Hello everyone, today we are going to discuss about food microbiology, another topic that is factors influencing microbial growth. So we had already started with food microbiology and dairy microbiology. Side by side we are going to study these topics.
So today we will just focus on factors which actually affect the microbial growth in food. The ability of microorganisms except viruses to grow or multiply in a food is determined by the food environment as well as the environment in which the food is stored okay designated as intrinsic and extrinsic environment of food okay so what is intrinsic so intrinsic factors are properties or we can say some essential um or properties which the food actually has like some like pH or water right these are some factors which actually the food is having it is the nature of that food okay so that is one factor and extrinsic are the environment in which food is stored for example the outside temperature of the environment then relative humidity, gaseous atmosphere. Okay, so these are extrinsic factors and intrinsic factors are essential properties of that particular food.
Okay, so for example, dry fruits, the water activity or the presence of water is very low as compared to the cooked rice. Okay, so these are the intrinsic factors. which each and every food item has and they differ. Okay.
So it is not possible to study the influence of any one factor on growth independently as the factors are interrelated. Right. Instead of influence of any one factor at different levels on growth is compared keeping other factors unchanged.
Okay. So here is a simple table where factors they are distinguished okay so in intrinsic factors you get nutrient content ph redox potential water activity antimicrobial constituents and barriers in case of extrinsic you have temperature relative humidity gases atmosphere and growth rate then in implicit factors there are synergism antagonism and commensalism then processing factors are irradiation washing slicing pasteurization and packaging okay so in this video or in this topic we will be just focusing on intrinsic and extrinsic okay the processing factors and implicate implicate factors they will depend on which particular food item you are studying okay so processing factors they will vary from vegetable to fruit or say for they will vary for each and every food item okay so those we will not be studying today so in this video we will be just focusing on extrinsic factor and in part two we will be covering intrinsic factors okay so yeah first is temperature of storage so temperature of storage is very important intrinsic factor and microorganisms have been found growing in virtually all temperatures So considering the total span of temperature where liquid water exists, the prokaryotes may be subdivided into several subclasses on the basis of one and another of their cardinal points of growth. OK, so you generally you study this in your FI and SY. So that is what the basic microbiology that we are going to apply here. So, for example, organism with an optimum temperature near 37 degree.
they are called as mesophils okay don't forget our first line microorganisms have been found growing in virtually all temperatures okay so they are going to be present in each and every uh temperature condition where you are going to store your food so you need to know what are the subclasses right so first we have seen is a mesophile then next organism with an optimum temperature between 45 to 70 they are thermophiles for example bacillus clostridium etc Some archaebacteria with an optimum temperature of 80 degree Celsius or higher and a maximum temperature as high as 115 degree Celsius are now referred to as extreme thermophiles or hypothermophiles. Okay, so we are moving forward from 37 we have reached till 80 degree Celsius. But what about lower temperatures? The cold loving microorganisms are psychrophiles defined by the ability to grow at 0 degree Celsius.
So now we had covered the range from 0 degree Celsius to 80 degree Celsius. A variant of psychrophile which usually has optimum temperature above 10 degree Celsius is a psychrotrop which grows at below 7 also but displays an optimum temperature in a mesophile range. near room temperature.
So they are known as psychotropic. One which grows well at zero degree that is psychrophile that is cold loving and another which is quite able to tolerate more temperature slightly more temperature that is say around 10 degree Celsius is a psychotropic. a psychotrop has sorry a psychotrop yeah psychotropes are the source of food storage in refrigerator since they are invariably brought in from their mesophilic habitats and continue to grow in refrigerator environment where they spoil the food okay so psychrophiles or psychotropes We are talking here about cyclotops. They cause scourge that is or which means a lot of trouble in food storage in refrigerators since they are invariably brought in from their mesophilic habitats and they continue to grow in refrigerated environment. Okay, so where they start acting on food and they spoils food.
Of course, they grow slower at 2 degree than that of 25 degrees celsius okay so you will find that even food in refrigerators it spoils after say two or three weeks okay the rate is slow in refrigerated environment but same food if you keep outside mesophiles which grow in say range of 25 to 37 degrees celsius in 24 hours you will find your food got rotten or spoiled okay so in food microbiology mesophiles and psychotropic organisms are of greatest importance okay so this okay so next is about relative humidity of the storage environment why because relative humidity and water activity they are interrelated how so when food with low aw aw is water activity they are stored in environment of high humidity water will transfer from the gas phase to the food okay and this will increase the water activity of the food leading to the spoilage of viable flora okay yeah spoilage by the viable flora okay so this is how the water activity will get affected and your food will get spoiled easily So there is a relationship between temperature and humidity which should be kept in mind. In general, the higher the temperature, lower should be the relative humidity or vice versa. Food that undergoes surface spoilage by molds, yeast and by some bacteria, they should be stored in conditions of low relative humidity to increase their shelf life.
This can also be done by proper wrapping of food material. however variations in storage temperature should be minimal to avoid surface condensation in pack okay so about the last point uh never do this thing okay keep your food inside refrigerator and you need to consume it or you need to reheat it so you take it out and you keep it uh outside for say two to three hours then again you hit it you consume it half of it and again you keep it inside the refrigerator again you next day take it out okay so what happens during this time the water from the food it starts condensing towards the surface of the material okay proper wrapping is what we are talking here so this will lead to get water condensed droplets okay on the food or food material the wrapping material and this will increase the contamination or this will attract more outside microbes which will start spoiling your food okay so never do that then about gaseous atmosphere so oxygen is one of the most important gas or gases which comes in contact with the food okay and it influences the redox potential and finally the microbial the inhibitory effect of co2 on the growth of microorganisms is applied in modified atmosphere packaging of foods the storage of foods in atmosphere containing 10% of CO2 is referred to as controlled atmosphere. Why?
Because CO2 shows inhibitory effect on growth of microbes. So it is referred to as controlled atmosphere. So this type of treatment is applied more commonly in case of fruits such as apples and pears. With regards to the effect of CO2 on microorganisms, molds and gram negative bacteria they are most sensitive.
But gram positive bacteria particularly lactobacilli it tends to be more resistant okay so there is always an exception for each and every uh treatment right so some is such as britanomyces species also shows considerable tolerance of high co2 levels and dominates the spoilage of microflora of carbonated beverages some microorganisms are killed by prolonged exposure of CO2 but usually its effect is bacteriostatic. Means it will stop the growth but it will not kill the microbes. Also the presence of CO2 tends to decrease the pH of foods and thereby inhibiting the microorganisms present in it by adversely affecting the solute transport.
Expression of key enzymes involved in carboxylation and decarboxylation reaction. okay so this was about gaseous atmosphere so we had covered extrinsic factors in this part in second part we will study about intrinsic factors okay so thank you for watching do like share and subscribe to my channel and keep supporting thank you