper packaging, storage and transport all contribute to the good produce quality.. Moreover, they are biologically active and carry out transpiration, respiration, ripening and other biochemical activities, which deteriorate the quality of the produce.

Proper post-harvest Processing and handling is an important part of modern agricultural production. Post-harvest processes include the integrated functions of harvesting, cleaning, grading, cooling, storing, packaging, transporting and marketing.

   Definition: post harvest physiology: include all the operations and processes applied on fruits and vegetables in the field such ripening, picking transporting, storage, marketing and consumption.

1. Fruit definition: a product of fertilization in a seed plant that consists of the ripened ovary of a flower with its included seeds; Apples, cucumbers, nuts, and blueberries are all

Horticultural maturity It is a developmental stage of the fruit on the tree, which will result in a satisfactory product after harvest. Physiological maturity It refers to the stage in the development of the fruits and vegetables when maximum growth and maturation has occurred. It is usually associated with full ripening in the fruits. The Physiological mature stage is followed by senescence. Commercial maturity: It is the state of plant organ required by a market. It commonly bears little relation to Physiological maturity and may occur at any stage during development stage. Harvest Maturity:

When the fruit develop acceptable flavor or appearance and having adequate shelf life. It may be defined in terms of Physiological maturity and horticultural maturity condition .

Ripening:  various  chemical changes occurيحدث inside the fruit which lead to make the fruit edible or suitable for consumption.

Senescence: It means biological aging  or the gradual deterioration of the fruit. The word “senescence” can refer to either  cellular senescence or  senescence of the whole organism.

HARVESTING: The goals of harvesting are to collect a commodity سلعة أي الثمار from the field at the proper level of maturity with a minimum of damage and loss, there are two ways of harvesting they are: 1. Hand Harvesting; Hand harvesting has a number of advantages over machine harvest. People can choose the fruit quality. This is particularly important for crops that have a wide range of maturity and need to be harvested several times during the season. Properly trained workers can pick and handle the product with a minimum of damage. Many fresh-fruit products have a short shelf life if they are bruised or damaged during harvest and handling.

2. Mechanical Harvesting: Mechanical harvest is currently used for fresh-market crops such as root crops, tubers, or rhizomes and  nut crops. The main advantage of mechanical harvest  is that machines can often harvest at high rates. Tree nut harvesters, for example attaching  a shaking mechanism to the tree and remove most of the nuts in few seconds. The nuts are either caught on a fabric- covered frame or picked up from the ground by other machines.. Disadvantages of Mechanical Harvesting: 1- Machines are rarely capable of selection.

2- Mechanical harvesting will not be feasible غير مجدية  because the techniques are modified to allow one time harvest.

 

POST HARVEST HANDLING:   Fruits are living organs, so they continue to respire even after harvesting when they have a limited source of food reserves. In addition to degradation of respiratory substrates, a number of changes in taste, color, flavor, texture and appearance takes place in the harvested commodities سلعة which make them unacceptable for consumption if these are not handled properly. Post harvest technology starts immediately after the harvest of fruits and vegetables through the following treatments: 1. Pre cooling: Pre cooling (immediate cooling after harvest) is important for most fruits and vegetables because they may deteriorate تفسد later. In addition to removal of field heat from the fruits. There are many methods of pre cooling such as:

1-cold air (room cooling).

2- forced air cooling

3-cold water (hydrocooling), التبريد المائي direct contact with ice (contact icing),

4- evaporation of water from the produce (evaporative cooling, vacuum cooling تفريغ الهواء) and combination of vacuum and hydrocooling  (hydrovac. cooling) التبريد المائي والفراغي سوية.

Some chemicals (nutrients/growth regulators/ fungicides) can also be mixed with the water used in hydrocooling .  

2-   Washing, Cleaning and Trimming:الغسل التنظيف وقطع الاجزاءالخضرية Before fresh fruits and vegetables are marketed various amounts of cleaning are necessary which involves the removal of soil dust, insects and spray residues. Chlorine in fresh water is often used as disinfectant to wash the fruits. Some fungicides like Diphenylamine (0.1 – 0.25%) or ethoxyquin (0.2 – 0.5%) may be used as post harvest dip تغمر to control the disorders لمعالجة الاضرار.  Many vegetable need trimming قطع, means( cutting and removal of  leaves or other vegetative parts). 3. Sorting, Grading and Sizing: Sorting is done by hand to remove unsuitable fruits for market or storage due to damage by insects, diseases or mechanical injuries. The remainder crop product is separated or sorted into two or more grades on the basis of the surface color, shape or visible defects العيوب الظاهرة . For e.g, in an apple packing house in India 3 grades are sorted:

1. Extra Fancy,فوق الممتازة

2-Fancy ممتازة

3-standard قياسي

packed for marketing

4- The fourth “culls” grade البقايا الصغيرة والمشوهة culls” (fruit that is not suitable to sell for eating due to cosmetic defects) is removed and sold for juice or other industrial uses. للتصنيع.

After sorting and grading, sizing is done either by hand or machine. Machine  sizers work on two basic principles:

a- weight         b- diameter.

