Using High Hydrostatic Pressure Processing Come-Up Time as an Innovative Tool to Induce the Biosynthesis of Free and Bound Phenolics in Whole Carrots

Abstract

High hydrostatic pressure (HHP) processing has been proposed as an innovative tool to induce the secondary metabolism of fresh produce, inducing the accumulation of health-promoting compounds. In the present study, the effect of HHP applied to whole carrots only for the time needed to reach 60 or 100 MPa (come-up time, CUT) on the content of free and bound phenolics immediately after processing and during storage (3 d at 15 °C) was evaluated. In addition, variables such as the phenylalanine ammonia-lyase (PAL) activity as well as the respiration rate and volatile organic compounds (VOCs) production (related with ethylene) were determined during storage. As an immediate response to HHP, samples treated at 100 MPa showed increases in the content of free [5-O-caffeoylquinic acid (63.9%) and 3,4-di-O-feruloylquinic acid (228.6%)] and bound [p-coumaric acid (82.6%)] phenolics. Furthermore at 1 day, samples treated at 60 MPa showed accumulation of free phenolics [4,5-di-O-caffeoylquinic acid (60.2%), and isocoumarin (98.9%)], whereas samples treated at 100 MPa showed increases of 5-O-caffeoylquinic acid (291.2%) and 3,4-di-O-feruloylquinic acid (466.1%). At 2 days of storage, whole carrots treated at 60 MPa showed accumulation of bound phenolics [rutin (85.5%) and p-coumaric acid (214.7%)], whereas at 3 days 100 MPa samples showed higher quercetin (371.2%). During storage, samples treated at 60 and 100 MPa showed higher respiration rate, and ethylene production, respectively. The main physiological changes induced by HHP in carrots are summarized in a physiological model. HHP-treated carrots could be used as fresh food or as raw material to produce functional food and beverages.