|Post Harvest Technology :: Frequently Asked Questions|
1. What is Food Preservation?
When the availability of food is more than the present use it is preserved for future consumption. Preservation helps the food to be available in off-season and in any place. Delay in the use of fresh food alters its freshness, it palatability and its nutritive value hence such food is preserved and used for long time. Many foods cannot be preserved as such and needs some type of treatment.
2. What are the reasons of Food Spoilage?
3. What are the methods for Food Preservation?
4. What are the principles of Food Preservation ?
Principles for F&V Food Preservation
5. What is heat processing?
The temperature and time used in heat processing a food will depend upon what effect heat has on the food and what other preservative methods are to be employed.
6. What is Pasteurisation?
Pasteurisation is a heat treatment that kills part but not all the microorganisms present and usually involves the application of temperatures below 100 . The heating may be by means of steam, hot water, dry heat or electric currents and the products are cooled promptly after the heat treatment.
7. What is Canning?
Canning involves the application of temperatures (to food) that are high enough to destroy all microorganisms present in sterilized containers to prevent re-contamination and to preserve the food.
8. What is preservation by use of Preservatives?
Preservatives are defined as "chemical agents, which serve to retard, hinder or mask undesirable change in food". These changes may be caused by microorganisms, by the enzymes of food, or by purely chemical reactions The preservatives generally used in fruit and vegetable products are benzoic acid and sulphur dioxide, which is generally used in the form of sulphites. The preservatives permitted in fruit and vegetable products in India are sodium benzoate, sulphites and sorbic acid.
9. What is preservation by Dehydration?
The word dehydration usually complies the use of controlled conditions of heating, with the forced circulation of air or artificial drying as compared with the use of sun drying. Drying as a means of preservation can be observed in cereal grains, legumes and nuts.
10. What are the methods of fruit & vegetable drying?
The methods of fruit and vegetable drying are Sun drying, Drying by mechanical driers, osmotic dehydration, Spray drying, Foam mat drying, Freeze drying.
11. What is Sun drying?
Sun drying is an old and traditional method of drying. It is limited to climates with a hot sun and a dry atmosphere and to certain fruits such as raisins, prunes figs, apricots, pears and peaches. It is a slow process. Vegetables like french beans, curd chilli are preserved by this method.
12. What are the fruit & vegetable products made using drying?
Fruit bars, raisins, dehydrated products from fruits like fig, pomegranate and vegetables like onion, carrot, cauliflower, okra, mushrooms etc.
13. What is Osmotic dehydration?
The moisture is drawn out from all cell tissues. The water is then bound with the solute, making it unavailable to the microorganisms. In osmotic dehydration of fruits, the method involves the partial dehydration of fruits by osmosis in a concentrated sugar solution or syrup.
14. Which are the fruits suitable for Osmotic dehydration?
Fruits such as apple, banana, cherry, citrus, grapes, guava, mango, papaya, pineapple, plum, etc. Osmotic Dehydration can remove 30-50% of the water from fresh ripe fruits e.g mangoes, pineapple, banana, sapota and papayas. The final drying of these osmotically dehydrated fruits by vacuum drying provides a product which has good quality, attributes with respect to appearance, taste, flavour and colour as compared to sun drying.
15. What are the advantages of Osmotic dehydration?
16. What are limitations of Osmotic dehydration?
Limitations of Osmotic dehydration:
17. What are the factors influencing Osmotic dehydration?
Factors influencing Osmotic dehydration:
18. What are the use of products made through Osmotic dehydration ?
The product is suitable as a ready to eat snack item. Also the dehydrated product could be powdered if desired, and mixed with milk powder for making other products and confectionery items.
19. What is Spray drying?
Thin fruit juices like pine apple, citrus are dried to a powder in spray driers in which the liquid is atomized and sprayed into a hot air stream for almost instant drying.
20. What is Freeze drying?
Freeze drying is a method of drying involving freezing and then the sublimates of the ice under vacuum. Removal of water from a product while it is frozen by sublimation is called freeze drying. Fresh flavours and textures are better preserved by freeze-drying. Freeze-dried fruits and vegetables generally have better texture and rehydration quality.
