Shelf-Life Assessment of Bread Partially Substituted with Soy Protein Isolate

Partial substitution of flour with soy protein isolate in bread making increases the protein content and nutritional value of baked goods as it contains more lysine than wheat flour. However, changes in the bread recipe alter the pH and amino acid content of the baked good, and product assessment is required to determine whether the product is a non-time/temperature control for safety food. This study examines the effects of substituting high-gluten flour with 2–8% soy protein isolate on bread quality and on the shelf life of the bread using the microbiological challenge test. The results indicate that increased soy protein isolate substitution reduces the volume and specific volume of bread. Six percent soy protein isolate-fortified bread also had a poorer taste, and, therefore, the optimal substitution amount is 4%. Based on the yeast and mold growth during the storage period, the 4% soy protein isolate-fortified bread has a shelf life of four days, while the 2% soy protein isolate-fortified bread has a shelf life of five days. The microbiological challenge test results revealed that the substitution of flour with soy protein isolate is conducive to Staphylococcus aureus growth within the bread. To summarize, the optimal soy protein isolate substitution in bread is 4%, which offers a four-day shelf life at room temperature.