4. Curing: التجفيف الوقائي Curing is an effective operation to reduce the water loss during storage from hardy vegetables like onions, garlic, potatoes and other tropical root vegetables. The curing of root and tuber crops develops a periderm over the cut, or broken or skinned surfaces for wound repair and healing.. For the curing of potatoes, onions and garlic , the bulbs are left in the field after harvesting under shade ظل for few days until the outer skins and roots are fully dried. 5. Waxing: Wax coating applied to the surface of fruit .Waxing generally reduces the respiration and transpiration rates, but other chemicals such as fungicides, growth regulators, can also be incorporated specially for reducing microbial spoilage, sprout inhibition etc. The advantages of wax application are: 1- Improved appearances of fruit. 2- Reduce moisture losses and retards wilting and shriveling تكرمش during storage of fruits. 3- Less spoilage specially due to chilling injury and browning. 4- Creates a diffusion barrier as it reduces the availability of 02 to the tissues thereby reducing respiration rate. 5-  Protects fruits from micro-biological infection.

   6- Wax coating are used as carriers for sprout inhibitors, Waxes cause a change in flavor due to inhibition of O2 and CO2 exchange thus, resulting in anaerobic respiration and elevated ethanol and acetaldehyde contents. Paraffin wax, Carnauba wax, Bee wax, Shellac, Wood resins and Polyethylene waxes used commercially. 6. Packaging: Proper or scientific packaging of fresh fruits and vegetables reduces the wastage of the produce by protecting them from mechanical damage, dirt, moisture loss and other undesirable physiological changes and pathological deterioration during the course of storage, transportation and subsequent marketing. a variety of containers are used such as wooden boxes, baskets woven from bamboo or twigs, sack/jute bags and corrugated مموج fiber board (CFB) boxes. 7.  Storage: A number of storage techniques (ground storage, refrigerated storage, air cooled storage, zero energy storage, modified atmospheric storage, and controlled atmosphere storage CA storage) are being used for fruits and vegetables depending upon the nature of the commodity and the storage period intended.

Pressure tester to measure fruit firmness

Signs or indexes of fruit ripening:

Many changes occur in fruits during development and ripening which give one or more sings of ripening such as:

1- Fruit firmness: measured by pressure tester, by scraping a circular area on both sides of the fruit and push the plunger into the flesh and read the pressure on the scale in kg.\ cm² .

2- Days from full bloom: for a specific variety.

3- Change of background color of skin. The color is compared with a constant color chart.

4- Total soluble solids: measured by refractometer for

5- Fruit size : measured by metal rings at different diameters.

6. Fruit acidity: which decrease by conversion to sugars.

7- Fruit shape:

8- Starch concentration: tested with iodine solution, to give a blue color which is proportional with starch concentration.

9- Seed color: change to brown color at ripening.

10- Ease of fruit drop: it happens because of ethylene production which form abscission layer between the petiole and the branch.

11-Oil percentage% as in olives and avocado.

12- Juice percentage%

13- Sugar\ acid ratio.

14. Fruit odor and flavor: which increase with ripening.

15.Flesh color.

16. Ethylene production: which is proportional with the increase respiration.
17. Respiration rate: proportional with ripening.

18- Specific fruit density.

19. Ease of seed separation from flesh.
20. Weight of dry matter: increase with the advance of ripening.

                      Fruit picking قطف الثمار

Fruit picking should be carried out at the proper stage of growth when they reach ripening or stage of suitable consumption such as apricots, apples , bananas, pears and peaches. Steps must be taken before picking to avoid problems as the following steps:

1. Preparation of picking tools and containers such as bags and baskets.
2. prepare ladders.
3. == = Bulk bins and boxes in the orchard.
4. === of packing houses.

5.=== of cooled stores and marketing places.

6 ===   trained workers to avoid fruit bruising كدمات or fruit injuries أضرار أو جروح or breaking tree branches and spurs.

Should know the following:

a- Type and variety of the fruit.

1. purpose of fruit usage.
2. Labor cost.

4.Yield quantity.

There are two main methods for fruit picking, they are:

1. Hand picking: or selective picking, this operation could be done several times to pick the ripe fruits every time . It is done by hand by twist the fruit and pull, or using a secateurs or knife for banana bunches

The following precautions aught  be considered when and after picking:

1. Pick in the morning because the temperature is low and the fruits water content is higher.
2. Do not leave the produce for long time in the orchard.
3. put the bulk bins containing the fruits in a shaded place.
4. Treat the fruits easily in a smooth way as they are living materials. The English saying says (treat apples as eggs).
5. Clipping the nails of the workers.
6. Pick the lower fruits of the tree first and move up after.
7. Wear gloves when picking.
8. Do not bruise or injure the fruits or throwing on the ground.
9. Handle the fruits with care.
10. Mechanical picking: Special machines or harvesters are used for different crops, which shake the tree or the branches. or use an air current to separate the fruits from the tree and collecting in special containers to avoid injuries.

Hitting the fruits with sticks or using hooks to pull fruits and using ladders or cranes.

Disadvantages of Mechanical harvesting:

1. Impossible to do selective picking.
2. Mechanically picked fruits are only used for industry.
3. Leaving some fruits on the tree.
4. Breaking the branches and bruising the fruits.
5. Difficult to separate the fruits from the falling leaves and branches.

