Waste Bread as a Biomass Source: Optimization of Enzymatic Hydrolysis and Relation between Rheological Behavior and Glucose Yield

Amongst the many forms of food waste, bread is a major contributor to the problem. Two aims of this research investigate waste breads potential of being a bioresource for the production of fermentable sugars which are precursor of valuable bioproducts by fermentation process: finding optimum substrate, water and enzyme ratio to produce the highest amount of fermentable sugars and investigating the rheological behavior of the system during hydrolysis. Two stage waste bread hydrolysis was performed with enzymes alpha-amylase and amyloglucosiades and response surface methodology was used to optimize substrate, water and enzyme ratio. Discovery Hybrid Rheometer-2 (TA Instruments) fitted with a parallel-plate geometry was used to investigate steady flow viscosity of the slurry during hydrolysis. 99 % of theoretical maximum glucose yield, a main fermentable sugar, is achieved by optimizing enzymatic hydrolysis conditions of waste bread at liquefaction and saccharification stages. Just after the addition of alpha-amylase enzyme, substantial decrease is observed in viscosity and Casson apparent yield stress of the slurry. During saccharification stage, glucose yield increases dramatically while viscosity of the slurries is very low and does not change considerably. The results imply that utilizing high concentrations of waste bread as a feedstock to produce fermentation products offers economic benefits without causing high power consumption, excessive wear on equipment, and reduced conversion which are generally expected consequences for high-solid processing.