Abstract: Gut microbiota exerts substantial influence on human health and thus attracts extensive research interests in recent years. Oral administration of living probiotics in adequate amount could alleviate inflammatory bowel disease,treat various types of diarrhea and promote digestion. Living probiotics in tablet form has been applied in clinical trials. In food industry,a relatively cost-effective and facile powder production approach is desired for manufacturing active probiotics product in order to reduce the cost and meet the need of the expanding market. Spray drying is a rapid powder production method with a high production capacity. However,during spray drying the atomized droplets will undergo a fast heating and dehydration process. The associated heat stress,dehydration stress,oxidative stress and other stresses will cause a substantial reduction of the viability of the probiotics in the droplets. Meanwhile,the structure of a spray dryer makes it difficult to track the drying process of each droplet. This issue represents a great challenge for studying the inactivation history of probiotics during drying and for exploring the interactions between carrier materials and probiotic cells. This article firstly discussed the droplet drying process inside a spray dryer,and then reviewed the changes in the probiotic viability as drying progresses,followed by a summary of common approaches to improve the viability of dried probiotics utilized in the literature. Three approaches were discussed,i.e.,improvement of the intrinsic stress tolerance of probiotic cells,optimization of the operation conditions of spray drying and incorporation of protective carrier. The interactions between carrier materials and probiotic cells and the influence of drying history are elucidated. This article shows that maximizing the viability of probiotics in spray dried powders requires a consolidated approach incorporating strategies from microbiology,process and food chemistry (material science). Development of high performance protectant formula based on understandings of microorganism-protectant interactions and designing novel production process from microbial culture to powder storage are key aspects to achieve high viability retention for mass production of active dry probiotics both in laboratory and in industries.

Key words: probiotics, spray drying, protective carrier, drying history, single droplet drying, drying kinetics

摘要： 肠道菌群对于人体健康具有重要影响。口服足量的活性益生菌，有助于缓解急慢性肠炎、治疗腹泄、改善消化，已在临床治疗中得到一定应用。在食品市场上，益生菌干粉制剂亟需一种生产成本低、制粉简便的生产方法。喷雾干燥的生产能力强、制粉快速，但干燥过程中，雾化液滴经历一个快速升温与脱水过程，对其中的益生菌带来热胁迫、脱水胁迫、氧化胁迫等多种不利因素，造成菌体活性的大量损失。而喷雾干燥塔的结构，使塔内的液滴干燥过程难以追踪，不利于研究益生菌的失活历程以及探索益生菌与载体材料间的相互作用。本文从雾化液滴在干燥塔内的干燥历程着眼，回顾了益生菌活性随液滴干燥动力学变化的趋势，讨论了益生菌在喷雾干燥中经受的亚细胞结构损伤与功能性损伤，并系统总结了目前文献中报道的提升干燥后益生菌活性的主要方法，包括提升菌体耐受性、优化喷雾干燥条件和采用合适的保护性载体，并着重阐述了载体材料与益生菌细胞间的相互作用关系以及干燥历程的重要影响。文章指出为最大程度上保存喷雾干燥粉末中益生菌的活性，应综合微生物、干燥过程与食品化学（材料学）等领域的保护策略，设计一体化统合生产方案。依据微生物-保护载体间的相互作用设计高效保护配方载体，研发统合从微生物细胞培养至粉末储藏的新型生产工艺，是实验室及工业中合理设计工业级喷雾干燥过程、大量生产高活性益生菌制剂的关键。

关键词: 益生菌, 喷雾干燥, 保护载体, 干燥历程, 单液滴干燥, 干燥动力学