Rye, especially in the form of whole grain, has a long history of consumption in northern Europe, where it has been a traditional staple grain. Being a notable source of dietary fibers and bioactive compounds, rye consumption as part of a varied and balanced diet can contribute to several potential health benefits (Åman, 2010; Andersson et al., 2009; Mattila et al., 2005). Dry rye crispbread is a flatbread made primarily from rye flour. It originated in Scandinavia as an essential component of human diet and it has recently gained popularity worldwide as alternative to rye bread for its crunchy texture, nutty flavor, and versatility (Leinonen et al., 1999). Indeed, its export from Norway quintupled from ca. 1.5 million equivalent euro in 2013 to ca. 7 million in 2016, with current previsions depicting a further growth in next years (Grimsby and Kure, 2019).

Rye crispbread offers several nutritional characteristics, such as low fat and high fiber content, making it a favorable choice for a wholesome and nutritious snack. In addition, the low water presence confers a long shelf life and valuable distribution opportunities (Grimsby and Kure, 2019). Notably, when compared to similar refined wheat foods, the consumption of crispbread has highlighted superior beneficial effects, including increased satiety and lower postprandial insulin and, in some cases, glucose responses (Zamaratskaia et al., 2017).

However, rye crispbread, like other leavened baked products, presents a relevant issue. During crispbread baking, some hazardous by-products such as acrylamide can be released in the crust as a result of a chemical reaction between amino acids and reducing sugars (Claus et al., 2008). Acrylamide concentration in processed foods has become a health issue due to its carcinogenic potential (Konings et al., 2007). Overall, the median acrylamide intake in humans was estimated between 0.02 and 1.53 μg/kg body weight/day based on data from >100 studies involving 26 countries in Europe, Asia and USA. In particular, in Europe the estimate reaches the range 0.4–1.9 μg/kg body weight/day across all age groups, and in children it ranges between 0.5 and 1.9 μg/kg body weight/day (Timmermann et al., 2021). Owing to its high daily consumption, bread represents the main source contributing to human exposure to acrylamide (Forstova et al., 2014). In particular, crispbread reaches average levels between 87 and 459 μg/kg according to the Joint FAO/WHO Expert Committee on Food Additives (Mollakhalili-Meybodi et al., 2021). Consequently, the Recommendation 2017/2158/EU defined the benchmark level of 350 μg/kg for the presence of acrylamide in crispbread (Commission Regulation (EU), 2017). Therefore, strategies able to reduce acrylamide in bread while maintaining its sensory and other nutritional attributes are essential. At the outset, the European Food Safety Authority and World Health Organization published several guidelines for industries to control acrylamide formation during food processing. Following that, the European Commission announced new regulations aiming to mitigate the level of acrylamide in cereals-based food products (Commission Regulation (EU), 2017). These measures belong to three groups: agronomy, formulation, and process-based strategies (Food Drink Europe, 2019). Agronomy-based strategies focus on the production of cereals with lower asparagine levels and sugar content; strategies related to formulation change include the use of refined flour instead of whole flour, the optimization of water and fat content, the change of baking agents or type of sugar, and the addition of organic acids, amino acids, cations, antioxidants and polyphenols, while the process-based strategies mainly aim to modify the baking process. However, some of these strategies significantly impact aroma, taste, color, and texture of final products (Gazi et al., 2023). Recently, the enzymatic treatment through asparaginase applications weas also proposed as a promising way to reduce acrylamide in bakery products without negative effects on surface color or spread ratio, but the enzyme was effective only in doughs with water activity values higher than 0.75 (Gazi et al., 2023). Therefore, effective methods which can be applied on a broad range of dough without alterations to the other properties of food products are still necessary (Nasiri Esfahani et al., 2017). Moreover, rye, being a cereal with a high concentration of asparagine (Stockmann et al., 2018), poses a critical challenge in reducing acrylamide levels in rye crispbread making. According to the available literature, biological approaches have emerged as effective tools in reducing acrylamide content and enhancing food quality, and they may contribute significantly alongside technological methods (Bartkiene et al., 2013, Bartkiene et al., 2017; Nachi et al., 2018; Nasiri Esfahani et al., 2017). In particular, sourdough fermentation revealed promising acrylamide removal capabilities (Nachi et al., 2018; Nasiri Esfahani et al., 2017). Several research demonstrated its effectiveness in reducing acrylamide content in wheat, whole-wheat and mixed rye breads. These studies have highlighted the strain-specific capabilities of LAB and yeasts (Bartkiene et al., 2013, Bartkiene et al., 2017; Nachi et al., 2018; Nasiri Esfahani et al., 2017) and suggested several potential mechanisms of action (Albedwawi et al., 2021) (Nasiri Esfahani et al., 2017) (Serrano-Niño et al., 2014), supporting the idea that the use of appropriate strains in tailored sourdough formulations can represent an efficient technology for acrylamide reduction.

It was estimated that the daily acrylamide intake due to bread consumption in human populations could be reduced 2–6 times through such approach (Nasiri Esfahani et al., 2017). In addition, many advantages were reported when isolated strains are used for rye sourdough production, like good growth and acidification rates, synthesis of suitable menu of amylolytic and proteolytic enzymes, capacity to ferment highly diverse carbohydrates and delayed staling in the resulting breads. Thus, the use of selected starters formulations was recommended for improving the quality of rye bread (Bartkiene et al., 2017). Notably, the intake of sourdough crispbread also increased satiety and reduced desire to eat compared to yeast-fermented refined wheat crispbread in an in vivo study (Zamaratskaia et al., 2017). However, despite these promising premises, the literature regarding the effects of sourdough fermentation on acrylamide content in bakery products is not comprehensive yet, and no previous studies investigated this mitigation strategy on rye crispbread. Thus, new efforts were recommended to enlarge study cases (Nachi et al., 2018).

In this study, we aimed to investigate the pro-technological and functional performance of fifteen mixed LAB together with Saccharomyces cerevisiae (wild type) under different time and temperature conditions in rye ecosystem. Thereafter, the capability of best inoculum starters for rye sourdough crispbread production to reduce acrylamide level while also maintaining valuable aroma profiles, and sensory and nutritional characteristics were highlighted. In broad sense, we aimed to design a tailored sourdough for making rye crispbread with lower acrylamide content and high sensory and functional features. On the best of our knowledge, this is the first time that attempts through such kind of biotechnological approach are made on rye crispbread.