For vegetable harvesting its different and some machines are especially designed . Harvesting is done in the morning or evening to avoid high temperatures.

Picking baskets: Are made of plastic or straw at certain sizes lined with sponge or fabric with plastic fingers on the internal wall to reduce the fruit injuries when they dropped or fall down in the basket.

Biological changes and deterioration of fruits after harvest:

There are two types of changes occur in harvested fruits, these are:

1. Natural changes: weight loss occur in the fruits because of the water evaporation and organic losses due to respiration such as sugars. Changes in fruit appearance occur such as the shape, dryness shriveling and hard skin , so they become not suitable for marketing.
2. Physiological disorder; Due to enzyme activities . Lack of oxygen O₂ causes anaerobic respiration which result in some physiological diseases such as black heart in potatoes and brown heart and sogginess in apples.
3. Other diseases and infections especially fungal diseases.

Fruits are divided into three groups according to their susceptibility for infection, these are:

1. Quick perishable fruits: such as grapes strawberries, tomatoes, peaches, apricots, and plums. Fruits shelf life is few days.
2. 2. Slow deteriorating fruits: such as apples, pears and citrus fruits, which could be stored for weeks or months.
3. Deterioration resisting fruits : example nut fruits which may stay for months or years.

 packing house: is a facility where fruit is received and processed prior to distribution to market.

Bulk fruit such as apples, oranges, pears, is delivered to the plant via trucks or wagons, into receiving bins and sorted for quality and size.

Packinghouse operations can be as simple as moving produce from a field into a shipping container, or may include a variety of handling practices, from cleaning, waxing, sizing, and quality grading to color sorting

Functions of the packing house:

1. receive the fruits coming from the field.
2. quick fruit cooling to remove the field heat.
3. Fruit washing, cleaning and drying.

4.Treatment with sterilizing chemicals .

5. Fruit sorting and grading.
6. Fruit packaging.
7. Applying artificial ripening for some fruits like bananas, kaki and tomatoes.
8. Degreening of citrus fruits.
9. Waxing of fruits.
10. labelling to identify its source and date of arrival.
11. checking for quantity or weight delivered.
12. sampling for quality, if necessary.

Vital heat:  result from respiration of fruits . You can feel the heat when you put your hand in a pile of cut grass.

Climacteric is a stage of fruit ripening associated with increased ethylene production and  rise in cellular respiration  Apples, bananas, melons, apricots, tomatoes , figs, pears , peaches, mango. Climacteric is the final physiological process that marks the end of fruit maturation with increase in sugar content with decrease in acidity and the beginning of fruit senescence.. After the climacteric period, respiration rates (noted by carbon dioxide production). The climacteric event also leads to other changes in the fruit including pigment changes and sugar release. For those fruits raised as food the climacteric event marks the peak of edible ripeness, with fruits having the best taste. Examples of climacteric fruits: apples, apricots, avocado, bananas, mangos, papayas, peaches, pears, plums, and tomatoes.

Diagram 1 showing stages of fruit growth.

Non climacteric fruits:

Fruits which cannot ripe after harvest because they cannot release ethylene or produce low quantity not enough for ripening. Citrus, grapes, strawberries are non-climacteric (they ripen without ethylene and respiration bursts). However, there are non-climacteric melons and apricots, and grapes and strawberries harbor several ethylene receptors which are active. Examples of non climacteric fruits strawberries, pineapple, oranges, grape fruit, lemon and cherries.  fruits: cucumber, melons.

Fruit growth and development:

In botany, a fruit is the seed-bearing structure in angiosperms formed from the ovary after flowerinug.A fruit passes different stages of growth during development:

1.cell division:  During early growth, the fertilized embryo and endosperm develop and seeds start to form.

2. cell enlargement: as well as tissue differentiation and fruit enlargement During the first 1–4 weeks, flesh volume increases rapidly and embryo volume remains small. Growth at this time is mainly the result of cell division. In many commercial fruit (e.g. apple, kiwifruit, tomato and peach), cell division may cease a few weeks after anthesis, and fruit growth slows down, reflected as an inflection in the growth curve, and signaling an end to the first sigmoid phase.
3. maturation stage: cell division stops and the fruit reach their full size.
4. Fruit ripening: associated with increase in sugar content and improve in taste and color.
5. Fruit senescence or aging: which mean the beginning of fruit deterioration and eventually the end of life.

Note: why do the fruit turn brown?

This occur because the cut area of the fruit is exposed to air and the polyphenol  oxidaze react with oxygen and cause oxidation with brown color. This phenomenon is noticed in potatoes, apples and other fruits.Citrus juice or cold water is applied on the wounded areas to overcome browning.

                     Respiration :

is the process by which plants take in oxygen and give out carbon dioxide. Oxygen from the air breaks down carbohydrates in the plant into carbon dioxide and water. This reaction produces energy in the form of heat as in the following equation:

Respiration, continue both in the field and after harvest the leaves continue to make carbohydrates, and cannot be stopped without damage to the growing plant or harvested produce. O₂ form 20% of the air and when it is lowered to 2% fermentation will start which causes unpleasant flavors in produce and promotes premature ageing. While CO₂ percentage in air is 0.03%

Fermentation is the production of ethanol. It occurs when yeast breaks down sugars in the absence of oxygen. Fermentation is used to make alcoholic drinks, such as beer and wine. Carbon dioxide gas is also produced during fermentation:

glucose (sugar) → ethanol (alcohol) + carbon dioxide

Fermentation is an example of anaerobic respiration in yeast.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ +Energy 24 k.calorie

Fresh produce cannot replace تعوض carbohydrates or water after harvest. Respiration uses stored starch or sugar and will stop when reserves of these are exhausted   تنفذthe ageing follows and the produce dies and decays.

