Citrus fruits freshness assessment using Raman spectroscopy

- Raman bands observed in citrus excited with 532 nm are attributable to carotenoids.
- A Raman coefficient of freshness derived from the peel signal is introduced.
- A linear decay of the coefficient of freshness was observed in time (days).
- Carotenoid Raman signal is a good indicator of citrus freshness.
- Portable Raman instruments are suitable for citrus freshness control.

The freshness of citrus fruits commonly available in the market was non-destructively assessed by Raman spectroscopy. Intact clementine, mandarin and tangerine species were characterised concerning their carotenoids skin Raman signalling in a time course from the moment they were acquired as fresh stock, supplying the market, to the physical degradation, when they were no longer attractive to consumers. The freshness was found to strongly correlate to the peel Raman signal collected from the same area of the intact fruits in a time course of a maximum of 20 days. We have shown that the intensity of the carotenoid Raman signal is indeed a good indicator of fruit freshness and introduced a Raman coefficient of freshness (CFresh), whose time course is linearly decreasing, with different slope for different citrus groups. Additionally, we demonstrated that the freshness assessment could be achieved using a portable Raman instrument. The results could have a strong impact for consumer satisfaction and the food industry.