| Soy flour was processed by a procedure that involved an incubation treatment followed by ultrafiltration and diafiltration. An initial solids concentration of 5% (w/w) was used in the process. The soy flour was treated in one of the following three ways prior to membrane filtration to study treatment effect on isoflavones: (1) at 45–50°C for three hours without pectinase enzyme, (2) at 45–50°C for three hours with pectinase enzyme (0.9% v/v), or (3) blanching at 80°C for three hours. The resultant products of filtration were a membrane soy concentrate (MSC), micro- and dia-filtered permeates, and an insoluble pellet fraction. The goal of this study was to characterize the isoflavone content and distribution of the four different isoflavone components to ascertain whether processing conditions had an influence on their distribution. Theoretically, the isoflavone concentrations of the MSCs prepared without enzyme, with pectinase, or by blanching were 41%, 31%, or 27%, respectively. This represents a significant difference in the migration of the isoflavones on a theoretical mass balance, based on processing conditions1. On a dry weight basis, however, there was no significant difference in the total isoflavone concentration for the three different MSCs. The isoflavone concentrations of the different membrane soy concentrates on a dry weight basis were 3.13 mg/g (no enzyme), 3.05 mg/g (pectinase), or 3.42 mg/g (blanching). These values reveal that membrane processing contributed to approximately 15%, 18%, or 8% decreases in total isoflavone content in the MSC prepared without enzyme, with pectinase, or with blanching, respectively.; Batches of MSC prepared with and without pectinase were stored for 6 and 11 months, respectively, in low-density polyethylene (LDPE) and glass. The isoflavone concentrations of each batch were tested at different time intervals to detect any degradation of the isoflavones. There was no significant decrease in the isoflavone content of either hatch stored in LDPE or glass. After 11 months, the isoflavone concentrations in a dried MSC are unaffected.; The antioxidant capacity of a MSC prepared without enzyme treatment was tested after 2 and 17 months storage. The 2 months old sample was assumed to give the initial antioxidant capacity of the membrane soy concentrate. After 17 months storage, the isoflavones in the MSC possessed approximately 30% less antioxidant activity than after 2 months storage, regardless of packaging in IDPE or glass. Both MSCs possessed more antioxidant activity than the standard without isoflavones.; 1Theoretical mass balance is an important concept to understand. Due to the physical limitations of the design of the ultrafiltration (UF) unit it is not possible to recover 100% of the retentate produced. Thus, calculations based on a theoretical mass balance were performed. Thus, calculations are based on the weight of the retentate fraction (50 pounds) determined by the total weight of soy solution minus the weights of the two permeate fractions. It is a theoretical value because the researcher did not actually obtain 50 pounds when recovering the retentate from the UF unit. |