Harvested fruits and vegetables of different plants have different rates of respiration; some respire at a faster rate (and thus are more perishable أكثر عرضة للتلف), while some respire at a relatively slow rate (less perishable  أقل تعرضا للتلف) In addition, storage conditions affect respiration, with higher temperatures leading to a faster rate of respiration; for every 10°C (18°F) rise in temperature, the respiration rate will double or even triple.

Respiratory Quotient RQ: Is the volume of CO₂ evolved from respiration divided by the volume of   O₂ used.

The result of this division is an absolute number which mean without unit. The value differ according to the type of the substrate used in respiration. As in the following examples:

Carbohydrates CHO: = 1

For Oils & fats RQ  = 0.71 Less than 1 because the fat molecule contain high number of C atoms and less O₂ atoms , thus this will need more oxygen atoms to complete oxidation. Example Tripalmitine acid when used in respiration:

C₅₁ H₉₈ O₆  + 72.5O_{2 ——————-} 51CO₂ + 49 H₂ O +759 kcal.

RQ = 51 CO₂/ 72.5O₂ =0.7

Proteins = 0.79

C₆ H₁₂ O₆ +6O₂————–6CO₂ + 6H₂ O + 686 Kcal

From the equation we can notice the value of RQ for CHO is:

6CO₂/ 6O₂ =1 RQ

While in case of anaerobic respiration the energy released will be much Lesser , as in the following equation:

C₆ H₁₂ O₆———-2C₂ H₅ OH + 2CO₂ + Energy 24 K.cal.                  

The cells use sugars as a substrate for respiration and when it is finished they start to use fats and oils and at last they start to use proteins as a substrate.

When organic acids are used in respiration such as  malic acid apple acid which cause the sour taste in fruits  with its formula C₄ H₆ O₅ is used as a substrate the RQ will be more than 1. Because it contain less oxygen atoms and release more CO_{2 :}

COOH.CH₂ CHOH.COOH + 3O₂ ———- 4CO₂ + 3H₂ O+ 320kcal. Thus :

RQ = 4CO₂/ 3O₂ = 1.33

Factors affecting respiration:

1. 1. Temperature: biological activities are promoted by enzymes. The enzyme activities increase with the increase of temperature, so when the temperature raises up by 10 degrees centigrade within the range between 0—35 C⁰ , this will duplicate the rate of respiration by 2- 2.5 and this is called Temperature coefficient. If the temperature exceeds 45C⁰ this will cause damage of the protoplasm.
2. Oxygen concentration: The O₂ concentration in fresh air is 20% , when it is lowered down to 5% the respiration rate will decrease, and when it reach 2% anaerobic respiration will occur which is not desired in fruit stores
3. CO₂ concentration: When the concentration of CO2 increase to 1-5% it will decrease the rate of respiration ,and may have a bad effect on fruits such as bad flavor failure to ripe and internal breakdown.
4. Substrate: Increase in sugar content will increase the respiration rate . When potatoes are stored in cold conditions this will increase the change of starch to sugar.
5. Water content in the fruit tissues: Decrease in water content will raise the rate of respiration and change of starch to soluble sugar. That’s why seeds have a long shelf life because they have a low water content.
6. Mineral salts: If the plant tissues are exposed to ions of mineral salt , the rate of respiration will increase and it is called Salt respiration.
7. Ethylene: Increases the rate of respiration.

 Ethylene : The Ripening Gas or Ripening Hormone:

Definition:  a colorless flammable gaseous unsaturated hydrocarbon C₂H₄ that is found in coal gas, can be produced by pyrolysis الانحلال الحراري of petroleum hydrocarbons, is used in medicine as a general inhalation anesthetic, and occurs in plants functioning especially as a natural growth regulator that promotes the ripening of fruit—called also ethene

It is naturally occurring, but it can also occur as a result of wood combustion  الاحتراقand other processes. You can’t see or smell it. Some fruit produce ethylene as ripening begins such as Apples and pears.

Ethylene is responsible for:

1. The changes in texture, softening, color, and other processes involved in ripening. Fruits such as cherries and blueberries do not produce much ethylene and it doesn’t influence their ripening.
2. Cause aging in plantsand cause plants to die. It can be produced when plants are injured, either mechanically or by disease.
3. 3. Cause fruit ripening, loss of chlorophyll, stem shortening, abscission of plant parts like flowers, leaves fruit drop.
4. 4. Cause epinasty تدلي أو انحناء (bending of stems).
5. 5. Cause yellowing of vegetables, bud damage in dormant nursery stock,

Responsiveness الاستجابة to ethylene depend on the following  factors:

1. The type of crop.
2. 2. The stage of plant development.
3. 3. The temperature.
4. The concentration of ethylene gas.
5. 5. The duration of exposure.

