Protein enrichment of gluten free bakery products by Arthrospira platensis (spirulina): in vitro study of the effect of formulation and sourdough process on colon microbiota through MICODE gut model

The production of Glute free (GF) foods is challenging for organoleptic and nutritional aspects. GF products are nutritionally less adequate than standard products because have low protein and high fat, content. Target audience for GF foods stretches beyond coeliac sufferers. In 2015, only 9% of US GF consumers followed a GF diet due to celiac disease, while others just did it believing it is healthier. Thus, it is necessary to know the impact of such food products on healthy subjects. In this work we compared two formulations of GF bread, with and without Arhtrospira platensis powder (AP) for protein enrichment, obtained by sourdough and plain (control) fermentations. Comparison was made after gastroduodenal digestion and proximal colonic fermentation performed for a short-term experiment on MICODE (Multi- Unit In vitro Colon Model), employing donations from healthy individuals. The aim is to highlight and compare the impact of formulation and process of the breads on the human colon microbiota, throughout microbiomics (qPCR and 16S MiSeq) and metabolomics (SPME GC-MS). Firstly, we have to consider that an aggravation of the Proteobacteria loads was observed during any fermentation, suggesting that there are less beneficial impact of GF breads on a healthy colon than what supposed. Notwithstanding, the outcomes from sourdoughs are generally better, and the bread enriched with AP has even superior performances than the standard. Actually, the results indicated that the GF sourdough containing AP could improve some general indicators of healthy condition of the healthy human colon in comparison to the not enriched GF sourdough bread. More specifically, at taxa level, the GF sourdough with AP in comparison to the standard one is able to; i) preserve microbial eubiosis; ii) increase the abundance of beneficial bacteria (Bifidobacterium, Akkermansia, Roseburia, Faecalibacterium and Ruminococcus); iii) limit opportunistics, sulfurate producers, and proteolytic bacteria (Escherichia, Bilophila, and Clostridium); iv) produce more bioactive organic fatty acids; v) reduce detrimental compounds (phenol, p-cresol); vi) generate a prebiotic effect. Our results evidence that a sourdough fermentation can mitigate the negative effect of GF foods on healthy condition, particularly when the product is enriched in proteins.