Buckwheat has been always considered a high-quality gluten-free (GF) cereal. Numerous studies have shown that long-term buckwheat and associated product consumption has been linked to a lower risk of developing constipation, dyslipidemia, hypertension, and cardiovascular disease (Yu et al., 2019). Especially, buckwheat can alleviate celiac disease (CD; Zhou et al., 2023), thereby reducing or preventing immune responses and intestinal damage caused by gluten. In the current baking industry, sourdough technology is frequently utilized in flour products such as bread, Chinese steamed bread, and partially fermented food (Diowksz and Sadowska, 2021) due to its excellent effects (Ua-Arak et al., 2017). Therefore, buckwheat sourdough has gradually become the preferred diet for celiac disease patients. However, buckwheat lacks gliadin and glutenin, which are necessary for forming the dough structure (Song et al., 2023; Zhou et al., 2022), resulting in poor sensory characteristics, hard texture, and small volume of the finished products. This makes it challenging for celiac disease patients to have a satisfying sensory experience while consuming related products. To overcome these quality defects, food additives such as gums and hydrocolloids (e.g., guar and lanthanum gums, alginate and hydroxypropyl methylcellulose; Sadat et al., 2023), other food ingredients (e.g., non-gluten proteins; Ziobro et al., 2013) or enzymes (e.g., transglutaminase, proteases, glucose oxidase; Matos and Rosell, 2015) have been assessed for their application potentials in buckwheat sourdough with the intention of speeding up their processing, as well as improving the structure and microbiota compositions of sourdough samples. However, using food additives may be extremely costly (Zhang et al., 2023). Particularly in recent years, consumer desire for natural foods free of chemical additives has grown. Casein hydrolysate (CH), a natural food ingredient, exhibits emulsifying, gelating, thickening properties, and promotes LAB growth. The application of CH offers new ideas and methods to improve the fermentation and quality characteristics of buckwheat sourdough.

Protein hydrolysates are becoming a more popular choice for an essential food ingredient due to several benefits such as promoting the growth and proliferation of lactic acid bacteria (LAB), building a strong network structure, and influencing textural and nutritional properties (Karimi et al., 2021). For example, the nontoxic milk protein casein is inexpensive and easy to obtain. Notably, casein hydrolysate, which are made from the separation of inexpensive casein, contain a variety of beneficial and bioactive peptides, and the functions include nutritional regulation, immune regulation, and antioxidation (Nielsen et al., 2017). Generally, bioactive peptides stimulate the proliferation of LAB cells during fermentation and slow down the declining viable bacterial cell count in the late growth period of LAB (De Vuyst et al., 2009; Zhang et al., 2010). Polypeptides with a lower molecular weight (< 3 kDa) have also been reported in CH, and can double the growth rate of Lactococcus lactis (Bouhallab et al., 1993). However, there is a relative scarcity of research on how CH affects the fermentation process of buckwheat sourdough, improves its texture, and enhances its nutritional properties. Therefore, further in-depth research and exploration into the effect of CH on naturally-fermented buckwheat sourdough will not only help us gain a more comprehensive understanding of the functions and applications of CH, but also provide powerful theoretical support and practical guidance for the development of novel, high quality GF foods.

In this study, CH was prepared by hydrolyzing casein with an alkaline protease, and then added into buckwheat sourdough; after then, the sourdough was assessed for its fermentation behavior and changes in textural and chemical features as well as bacterial microbiota during a naturally-fermentation of 12 h. This study aimed to explore a practical method to improve the processing properties of buckwheat sourdough to enhance consumer acceptance and shorten the fermentation time, more importantly, provide more choice for the celiac disease-friendly GF foods.