Abstract An efficient drying process for high-value products such as bacterial cultures is characterized by high retention of viability or activity, but low energy demand. Microwave-vacuum drying was tested in this work as a new technique for the preservation of probiotics and starter cultures, which has the potential to fulfill all of these requirements. The impact of chamber pressure (7, 15, 30 mbar), microwave power (1–5 W g −1 ) and maximum product temperature (30–50 °C) on drying time, drying rate, efficiency of microwave input and survival rate of the model strain Lactobacillus paracasei ssp. paracasei F19 ( L. paracasei F19) was studied. Microwave drying time ranged from 50 to 240 min with microwave power as main influencing factor on drying behavior and efficiency. The maximum product temperature and vacuum pressure did not affect the drying time, absorbed energy and thus microwave efficiency significantly, but both parameters had a great impact on survival rate. The combination of 3 W g −1 microwave power input and 35 °C maximum temperature at a low chamber pressure of 7 mbar resulted in a very short drying time of 64 min, a high level of energy efficiency (27%) and also the best product quality in terms of survival rate (33%). Thus, a microwave-vacuum drying process is a potential alternative to conventional freeze or vacuum drying.

中文翻译：

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乳酸菌的温控微波真空干燥：干燥条件对工艺和产品特性的影响

摘要 一种用于高价值产品（如细菌培养物）的高效干燥工艺的特点是存活率或活性保持率高，但能量需求低。在这项工作中测试了微波真空干燥作为一种保存益生菌和发酵剂培养物的新技术，它有可能满足所有这些要求。腔室压力 (7, 15, 30 mbar)、微波功率 (1–5 W g -1 ) 和最高产品温度 (30–50 °C) 对干燥时间、干燥速率、微波输入效率和存活率的影响模型菌株副干酪乳杆菌 ssp。研究了副干酪 F19 (L. paracasei F19)。微波干燥时间为 50 至 240 分钟，微波功率是影响干燥行为和效率的主要因素。产品最高温度和真空压力对干燥时间、吸收能量和微波效率没有显着影响，但两个参数对成活率都有很大影响。3 W g -1 微波功率输入和 35 °C 最高温度相结合，在 7 mbar 的低腔室压力下，干燥时间非常短，仅为 64 分钟，能量效率高 (27%)，同时也是最佳的产品质量的存活率（33%）。因此，微波真空干燥工艺是传统冷冻或真空干燥的潜在替代方案。3 W g -1 微波功率输入和 35 °C 最高温度相结合，在 7 mbar 的低腔室压力下，干燥时间非常短，仅为 64 分钟，能量效率高 (27%)，同时也是最佳的产品质量的存活率（33%）。因此，微波真空干燥工艺是传统冷冻或真空干燥的潜在替代方案。3 W g -1 微波功率输入和 35 °C 最高温度相结合，在 7 mbar 的低腔室压力下，干燥时间非常短，仅为 64 分钟，能量效率高 (27%)，同时也是最佳的产品质量的存活率（33%）。因此，微波真空干燥工艺是传统冷冻或真空干燥的潜在替代方案。