Mohammed Maged, Alqahtani Nashi, El-Shafie Hamadttu
Date Palm Research Center of Excellence, King Faisal University, Al-Ahsa 31982, Saudi Arabia.
Agricultural Engineering Department, Faculty of Agriculture, Menoufia University, Shebin El Koum 32514, Egypt.
Foods. 2021 Apr 26;10(5):949. doi: 10.3390/foods10050949.
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 at the outlets of the DUH ducts produced a mist amount of 6.8 kg h 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.
枣在储存期间会因水分流失、发酵、虫害和微生物腐败而遭受采后质量和数量损失。冷藏是用于水果保鲜的采后质量管理的主要要素。虽然枣采用了冷藏，但迄今为止尚未使用超声波应用精确控制相对湿度（RH），或者只是小规模应用于其他水果。因此，我们设计并构建了一种用于枣冷藏库（CSR）中控制RH的超声波加湿器（DUH）。在48 V的施加电压和2600 kHz的换能器频率下，DUH管道出口处3 m/s的最佳风速产生了6.8 kg/h的雾量，平均液滴直径为4.26±1.43 µm。通过将由DUH控制的CSR与两个传统CSR进行比较来进行实验验证。三个测试的CSR在尺寸、冷却系统和储存枣的数量方面相似。在受控CSR中将800 kg枣从25°C冷却到目标温度5°C所需的时间约为48小时。DUH在5°C的测试CSR中，将RH精确控制在最大RH设定点80%。80%的受控RH对储存枣的理化特性有积极影响。它显著降低了水果的重量损失，并保持了果实质量、水分含量、水分活度、硬度和颜色参数。然而，在果实尺寸、球形度和纵横比方面未观察到显著影响。在所有测试的CSR中，嗜温需氧菌、霉菌和酵母菌的微生物负荷均在可接受范围内。在5°C温度和80%RH的受控CSR中，储存的枣果实和人工感染的枣均未显示出昆虫活动的迹象。DUH被证明是一种用于枣冷藏期间采后质量管理的有前途的技术。
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