Explain Use of food Additives - method of food preservation?

Food additives may be defined as substances added intentionally to food, generally, in small quantities to improve its appearance, flavour, texture or storage properties. These may be classified into different broad groups. Those food additives, which are specifically added to prevent the deterioration or decomposition of a food, have been referred to as chemical preservatives. In food preservation, the added substances may be grouped into two. The first one includes the use of sugar, salt, spices, acetic acid (vinegar) and alcohol, and is referred to as class I preservatives and is considered to be relatively safe to humans. The second group includes the use of benzoic acid, sulfur dioxide, nitrates and nitrites and a variety of neutralizers, firming agents and bleaching agents and referred to as class II preservatives and is considered to be relatively safe to humans, but within the permissible doses prescribed by the Food Regulatory bodies because higher concentrations can be a health hazard. Preservation of foods by the chemicals is effected by interfering with the cell membrane of the microorganism, their enzyme activity and genetic mechanism; by acting as antioxidants.