Freezing and cold chains are very much needed to protect our food from spoilage and saving our country from huge losses. Therefore, it is imperative to understand the importance of freezing and maintaining a cold chain in the production of processed frozen foods writes O.S Gautam
We lose a whopping 30% of our total produce as waste due to spoilage. The tropical climate, poor handling practices, poor hygiene, lack of infrastructure, lack of cold chain, lack of technical knowledge and technological advancements in food processing are some of the attributes for such losses. Freezing and cold chains are very much needed to protect our food from spoilage and saving our country from huge losses. These are very much needed in today’s context.
It is imperative to understand the importance of freezing and maintaining a cold chain in production of processed frozen foods. It is also desired to know why it is needed and how it works. Let us first understand what spoilage is and how it happens-
Any commodity or food product spoils in the following three ways:
1 Microbial spoilage
Microbes are part of nature and are present in every environment – water, soil and air. Foods coming from land or water contain microorganisms specific to their environment however most of the pathogenic organisms (disease-causing ones to human beings) are terrestrial in nature. Foods of terrestrial origin may bring in contaminations from the farm itself like root vegetables and tubers. Fruit and leafy vegetables may get contamination from the soils in contact, dust, bird droppings, human excreta, through insects found in that environment. Water used in irrigation is also a potent contamination source. Farmworkers and food handlers during post-harvest operations can contribute to contamination if it is carried out under unhygienic conditions.
Seafood immediately after catch are considered free from pathogenic contamination. This is a generalized concept and has several exceptions.
There are various species of salt-loving pathogenic microorganisms who live and multiply in saline environments (Vibrio paraheamolyticus). Sea foods get contaminated from pathogenic organisms during their handling by fishermen either in the boats or in the landing centers or beaches or from dirty contaminated contact surfaces, during transport, processing plants, storage facilities, processing workers etc.
Saprophytic microorganisms, responsible for biodegradation of dead animals and plants, are present in all the environments and on the body surface of all the animals and plants. They live as commensals on the body surface without damaging the host and start working immediately after its death.
Bacteria are categorized into three groups. The first group is thermophils. They are heat-loving ones, like Clostridium botulinum, Clostridium tetani, Listeria monocytogenes. They can even withstand boiling water temperatures.
The second group is called mesophils who survive and multiply in room temperatures with optimum to 30 to 40 degree Celsius. Most of the diseases causing bacteria fall in this category. Multiplication of the mesophilic bacteria is directly proportional to the temperature. Higher is the temperature, higher will be their metabolism and higher rate of their multiplication therefore higher will be the spoilage of the commodity. In average each microbe multiplies in every four minutes. Lowering temperature reduces their metabolism and therefore multiplication and this gets stopped when temperature of the product reaches to –12 degree Celsius.
The third group of bacteria called cryophils or psycrophils can withstand and multiply even in sub zero temperatures. They are however not considered very significant, as they are not known for pathogenesis, although they can render a food inedible after a prolonged abuse.
Vegetables carry their contamination from the soil and dust apart from handling, contact surfaces and storages as in the case of seafoods. Soil is the mother of all microbes and vegetables are grown directly in the soil. Vegetables may therefore carry much more bacterial load than any other food. Plant products are rich in cellulose and are rich in proteins.
2 Autolytic spoilage (enzymatic)
Animals, vegetables and fruits have their own enzymes, which are essential for digestion and other metabolic activities while they are alive. After death, these enzymes start digesting their own tissues and carry out break downs of proteins, carbohydrates and fats and spoil the product. Enzymatic reactions are also like microbial ones and are directly proportional to atmospheric temperatures, thus with a reduction in the temperature enzymatic spoilage slows down and almost stops (approx 90%) at –18 degree Celsius and 100% at below –60 degree Celsius.
3 Oxidative spoilage
All products either from plant or animal origin contain some percentage of oil and fats. In chemical language they are called triglycerides (three molecules of fatty acids bonded with one molecule of Glycerol) and partially are unstable in nature. Triglycerides keep breaking in higher temperatures into glycerol and fatty acids, reaching to highest levels at cooking or rather frying temperatures. As they are free from the bond they are called free fatty acids. Free fatty acids are highly reactive with oxygen which they derive from surrounding air and get converted into peroxides and other compounds which are not in good taste and aroma and sometimes unhealthy too.
Once again these fatty acids are available for reaction when they are in liquid form. Once they are frozen they take solid form and are less reactive.In fruits and vegetables there are various other compounds necessary for human health and nutrition. Terpentenoids (most of the aromatic substances), flavonoids (various colors in the fruits and vegetables), chlorophyll & carotenes, who provide special aroma, flavour and colour to a fruit and vegetable also undergo oxidation and render a food unsuitable for human consumption.
Refrigeration and Freezing
All these three types of putrefactions processes are directly or indirectly related with temperature abuse and can be controlled by keeping the food in a temperature-controlled atmosphere.
The raw material may undergo various handling, pre-processing and processing stages. During these processes product may be subjected to mechanical, chemical and physical stresses that may affect the rate of metabolism and rate of putrefactive processes hence the quality of product. Therefore it is imperative that raw material is handled properly to minimize physical damages, bruises and temperature abuse. Physical damages and bruises may facilitate entry of microorganisms and temperature abuse will enhance rate of putrefaction. Once a raw material is degraded there is no method to reverse the process and “GARBAGE IN IS GARBAGE OUT”. Therefore raw material in all stages i.e. storage, pre-processing and processing should be kept under controlled temperature. Most of the animal origin products keep better at or close to 0 degree Celsius (0 to 4 for operations ease) whereas plant origin products keep better at around 10 degree Celsius.
Animal origin raw materials are dead with the death of animal. but most of the plant origin products are however alive even after they are plucked from the plants. They need respiration, transpiration and utilize their stored energy for keeping themselves alive. Therefore their requirements for storage are different than the animal origin products. They may need more windy and more humid environment to facilitate proper respiration and to prevent loss of biological water through Transpiration. Lower temperature helps to reduce the rate of respiration and transpiration and keeps vegetables and fruits fresh and juicy.
We can control all three type of spoilage by freezing a commodity to a temperature of –18 degree Celsius,. Even at this temperature some reactions are going on. They are however very slow and do not have any impact on the edible qualities till at least up to 18 months, if temperature is maintained at -18 degree Celsius continuously. At any stage if product temperature is allowed to go up all above three processes will resume their activities and render the product inedible or spoiled.
In case of fresh foods also same is true. Therefore till product is taken for consumption, it should be stored under refrigeration if time required for storage is less or it should be frozen and stored to a temp of –18 degree Celsius.
Quality of Frozen Food vs Fresh
The quality of frozen foods had been always under doubt. In fact unfrozen products the so-called “FRESH” may not be always fresh. The unsold fruits, vegetables and meat products are kept for next day sales by vendors and this process continues till either it is sold or till gets spoiled. As cold chain infrastructure in India is still not available widely, fruits and vegetables are left at ambient temperatures for next day sales. Vegetables and fruits keep metabolizing. most of their stored energy and nutrients and might have consumed most of it before a customer has purchased these after few days. If same vegetable has been frozen immediately after harvesting and stored at desired temperatures, it will still be close to fresh preserving fully its chemical, organoleptic and nutritional values. In similar way meat products too keep deteriorating slowly even if they are kept under refrigeration.
Therefore frozen is better than the so-called fresh.