Processing of Horticultural Crops (1+2)

Factors affecting Sterilization

Factors effecting sterilization

• Altitude: As boiling point of the water decreases with the increase in altitude, the processing time for a particular product standardized at sea level should be increased with the increase in altitude.
• For every increase of 152 meters above mean sea level (a.m.s.l.) in altitude, the boiling point of water decrease by about 1oC and normal processing time has to be increased by about two minutes.
• Similarly, as the altitude above mean sea level increases, the pressure required to maintain the specified processing temperature also increases.
• It is necessary to maintain higher gauge pressure if processing is carried out at altitude greater than 305 meter a.m.s.l. (1000 ft a.m.s.l.).

• pH: Inherent pH value of the food commodity greatly influence the processing schedule to achieve required destruction of micro-organisms. The lower the pH, the greater is the ease with which a product can be processed or sterilized. On the basis of pH, the foods are classified into following four distinct classes:

i) Low acid foods (pH = 5.0): The low acid foods is the class of foods which require greater care in its preservation as they are subjected to spoilage by thermophilic and mesophilic putrefactive anaerobes including Clostridium botulinum. These foods include most of the vegetables like peas, beans, corn, asparagus, mushroom and corn etc. They are necessarily required to be processed above 110^oC temperature and under steam pressure.

ii) Medium acid foods (pH 5.0-4.5): Medium acid foods like meat and vegetable mixtures, spaghetti, soups and sauces also need processing above 110^oC under steam pressure. They are subjected to spoilage by thermophilic and mesophilic anaerobes. They also include thermophilic anaerobes not producing hydrogen sulphide but causing flat sours.

iii) Acidic foods (pH 4.5-3.7): Most of the fruits including peas, fig, pineapple, nectarines, mango, apple, tomato, subject to spoilage by non spore forming aciduric, butyric anaerobe like Clostridium pasteurinum and thermophilic anaerobe are classified as acidic foods. They can be processed in boiling water at temperature of 100^oC.

iv) Highly acidic foods (pH = 3.7): Highly acidic foods like Sauerkraut, berries, citrus juices, grapefruit, rhubarb and pickles are included in this group. As the bacterial spores do not germinate and grow at pH values below 4.5 and do not harm the product even if they are not destroyed in canned fruits. A canned product having pH value of less than 4.5, can be processed in boiling water at 100^oC, but a product with a pH value above 4.5 requires processing at 115-121^oC under pressure of 0.7 to 1.05 kg cm-2(10-15 pounds inch-2).

15. Cooling: Immediately after processing, the sealed cans are rapidly cooled to approximately 35-40^oC to stop the cooking process and to prevent stack burning. Prolonged heating results in an inferior and uneven product, like peaches and pears become dark in colour, tomatoes turn brownish and become bitter in taste while peas becomes mushy with a cooked taste. Cooling is done by immersing or passing hot cans in cold water tanks, by spraying cans with jet of cold water, by passing cold water in to a pressure cooker or exposing cans to air. Water used for cooling should be non corrosive, low in bacterial and yeast count and chlorinated with 2 ppm of available chlorine.

16. Storage: After cooling, the cans are stacked to allow the outer surface to dry, as even a small traces of moisture are likely to induce rusting. The cans are then labelled either manually or by using labeling machine and packed in wooden or corrugated cartons. They should be stored in cool and dry place (below 30⁰C). Adequately processed cans usually ensure an acceptable product quality up to at least one year. Storage of cans at higher temperatures should be avoided to prevent the risk of thermophilic growth and spoilage.

Bottling of fruits and vegetables
Bottles have proved to be very good containers for home preservation of fruits. Although their initial cost is high, they can be used several times and last for many years if carefully handled. The fruits look attractive through the glass and do not develop metallic flavour. Bottling does not need a sealing machine but is not suitable from the manufacturer’s point of view as the initial capital required is high. There are many types of glass containers of different shapes and sizes and with various types of hermetic seals. Jars fitted with wire clamps are considered to be the best. The products remain in a very hygienic condition and do not come into contact with rubber or metal.