21. What is the method for drying of grapes?
Dehydration of grapes (Raisin making): The process of raisin making involves selection of raw material, preparation of bunches, lye treatment, dipping oil treatment, sulphur fumigation, drying in sun or shade or drier, separation of raisins, washing in luke warm water, curing, packing, storage for marketing.
22. What is the quality of good raisins?
The desirable characters of raisins are small size, round and plumpy shape, very sweet taste with greenish or light brown colour.
23. What is freezing preservation?
Freezing may preserve foods for long periods of time provided the quality of the food is good to begin with and the temperature of storage is far enough below (-18 ) the actual freezing temperature of food for long preservation.
24. What is IQF or Quick freezing process?
In this case the lower temperatures (–32 to –40 ) to freeze foods. The crystals are formed and the time of freezing is greatly reduced. In quick freezing, large amount of food can be frozen in a short period of time.
25. Which vegetables can be preserved by freezing?
Vegetable like peas, carrot, cauliflower, french beans and mushrooms can be frozen.
26. Whether all the fruits and vegetables can be processed?
Practically any fruit and vegetable can be processed, but some important factors which determine whether it is worthwhile are:
27. Which location will be appropriate for processing activity?
The basic objective is to choose the location which minimizes the average production cost, including transport and handling and to locate a processing unit near the fresh raw material supply. An adequate supply of good water, availability of manpower, proximity to rail or road transport facilities and adequate markets are other important requirements.
28. What are the processed products prepared from vegetables?
Various processed products can be made from vegetables are given below:
Tomato - Canned whole or in form of pulp, puree, paste or juice and also in form of sauce or ketchup.
29. What are the simple methods for processing of fruits and vegetables?
Processing into pulp or puree
30. How to preserve tomatoes using simple techniques?
Tomatoes can be processed into a simple and intermediate product like puree which can be used as a substitute for tomatoes or can be converted into ketchup, sauce etc., during later stages.
31. Which are the commonly used chemical preservative in fruit and vegetable processing?
Two chemical preservatives.
32. What are the permitted levels of preservatives?
The upper limit of chemical preservative allowed varies from product to product. Eg. For raisin 750ppm of sulphur dioxide, jams 40ppm, fruit pulps 1500ppm, etc.
33. How to preserve fig fruits?
Fig fruits can be preserved by dehydration after suitable pre-treatments.
34. What are the main type of beverages that can be made from fruits and vegetables?
RTS – Ready to serve type which need not be further changed in composition while serving
Concentrates: Which needs to be changed in composition while serving by diluting with water.
35. What are the products that can be prepared from grapes?
Grapes can be processed into wine, juice and raisin.
36. What type of juice can be prepared from grape?
Both RTS and squash/concentrate type products can be prepared.
37. Which variety of grapes are ideal for juice?
‘Gulabi’ variety makes juice with very good taste and flavour.
38. Whether Bangalore Blue varieties can be used for juice?
It can be used. It is desirable to blend Bangalore Blue with ‘Gulabi’ in the proportion of 50:50 in order to enhance taste and flavour of the end product.
39. Whether juice can be prepared from pulpy fruits like banana, sapota, jackfruits?
It is possible. But before making the product the extracted pulp has to be liquefied using suitable enzymes so that the pulp becomes thin and usable for juice.
40. What is the difference between jam and jelly?
Jams are prepared using the fruit pulp, while jelly is prepared using fruit extract only and hence jelly will be somewhat transparent or translucent type.
41. What products can be prepared from fruits like tamarind?
Products like tamarind juice concentrate, ready-to-serve and tamarind sauce can be prepared.
42. What are the improved methods of dehydration?
Osmotic dehydration is the simple and improved method of dehydration which can be adopted even in rural areas without much investment on machinery.
43. How processing of fruits and vegetable is beneficial to growers?
During peak season, the price for fresh fruit will be very low leading to losses to growers. In such situation, processing of these perishables into suitable products will help in realizing better prices for their produce.
