Chair of Food and Bioprocess Engineering, Technical University of Munich, Freising, Germany.
J Appl Microbiol. 2018 Oct;125(4):1128-1136. doi: 10.1111/jam.13935. Epub 2018 Jul 17.
Microwave freeze drying (MWFD) in comparison with conventional freeze drying allows for intensification of the preservation process of lactic acid bacteria without imposing additional processing stress. Viability as a function of storage time of microwave freeze-dried Lactobacillus paracasei ssp. paracasei F19 was investigated in comparison to conventionally lyophilized bacteria of the same strain. Furthermore, the impact of the protectants, sorbitol, trehalose and maltodextrin, on shelf life was analysed.
The highest inactivation rates of 0·035 and 0·045 day , respectively, were found for cultures without protectants. Thus, all additives were found to exhibit a protective effect during storage with inactivation rates between 0·015 and 0·040 day . Although trehalose and maltodextrin samples were in the glassy state during storage, in contrast to samples containing sorbitol as protectant, the best protective effect could be found for sorbitol with the lowest inactivation rate of 0·015 day .
Due to its low molecular weight, it might protect cells owing to better adsorption to the cytoplasma membrane. Sorbitol additionally shows antioxidative properties. Storage behaviour of microwave freeze-dried cultures follows the typical behaviour of a product dried by conventional lyophilization. No significant influence of the drying technique on storage behaviour was detected.
General findings concerning storage behaviour in freeze drying are likely to be applicable in MWFD with only slight adjustments.
与传统冷冻干燥相比，微波冷冻干燥可以在不施加额外加工应力的情况下强化乳酸菌的保存过程。本研究比较了微波冷冻干燥的副干酪乳杆菌亚种副干酪乳杆菌 F19 与同株传统冻干菌的储存时间与存活率的关系。此外，还分析了保护剂山梨糖醇、海藻糖和麦芽糊精对保质期的影响。
未添加保护剂的培养物的失活动力最高，分别为 0.035 和 0.045 天。因此，所有添加剂在储存过程中都表现出保护作用，失活动力在 0.015 和 0.040 天之间。尽管海藻糖和麦芽糊精样品在储存过程中处于玻璃态，与含有山梨糖醇作为保护剂的样品相反，但山梨糖醇的保护效果最好，失活动力最低，为 0.015 天。
由于其分子量低，它可能通过更好地吸附到细胞质膜来保护细胞。山梨糖醇还具有抗氧化特性。微波冷冻干燥培养物的储存行为遵循传统冻干产品的典型行为。未检测到干燥技术对储存行为的显著影响。
关于冷冻干燥储存行为的一般发现可能适用于 MWFD，只需稍加调整。