Glass containers: Glass containers are chemically inert, clear, transparent, rigid, resist internal pressure, heat resistant and are cheap in comparison to other packaging materials. Glass containers are the excellent barriers to solid, liquids and gases. They preserve food against odor and flavour contaminations. But when faulty closures are used odour and flavour contamination may occur, hence; the closure should be air tight. Glass does not deteriorate with age in comparison to other packaging material but are light in weight and are fragile (breakable) with thermal shock and impact.

Types of glass containers

1. Bottles: The bottles have narrow neck and small closure over the top. Narrow neck facilitates pouring and reduces the size of closure. Bottles are used for packing liquids and small sized solids.
2. Jars: They do not have any appreciable neck but are wide mouthed bottles. They are easy to clean and easy to take out product from them. They are used for packing jams and powders.
3. Tumblers: They are similar to jars but do not have any neck and no finish. They can be used for packing jams and jellies.
4. Jugs: These are large sized bottles with carrying handlers. Used for packing liquids, foods in large quantities like ½ gallon or more.
5. Vials: These are small glass containers. Vials used for packing pharmaceuticals while ampoules are used for packing small quantity like spices, food colors, aroma, essences etc.

Properties of glass containers
1. Glass containers are chemically inert: Almost all types of chemicals can be packed in the glass containers except hydrofluoric acid (it eats the glass hence packed in plastic container). Oils and fats have no reaction with the glass. Water has little or negligible reaction with the glass at low temperature. The products like drugs and transfusion liquids are packed in specially treated glass containers as at higher temperature (during sterilization) the hydrogen from the water is displaced.

2. Clarity of glass containers: Products packed in glass containers are easily visualized from outside especially useful for the products kept on the shelves. But some nutrients are packed in colored bottles e.g. brown bottles, amber colored bottles. Opal glass is a ground glass, in which visibility is lost. Gin or opal glass is also used in bathrooms.

3. Glass containers are rigid containers

• Rigidity helps in filling of containers and
• Make it possible for stacking
• It also helps in loading and vacuum filling of containers. It also provides support to the material.

4. Glass containers resist the internal pressure: Glass containers offers resistant against internal pressure brought about by CO₂ or other gases in the product e.g. beer, beverages, soft drinks etc.

5. Heat resistant: Glass containers are heat resistant in comparison to other packaging material except cans. A temperature of 1500⁰C is applied during manufacturing of glass. Melting point of alumina is 2000⁰C, which is used for making glass. Viscous hot materials are poured into glass containers while they are still hot.

Disadvantages of glass

• Glass containers are fragile/brittle, hence great care is required to be exercised during handling.
• Glass containers are heavy in weight.
• Glass containers are not easy to dispose.

Closures: Closures should prevent loss of contents and must make reseal (crown corks do not make reseal). Closure should not react with the product e.g. in ketchup, formation of black neck takes place. Different types of closures are Crown corks, roll on cap, lug cap, vacuum seal, temper proof, snap fit, press on caps and screw caps.

Procedure for bottling

• The bottles are thoroughly washed and sterilized.
• The fruit slices are filled leaving about 3 cm space at the top of the jar or bottle.
• The sugar syrup recommended for different fruits is filled boiling hot leaving a head space of 1-1.5 cm.
• Exhausting and sterilization: Separate exhausting of bottles is not required and it is done simultaneously with sterilization by putting a pad of cloth (false bottom) under the bottles.
• The bottles should not be abruptly immersed in hot water, otherwise they may break because of sudden rise in temperature. The temperature of the water should be about the same as that of the contents and should be raised gradually and the bottles kept in the boiling water for the required time.
• At the start of sterilization the lids are left loose and the level of boiling water should come up to the neck of the bottle.
• When sterilization is over, the mouths of bottles and jars should be immediately closed or corked tightly.
• Cooling of bottles is done and the bottles are labeled after drying. The products preserved in bottles require more attractive labels.
• Store in cool and dry place.

Thus, canning and bottling is a well tested acceptable method of preservation of fruit and vegetable for conversion into stable products. For canning no chemical preservative is used. Shelf-life of adequately processed product in cans is around one year. Keeping in view the versatility of the process, canning and bottling of fruit and vegetable can be adopted as a successful enterprise.