ABUSIVE ISOTHERMAL CONDITIONS IMMEDIATELY AFTER HARVEST AFFECT BUTTERHEAD LETTUCE WATER STATUS

Abstract

ABSTRACT The purpose of this study was to evaluate water status and overall visual quality (OVQ) of fresh butterhead lettuce during the first hours after harvest when plants were exposed to three different isothermal conditions: T1 = 0–2C, T2 = 10–12C and T3 = 20–22C (all with optimal relative humidity). Relative water content (RWC), water content (WC), free water (FW), bound water (BW), free water-to-total water ratio (FW/TW) and OVQ were evaluated in external (E), middle (M) and internal (I) zones of lettuce. High temperatures affected the tissue response to the uptake of water, diminishing the tissue turgid mass and increasing RWC, being I the most affected zone. Water movements (decreases in FW with simultaneous increases in BW) were detected immediately after harvest, even if conditions were optimum. However, the exposition temperature was a significant factor that affected the exchange between FW and BW. Texture and browning of lettuce heads were affected by inadequate temperature. PRACTICAL APPLICATIONS Lettuce is a highly perishable vegetable whose quality and shelf life are limited by the storage conditions. Inadequate temperature immediately after harvest is a climatic stress that produces unfavorable changes to consumer acceptability. Uncontrolled conditions (especially high temperature) are recurrent during transport towards the distribution center. These first hours after harvest are crucial for vegetable shelf life because quality losses at these earlier stages can not be recovered. Therefore, knowledge of the events occurring within the plant when temperature is uncontrolled is of fundamental importance to improve and optimize lettuce management.