Degradation of carotenoids in pumpkin (Cucurbita maxima L.) slices as influenced by microwave vacuum drying

ABSTRACT

The aim of this study was to investigate the influence of microwave vacuum drying on carotenoids in pumpkin (Cucurbita maxima L.) slices. Carotenoids were measured using the reverse-phase high-performance liquid chromatography technique. It was shown that compared with hot air drying, microwave vacuum drying inhibited color changes and significantly (p < 0.05) improved total carotenoid retention (89.1%) in pumpkin slices. During the microwave vacuum drying process, microwave power had an important effect on total carotenoid and all-trans carotenoids. As microwave power increased, the total carotenoid content significantly decreased (p < 0.05), and the levels of individual carotenoids, including all-trans-α-carotene, all-trans-β-carotene, and all-trans-lutein, generally decreased. However, there was an overall upward trend for the levels of 13-cis-β-carotene, 15-cis-β-carotene, 9-cis-β-carotene, and 9-cis-α-carotene. The trans carotenoid quality of the finished products was improved within a certain range of vacuum levels. In addition to the degradation induced by microwave energy, isomerization was considered to be responsible for the loss of all-trans carotenoids. These results indicated that inappropriate drying methods and conditions might result in high losses of all-trans carotenoids in pumpkins.

KEYWORDS:

• Carotenoids
• MVD
• Pumpkin
• Degradation

Conclusion

The present study demonstrated that compared with FD, the retention of TCs in pumpkin slices after MVD was significantly higher (p < 0.05) than after HD. Microwave power had a significant effect on TC. With an increasing microwave power, the TC content significantly decreased (p < 0.05). Moreover, the levels of individual carotenoids, including all-trans-α-carotene, all-trans-β-carotene, and all-trans-lutein, generally decreased during MVD. However, the contents of 13-cis-β-carotene, 15-cis-β-carotene, 9-cis-β-carotene, and 9-cis-α-carotene exhibited an overall upward trend. In addition to the degradation induced by microwave energy, isomerization was also considered to be responsible for the loss of these all-trans carotenoids. The results showed that inappropriate drying methods and conditions resulted in a large loss of all-trans carotenoids. The significant findings of this research can provide a technical basis for the drying of pumpkin and can serve as a reference for optimisation of the drying process for other fruits and vegetables.

Funding

The research was financially supported by the special fund for agro-scientific research in the public interest (No.201503142-5) and the basal research fund for the Jiangsu Academy of Agricultural Sciences (major cultivation project No. ZX(15)1008).

Additional information

Funding

The research was financially supported by the special fund for agro-scientific research in the public interest (No.201503142-5) and the basal research fund for the Jiangsu Academy of Agricultural Sciences (major cultivation project No. ZX(15)1008).