Development and Evaluation of an Ultrasonic Humidifier to Control Humidity in a Cold Storage Room for Postharvest Quality Management of Dates

Abstract

Dates are subjected to postharvest losses in quality and quantity caused by water loss, fermentation, insect infestation, and microbial spoilage during storage. Cold storage is the main element in the postharvest quality management used for fruit preservation. Although cold storage is used for dates, precision control of the relative humidity (RH) using ultrasonic applications is not used thus far, or it is applied to other fruits on a small scale. Therefore, we designed and constructed an ultrasonic humidifier (DUH) for RH control in the cold storage room (CSR) of dates. The optimum air velocity of 3 m s−1 at the outlets of the DUH ducts produced a mist amount of 6.8 kg h-1 with an average droplet diameter of 4.26 ± 1.43 µm at the applied voltage of 48 V and frequency of 2600 kHz of the transducers. The experimental validation was carried out by comparing a CSR controlled with the DUH with two conventional CSRs. The three tested CSRs were similar in dimensions, cooling system, and amount of stored dates. The time required for cooling 800 kg of dates in the controlled CSR from 25 °C to the target temperature of 5 °C was approximately 48 h. The DUH precisely controlled the RH at the maximum RH set point of 80% in the tested CSR at 5 °C. The controlled RH at 80% has a positive impact on the physicochemical characteristics of the stored dates. It significantly reduced the weight loss of the fruits and preserved fruit mass, moisture content, water activity, firmness, and color parameters. However, no significant effect was observed on fruit dimensions, sphericity, and aspect ratio. The microbial loads of mesophilic aerobic bacteria, molds, and yeasts fell within the acceptable limits in all tested CSRs. Both stored date fruits and artificially infested dates showed no signs of insect activity in the controlled CSR at the temperature of 5 °C and RH of 80%. The DUH proved to be a promising technology for postharvest quality management for dates during cold storage.

Prediction of Date Fruit Quality Attributes during Cold Storage Based on Their Electrical Properties Using Artificial Neural Networks Models

“…The obtained fruits were cleaned, air-dried, and then placed into aerated plastic containers (65 cm × 14 cm × 21 cm) and left at room temperature (25 °C) for 24 h. Then, they were transferred for storage in a cold storage room (48.8 m 3 total capacity) with a set-point temperature of 5 °C [ 5 ] at the Date Palm Research Center of Excellence, King Faisal University, Saudi Arabia.…”

“…Therefore, it is imperative to preserve date fruits in cold storage to maintain their supply chain. The fully ripe date palm fruits (Tamar) can be stored at 0–5 °C for 6–12 months [ 3 , 4 , 5 , 6 ]. Stored date fruits (cv.…”

“…The most critical factors that affect the longevity of fruits after harvesting and during storage are temperature and relative humidity [ 12 , 13 , 14 ]. Optimal relative humidity helps prevent weight loss, the spread of fungal diseases, and physiological disorders [ 5 , 15 ]. Lowering these factors to a suitable level is one approach to slow down the deterioration of fruits and hence increase the fruit preservation time during storage [ 16 , 17 ].…”

Effects of Deficit Irrigation Scheduling on Water Use, Gas Exchange, Yield, and Fruit Quality of Date Palm

“…The fruit total soluble solids (TSS), moisture content, and pH were determined according to standard AOAC analysis methods [44]. The fruit moisture content (%) was measured by drying the samples under vacuum at 70 • C using a vacuum-drying oven (LabTech, LVO-2041P, Korea) [45][46][47]. The TSS was determined using a laboratory refractometer (RFM 860, Bellingham & Stanley Ltd., Kent, UK).…”

The Combined Effects of Precision-Controlled Temperature and Relative Humidity on Artificial Ripening and Quality of Date Fruit

“…The heating unit has consisted of an electrical DC fan and a nickel-chrome heat coil with a maximum power of 500 W. To adjust the RH inside the treatment chamber, we used an ultrasonic humidifier (model: HM3000-B5, Black & Decker, Suzhou, China). The ultrasonic humidifier is developed based on the methods described by the authors in [31][32][33][34] for adjusting RH in the systems. The image of six automated artificial ripening systems is shown in Figure 3.…”