Tomato (Lycopersicon esculentum) was originated in South America. The improved variety of the wild fruit are grown throughout the world. Its high vitamin content and multiple uses make the tomato an important vegetable. Tomatoes are highly perishable and cannot be stored at low temperature and requires special care in handling, transportation and marketing.
Chemical composition of tomato
Carbohydrate have negligible amount of sucrose but carbohydrate in the form of Dextrose and fructose (1:1). Dominant acids in tomatoes are citric acid and malic acid which cover about 70 – 80 % of total acid. Other acid includes pyrrolidone carboxylic acid (PCA), glutamic acid and phosphoric acid. Lycopene constitutes 95 % of total pigment in tomato, followed by α-carotene and β-carotene. Polygalacturonase (PG) and pectin methyl esterase (PME) are the major enzymes found in tomato.
Maturity stages of tomato
1. Green (mature): well round
2. Breaker: ≤ 10 % of surface is tannish yellow, pink or red
3. Turning stage: >10 % and < 30 % is tannish yellow, pink or red
4. Pink stage: >30 % and <60 % is pink or red
5. Light red: >60% and <90 % of surface is pinkish red or red
6. Red: >90 % of the surface is red
Tomato juice: Tomato juice may be defined as the unconcenrated liquid extracted from mature tomatoes of reddish varieties with or without scalding (removing skin) followed by straining (filtering). In extraction of such liquid, heat may be applied by any method which doesn’t add water. Such liquid is strained free from skin and seed but may carry fine insoluble solids from the flesh of tomato. Such liquid may be homogenized and may be seasoned with salt. When sealed in a container, it is slow processed by heat before or after sealing as to prevent spoilage. Fruit product order (FPO) specification of tomato juice is given below
|Total soluble solids (TSS)||≥ 5.1 %|
|Salt||≤ 1.5 %|
|Incubation test||No sign of fermentation when incubated at 37°C for seven days|
|Mold count||≤ 30 % of the field examined|
|Insect fragments and filths||Not permitted|
Quality attribute of tomato juice:
Color, flavor, consistency and nutritive value are the main quality attributes of tomato juice. To secure a product of high quality, plant ripened tomato should be used. Iron equipment should not be used at any stage of processing because lycopene turns brown when it comes in contact with iron. Copper also adversely affect the color. The fibrous portion should be incorporated in the juice in finely divided condition to extract the red color of the juice, as the serum doesn’t consists of any color.
Cold break: tomatoes are chopped or crushed and then extracted following mild hating. Tomatoes that are extracted by cold break are usually scalded to loosen the skin so that no tomato flesh will cling to them during extraction. Failure to scald at this point reduces the yield of tomato juice. The cold break procedure in which fruit temperature is < 60°C is claimed to give a good flavor juice. However, quick processing of the extracted juice is necessary to produce high quality juice. Characteristics of cold break are as follows
1. Extraction of juice is difficult and yield is less
2. Juice obtained is rich in color. It is generally necessary to heat the skin to release the color from fibrous tissue.
3. The process has to be completed quickly to avoid microbial spoilage but the product has more natural tomato color and have fresher tomato flavor.
4. Loss of Vitamin C is more in cold break than in hot break because of oxidation of vitamin C during processing.
Hot break: The crushed tomatoes are boiled in their own juice in jacketed stainless steel pan or in aluminum pans for 3 – 5 minutes to facilitate pulping. Characteristics of hot break are as follows
1. Tendency of fruit juice to separate into liquid and pulp is prevented. The pectin naturally present in the seed and skin can be incorporated in the juice. During preliminary boiling, pectin is released and it thickens the pulp. The pectinase enzyme which would otherwise hydrolyze the pectin present in tomato thereby making the juice thin are also destroyed during boiling.
2. Boiling sterilize the juice partly thereby preventing growth of microorganisms to some extent. Microorganism causes fermentation in pulp or juice. It also inactivates the oxidative enzyme which are responsible for destruction of vitamin C in the juice.
3. A light cooking releases red color present in the skin
4. Higher yield is obtained.
Extraction of tomato juice:
1. Screw type: the processing action of juice extractor consists of a expanding helix, which press the tomato pulp against the screen at continuous and increasing pressure. The screen pore size is 0.02 to 0.03 inches. Thus pressing action doesn’t churn the product so very little air is incorporated into the expressed juice giving yield up to 80 %.
2. Paddle type: This type of extractor beat the tomato against the screen. The yield is more than 80 %. Commercially acceptable extraction yield is 70 – 80 %. Acidification is an excellent way to improve tomato juice flavor.
Homogenization: tomato juice is sometimes homogenized before canning. Homogenization prevents settling down of solids and produce thicker juice. It is generally used juice prepared by cold break technique. The juice is forced through a narrow orifice at pressure of 1000 – 1500 psi at 66°C.
Salting and filling: salting may be added to extracted juice by direct dissolution in batch quantities by use of tablets added to each can at the time of filling or injecting concentrated brine made by dissolving salt in tomato juice. NaCl added to tomato juice will range from 0.5 – 1.5 % by weight.
Thermal processing: Heat resistant strain of Bacillus thermoacidulants may be present in the juice which causes flat sour spoilage. The juice is heated at temperature of 116 – 121°C for 0.7 min or at 93.3 to 96.1°C for 15 – 20 minutes.
Tomato concentrate: It is the product prepared by concentrating the liquid from substantially sound, mature and red tomato but free from seeds, skin and other coarse or hard substances in the finished product. Salt or seasoning may or may not be added. They are generally preserved by physical means. Example include tomato puree and tomato paste
1. Tomato puree: It is a concentrate containing natural tomato solids not less than 8 % and not more than 24 %.
2. Tomato paste: It is a tomato concentrate containing 4 % or more of natural tomato solids. Permitted ingredients may be salt, natural vegetable product, onion and others but not sugar and sweeteners. Lime juice may be added as acidulants. Permitted additives are sodium bicarbonate to raise pH to level not more than 4.3 and citric acid, malic acid, tartaric acid to maintain pH not above 4.3.
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.