microbes and bacteria, and yeast cannot breed and reproduce there.
3 3. Vinegar: Vinegar is also a natural preservative which everyone has in their kitchen helps in the preservation of meat and poultry food items. It also elevates the taste and antimicrobial property is also present in it. The fermentation of sugar is the process which helps in the formation of the vinegar. Vinegar has acetic acid in it which destroys the microbes and stops the food degradation. We have a very common example, i.e., “Pickling” which acts as a preservative.
4 4. Onion: Onion has some antioxidant and antimicrobial properties which makes it as another type of natural preservative. Onion has some components which has these properties. Basically, the onion extracts are considered as the natural preservatives. They stops the growth of microorganisms on the food.
5 5. Olive Oil: Olive oil acts as natural preservative as it segregates/separates the food from coming in contact with the air which detains oxidation, degradation and molding.
6 6. Cloves: It is the most traditional food preservative which we use from ancient times. It contains phenolic compounds in a large amount which consist of antioxidant properties which makes sure that it prevents the breeding of fungus and bacteria on the food. It is a very useful and effective method since the beginning.
7 7. Ginger: Ginger is also a natural preservative which helps in the preservation of the food due to its “antimicrobial” property.
8 8. Castor Oil: Castor oil has anti-fungal property which helps in the food preservation. It inhibits the growth of the fungus on the food. Many grains and pulses are coated with the castor oil so that they can be stored for the long time.
1.7.6 Methods of Food Preservation
1 1. Drying: It is an ancient method used for the food preservation. This method prevents hydrolysis makes the environment for bacteria unfit for the growth. It uncovers the food to the high temperature which helps the food to be demoisturized. Electric dehydrator is consider to be the best unit for process of drying [90].
2 2. Freezing: It is storing the food stuffs in the storages which are cold. Potatoes are being kept in the dark room but the potatoes should be frozen.
3 3. Smoking: It is the process in which food gets exposed to the smoke from the burning wood as smoke has a property of being antioxidant and antimicrobial, mostly meats and fish are burned and smoked. Hot smoking and cold smoking are the different methods of smoking but it has a disadvantage that it increases the probability of cancer [87].
4 4. Vacuum Packing: In this process, the bags and bottles are being air tight and makes it a place where no oxygen could be present and bacteria dies there.
5 5. Pickling: In this process, it helps to remove the moisture from the food making the environment unfit for microorganisms to grow. Chemical pickling and fermentation pickling are the types of it. EDTA is added in commercial pickles to increase its life span [90].
6 6. Sugar: It is also a natural preservative which can be found in everyone’s kitchen as the major role of it is to act as a sweetener. Sugar also helps to prevent the spoilage by the help of the process osmosis in which it dehydrates the microbes and bacteria, and yeast cannot breed and reproduce there [89].
7 7. Lye: It helps to convert the food alkaline and helps to prevent the bacterial growth on it.
8 8. Canning: It is the process in which food is being sealed in cans and sterile bottles. Boiling is done in order to make sure that the bacteria is killed, and then, it is being sealed. When the seal is broken, then the chances of food spoilage increases again.
1.8 Antioxidants
Antioxidants usage in the field of food preservatives to save food from degradation has proved to be very effective. The oxidation of food is responsible by the two factors: oxygen and sunlight; so, the preservation procedure involves keeping food away from the contact of air and sun, keeping food in the dark and sealed container or maybe when required sealing it with the help of wax and cucumber where there is no chance for the food to get close or comes in the contact with the sunlight or oxygen but it does have one advantage as oxygen is the primary source for the respiration of plants so the plant products present there smells really bad and also the color of the products sometimes change. In addition, 8% oxygen is contained in the packaging of fresh fruits and vegetables. Antioxidants play an important part as preservatives, It helps to prevent the spoilage by fungi and bacteria [88].
Unsaturated fats are the most widely recognized atoms attacked by the process “oxidation” that makes them rancid. Oxidized lipids are regularly stained and result in displeasing tastes, for example, metallic or sulfurous flavors. It is essential to keep away the food from oxidation. These kinds of food are hardly preserved with the help of drying, and they are usually preserved with the help of salting/pickling, smoking, and fermenting. Before air drying the fruits which are less fatty foods are sprayed with antioxidants (sulfurous). Metals act as a catalysis in the process of oxidation, so it is better if fat oils like butter should not be kept in the Al foil or in any other metal container. Olive oil are halfway shielded from oxidation by their inherent antioxidant property but rest is sensitive toward photooxidation. Antioxidant additives are additionally added to fat based beautifying agents, for example, lipstick and lotions to forestall rancidity.
1.9 Oils and Spices
These are used as preservatives in pickles. Oil makes a protective covering and prevents contact of microorganisms and air with the food. Spices do not have bactericidal effect in concentrations usually used. Cinnamon and cloves containing cinnamic anhydride and eugenol, respectively, are more bacteriostatic than other spices. Extracts of garlic onion cabbage are inhibitory to Bacillus subtilis and E. coli [92].
The essential oils are the liquids that are extracted from the plant materials (such as fruits, flowers, barks, and peel), which are aromatic and volatile in nature. There are many uses of essential oils such as in medicine, perfumes, cosmetics, and as food spice and preservative. The initial use of essential oil was in medicine in the 19th century then they were used as odor and flavor ingredients and their business and usage increased in this field and became the priority. Out of 3,000 essential oils which are known yet, 300 out of them are used in the fragrances and flavor industry.
Essential oils has antimicrobial properties so they are regarded as secondary metabolites and they are essential for flora defense. Secondary metabolites “antimicrobial” property was tested by using vapors of essential oils by De la in 1881. From then, essential oils have been proved as the greatest examples that shows this property [94], and not only antimicrobial but also insecticidal, antiparasitic and antioxidant properties too. They act as the builders for the growth of animals.
In spite of the fact that the food business utilizes essential oils as flavoring agents, they also proved to be as the major source of antimicrobials in the process of food preservation. But, one should have all the knowledge about the properties of essential oils, i.e., the MIC (minimum inhibitory concentration), the mode of action, the range of target organisms, and the impact of food matrix components on their antimicrobial properties.
The diversity of compounds is created by plants containing antimicrobial activity. Some are constantly present while others are delivered because of the physical injury or microbial invasion. Essential oils are the blend of at least 45 various components so recognizing the most active component is not an easy task. There are various methods to extract the oil by mixing few components. Essential oils is widely spread family of organic compounds having low molecular weight with having huge contrasts in the antimicrobial activity [96]. There are four divisions in the active compounds as indicated by their chemical structures which are terpenoids, terpenes, phenylpropenes, and others.
1.10 Introduction to Hurdle Technology
Hurdle technology is a technique to control and eliminate pathogens by combining two or more factors. These factors are called hurdles. The pathogens have to overcome these hurdles to survive the