In recent years fast-paced lifestyle has increased the demand for ready-to-eat food including fruit and vegetable products. Thermal processing has enabled food manufacturers to create a number of thermally processed food options for consumers. The basic purpose for the thermal processing of foods is to reduce or destroy microbial activity, enzyme activity and to produce physical or chemical changes so the food meets a certain quality standard. Pasteurization and Sterilisation are the two main heating categories employed in thermal processing to inactivate microorganisms in processed foods.

Thermally processed food

According to Agricultural and Biological Engineering Department, University of Florida USA, “thermal processing or canning is a method of sterilizing of foods by heat in thematically sealed (airtight) containers which allows ready to eat foods that are neither frozen nor dehydrated to remain safe and wholesome during months and even years of storage at room temperatures without the use of additives or preservatives.”

What are the processes used in thermally processed foods 

Pasteurisation can be defined as a process that inactivates food borne pathogens which are vegetative bacterial cells with relatively low heat resistance between 75ºC to 95 ºC which is below boiling point of water in standard conditions. The process prolongs the safety and wholesomeness of fresh foods for limited periods under refrigerated storage.

In sterilisation microorganisms are inactivated at temperatures that range from 110 ºC to 115 ºC which is above boiling point of water in standard conditions. This is achieved by using water or steam under pressure in sterilised equipment which makes these foods commercially sterile. Sterilisation ensures longer shelf life. Two methods are used for sterilisation of foods

  • retort processing or “in container sterilisation” which is used for all foods
  • aseptic processing or “out of container sterilisation” which is used for only liquid foods

In retort processing, cans, jars and other retort containers are filled with foods and sealed then heated using saturated steam under pressure until heat penetrates the product from the can wall inward and both product and can become sterilised. In aseptic processing a liquid food is first sterilised outside the container by pumping it through heat exchangers that deliver very rapid and cooling rates. The cooled product is then filled and sealed in a separately sterilised package in a sterile environment at room temperature. In India for all foods whether solid or liquid both “in container” and “out of container” methods of food sterilisation are used.

According to Codex Alimentarius; when establishing a thermal process, the food manufacturers have to take into consideration

  • pH of the product and time to reach equilibrium pH
  • product composition /formulation
  • levels and types of preservatives used
  • water activity
  • microbial flora including C. Botulinum and spoilage microorganisms
  • container size and type
  • organoleptic quality
  • product code or recipe identification

Thermally processed products according to FSSAI regulations 

Thermally processed fruit means fruits which could be obtained from sound and mature dehydrated, fresh or frozen, peeled or un-peeled, previously packed, whole, halves or cut pieces of fruits. 

Thermally processed fruit cocktail / tropical fruit cocktail means the product prepared from a mixture of fruits. Such fruits may be fresh, frozen, dehydrated or previously processed. 

Thermally processed vegetables means the product obtained from fresh, dehydrated or frozen vegetables either singly or in combination with other vegetables, peeled or un-peeled, with or without the addition of water, common salt and nutritive sweeteners, spices and condiments or any other ingredients suitable to the product.

Thermally processed curried vegetables  and Ready to Eat vegetables means the product prepared from fresh, dehydrated or frozen or previously processed vegetables, legumes, cereals or pulses, whether whole or cut into pieces. The vegetable(s), either singly or in combination, may be prepared in any suitable style applicable for the respective vegetable in normal culinary preparation. It may contain salt, nutritive sweeteners, spices and condiments, edible vegetable oils and fats, milk fat and any other ingredients suitable to the product. 

Thermally processed vegetable soups means unfermented but fermentable product, intended for direct consumption, prepared from juice/ pulp/puree of sound, mature vegetables, fresh, dehydrated, frozen or previously processed, singly or in combination, by blending with salt, nutritive sweeteners, spices and condiments and any other ingredients suitable.

Thermally processed fruits juices means unfermented but fermentable product, pulpy, turbid or clear, intended for direct consumption obtained by a mechanical process from sound, ripe fruit or the flesh thereof. The juice may have been concentrated and later reconstituted with water suitable for the purpose of maintaining the essential composition and quality factors of the juice. It may contain salt. One or more of the nutritive sweeteners may be added in amounts not exceeding 50 g/kg but not exceeding 200g/kg in very acidic fruits except in case of Apple Juice, Orange Juice (reconstituted from concentrate), Grape Juice, Pineapple Juice (reconstituted from concentrate). 

