Physicochemical and sensory properties of soy bread made with germinated, steamed, and roasted soy flour

Abstract

For the development of healthful gluten-free soy bread acceptable to consumers, we evaluated the effects of various processing procedures for soy flour on bread quality, in terms of beany flavour and texture. We pretreated soy flour by both non-heating (raw:NS and germinated:GS) and heating (steamed:SS and roasted:RS) methods. In addition, to improve the loaf volume, we added 1% hydroxypropyl-methylcellulose (HPMC) to RS flour. Lipoxygenase activity was retained in the non-heat-treated flours (279U/g for NS and 255U/g for GS), but was significantly reduced in the heat-treated flours (106U/g for SS and 69U/g for RS). Moreover, heat-treated flour had higher isoflavone and ferric reducing antioxidant power than had non-heat-treated flour. However, RS flour had the lowest moisture content and lowest L∗ value. The GS bread had the highest specific loaf volume (3.53cm3/g), followed by NS (2.96cm3/g), RS (2.25cm3/g), and SS (1.81cm3/g) bread. GS bread had the lowest hardness (1.53N), followed by NS (1.65N), RS (2.00N), and SS (3.75N) bread. The addition of 1% HPMC to RS increased the loaf volume (2.44cm3/g), but decreased the bread’s hardness (1.80N). As to the sensory properties, the bread with heat-treated flour was perceived to have a less beany odour and taste than was the bread with non-heat-treated flour. However, the latter had a better appearance than the former. These results indicated that soy flour pretreatment could enhance the loaf volume and reduce the beany flavour of whole soy bread.