Adding powdered almond skin to sourdough bread changed its microbes and antioxidants
What it found
Replacing some semolina with powdered almond skin made sourdough bread darker, raised its antioxidant capacity, and released almost all plant compounds during lab digestion.
It also introduced unwanted bacteria into the dough.
What they found
Animal and lab studies
Unwanted bacteria in dough
Doughs containing almond skin carried coliforms and Enterobacteriaceae, which are markers of poor hygiene. Regular dough did not have these. Lab tests also found Bacillus bacteria in the almond skin dough, and their spores survived baking.
Antioxidant capacity rises
Swapping in 5 % or 10 % almond skin boosted the bread's antioxidant power by 1.5 and 1.8 times before digestion. After lab digestion, the boost was 3.5 and 5.2 times higher than plain bread.
Plant compounds released
Before digestion, only about half the plant compounds from the almond skin came out of the bread. After simulated digestion, almost 100 % of them were released.
Protection in gut cells
When human intestinal cells in a dish were stressed, digested 10 % almond skin bread completely blocked the damage. The 5 % version cut it by about half.
Other findings
Bread colour and texture
Loaves made with almond skin were darker on the outside and inside. They had fewer air holes and felt firmer than regular semolina bread.
Aroma changes
Breads with almond skin gave off more terpenoid scents like limonene and pinene. They released fewer alcohols and aromatic hydrocarbons than plain bread.
What the authors conclude
- They suggest powdered almond skin can enrich sourdough bread with extra antioxidants and plant compounds.
- They warn that almond skin carries unwanted bacteria and spores that survive baking, so storage conditions must be controlled to avoid health risks.
How it was done
Almond processing leaves behind large amounts of skins that are usually thrown away. The authors wanted to see if this leftover material could be used to add useful plant compounds to traditional Italian sourdough bread.
The researchers baked sourdough breads using semolina flour where 5 % or 10 % was replaced by powdered almond skin. They tracked the bacteria in the dough over an 8 hour rise, measured the baked loaves, and tested how the bread behaved during simulated digestion and in human gut cells in the lab.
What it can’t tell you
- Lab digestion and cell tests cannot show exactly what happens when people eat this bread.
- Finding hygiene marker bacteria in the dough does not prove the final bread would make someone ill.
Who paid
- Conflicts
- Declaration of competing interest The authors declare that there is no conflict of interest for this research.
- Authors work at
- Università degli Studi di Palermo, Italy; Research and Innovation Centre, Italy; University of Palermo, Italy
The paper
- Title
- Reuse of almond by-products: Functionalization of traditional semolina sourdough bread with almond skin
- Type
- Study
- Evidence
- Animals and lab studies
- Summarised from
- Full text
- Cite
- Gaglio R, Tesoriere L, Maggio A, et al (2023). Reuse of almond by-products: Functionalization of traditional semolina sourdough bread with almond skin. International journal of food microbiology. doi:10.1016/j.ijfoodmicro.2023.110194Free full textPubMed 37004495DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error