Effect of salt solution on the mycelial growth of orange fruit spoilage fungi in passive evaporative cooling structures

Abstract

A study was carried out on the effect of salt solution on mycelial growth of fruit spoilage fungi in passive evaporative cooling structures.  Three sets of four different types of passive evaporative cooling structures made of two different materials, clay and aluminium were constructed.  One set consists of four separate cooling chambers.  Two cooling chambers were made with aluminium container (cylindrical and square shapes) and the other two were made of clay container (cylindrical and square).  These four containers were separately inserted inside a bigger clay pot inter- spaced with clay soil of 5 cm (to form tin-in-pot, pot-in-pot, tin-in-wall and wall-in wall) with the outside structure wrapped with jute sack.  The other two sets followed the same pattern with interspacing of 7 cm and 10 cm respectively.  The set with 7 cm interspace served as the control in which the interspace soil and the jute sacks were constantly wetted at intervals of 2 to 4 h depending on the rate of evaporation with water at room temperature.  The other two sets (5 cm and 10 cm interspaced soil) were constantly wetted with salt solution (table salt (Nacl)) at the same interval to keep the soil in moist condition.  In addition, the control has no fans and the inner cooling chambers were not lined with polyethylene nylon, while the other two sets have fans and their inner cooling chambers lined with polyethylene nylon.  Freshly harvested oranges were used for the experiment, and the temperature, relatively humid and decayed were monitored daily, while the fungal counts were determined at interval of three days for a period of three weeks.  The oranges kept inside the 7 cm soil interspace recorded higher values of fungi count compared to those stored inside 5 cm soil interspace throughout the storage period.

The total fungi count values for the oranges stored inside 7 cm soil interspace were 7.6 ´ 10 CFU g^-1, 8.5 ´ 10 CFU g^-1,  8.6 ´ 10 CFU g^-1, 9.2 ´ 10 CFU g^-1, 9.2 ´ 10 CFU g^-1, 9.0 ´ 10 CFU g^-1, and 8.8 ´ 10 CFU g^-1.  The total fungi count values for the oranges stored inside 10 cm soil interspace were 8.2 ´10 CFU g^-1, 7.8 ´ 10 CFU g^-1, 10.0 ´10 CFU g^-1, 9.2 ´ 10 CFU g^-1, 9.0 ´10 CFU g^-1, 9.2 ´ 10 CFU g^-1, and 8.4 ´ 10 CFU g^-1, while those inside 5 cm interspace were 7.4 ´ 10 CFU g^-1, 7.5 ´ 10 CFU g^-1, 8.5 ´ 10 CFU g^-1, 9.2 ´ 10 CFU g^-1, 8.7 ´ 10 CFU g^-1, 8.4 ´ 10 CFU g^-1, and 8.6 ´ 10 CFU g^-1.  From the results, higher values of fungi counts were recorded on the 5^th, 15^th and 21^st day of storage in oranges stored in 7 cm soil interspace structure, as well as on the 1^st, 8^th_, and18^th day of storage in oranges stored in 10 cm soil interspace structure.  However, the three soil interspaces have the same number of fungi count on the 11^th day of storage.   

Keywords: fungi, sodium chloride, solution, oranges, mycelial, soil