Ethylene gas is used commercially to ripen tomatoes, bananas, pears, and a few other fruits. Ethylene can be explosive if it reaches high concentrations, so it has to be used cautiously. Several commercial liquid products release ethylene like (ethephon, trade name الاسم التجاري Ethrel). These are only used preharvest. There are few ways ways to produce ethylene:

1) Gas from a cylinder.

2) Catalytic generator.

3) Ethephon .

4. 4. Other sources of ethylene include ripening fruit,
5. 5. Exhaust العادم أي الكزوز from internal combustion engines/heaters, smoke الدخان (including cigarettes), welding مكائن اللحيم, rotting vegetation النباتات المتعفنة, natural gas leaks تسرب الغاز الطبيعي,

Factors affecting the production of ethylene gas:  

1. temperature: Raise of temperature increase the ethylene production, such as the temperature of apples when reach 18 C⁰.
2. Oxygen: increase of O₂ concentration increases ethylene production.
3. CO₂ : The increase in CO₂ concentration decrease ethylene production.
4. 4. Mechanical injuries: increases ethylene production.

Transpiration of Fruits and Vegetables:

 

Definition: Transpiration is the process by which fresh fruits and vegetables loose moisture. This process includes the transport of moisture through the skin of the fruits, it is difficult to bring back this water again to the fruit. This water loss cause many changes in the fruit  such as shriveling, wilting, shape, size and color and weight loss which decrease the marketing value of the fruits. For example lettuce water content is 95% , when loosing 5-7% water they wilt. While apples contain 84%  water and by loosing  5-7% water they become unacceptable for the consumer.

Definition:

Relative humidity (RH):  is the amount of moisture in the air compared to what the air can “hold” at that temperature. When the air can’t “hold” all the moisture, then it condenses as dew.

The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapor density.

The most common units for vapor density are gm/m³. For example, if the actual vapor density is 10 g/m³ at 20°C compared to the saturation vapor density at that temperature of 17.3 g/m³ , then the relative humidity is

Relative humidity is normally expressed as a percentage; a higher percentage means that the air-water mixture is more humid.

Factors affecting the water loss of harvested fruits:

 

1. Harvest time: fruits picked before maturation loose more water ,while ripe ones loose less because the skin growth is completed and the wax material cover the skin, preventing or decreasing evaporation.
2. When the Relative humidity in the air is low the transpiration will increase, while when the R.H is high around the fruits water loss will be low.
3. Surface area: for example one kilogram of lettuce loose more water than on kg. of onions, because the surface area of lettuce is bigger.
4. Cuticle : thickness of the skin and presence of cuticle layer wax form a barrier of water loss from the fruit.
5. Stomataare minute aperture structures on plants found typically on the outer leaf skin layer, also known as the epidermis. They consist of two specialized cells, called guard cells that surround a tiny pore called a stoma.( stoma means mouth in greek). 90% of the water loss is through stomata which is affected by turger  pressure of the guard cells.Wilting cause stomata closure.
6. ALenticel: is a porous tissue consisting of cells with large intercellular spaces in theperiderm and the bark of woody stems and roots of dicotyledonous flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark. The name lenticel,  derived from its lenticular (lens-like) shape. Water is lost also from scars and cracks of the fruit.

7.Epidermis : In potato tubers the presence of the periderm decrease the water loss, while the unncomplete  or cracked periderm increase the water loss.

8. Fuzzes: presence of fuzzes decrease the water loss, they work as wind breaks againt wind around the stoata and lenticels . Example peach fruit.

Ways or methods of decreasing transpiration from fruits:

1. Store fruits at low temperature and high relative humidity to decrease water pressure, which depend on the type of fruit. For example apples are stored at 1-4 C⁰ , while bananas are stored at 12 C^O.
2. Apply precooling after picking the fruits, to remove the field heat and decrease water loss.
3. Waxing fruits will close the pores and decrease water loss, such as apples, cucumbers and tomatoes.
4. Packing in polyethylene bags: to lowerdown waterloss.

            Artificial ripening of fruits:

 

Ripening: is a process in fruits that causes them to become more palatable. In general, a fruit becomes sweeter, less green, and softer as it ripens.

ARtificial ripening could be achieved by using hydrocarbon gases, or by controlling temperature and relative humidity around the fruits, or using growth regulators. This operation activates the biological activities of the fruit such as:

1- increasing the ethylene concentration which enhance ripening.

2- Disappearance of chlorophyll pigment and appearance of the normal color of the variety.

3- Overcome the tannin substances which give the astringent taste.

4- Improvement of taste , flavor and odor.

Goals of artificial ripening:

1. Production of fruits early in the season.
2. Availability of the fruit in the market for longer time during the year.
3. 3. Decrease the number of pickings, as the vast majority is being harvested once mechanically and ripened according to the market needs.
4. Improving the eating characteristics of the fruits by removing tannins, acidity, color, taste and odor as in kaki, mango and banana.