44. What are the common products that can be prepared from different fruits?
The products that can be prepared from major fruits are:
45. What is the normal shelf life of processed products?
Normally at ambient conditions of storage the processed products will have a minimum shelf life of 6 months. Canned products will have one year shelf life at ambient conditions of storage itself. The shelf life of others can be doubled by storing at refrigerated conditions.
46. Are processed foods as nutritious as fresh foods?
Some processing methods can cause the loss of certain nutrients. The processing of foods can also add nutritional benefits. Lycopene, a powerful antioxidant (a protective substance for the body) found in tomatoes and watermelons, has been shown to become more available to the body (“bio-available”) when the tomatoes are processed into tomato paste, ketchup or soup.
47. Are there nutritional differences between fresh and frozen berries?
Berries in all varieties are little storehouses of fibre, vitamins such as vitamin C, vitamin A and folic acid, minerals such as potassium and calcium and phytochemicals, such as polyphenols, phenolic acids, flavonoids (e.g. anthocyanins). These phytochemicals are powerful antioxidants, have anti-inflammatory and anti-carcinogenic properties. Very low temperatures inhibit growth of microorganisms and retard enzymic and chemical activity (minus 18 degrees Celsius). Fresh and frozen berries almost have the same nutritional value.
48. Can you give 5 Examples of foods processed in Modified Atmosphere Packaging (MAP)?
Meat, seafood, minimally processed fruits and vegetables, pasta, cheese, poultry, cooked and cured meats, ready meals and dried foods.
49. Do fruit and vegetables have the same nutritional qualities when cooked or raw?
The longer they are cooked, the more vitamins and minerals are lost: cooking vegetables in boiling water for a prolonged period can cause 40% loss of vitamin and minerals. Antioxidant properties of tomato become much more bio-available when the tomato is cooked or processed. Processing extends the shelf life of foods. Processing also improves food safety by a variety of methods– for example; heating to sufficiently high temperatures destroys harmful bacteria; certain additives help prevent rancidity and prevent the growth of harmful fungus and bacteria; packaging helps to prevent product tampering.
50. Does microwave cooking reduce the nutrients in vegetables?
Vitamin retention in some cases of micro wave cooked foods can be even better than in conventionally cooked foods. Minerals cannot be destroyed during food treatment, they can however, be lost in cooking water or meat juices.
51. Is it true that vitamins are not destroyed while processing milk (UHT)?
The pasteurization process heats milk to 70 – 75 °C for 15 seconds, inactivating or killing all of the disease-producing microorganisms in milk while preserving most of the nutritional value of milk. The Ultra High Temperature process ensures total microbial and enzyme inactivation, because the milk is heated up to 150 °C for 5 seconds.
52. What are fortified and enriched food products?
53. What are the advantages of vacuum sealing of food? Are there other kinds of preservation of nutritional value of food by eliminating contact with food?
The product is placed in a plastic or aluminium foil pouch and most of the air is removed in vacuum packaging. The package around a food allows the internal atmosphere to be retained so the food stays fresh and safe. Eg. Coffee and spices.
54. Why do foods get brown during cooking/baking?
The unique colour and flavour of baked bread is produced when the food’s surface is exposed to an intense source of heat. The process is known as the Maillard reaction. The Maillard reaction is non-enzymatic and involves the interaction of sugars, amino acids, and proteins.
Some products with Maillard reactions:
55. What are the storage times for foods in a freezer or fridge?
56. What is the difference between wholemeal bread and white bread? What are the advantages of using whole meal flour?
White flour and whole meal flour are the two main types of wheat flour. White flour is refined. The bran and nutrient-packed germ are separated from the rest of the grain losing many nutrients. The whole meal flour contains all parts of the grain: the fibre-rich bran (outer layer), the endosperm (middle layer) and the germ (inner layer). The bran provides fibre, B vitamins, minerals, protein and other phytochemicals. The endosperm contains carbohydrates, proteins and small amounts of B vitamins. The germ is packed with minerals, B vitamins, vitamin E and other phytochemicals.
