may get affected by the adjustment of the pH. Mostly, preservatives are less determined by the pH.
1.7.2 Factors Affecting Chemical Preservation
| Intrinsic | Extrinsic | Microbial | Processing |
| Food nutrients composition [73] | Processing temperature | Inherent resistance (vegetable cells/spores/strain/differences) | Changes in composition |
| pH/acidity [74] | atmosphere | Initial number | Changes in microbial composition |
| Buffering capacity [75] | Relative humidity | Growth rate | Changes in food microstructure |
1.7.3 Classification of Chemical Preservatives
Many chemicals are used as a chemical preservative and are added into the food. According to Food Safety and Standards Authority of India (FSSAI), chemical preservatives are classified into two classes [76–78]:
Class 1: These are the preservatives that we can usually find them in our house in kitchens. They are the preservatives that are derived from the nature. They are not harmful in nature for our body. Example: common salt, sugar, spices, vinegar, vegetable oil, honey, and wood smoke.
Class 2: These are the man-made preservatives that are chemically prepared. There are more chances that they could react with the body and causes harmful effects to the body. Example: calcium or sodium propionate, sorbic acid or its sodium potassium and calcium salt, and acidulants.
1.7.4 Types of Chemical Preservatives
These preservatives are used in foods either as direct additives or are themselves developed during processes such as fermentation or decomposition [79, 80]. There are certain preservatives which can be used.
| Natural | Sugar, Salt |
| Weak organic acid (Acidulants) | Acetic acid, lactic acid, sorbic acid and its salt, benzoic acid and its salt, propionic acid and its salt, malic, tartaric, citric, and ascorbic acid |
| Inorganic Salt | Nitrites and nitrates, chlorine, iodine, hydrogen peroxide phosphoric acid, and borax |
| Gaseous | Sulfur dioxide and sulfites, carbon dioxide and ethylene and propylene oxides |
| Other | Antioxidants, oils, and spices |
1.7.5 Natural Chemical Preservatives
From ancient times, the salt and sugars are used as chemical preservatives. They are the regular part of our diet. The salt causes the food dehydration by drying out the water and tying up from the tissues of the food. It also ionizes yielding chlorine ion and interfere with the action of proteolytic enzymes which is harmful to the microorganisms. Similarly, sugar is also a part of our regular diet. It also produces the condition of high osmotic pressure that are unfavorable. Natural preservatives are the part of ancient method to save food from decaying. It delays the growth of unwanted substances like bacteria in the food for some time. They have different properties like antioxidative, antifungal, and antimicrobial which helps in the delay and prevention of the growth of unwanted substances [81–86].
1 1. Salt (Sodium Chloride, NaCl): It can be found in everyone’s kitchen. It is considered as one of the best natural preservative. It helps in the preservation of non-vegetarian food like meat, chicken, and some vegetables, too. Different unwanted substances sometimes breed on the food in the aqueous medium like bacteria and yeast, and they feed and degrade the food making it unfit to eat so salt helps to prevent this spoilage by the help of the process osmosis in which it dehydrates the microbes.
2 2. Sugar (Sucrose, C12H22O11): 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.
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