Methods of artificial ripening:

 

There are several old and modern methods for fruit ripening such as the following ways:

1. Chemical treatments: المعاملة بالمواد الكيميائية example treatment of kaki fruits with alcohol or vinegar at low concentrations, and treatment of dates with salt solution or benzoic acid, oxalic acid or sodium acetate. But these treatments causes a bad taste in the fruits and decrease their shelf life.
2. Covering method: طريقة الكمر أو التغطية it is an old method by covering the bananas, pears, tomatoes and mangos hay or flour or نخالة to keep the vital heat which promote ripening.
3. By burning coal and kerosene: in closed rooms to raise the temperature and releasing ethylene gas used so often for bananas.

4 . Using controlled rooms: under 20-25C⁰ and 85-95% relative humidity at different periods of treatment according to the type of fruit. The temperature increase the respiration rate which will release more ethylene.

5. Using acetylene gas C₂ H₂ in closed rooms because it is poisonous for humans and highly combustible. Ethylene will be released. Used for banana and tomato ripening.
6. Using ethylene gas: It is a poisonous gas, combustible and explosive. So certain safety precaution must be taken to avoid poisoning or burning. It is available compressed in cylinders, The room should be well ventilated with temperature of 18-20 C⁰ and R.H. of 85-95%. Fans must be available in the room for even distribution of the gas. The gas concentration depend on the type of the fruit: for example 1000 ppm. جزء بالمليون (part per million) is used for ripening of Bananas, pears, kaki, dates, mango, avocado. While 500-1000 ppm. Is used for orange, Lemon, tomatoes and melons.
7. Ethephon usage: the commercial name is Ethrel : it is available as a solution it is used as a spray on the fruits while they are on the fruits  when they are mature green at 250-2000 ppm. Also could be used in the room after harvest especially on tomatoes.

Ethephon is used for degreening أزالة اللون الاخضر of citrus fruits by dipping the fruits in a 1000 ppm. Solution for 3 seconds.  Also for bananas by soaking in 2500  ppm.  Solution. Also used on green melons by spraying one week before harvest at 1000 ppm. The fruits will ripe in the same time. Spraying fig trees with 250-500 ppm. Will ripen the fruits by 2-3 weeks earlier.

Cold storage:ألخزن المبرد

Why cool as soon as possible after harvest?

Horticultural crops are living organisms after harvest and must remain alive and healthy until they are processed or consumed (Kader, 2002). The energy needed to stay alive comes from food reserves in the produce through a process called respiration. Heat energy is released during respiration. However, the rate of release depends on the type of produce, maturity, injuries and internal temperature.

Definition of refrigeration: Is the absorption of heat from material or body have a higher temperature than the surrounding environment, or the removal of heat from a hot material.There are several ways of cooling:

1. Room cooling:

Room cooling is a method used for sensitive commodity to moisture. Because this type of cooling is slow, room cooling is only appropriate for very small amounts of produce  which do not deteriorate rapidly. Cold air is circulated within the room and around the produce by the refrigeration fan/s. This is a slow method of pre-cooling because the cold air does not circulate readily through the produce especially the packaged produce.

2. Forced-air cooling:

Forced air cooling is used mainly for bulk produce and palletized الثمار المعبأة في عبوات ومرتب بشكل مجاميع في المخزن produce. It is the most versatile متعدد الجوانب and widely used of all cooling methods. In forced air cooling, chilled air is forced to flow around each piece of produce. This close contact of chilled air with the produce results in rapid, even cooling throughout the mass of produce.

The air can be channeled to flow either horizontally or vertically

 

3. Hydro-cooling:

In hydrocooling, cold water is used to pre-cool produce. Produce may be immersed in a tank of circulating cold water or as in other techniques, cold water is sprinkled or sprayed over the produce. The equipment used for hydrocooling is often equipped with a water chiller جهاز لتبريد الماء. This method of pre-cooling is faster than forced air cooling because water is in direct contact with the produce has a higher heat removal capacity than air. If ice is available, it can be used to chill the water. However, not all types of produce can be hydrocooled. Strawberries and cauliflower, for example, should not be cooled by this method because it results in rapid spoilage of the produce. Hydro-cooling requires particular attention to water quality and sanitation. Chemicals may be used to kill molds and bacteria in the water and on the produce.

4. Ice cooling:

In ice cooling, crushed or fine granular ice is used to cool the produce. The ice is either packed around the produce in cartons or sacks, or it is made into a slurry خليط من الماء والثلج المجروش with water and injected into waxed cartons packed with produce. The ice then fills the voids الفراغات around the produce. Ice cooling is faster than hydrocooling because it is in contact with the produce, and ice has a higher heat removal capacity than water. It takes 144 BTUs of energy to melt 1 pound ( 1 pound= 454 gram) of ice (A BTU is the amount of heat required to raise the temperature of 1  pound of liquid water by 1 degree Fahrenheit at a constant pressure of one atmosphere). 

. This amount will theoretically lower the temperature of 4 pounds of produce by at least 36 degrees Fahrenheit. 5. vacuum cooling:

In vacuum cooling, containers of produce are put in a vacuum chamber حجرة. Air is drawn يسحب out of the chamber creating a high vacuum يخلق فراغا كبيرا. Under the high vacuum, the boiling temperature of water is highly lowered. For example, water at the freezing point boils when the pressure is reduced to 0.08859 psi ( pound/ squared inch)  absolute مطلق. Normal atmospheric pressure is about 14 psi absolute. As a result, a small Vacuum cooling is the fastest and most uniform method of pre-cooling because of the high amount of heat required for evaporating the water (about 1000 BTUs per pound of water evaporated). It is, however, one of the most expensive systems to set up.

