The analytical performance of the proposed laser-based photoacoustic spectroscopy (LBPAS) and optothermal window (OW) method for quantification of β-carotene content in sea buckthorn juices is compared to that of the conventional high-performance liquid chromatography (HPLC). Both photothermal techniques (laser-based photoacoustic spectroscopy (LBPAS) and optothermal window (OW)) are direct methods that unlike HPLC obviate the need for the extraction of the analyte. The outcome of the study leads to the conclusion that LBPAS and OW are both suitable for quick screening of ß-carotene in sea buckthorn juices. The β-carotene content of the samples changed due to the added sea buckthorn pomace and storage time. The correlation between the two methods and HPLC is linear with R2=0.9897 for LBPAS and R2=0.9928 for OW, respectively. Both methods are capable of the rapid and non-destructive determination of β-carotene in sea buckthorn juices without a need for sample pre-treatment.

Background. Photoacoustic spectroscopy (PAS) is a tool for the rapid and non-destructive identification of materials even without contact. In recent years, there have been several works concerning the applicability of PAS in food analytical measurements. The intention of this work is to identify whether there is a correlation between total carotenoid and the β-carotene content of pumpkin and squash measured by high-performance liquid chromatography (HPLC), spectrophotometry (SP) and PAS. Material and methods. 'Crown prince F1', 'Veenas F1', 'Atlas F1' and 'Apollo F1' (SAKATA) were used as experimental materials. The samples were measured in a fresh state and in a lyophilised condition with HPLC, SP and PAS. Results. The results of SP show that total carotene content varies according to the species and variety. Lyophilisation resulted in lower, although varying carotene content compared to the raw form. Typical PA spectra of pumpkins were determined (300-550 nm), normalized to the carbon black powder. At 17 Hz the amplitude and carotene content shows direct proportionality in the range investigated. Photoacoustic (PA) signal and carotenoid content of pumpkin samples gave a linear correlation (R² = 0.9821). Conclusion. The measurement of PA spectra gives reliable information about the total carotene content of pumpkin and squash samples. These findings may allow the use of PAS as a fast tool for the carotenoid determination in squashes and give the possibility of instead for the results to be used for the evaluation of squash varieties currently used for industrial processing in functional food development.