This research investigates the production of kefir using Turkish and Kazakh kefir grains and commercial starter cultures, followed by storage at 4 °C for 30 days. The study monitors the rheological properties and microbiological characteristics of kefir on the 1^st, 15^th, and 30^th days of storage, as well as during dynamic in vitro gastrointestinal digestion. Kefir samples were passed through a dynamic in vitro gastrointestinal model simulating the digestive processes of the mouth, stomach, and small intestine which was designed in laboratory conditions. Kefir from Turkish kefir grain exhibited the lowest average titratable acidity, apparent viscosity, and flow behavior index, while kefir from Kazakh kefir grain had the highest average pH. Over the storage period, pH and flow behavior index decreased, while titratable acidity, viscosity, and consistency coefficient increased. The kefir samples showed non-Newtonian pseudoplastic flow characteristics. The acetic acid bacteria and Leuconostoc counts of kefir samples produced with commercial starter cultures were higher than those produced with kefir grains, while yeast counts were higher in kefir samples produced with kefir grains. During storage and in vitro gastrointestinal digestion, the number of microorganisms in kefir samples decreased. Turkish kefir grain resulted in the lowest reduction (%) of microorganism counts during in vitro gastrointestinal digestion. These findings shed light on the rheological, microbiological, and in vitro digestive properties of kefir during storage, which may contribute to improving the quality and health benefits of kefir products. The present study revealed that the kefir produced with kefir grains had a lower decrease in the viability of microorganisms compared to the kefir produced with starter culture after passage through the gastrointestinal model, so kefir produced with kefir grains may be more preferred due to its possible health benefits.

Keywords: Kefir grain; in vitro digestion; microbiological characteristics; rheological properties; starter culture.

这项研究调查了使用土耳其和哈萨克族的 kefir 粒子以及商业发酵剂生产 kefir，并在 4°C 下储存 30 天的情况。该研究监测了 kefir 在存储第1天、第15天及第30天的流变学性质和微生物特征，以及动态体外胃肠消化过程中的特性。kefir 样品通过模拟口腔、胃和小肠消化过程的动态体外胃肠模型进行处理。

由土耳其 kefir 粒子生产的 kefir 显示出最低的平均可滴定酸度、表观粘度及流动行为指数，而由哈萨克族 kefir 粒子生产的 kefir 则具有最高的平均pH值。在整个储存期间，pH 值和流动行为指数下降，而可滴定酸度、粘度及一致性系数上升。kefir 样品显示出非牛顿假塑流特性。

由商业发酵剂产生的 kefir 样品中的醋酸菌和Leuconostoc数量高于用 kefir 粒子生产的样品，而酵母的数量在用 kefir 粒子生成的样品中更高。在储存期间及体外胃肠消化过程中，kefir 样品中的微生物数量减少。土耳其 kefir 粒子导致在体外胃肠消化过程中的微生物计数下降幅度最小。

这些发现揭示了 kefir 在存储期间的流变学、微生物和体外消化特性，有助于提高 kefir 产品的质量和健康效益。目前的研究表明，使用 kefir 粒子生产的 kefir 在通过胃肠模型时，其微生物存活率降低的程度比使用商业发酵剂生产的 kefir 更低，因此由于其可能的健康益处，用 kefir 粒子生成的 kefir 可能更受欢迎。

关键词：kefir 粒子；体外消化；微生物特性；流变学性质；商业发酵剂。