Effect of Drying Temperatures on the Peanut Quality during Hot Air Drying

Abstract

than 10 w. b. 6, 7 , it was susceptible to mold development and toxin production 8. The peanut drying process can be performed based on many drying methods, such as solar radiation, hot air drying, microwave and radio frequency heating etc. 9. But the most commonly used methods were solar radiation and hot air drying 9. Drying by sun usually took a long time and was affected by weather. Hot air drying process can be performed by traditional bin dryers or semitrailers with heated air passing through the bed of peanuts 10. Studies on peanut drying by hot air mainly focused on drying parameters 7 , the uniformity of peanut drying 11 , the effective diffusion coefficient and the main thermodynamic properties 12 , the mathematical model of thin layer drying 12, 13 , the non-isothermal drying models 14. In addition to the above researches on peanut drying, there were also some studies on the quality of raw peanut Abstract: Peanuts are usually with high moisture after harvest and must be dried to prevent mildew. Hot air drying is the most commonly used method for peanut drying. The purpose of this study was to evaluate the drying temperatures on the peanut qualities. In this paper, fresh peanuts were dried with solar radiation (control group) and hot air at 35-60℃ until the moisture content of peanut reduced below 10%. The physical (texture, damaged percentage of red testa and breakage percentage of peanut kernel), physiological (germination) and biochemical (the contents of vitamin E and aflatoxin B 1 ; acidity values, iodine values, peroxide values and fatty acid composition of peanut oil; solubility, emulsifying, foaming, water-holding capacity and oil-binding capacity of peanut protein) properties of peanut kernel were determined under different drying conditions (solar radiation, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃). The results showed that hot air temperatures had obvious influences on peanut qualities. The damaged percentage of red testa and breakage percentage of peanut kernel increased remarkably when the drying temperatures were above 45℃. Meanwhile, when drying temperatures were more than 45℃, the acid value and peroxide value of the extracted oil increased significantly. Furthermore, some properties exhibited prominent changes when the temperatures were higher than 50℃, such as hardness, brittleness, germination percentage, and the Vitamin E content of peanut kernel. In addition, the research results revealed that hot air can increase hydrophobicity of peanut protein and affect the functional properties of peanut protein. Therefore, it could be concluded that peanut should be dried by hot air below 45℃ for quality maintenance. It also provided reference to choose suitable drying temperatures based on the final use of peanut.

Efficient Production of Dried Whole Peanut Fruits Based on Infrared Assisted Spouted Bed Drying

“…However, this drying method is limited by weather factors, and the product quality is low, which is inconsistent with the current consumer demand for high-quality dehydrated products [3]. Hot-air drying and heat pump drying are also common dehydration methods in industrial dried peanut production [4,5]. However, due to the relatively low drying efficiency, these methods consume a lot of time and energy resources [6].…”

Effect of Drying Methods on Peanut Quality during Storage

“…And the initial moisture contents of the peanut were tested between 17.7％ and 22.9％. Some of the wet peanuts were spread on the ground and dried by the sun as called solar radiation for 3 days, and some of them were dried by hot air at 35, 40, 45, 50 and 55℃ for 18 h, 14 h, 10 h, 8 h and 6 h, respectively until the moisture contents were all below 10％ as mentioned in our previous study 25) . Dried peanuts obtained under different drying conditions were then shelled by a dehusking machine (Yuexin Machinery Factory, Gongyi, China) , respectively.…”

“…Soxhlet extraction 25) , aqueous enzymatic extraction 28−30) and thermosonication assisted extraction 3) were the common extraction method of peanut oil. In this paper, peanut oil was extracted from the sliced peanut kernels by petroleum ether, and then the petroleum ether was removed with a rotary vacuum evaporator according to Qu et al 25) The extracted oil was then used for further chemical analysis.…”

“…The peroxide values of peanut oil were measured by the Chinese National Standard GB 5009.227-2016, using 3 g oil from each sample and expressed as millimoles of active oxygen in 1 kg oil 25) .…”

“…Method for iodine values determination of peanut oil followed Chinese National Standard GB/T 5532-2008. Iodine value of peanut oil was expressed in grams of iodine absorbed by 100 g oil 25) .…”