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Simple and Rapid Quantification of Total Carotenoids in Lyophilized Apricots (Prunus armeniaca L.) by Means of Reflectance Colorimetry and Photoacoustic Spectroscopy

Photoacoustic spectroscopy (PAS) and reflectance colorimetry are suggested as new analytical tools for analysis of total carotenoids in lyophilized apricot powders. The data obtained by these two techniques from seven apricot cultivars was compared to that acquired by spectrophotometry and high performance liquid chromatography (HPLC). Best correlations were found between the total carotenoids (TC) content (obtained by VIS spectrophotometry: 1.2-3.4 mg TC/100 g, fresh mass basis) and colorimetric index a* (a* represents the redness of the investigated sample), as well as either Ar-ion laser (or Xe-lamp) based PAS. In all three cases linear correlation was comparable. However, according to the sensitivity and precision data, expressed via limit of detection (LOD) and measurement repeatability, the Xe-lamp based PAS is a preferred approach followed by colorimetric index a* and Ar-ion laser PAS. Both PAS methods exhibit practically the same Pearson correlation coefficient (R=0.987 and R=0.991) values. Nevertheless, residual sum of the squares (RSS) and residual standard deviation of the linear regression (sy/x) differ markedly. For Xe-lamp based PAS these parameters were much lower than in the case of Ar-ion laser PAS. Likewise, analysis imprecision amounted to RSD of 1-3% for Xe-lamp PAS and 2-6% for Ar-ion laser PAS. On the other hand, as expected, the calibration sensitivity achieved for the PAS signal induced by an Ar-ion laser at 481 nm was substantially higher than that of a Xe-lamp at 470 nm. However, according to much lower sy/x the corresponding LOD for Xe-lamp PAS was still two times lower than that of Ar-ion based laser PAS (0.59 vs. 1.10 mg TC/100 g). Unlike this, Ar-ion laser PAS showed more favourable instrumental precision and standard error of the weighted mean when compared to Xe-lamp PAS (0.1-0.6 and 0.1-0.3% vs. 0.5-8.0 and 0.4-1.7%, resp.). As far as colorimetric indices are being concerned, only a* proved to be analytically useful ; excellent R but rather modest RSS and sy/x resulting in LOD value of 0.70 mg TC/100 g and acceptable analysis imprecision of up to 3%. The outcome of this research provides sufficient amount of evidence that analytical methods such as reflectance colorimetry and PAS are feasible without the use of any chemicals for reliable quantification of total carotenoids in freeze-dried apricot homogenates.

total carotenoids; beta-carotene; apricot (Prunus armeniaca L.); photoacoustic spectroscopy; colorimetry

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