The preservation of food has always occupied a large portion of man’s time and effort. Since the early days, man has been preserving his foods by application of natural methods from the environment. These methods included the sun drying, smoking, salting, and fermentation (Karel & Lund, 2003). These methods altered the quality and taste of the foods. In addition, as civilization developed the demands of large quantities of quality processed foods also increased. This has led to the development of large preservation methods that attempt to retain the natural taste of the foods processed.
One crucial fruit that the food industry can preserve is the plums. Plums may be used in the manufacture of jam, juice, as well as other recipes (Schuegraf, 2001). They are also be used to manufacture brandy and other alcoholic beverages when distilled. It is also high in the antioxidants and has a laxative effect when eaten. Dried and salted plums can also be used as snacks. The wide range of uses of plums supports its choice in preservation. Plums are exceedingly perishable commodities under the normal room temperatures. Their accelerated spoilage is due to their high sugar content. The high sugar content allows for the thriving of the microbes.
Heat processing is one of the new methods in the markets, which are more convenient in preservation of the food. It emerged due to the need to improve on the processes inefficiency and the quality of the final product of the existing methods. This consequently led to the development of new developments and improvements in existing thermal processing technologies (Bhat, 2012). Three commonly used methods in the thermal processing are the electro-heating technology, microwave heating and ohmic heating technology. These technologies inactivate microbes in many kinds of foods. Electro-heating can be done either directly (e.g. ohmic heating) or indirectly (e.g. radio frequency or microwave heating). Direct heating involves applying the electrical current to the food directly. In indirect heating, electrical energy is first converted into electromagnetic radiations and directed to the food. The electromagnetic radiations, subsequently generates heat within the product. Indirect electro-heating overcomes the problem of excessive cooking times, leading to low power consumption (Bhat, 2012). The major application of this method is in the processes of pasteurization, sterilization, defrosting, thawing, cooking and drying. Heat processing, work by thermal inactivation of microorganisms in the food materials, through irreversible denaturing of the enzymes, proteins, nucleic acids, or other cellular constituents vital to the cell metabolism and reproduction in microbes thereby, resulting to cellular death (Bhat, 2012).
The establishment of safe thermal process requires the knowledge of time/ temperature combination in order deactivate the most heat-resistant pathogen. In addition, the knowledge on heat-penetration characteristics of the food system (heat transfer rate) is applied. This information is necessary to establish scheduled processes, for the inactivation of pathogens in the food products and thus, prolonging their shelf life (Ranken, Kill, & Baker, 1997).
Dehydration method of food preservation, work by the principle of depriving microorganism’s moisture necessary to remain active. Removal of water also ensures that, the chemical processes stops. Dehydration leads to reduction in weight and volume in most cases. The most decisive factor to consider in the fruit and vegetable preservation by dehydration method is the water activity (aw). Water is a useful solvent for growth and metabolism of the microbes. It also supports many chemical reactions occurring in the food products. The free water in fruits or vegetables is enough for chemical reactions, supporting microbial growth, and as a transport medium for the spoilage compounds (Barbosa-Cánovas, Fernardez-Molina, Alzamora, Tapia, Lopez-Malo, & Chanes, 2003). It is essential that, the appropriate water activity (aw) in which the pathogenic or spoilage microorganisms cannot grow be attained for preservation. Most pathogenic organisms cannot grow at aw< O.82. Yeasts and molds, on the other hand, cease to grow when aw< 0.62 (Bhat, 2012). Low water activity produces conformational changes in the enzyme, thereby affecting its catalytic activity. Any dehydration method should ensure that, the water activity (aw) is below the growth of the microbial organisms, so as to prolong their shelf life and preservation time (Karel & Lund, 2003). It should also be noted that low water values do not kill the microbes immediately. Therefore, they may remain dormant in the food for prolonged periods of time. Because it does not sterilize the food, means must be provided to maintain the equilibrium and prevent the food staff from regaining the moisture until its usage arises (Ranken, Kill, & Baker, 1997).
Having the two processes will substantially lower the cost on other methods of preservation. For example, the dehydration of the food materials can be done by the electrical heater. On the other hand, these two methods can be easily incorporated to other methods of food preservation thereby reducing costs. Lastly, these two methods require just the initial supply of power unlike the refrigeration that requires a constant supply all the time.
The effectiveness of any preservation method is dependent on how well the agents responsible for spoilage are inhibited or destroyed. This spoilage occurs due to the activities of microorganisms and the enzyme in the food to be preserved (Karel & Lund, 2003).