Methods of fruits and vegetables storage:

There are many old and modern ways for storage, these are:

1. Storage on trees: by leaving the fruit on the trees after ripening, such as oranges and grape fruit for few months, also apples and pears for few weeks.
2. Storage in the field: examples the storage of potatoes, garlic, sweet potatoes and onions in the soil. But it may destroy the crop because of the increase in temperature. Tomatoes and oranges are stored sometimes in hay for days or weeks.
3. Storage in aerated rooms: fruits are stored in shade away of sunlight because light will cause damage to fruits , due to increase in respiration rate. Examples: apple, pear, bananas, pomegranates, and lemon. This method is not suitable for hot regions.
4. Storage under refrigeration or cold storage: Fruits are stored under low temperatures between zero degree C⁰ – 12C⁰ according to the type of fruit, with high relative humidity. This is a good kind of storage because it has some advantages:
5. It decrease the rate of respiration.
6. Elongate the shelf life of the fruit.
7. Decrease the infection with fungi and bacteria.
8. Also delay deterioration and senescence.
9. Lower down the all the physiological activities of fruits.
10. Decrease the evaporation and transpiration of fruits.
11. Inhibit fruit sprouting of dormant buds such as potatoes, garlic and onions during storage.
12. prevent greening in potatoes which occur due to exposure to light as the poisonous solanine ( glycoalkaloid poison) pigment is formed.

Some disadvantages of cold storage that it cause chilling injuries or physiological disorders to fruits: like brown heart or brown core in apples and potatoes.

 Controlled atmosphere storage:CA Storage:

 Definition:  A controlled atmosphere is an agricultural storage method. An atmosphere in which oxygen, carbon dioxide and nitrogen concentrations as well as temperature and humidity are regulated.

or  Controlled atmosphere storage is a system for holding produce in an atmosphere that differs substantially تختلف جوهريا from normal air in respect to CO2 and O2 levels. Two major classes of commodity can be stored in controlled atmosphere:

1.Dry commodities: such as grains, legumes and oilseed. In these commodities the primary aim of the atmosphere is usually to control insect pests. Most insects cannot  exist indefinitely الى أمد غير محدد without oxygen or in conditions of raised  carbon dioxide. and lower temperatures (less than 15 °C).

2. Fresh fruits: most commonly apples and pears, where the combination of altered atmospheric conditions and reduced temperature allow prolonged لفترة طويلة storage with only a slow loss of quality.

Long-term storage of vegetables and fruit actually involves inhibiting the ripening and ageing processes, thus retaining ابقاء flavor and quality الطعم والنوعية. Ripening is, in fact, postponed  يؤخر. This occurs as a result of modifying the gas conditions in the store and the cool cell so that the respiration of fruit and vegetables is reduced. Controlled Atmosphere (CA) is a storage technique whereby the level of oxygen is reduced and CO2 is increased. Quality and the freshness of fruits and vegetables are retained under Controlled Atmosphere conditions without the use of any chemicals. Under CA conditions, many products can be stored for 2 to 4 times longer than usual فترة أطول من الاعتيادي.

IMPORTANCE OF CONTROLLED ATMOSPHERE:

CA storage has been the subject of an enormous هائل number of biochemical, physiological and  technological studies, The actual effects of varying the levels لتغيير نسب of O 2 and CO2 in the atmosphere which affect crops varies with the following factors as:

1. a. The species of crop.نوع المحصول
2. b. The cultivars of crop.صنف الحاصل
3. c. The concentration of the gases in the store. تركيز الغاز في المخزن
4. d. The crop temperature. درجة حرارة المحصول
5. e. The state of maturity of the crop at harvest. حالة اكتمال نمو الثمار
6. f. The degree of ripeness of the climacteric fruit. درجة اكتمال نمو الثمار الكلايمكتيرية
7. g. The growing conditions before harvest. ظروف النمو قبل الحصاد
8. h. The presence of ethylene in the store ,وجود الاثلين في المخزن

Advantages of CA storage:

  can be summarized تلخص as follows:

1. 1. A considerable decrease in respiration rate, and transpiration with extension of both pre-climacteric and post-climacteric periods
2. 2. A reduction of ethylene effect on metabolism due to the interaction of O2 with ethylene, with a delay of senescence symptoms.
3. 3. An extension in storage life, which can be doubled.
4. 4. The preservation of an excellent firmness of flesh, due to effect of CO2 concentration on the enzymes acting on cellular membranes.
5. A high turgidity امتلاء الخلايا بالماء is achieved, such that fruits are more juicy and crisp طرية.
6. A smaller loss of acidity, sugars and vitamin C, so that the nutritional quality is higher.
7. A limited degradation of chlorophyll, with a higher stability of color.
8. 8. Some physiological alterations, such as chilling injuries, spot, التبقع decay, التحلل browning, الاسمرار water core القلب المائي and scald ضربة تصيب ثمار التفاحيات في المخزن are prevented, or greatly limited

9.Inhibition or retardation of growth of microorganisms such as moulds فطريات and bacteria and yeasts, which can be reduced, in particular under low O₂, high CO₂ atmospheres.

