Lycopene degradation and color characteristics of fresh and processed tomatoes under the different drying methods: a comparative study

Tomato is a potentially valuable source of bioactive compounds such as lycopene. The degradation/isomerization rate of lycopene can be highly enhanced by the drying process of tomato pulps. In this study, the dehydrated tomatoes by osmotic solutions were processed by drying methods of hot air (HA), vacuum-assisted hot air (VA-HA), sun-assisted hot air (SA-HA), and microwave-assisted hot air (MA-HA). The lycopene content and color characteristics (L*, a*, b*, and increment E values) of the dried samples to determine the favorable processing were analyzed using HPLC and Hunter-Lab colorimeter systems, respectively. Results showed that the osmotic pretreatment with a significant decrease in drying time led to a better-preserved color by reducing the degradation rate of lycopene. The samples processed with MA-HA showed the highest drying rate with a drying time of 150 min (p < 0.05). The tomatoes dried with MA-HA contained the lowest lycopene content (174.9 mg/100 g) due to serious damage to the cell wall. HA and SA-HA drying methods resulted in a similar lycopene content (1191.1 and 1287.3 mg/100 g, respectively), while the color values of samples dried by SA-HA were undesirable compared to HA ones (a*/b* = 1.36 and 3.09, respectively). A significantly negative association between lycopene content and increment E value for osmo-dehydrated samples dried by the different methods was found (p < 0.01; r(2) = 0.756-0.906). It seems that the choice of appropriate drying method accompanied by the osmotic dehydration can maintain the color of dried samples with a low degradation rate of lycopene.

Automated summary

The degradation/isomerization rate of lycopene in dehydrated tomatoes can be affected by different drying methods. Osmotic pretreatment can reduce drying time and degradation rate of lycopene, leading to better color preservation. Microwave-assisted hot air drying showed the highest drying rate but the lowest lycopene content, while sun-assisted hot air drying had similar lycopene content to hot air drying but undesirable color values.