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真空脉动干燥条件对红枣片干燥特性和挥发性风味成分的影响

Effects of pulsed vacuum drying conditions on drying characteristics and flavor quality in jujube slices

  • 摘要: 为探究真空脉动干燥(pulsed vacuum drying, PVD)条件对红枣片干燥特性和风味品质的影响,该研究以热风干燥(hot air drying, HAD)作为对照,探究不同PVD条件下:干燥温度(65、70、75 ℃)、真空保持时间(10、15、20 min)以及常压保持时间(2、4、6 min)对红枣片干燥特性、理化特性及风味物质的影响。结果表明,干燥时间随干燥温度的提高而缩短,随真空保持时间、常压保持时间的增加而延长。在色泽方面,干燥温度70 ℃、真空保持时间15 min、常压保持时间6 min(PVD-70 ℃-15:6)处理条件下的红枣片L*值(明亮度)最高(55.50),∆E*值(色差)最小(1.97),样品色泽最接近鲜样;在微观结构方面,对照组红枣片细胞结构排列紧密,故其硬度最高,脆度较低;而PVD-70 ℃-15:6红枣片具有均匀的蜂窝状结构,故其硬度小、脆硬度适中。雷达图与主成分分析结果表明,不同处理条件显著(P < 0.05)影响红枣片的挥发性风味轮廓。采用顶空固相微萃取-气相色谱-质谱联用方法共检出77种挥发性风味物质,包括酸类11种、酯类14种、烃类42种、醇类2种、醛类3种、酮类1种、其他类化合物4种;其中酸类物质相对含量达到16.66%~27.92%,是红枣片风味的主要贡献者;与对照组相比,PVD-70 ℃-15:6处理组的醛类和酸类物质相对含量分别增加了33.55%和21.82%,表明PVD处理对醛类物质生成具有促进效应,而酸类物质变化相对温和。综合分析,PVD-70 ℃-15:6条件下得到的红枣片品质最优。研究结果可为真空脉动干燥技术在高品质红枣深加工的应用提供一定的理论参考和技术依据。

     

    Abstract: This research aims to systematically investigate the influence of pulsed vacuum drying (PVD) parameters on the drying kinetics, physicochemical attributes, and volatile flavor profiles of red jujube slices. Various PVD parameters were evaluated, including drying temperatures (65, 70, and 75 °C), vacuum holding durations (10, 15, and 20 min), and atmospheric holding durations (2, 4, and 6 min). Hot air drying (HAD) was utilized as the control group. The experimental results demonstrated that the total drying duration was shortened significantly as the drying temperature escalated, whereas it was moderately extended with the prolongation of both vacuum and atmospheric holding times. The drying kinetics were attributed to the complex interplay between thermal energy transfer and the pressure-driven moisture diffusion in the PVD process. Color preservation was one of the most critical quality indicators for fruit processing. Once the treatment group was subjected to a drying temperature of 70 °C, a vacuum holding time of 15 min, and an atmospheric holding time of 6 min (designated as PVD-70 °C-15:6), the color preservation was characterized by the highest luminosity (L* value of 55.50) and the minimum total color difference (∆E* value of 1.97), indicating the most favorable appearance similar to the fresh samples. The macro-level observations were further supported by microstructural analysis via scanning electron microscopy. While the HAD-treated slices displayed a densely packed and collapsed cellular arrangement, leading to maximum hardness and diminished crispness. By contrast, the PVD-70 °C-15:6 samples shared a well-developed, uniform honeycomb-like porous structure to facilitate a better balance between low hardness and moderate crispness after the mitigation of structural shrinkage. Furthermore, the landscape of volatile flavor was dominated by the drying parameters. Radar plot analysis and Principal Component Analysis (PCA) indicated that there were significant (P<0.05) variations in the aromatic profiles under the different treatments. According to the headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), a total of 77 volatile compounds were identified and then quantified, including 11 acids, 14 esters, 42 hydrocarbons, 2 alcohols, 3 aldehydes, 1 ketone, and 4 other compounds; Among them, organic acids, with the relative content from 16.66% to 27.92%, were identified as the predominant contributors to the characteristic aroma of the red jujube slices. Notably, the PVD-70 °C-15:6 treatment demonstrated that the relative content of aldehydes and acids substantially increased by 33.55% and 21.82%, respectively, compared with the HAD control. A relatively stable acidic profile was obtained to promote the synthesis and retention of key aldehyde-based flavor precursors after the fluctuations of cyclic pressure in the PVD process. In the PVD-70°C-15:6 treatment, the optimal overall quality was achieved to effectively balance the drying efficiency with the preservation of the structural, aesthetic, and aromatic integrity of the red jujubes. The findings can also provide a robust theoretical and technical framework for pulsed vacuum drying in high-quality dehydrated functional foods.

     

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