Impact of industrial freezing on quality attributes of carrot slices

Summary

Freezing is one of the most popular and widely used methods for preservation of vegetables. Still, the impact of freezing on important quality attributes of vegetables, such as texture and phytochemical content, is not fully investigated. The main objective of this study was to evaluate the effect of industrial flow-freezing on selected quality attributes of carrot slices. Carrot quality was monitored ‘from field to fork’, i.e., sampling was performed after harvest, after industrial flow-freezing (in situ) and after cooking. For reference, carrots from the same harvest batch were stored fresh for 14 d under conditions that simulated commercial distribution (11 d, 4°C) and retail sale (3 d, 20°C, light 16 h d‑1). Industrial flow-freezing was also compared with two other freezing techniques for impact on carrot quality; magnetic field freezing, and static freezing in a domestic cabinet freezer (‘home freezing’). Changes in carrot quality were documented by texture analyses and selected chemical analyses; vitamin C (HPLC-DAD) and plant metabolomics (LC-Q-TOF-MS/MS). The results show that industrial flow-freezing preserves the phytochemical content in carrot slices well. Though there was a slight loss of vitamin C during freezing processing, the vitamin C content of frozen carrot was similar to that of fresh carrot after simulated distribution and retail sale, both before and after cooking. The metabolomics data revealed that heat processing was of most importance regarding changes in the carrot metabolome. Industrial flow-freezing and magnetic field freezing retained a higher vitamin C content after cooking than ‘home freezing’. However, none of the tested freezing techniques could prevent a softer texture after cooking of frozen carrot compared to fresh-cooked carrot.