57. Are preservatives bad for you?
Nitrates and nitrites used in processed meats protect against the deadly Clostridium botulinum, bacteria while mould inhibitors used in cereals help to stop the growth of potential carcinogens that could otherwise lead to stomach cancer.
58. Are the additives in processed foods really necessary?
Food additives play an important role in preserving the freshness, safety, taste, appearance and texture of processed foods. Antioxidants prevent fats and oils from becoming rancid while preservatives prevent or reduce the growth of microbes.
59. What should a label indicate in packed food?
Packed food must indicate
a) The name of the food
60. What’s the difference between ‘reduced fat’, ‘fat free’ and ‘low fat’?
Reduced fat foods must have at least 25% lower fat than that present in the standard product.
Good freezing materials include rigid containers made of aluminum, glass, plastic, tin or heavily waxed cardboard; bags and sheets of moisture-vapor resistant wraps; and laminated papers made especially for freezing.
62. What are phytonutrients?
Phytonutrients are nutrients from plants. These nutrients act as antioxidants and detoxifiers that protect the plants from oxidants and toxins.
63. What are antioxidants?
Antioxidants are natural substances that fight harmful molecules called free radicals. Eg fruits, vegetables, sprouted shoots and greens, algae, herbs and spices.
64.Do fruit and vegetables need to be washed to remove pesticide residues?
Fresh fruits and vegetables are safe to eat. Historically, it was believed that washing fruit and vegetables would remove any traces of residues.
65.What is Amchoor (Amchur)?
Amchoor is powder of raw green tangy mangoes. It is added to curries for its sour taste
66. How is Amchoor made?
Amchoor is made from raw mangoes that have minimum fibrous material in the meat. The mangoes are peeled, sliced and the thin slices dried in hot sun. The dried pieces are powdered.
67. What is the difference between Tomato Puree and Tomato paste?
The Tomato Puree and Paste differ by the amount of Tomato Soluble Solids (TSS). The USDA specifies that tomato puree must contain 8% to 23.9% TSS, the paste must contain minimum of 24% TSS.
68. How do greens be prevented from turning brown?
Add citric acid while cooking. To maintain bright green color of green vegetables, add a little lemon or lime juice to the cooking water.
69. How to cook beans to reduce gas discomfort?
A complex sugar called 'Raffinose' in the beans passes through small intestines to large intestines where it forms gas and to prevent this the lentils/beans/pulse should be presoaked in water for a minimum of eight hours at room temperature. The water should be discarded, rinsed in cold water
70. How to use papaya to tenderize meats?
The most common meat tenderizer used in India is raw (un-ripened) papaya. The leaves and green skin of raw papaya contain an enzyme called Papain. The connective tissue in the meat breaks down when it comes in contact with Papain. Papaya is preferred tenderizer for red meat (Lamb, Mutton, Goat, Beef).
Preparing Papaya Tenderizer Paste
Peeled the green skin of Raw Papaya added ¼ teaspoon of salt per two tablespoons of papaya and ground to a paste. 2 tablespoon of papaya paste is needed for one pound of meat.
71. How long to tenderize meat?
It depends on pH factor, temperature, type of meat (mutton takes longer than spring lamb), fat in the meat and cut of meat. It also depends on the level of tenderness sought.
72. What is homogenized milk?
The fat globules are mechanically reduced in size so they don't rise up to the top of milk
73. What is Pasteurized milk?
The harmful bacteria and enzymes are killed by raising the temperature of milk
Milk is heated to 162º F for 15 seconds. This kills bacteria and enzymes.
74. What is Evaporated Milk?
This is made from un-pasteurized whole milk by removing 60% of water, exposed to Ultra High temperature and then canned.
75. What is Dry-milk?
All the water is removed from pasteurized milk. The shelf life of dry milk is three years if stored properly.
76. What is the difference between paneer and cottage cheese?
To make cottage cheese, milk is coagulated at room temperature by adding yoghurt with live culture and Rennet. The live culture from yogurt converts lactose to lactic acid changing the pH factor of milk. The enzyme in the rennet coagulates the milk at room temperature forming a gel which is cut into small or large curds.
