Valorization of bread waste, a nonconventional feedstock for starch extraction using different methods: a comparative study

Bread is one of the most wasted food products worldwide owing to its short shelf life. However, bread residues present an inexpensive, abundant, and underutilized renewable substrate that is highly available for valorization into value-added products. In the present study, the feasibility of starch extraction from white bread waste is investigated. The composition of dried bread waste was analyzed for moisture, lipid, protein, carbohydrates, and ash contents. The study aimed to compare the physicochemical properties and the extraction yield of starch using different extraction methods. Starch extraction from bread waste involved four techniques: conventional distilled water extraction, alkali extraction, enzyme extraction using cellulase, and enzyme extraction using protease. The primary findings demonstrated that the enzymatic technique utilizing Aspergillus oryzae protease (900 units per 120 g of ground bread) had the greatest yield of 88%. It also showed the highest swelling and solubility power of 23.564 and 60%, respectively. Meanwhile, nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) results showed that starch extracted using the enzymatic method has a stronger interaction with water, explaining its high solubility and swelling power. The enzymatic method with protease produced starch with a structure similar to commercial-grade starch. Both the alkali and enzymatic methods revealed A-type crystalline structure indicating that they resulted in starch with low lipid content compared with the conventional method and did not change the crystal type of bread waste starch. These findings demonstrate that enzymatic extraction using protease is highly beneficial in preserving the physicochemical properties of the extracted starch, making it more efficient. Graphical abstract