Discoloration investigations of freeze‐dried carrot cylinders from physical structure and color‐related chemical compositions

Abstract

BACKGROUND High carotenoid content always lead to a yellower/redder color in carrots, while a puzzling phenomenon still exists that freeze‐dried carrots (FDC) have a higher carotenoid content but a lighter color compared with thermal‐dried carrots. It seems that carotenoid is not the only main factor affecting sample color. Hence the discoloration characteristics of freeze‐dried carrots were comprehensively analyzed from physical structure and color‐related chemical composition profile. RESULTS Outcomes of low‐field nuclear magnetic resonance and scanning electron microscopy showed that sublimation of immobilized water preserved the intact porous structure of FDC, which kept the volume shrinkage below 30% and led to less accumulations of color‐related compositions. Besides, results of correlation and principal component analysis‐X model proved that lutein and caffeic acid mainly affected a* value (r = 0.917) and b* value (r = 0.836) of FDC, respectively. Moreover, lipoxygenase indirectly affected sample color by degrading carotenoids, and the lutein content loss for fresh and blanching FDC was 41.56% and 47.14%, respectively. CONCLUSIONS The discoloration of FDC was significantly affected by both physical structure and color‐related chemical compositions. © 2021 Society of Chemical Industry