2.1. Plant material
For ripening transition assay, Fragaria vesca ‘Mara des Bois’ strawberries were harvested in 2017 from a commercial planting in San Sebastian de los Reyes (Madrid, Spain) were selected by colour and transported to the laboratory and classified into three ripening stages as 3/4 red (AR), full red (FR) and dark red (DR). Immediately after harvest, half of the collected fruits were frozen in liquid nitrogen and the other half of fruit was used for quality parameter assessments.
The postharvest treatment assay was performed using fruit harvested in 2018 of an intermediate stage between FR and DR from the same commercial planting. Two hours after harvest, selected strawberries free from physical defects were transferred into covered polyethylene boxes of 200 g of fruit equipped with inlet-outlet ports. Strawberries immediately after harvest were the control sample of storage period analysis (0d). One lot of 20 samples of freshly harvested fruit placed directly at 20 ºC during two days and they were the shelf-life control (SLC). A total of 80 boxes of fruit were equality divided into 2 lots. Two lots of 40 subsamples each were stored at 0 ±1 ºC (Low temperature, LT) in two containers with a capacity of 1 m3 and 90 % relative humidity (RH). One container was fluxed with a continuous flow of air during 2 days or 7 days (2d Air and 7d Air), and the other one under continuous flow of 17% CO2 in air for 2 days (2d CO2). At the end of CO2 treatment, 10 samples were evaluated and 30 were air-ventilated for 5 additional days (2d CO2+5d Air). Following 7 days of storage at 0 ºC, fruit from each treatment were transferred to a chamber at 20 ºC and the atmosphere was saturated with water vapour to reach 80 % RH. After 1 and 2 days of shelf-life at 20 ºC (SL), samples from those stored in air at low temperature (LTA) or under high CO2 (LTC) were evaluated. Fruits were rapidly frozen in liquid nitrogen and stored at -80 ºC. Observation of external appearance of fruit of each treatment was made every day and total soluble solids, titratable acidity and weight loss were also determined. All strawberries were kept in the dark throughout the trials.