穿刺协同乙醇预处理对胡萝卜片热风干燥特性影响

干燥效率低导致的能耗高、品质劣变是果蔬热风干燥加工面临的严峻挑战。为改善胡萝卜热风干燥特性，该研究以横切和纵切方式获得的胡萝卜片为研究材料，对其进行穿刺（perforation pretreatment，PT）、乙醇浸渍（alcohol pretreatment，AT）和穿刺协同乙醇浸渍预处理（perforation synergistic alcohol pretreatment，PAT）。研究发现：同未预处理的胡萝卜片相比，PT、AT和PAT预处理技术的应用均显著提高了胡萝卜有效水分扩散系数及热风干燥速率，并将干燥时间缩短10.61%～50.00%，其中PAT样品干燥时间最短。相同预处理方式下，纵切的胡萝卜片相比于横切表现出较高的有效水分扩散系数、较快的干燥速率及较短的干燥时间。进一步，我们提出了PAT预处理具有较高干燥效率的“三重奏机制”：预脱水降低干燥负荷、毛细管流促进水分传质、细胞通透性的增强降低水分传质阻力。在品质方面，PAT预处理显著改善了纵切胡萝卜片的体积收缩、复水性、色泽、总类胡萝卜素和抗坏血酸含量、抗氧化活性及风味等品质特性。因此，为高效获得品质相对较优的脱水胡萝卜，可在其纵向切片后进行PAT预处理。该研究为改善胡萝卜热风干燥提供了一种简单有效的预处理技术，同时也为其他果蔬提质、增效、节能干燥提供参考。

Effects of puncture combined with ethanol pretreatment on the hot air drying characteristics of carrot slices

Hot air drying is required for the short duration, energy saving, and high quality of food products. In this study, an artificial perforation and alcohol (PAT) pretreatment was proposed to enhance the hot air drying of carrot slices. The carrot was first cut in the transverse and longitudinal sections. Various parameters were then evaluated, including the effective moisture diffusion coefficient, drying rate and time, color, volume shrinkage, rehydration potential, total content of carotenoids and ascorbic acid, antioxidant activity, and flavor. Control samples were selected without pretreatment or subjected to separate perforation (PT) and alcohol maceration (AT) pretreatments. The results demonstrated that the effective moisture diffusion coefficients of pretreated carrot slices ranged from 1.07 to 1.69 times higher in the AT, PT, and PAT pretreatments, compared with the unpretreated samples. The high drying rates enhanced the drying efficacy of carrot slices during hot air drying in the PT, AT, and PAT pretreatments. The drying duration was reduced by 10.61%~50.00%, compared with the unpretreated samples, when the moisture content fell to 0.1 (g water/g dry basis). There was a positive correlation between the drying duration and energy savings. The energy savings were reduced from 10.61% to 50.00% at the constant drying temperature, air velocity, and loading. Among them, the PAT pretreated samples exhibited the highest effective moisture diffusion coefficient and drying rate, with the shortest drying duration, followed by the AT, PT, and unpretreated samples. Additionally, a triple enhancement was proposed for the carrot slices drying in the PAT pretreatment: 1) The dehydration load was reduced at the initial dehydration stage in the pretreatment during hot air drying; 2) Capillary water flow was induced by the porous structure that created by artificial perforation; 3) Cell permeability increased to reduce the water flow resistance. Three factors improved the hot air drying of carrot slices. Importantly, the longitudinally-cut carrot slices shared a higher effective moisture diffusion coefficient and drying rate, but a shorter drying time in all pretreatments, compared with the transversely-cut slices. This was attributed to the severe volume shrinkage in the transverse cuts during drying, leading to the less microchannels and impeded moisture diffusion. In physicochemical quality, the hot air drying negatively impacted the quality of fresh carrots. However, the PT, AT, and PAT pretreatments improved the quality of dried carrot slices, in terms of color, volume shrinkage, rehydration, total content of carotenoids and ascorbic acid, antioxidant activity, and flavor. Specifically, PAT pretreatment significantly mitigated the volume shrinkage of longitudinally-cut carrot slices during drying, leading to the least color alteration, the highest saturation and rehydration capacity, as well as the highest content of volatile components. Furthermore, there was the strongest antioxidant activity, due to a relatively high concentration of total carotenoids and ascorbic acid. In conclusion, PAT pretreatment on longitudinal slicing can be an efficient strategy to produce dehydrated carrot slices with superior quality. This research offers practical and effective implications to enhance the hot air drying of fruits or vegetables at an industrial scale.