不同干燥方法对紫薯干燥效率及品质的影响

doi:10.3864/j.issn.0578-1752.2014.07.017

摘要/Abstract

摘要： 【目的】为了提高紫薯干燥效率及干制品质，研究不同干燥方法对紫薯水分散失、色泽、花青素、酚类化合物及抗氧化能力的影响。【方法】采用穿流式热风干燥、鼓风干燥、气体射流冲击干燥及低氧气体射流冲击干燥4种干燥方式处理紫薯。首先探讨了穿流式热风干燥、鼓风干燥和气体射流冲击干燥3种干燥方式分别在干燥风温70℃，物料切片厚度1.93 mm以及微波预处理3 min的条件下对紫薯干燥曲线、干燥速率曲线及有效水分扩散系数的影响。其次探讨了穿流式热风干燥、鼓风干燥、气体射流冲击干燥和低氧气体射流冲击干燥4种干燥方式在干燥风温70℃，物料切片厚度1.93 mm以及微波预预处理3 min的条件下对紫薯干燥后的色泽、总花青素含量、总酚含量及酚类化合物对DPPH•清除率的影响。最后探讨了不同低氧气体射流冲击干燥风温、风速、喷嘴高度和切片厚度4个因素对紫薯干燥后的色泽、总花青素含量、总酚含量及酚类化合物清除DPPH•的影响。【结果】紫薯与大多数食品原材料在干燥过程中的水分散失规律相似。紫薯的气体射流冲击干燥、鼓风干燥和穿流干燥均属于降速干燥，物料在整个干燥过程中未有明显的恒速干燥阶段。气体射流冲击干燥最高干燥速率比鼓风干燥高84.04%，比穿流干燥高61.60%。紫薯在气体射流冲击干燥过程的前40 min内水分含量快速降低，在之后的干燥过程中水分含量却以非常缓慢的速率下降。鼓风干燥、穿流干燥和气体射流冲击干燥的有效水分扩散系数分别为9.62×10-9、10.23×10-9和15.02×10-9 m2•s-1。本研究所选鲜紫薯的总花青素含量为90.85 mg•100g-1，总酚含量为262.14 mg•100g-1，紫薯酚类化合物对DPPH•的清除率为40.84%。低氧气体射流冲击干燥比普通气体射流冲击干燥、鼓风干燥和穿流式热风干燥具有更好的干后色泽和更高总花青素含量、总酚含量及DPPH•清除率。经低氧气体射流冲击干燥后的紫薯色差值为20.35，总花青素含量为34.79 mg•100g-1，总酚含量为139.26 mg•100g-1以及酚类化合物对DPPH•的清除率为28.49%。在探讨不同低氧气体射流冲击干燥条件对紫薯品质的影响试验中，紫薯的总花青素含量、总酚含量及DPPH•清除率随着干燥风温的增加以及随着干燥风速、喷嘴高度、切片厚度的降低而降低。而色差值却随着低氧气体射流冲击干燥的风温增加及风速、喷嘴高度、切片厚度的降低而增加。且干燥后紫薯的总花青素最高保存率为59.58%，最高总酚保存率为82.35%，最高抗氧化活性保存率为82.05%。【结论】紫薯的气体射流冲击干燥与鼓风干燥和热风干燥相比具有更高的干燥效率和干后品质，且采用低氧气体射流冲击干燥可在普通气体射流冲击干燥的基础上进一步提高紫薯的干后品质。

关键词: 干燥 , 低氧 , 气体射流冲击 , 紫薯 , 抗氧化

Abstract: 【Objective】In order to improve the drying efficiency and drying quality of purple sweet potato (PSP), the effect of different drying methods on moisture lost, value of color difference, anthocyanins, polyphenol and antioxidant of PSP were studied.【Method】The PSP were dried by hot air cross-flow drying, forced air drying, air-impingement jet drying and hypoxia air-impingement jet drying. Firstly, the effect of the three kinds of drying methods including hot air cross-flow drying, forced air drying and air-impingement jet drying on drying curves, drying rate curves and effective moisture diffusion coefficient under the conditions of drying temperature of 70℃, slice thickness of 1.93 mm and microwave pre-treatment for 3 min was studied. Secondly, the effect of four kinds of drying methods including hot air cross-flow drying, forced air drying, air-impingement jet drying and hypoxia air-impingement jet drying on color, total anthocyanins content, total polyphenol content and DPPH• scavenging activity of PSP was analyzed under the conditions of drying temperature of 70℃, slice thickness of 1.93 mm and microwave pre-treatment for 3 min. Furthermore, the influence of four factors including air temperature, air velocity, nozzle distance and slice thickness of hypoxia air-impingement jet drying on the color, total anthocyanins content, total polyphenol content and DPPH• scavenging activity of PSP were studied. 【Result】According to the experimental data, there was a similarity law in water loss of PSP, compared with the most results of food material drying test. Forced air drying, hot air cross-flow drying and air-impingement jet drying of PSP mainly occurred in the falling rate drying period. There was no stage of constant rate drying in the drying process. The drying rate of air-impingement jet drying was 84.04% higher than the forced air drying, and it was also 61.60% higher than hot air cross-flow drying. The moisture content of PSP decreased very fast during the first 40 min of air-impingement drying process. But the moisture content of PSP decreased very slowly in the later drying process. Effective moisture diffusion coefficient of forced air drying, hot air cross-flow drying, air-impingement jet drying was 9.62×10-9, 10.23×10-9, and 15.02×10-9 m2•s-1, respectively. In this research, the total anthocyanins content, total phenols content and DPPH• scavenging activity of the PSP sample was 90.85 mg•100g-1 and 262.14 mg•100g-1, respectively. Compared to the forced air drying, hot air cross-flow drying and air-impingement jet drying, the color was better and the total anthocyanins content, total phenols content and DPPH• scavenging activity were higher by hypoxia air-impingement jet drying. The total color difference, total anthocyanins content, total phenols content and DPPH• scavenging activity of hypoxia air-impingement jet dried PSP was 20.35, 34.79 mg•100g-1, 139.26 mg•100g-1 and 28.49%, respectively. In the experiments of the effect of different hypoxia air-impingement jet drying conditions on quality of dried PSP, with the drying temperature increase and air velocity, nozzle distance and slice thickness decrease, the total anthocyanins content, total phenols content and DPPH• scavenging activity decreased, but the value of color difference reduced. In addition, the highest survival rate of total anthocyanins content, total phenols content and DPPH• scavenging activity of dried PSP was 59.58%, 82.35% and 82.05%, respectively.【Conclusion】The drying efficiency and quality of air-impingement jet drying PSP is higher than the forced air drying and hot air cross-flow drying. In addition, the hypoxia air-impingement jet drying can improve the dried sample quality of PSP based on the normal air-impingement jet drying.

Key words: drying , hypoxia , air-impingement jet , purple sweet potato , antioxidant

李文峰, 肖旭霖. 不同干燥方法对紫薯干燥效率及品质的影响[J]. 中国农业科学, 2014, 47(7): 1397-1408.

LI Wen-Feng, XIAO Xu-Lin. Effect of Different Drying Methods on Drying Efficiency and Quality of Purple Sweet Potato[J]. Scientia Agricultura Sinica, 2014, 47(7): 1397-1408.

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