10. 10. A longer shelf life in the post storage.

 

NOTE: Selection of the most suitable atmosphere الجو المناسب للخزن depends on  يعتمد على :

1. Cultivars.الاصناف
2. Stage of maturity.مرحلة النمو
3. Environmental and cultivation parameters. المعايير البيئية والزراعية

No one atmosphere is best for all produce, specific recommendations and cautionsمحاذير  must be determined  اتخاذها for each crop over the range of storage temperature and periods.

 

FRUITS AND VEGETABLES STORAGE UNDER CA:

The storability of fruits and vegetables is strictly related to their respiration rate, which is an

Expression تعبير of metabolic activity عن النشاطات الحيوية. Aerobic respiration requires O2, and results in CO2 and heat

release. More than 95% of the energy released is lost as heat. The temperature decrease leads to a reduction in respiration rate,

and therefore to an increase in storage life in fruits with climacteric respiration.

Historical background of CA stores:

The first refrigerated store by ice were established for apple storage in 1900 A.C. in Illinois in America by Benjamin. While the first mechanical refrigeration store started in Boston 1881.

Types of gases used in refrigeration:

1. Fluorocarbons such as: Freon, 11,12 , 21, 22, 113, 114. The most common gases used are freon 12 and 22. Is the most safe gas. ألاكثر أمانا الغاز
2. Ammonia. It is poisonous and flammable. سام وقابل للأشتعال
3. Methyl chloride. Is poisonous and flammable. = = =  =
4. Sulphur dioxide SO₂ ثاني أوكسيد الكبريت Is corrosive, يسبب تآكل المعادن poisonous سامwith pungent لاذع odor.

Characteristics of suitable refrigerant:

1. Should have a low degree of evaporation and condensation.
2. Should have a high latent heat حرارة كامنة, which means the ability to absorb large quantity of heat during evaporation تبخر.
3. Easy to be transformed تحول to liquid state الحالة السائلة.
4. Have a high density. ذو كثافة عالية
5. Should not be corrosive.
6. Non combustible غير قابل للأشتعال and have no pungent odor.
7. Must be cheap رخيص الثمن and available متوفر in the market.
8. Should Not mix لا يمتزج with water or humidity.
9. Should be not poisonous to humans. أن يكون غير سام للأنسان

Refrigeration Equipment:

The machine consist of the following parts:

1. Evaporator: consist of metal coils made of copper where the gas is transformed from the liquid to the gaseous state. It is placed in the storage room to absorb the heat from the produce.
2. Condenser: This apparatus is located outside the store to get rid of the heat absorbed by the cooling gas by changing the gas into liquid again.
3. Compressor: found out of the store. Its function is compressing the gas and complete the cycle.

 

Store insulation: the stores should be insulated with a variety of insulators to prevent loss or leakage of heat and coldness. Such materials may be incorporated in the walls , ceiling and floor of the storage room. These materials include metal linings, or sponge or polystyrene or wood or plastic or cork or fiberglass صوف زجاجي or rock wool صوف صحري.

Refrigerating Unit: وحدةالتبريد

Is measured by calories for example one kilo refrigeration or kilo cooling equal to 79.9 calorie and a Ton  refrigeration equal to 1000 × 79.9 = 79900 calorie.

Fruits are divided into two groups according to their need to storage temperature these are:

1. Fruits stored at low temperatures: close to zero C⁰ such as also apples, pears, grape and pomegranates.
2. 2. Fruits stored at intermediate temperature : this include tropical and subtropical fruits. Examples: cucumber, aubergenes, tomatoes, Peppers, melons, citrus fruits, bananas and olives.

 Physiological disorders of fruit in cold storage:

 

1. Bitter pits: البقع المرة on the fruit skin in apples, with brown color.
2. Cork spots: البقع الفلينية they appear in the orchard when the fruits are still on the trees.
3. Internal breakdown: الانحلال الداخلي the flesh become spongy.

4.Brown core: القلب البني caused by cold storage.

5. Fruit freezing: انجماد الثمار
6. Core breakdown: انحلال المركز mostly happens with pear fruits as a brown color in the center.
7. Loss of ripening capacity: عدم القدرة على النضج it happens with some pear varieties أصناف example comice variety as a result of cold storage.

Pathogenic diseases in stores:

1. Blue mold: العفن الازرق
2. Bulls eye rot: عفن عين الثور
3. Gray mold: العفن الرمادي
4. Bitter rot:ألعفن المر
5. Brown rot : cause brown to deep brown spots. ألعفن البني
6. Rhizopus rot : عفن الخبز

7.Cladosporium rot. cause brown to black color.عفن الكلادوسبوريوم

8. Black mold rot: ألعفن الاسود Infect figs causing dark and yellow spots in the flesh.
9. Souring in figs: مرض تحمض الثمار
10. Alternaria in grapes : عفن الالترناريا في العنب
11. Brown staining in citrus fruits:ألبقع ألبنية في الحمضيات
12. Blue and green mold rots in citrus fruits:
13. Oil spotting in citrus: ألتبقع الزيتي في الحمضيات لون البقع خضراء أو سمراء أو صفراء.

        Finished by the support of Allah the almighty