To make paneer , the milk is heated to over 200º F, and an acid is added to coagulate milk. Lemon juice or vinegar is used as acids. The starting culture of yoghurt is not used, as it dies at these high temperatures.
77. What is radiation processing of food?
Radiation processing of food involves the controlled application of energy from ionizing radiations such as gamma rays, electrons and X-rays for food preservation.
78. How irradiation works?
Irradiation works by disrupting the biological processes that lead to decay. The reactions with the DNA cause the death of microorganisms and insects and impair the ability of potato and onion to sprout.
79. What are the advantages of radiation processing of food?
Irradiation is a cold process and can be used to pasteurize and sterilize foods without causing changes in freshness and texture of food unlike heat. Irradiation does not leave any harmful toxic residues in food and is more effective. It is efficient and can be used to treat prepacked commodities.
80. Does the irradiation process make food radioactive?
No. The irradiation process involves passing of food through a radiation field allowing the food to absorb desired radiation energy. The food itself never comes in contact with the radioactive material. Gamma rays, X-rays and electrons prescribed for radiation processing of food do not induce any radioactivity in foods.
81. Does irradiation adversely affect the nutritional value of food?
No. In comparison to other food processing and preservation methods, the nutritional value is least affected by irradiation. Irradiation has very little effect on the main nutrients such as proteins, carbohydrates, fats and minerals. Vitamins show varied sensitivity to food processing methods including irradiation.
82. What should be the criteria for the best quality of cane juice?
83. What are the factors that affect the quality of the juice?
Factors like variety, nutrient management practices, stage of maturity, soil condition, growing condition, time and method of harvesting and time of transport to mill, incidence of pests and diseases etc., have profound influence on the accumulation of sucrose and other non-sugars in cane juice.
84. What is the composition of cane juice?
The constituents of the normal cane juice fall within the following limits:
85. How long a harvested cane can be kept without deterioration?
A well ripened harvested crop may lose its sugar within a few days after harvest, which tends to increase further due to high ambient temperature, pre-harvest burning, harvest and transportation injuries and microbial infestation.
86. How to minimize post harvest deterioration in sugarcane?
87. What is the composition of cane jaggery?
The jaggery contains approximately 60-85% sucrose, 5-15% glucose and fructose. Along with 0.4% of protein, 0.1 g of fat and 0.6 to 1.0g of minerals (8 mg of calcium, 4 mg of phosphorus and 11.4 mg of iron). It is also found to contain traces of vitamins and aminoacids.100g of jaggery gives 383 Kcal of energy.
88. What are the vegetable clarificants that are used for jaggery making?
Stem and root of green plant of Deola and Bhindi, green bark of the Sukhlai plant, seeds of castor, groundnut and soybean. the quantity of clarificant is approximately 40-70g per 100 liters of cane juice.
89. What are the chemical clarificants that are used for jaggery making?
Hydros (sodium hydrogen sulphite), lime (Calcium oxide), sodium carbonate, sodium bicarbonate, sajji (50% sodium carbonate, 6.4% sodium chloride), super phosphate and alum are used. Use of various chemicals as juice clarificants during jaggery preparation results in presence of harmful chemicals like SO2 in jaggery and also affects the taste and storability of such jaggery.
90. How to prepare liquid jaggery?
Liquid jaggery is an intermediate product obtained during jaggery making. After the juice is extracted, potassium alu crystals added to the juice. This facilitates sedimentation of solid particles. The clear juice is poured into boiling pan. About 50g of lime is added to bring the pH to 6.0. Bhendi mucilage is added and the first scum is removed when the temperature is 85 . Boiling is continued and the second scum is removed at 98 . The strike point is 106 and at this stage the pan is removed and 0.04% of citric acid is added.
101. What is value added jaggery?
Value addition to solid jaggery by inclusion of nutritive substances through puffed rice, gum, gingelly and various kinds of nuts (cashew, almond), vitamins, iron and taste enchaners like chocolate powder will increase demand for this kind of jaggery.
102. How to prepare bottled sugarcane juice?
Sugarcane Breeding Institute, Coimbatore