Chemical deterioration and discoloration of semi-dried tilapia processed by sun drying and microwave drying

Drying methods can affect the chemical deterioration and discoloration of fish muscle. This study aimed to monitor the effect of microwave drying at different effective powers in comparison with sun drying on the physicochemical changes of semidried tilapia. Lipid deterioration, protein oxidation and discoloration of semidried tilapia (Oreochromis niloticus) muscle processed by sun drying and microwave drying were investigated. Results of the study revealed that the pH of microwaved tilapia was higher than that of the sun-dried tilapia (p < 0.05) and the pH increased with increasing microwave power (p < 0.05). The sun drying possessed higher degree of lipid oxidation as indicated by thiobarbituric acid-reactive substances (TBARS) with a greater level of lipolysis when compared to microwave drying (p < 0.05). Higher protein carbonyl content was in microwaved tilapia compared to sun-dried one (p < 0.05) and this content increased with increasing microwave power (p < 0.05). Sun drying resulted in a brown discoloration correlated with the highest metmyoglobin formation (p < 0.05), whereas microwave drying, particularly with high power, caused a green discoloration of semidried tilapia as revealed by a negative a* value with a significantly decreased redness index (p < 0.05). Therefore, lipid deterioration, protein oxidation and discoloration of semidried tilapia muscle were strongly influenced by drying methods.