Combined Use of Blanching and Vacuum Impregnation with Trehalose and Green Tea Extract as Pre-treatment to Improve the Quality and Stability of Frozen Carrots

Abstract

The use of green tea extract (GTE) and trehalose for the production of frozen carrots fortified with bioactive compounds was investigated. Carrot enrichment was performed by blanching and vacuum impregnation (VI). Functional properties and quality attributes of carrots were evaluated after pre-treatments, freezing and frozen storage (FS). Blanching effectively inactivated peroxidase and pectinmethylesterase enzymes. Blanching in trehalose and VI in trehalose and/or GTE solutions limited the soluble solid and firmness losses through pre-treatments, while effect on colour was similar to other pre-treatments (Δh° ≈ +6; ΔL* ≈ −6). Pre-treatments did not affect the carotenoid content while increased the total polyphenol content (TPC) and antioxidant activity (AOA), which in samples enriched with GTE resulted respectively three and two times higher than the fresh vegetable. After FS, carrots showed a drastic firmness loss, and colour change. Trehalose showed a cryoprotective effect on carrots’ firmness and colour only when its penetration in plant cells was promoted by blanching. All samples highlighted a significant carotenoid loss (−40%), whilst a TPC decrease was observed only on GTE polyphenol fortified carrots. Despite this loss, AOA of carrots enriched with GTE after 60 days of frozen storage was two times higher than AOA of fresh carrots.