Thermally processed vegetable juices means the unfermented but fermentable product or may be lactic acid fermented product intended for direct consumption obtained from the edible part of one or more vegetables, including roots, and tubers (e.g. carrots, garlic) stems and shoots (e.g. Asparagus), leaves and flowers (e.g. spinach and cauliflower) and legumes (e.g. peas) singly or in combination, may be clear, turbid or pulpy. It may contain salt, nutritive sweeteners, spices and condiments, vinegar, whey or lactoserum having undergone lactic acid fermentation not more than 100gm/kg and any other ingredients suitable to the product.

Thermally processed tomato juice means the unfermented juice obtained by mechanical process from tomatoes of proper maturity. The product may contain salt and other ingredients suitable to the product. The product shall be free from skin, seeds and other coarse parts of tomatoes. The product shall have pleasant taste and flavour characteristic of tomatoes free from off flavour and evidence of fermentation. 

Thermally processed fruit nectars means unfermented but fermentable pulpy or non-pulpy, turbid or clear product intended for direct consumption made from fruit singly or in combination, obtained by blending the fruit juice / pulp/fruit juice concentrate and/ or edible part of sound, ripe fruit(s), concentrated or not concentrated with water, nutritive sweeteners and any other ingredient appropriate to the product. Lemon and Lime juice may be added as an acidifying agent in quantities which would not impair characteristic fruit flavour of the fruit used.

Thermally processed fruit beverages / fruit drink/ ready to serve fruit beverages means an unfermented but fermentable product which is prepared from juice or pulp/puree or concentrated juice or pulp of sound mature fruit. The substances that may be added to fruit juice or pulp are water, peel oil, fruit essences and flavours, salt, sugar, invert sugar, liquid glucose, milk and other ingredients appropriate to the product.

Thermally processed mango pulp / puree and sweetened mango pulp / puree means unfermented but fermentable product intended for direct consumption obtained from edible portion of sound, ripe mangoes by sieving the prepared fruits, whereas the puree is obtained by finely dividing the pulp by a finisher or other mechanical means. 

Thermally processed fruit pulp / puree and sweetened fruit pulp / puree other than mango means unfermented but fermentable product intended for direct consumption obtained from edible portion of sound, ripe fruit of any suitable kind and variety by sieving the prepared fruits, whereas, the puree is obtained by finely dividing the pulp by a finisher or other mechanical means. 

Thermally processed concentrated fruit / vegetable juice pulp/ puree means the unfermented product which is capable of fermentation, obtained from the juice or pulp or puree of sound, ripe fruit(s) / vegetable(s), from which water has been removed to the extent that the product has a total soluble content of not less than double the content of the original juice/ pulp/ puree prescribed in the Regulations

Natural volatile components may be restored to the concentrates where these have been removed. It may be pulpy, turbid or clear and preserved by heat, in an appropriate manner.

Thermally processed tomato puree and paste means unfermented product which is capable of fermentation, obtained by concentrating the juice of sound ripe tomatoes to the desired concentration. It may contain salt and other ingredients suitable to the products.

Common guidelines for thermally processed foods according to regulations:

  • All these products can be sterilised (processed by heat in an appropriate manner) by either “in container sterilisation” or “out of container sterilisation.”
  • Products will conform to the microbiological requirements given in the Regulations.
  • They can be canned or bottled, or flexible packaged or aseptically packed fruits.
  • Besides other ingredients as required all these products may contain food additives permitted in the FSSAI Regulations.
  • The juices may have been concentrated and reconstituted with water for the purpose of maintaining the essential composition and quality factors of the juice. Juice product will be called sweetened juice till the added nutritive sweeteners are not in excess of 15g/kg.
  • All pulps including mango pulp may contain one or more nutritive sweeteners in amounts not exceeding 50gm/ kg. However, the product shall be described as sweetened (name of fruit) pulp/ puree if the amount of nutritive sweeteners is in excess of 15gm / kg.
  • All the products have various specific parameters for minimum weight of the contents of the products in respect of the liquid inside the containers (available from regulations)
  • The packing medium along with its strength shall be declared on the labels of all these products.
  • The names of the fruits/ vegetables used in the products and the preparation in any style shall be declared along with the range of percentage of each fruit or vegetable used in the individual products shall also be declared on labels.
  • The container shall be well filled with the product and shall occupy not less than 90.0 per cent of the water capacity of the container, when packed in the rigid containers. The water capacity of the container is the volume of distilled water at 20ºC which the sealed container is capable of holding when completely filled.