Solid state fermentation turns waste bread into new protein food

Scientists at Aberystwyth University have proposed a circular solution for recovering the discarded but still edible bread. With fermentation, nutritional content increases

by Matteo Cavallito

Every year, millions of tons of still perfectly edible bread are thrown away worldwide without any recovery initiative. A significant waste that contributes to the growth of the overall impact of food production on the Planet. Recently, however, researchers at Aberystwyth University in Wales have proposed a particular circular solution: reusing waste to produce plant-based protein food.

The process, they explain, would rely on a peculiar system that has always been used in traditional cooking in Asia: so-called solid-state fermentation. That is, that process of cultivation in which microorganisms grow on solid materials without free liquids.

Worldwide, 10 percent of bread is wasted

“Wheat is one of the world’s most consumed crops, accounting for 20% of the calories and proteins in our diets,” the researchers noted in an article published by the Australian network The Conversation and reported by the Aberystwyth University. According to FAO, they added, “About 760 million tonnes of wheat flour are produced globally each year, much of which is used to bake bread.” This is a huge production effort that comes not without consequences.

In fact, a study by the University of Sheffield recalled how wheat cultivation, which is often accompanied by the use of fertilizers, alone is responsible for about 40 percent of the greenhouse gas emissions associated with bread production. Another British study, published in the journal Sustainable Energy & Fuels, estimates that 10 percent of the 185 million tons of bread produced worldwide each year is wasted. With a visible environmental impact.

The experiment

The fact, however, is that much of this uneaten bread is still fully edible. And, as such, it can be enhanced by fermentation. To test this possibility, the authors subjected a certain amount of the product to this process with the addition of  Lolium perenne, a grass from Asia found in an experimental plot at the same Welsh university.

“Surplus bread crusts (BC) have the structural capacity to serve as a solid-state fermentation (SSF) scaffold, and their nutritional value could be increased in combination with perennial ryegrass (PRG), a biorefining feedstock with high-quality protein but an unpleasant sensory profile,” explains the study published in the journal Science of Food. “SSF with Rhizopus oligosporus was investigated with these substrates.” The operations, which took place in the space of 72 hours, showed promising results.

Nutritional content increases with fermentation

During the experiment, the study continues, “the starch content had decreased by up to 89.6%, the total amino acid (AA) content increased by up to 141.9%, and the essential amino acid (EAA) content increased by up to 54.5%.” The study, in short, “demonstrated that this process could potentially valorise BC and PRG, both widely available but underexplored substrates, for the production of alternative proteins.”

The implications are significant. “In the long run, this innovative approach could play an important role in enhancing global food security and sustainability,” the authors write.

The fermentation process, in particular, can reduce waste sent to landfills and greenhouse gas emissions. In line with circular economy principles, moreover, the reuse of surplus bread makes it possible to produce unconventional plant proteins that can be included in the food chain while making the best use of available resources. This is a decisive advantage in the scenario of a growing global population destined, according to United Nations estimates, to exceed 11 billion individuals by the end of the century.