Water Hydration Properties Research Articles

Modified Soy Proteins with Improved Foaming and Water Hydration Properties

ABSTRACTSoy proteins were modified by alkali treatment at pH 10.0, followed by papain hydrolysis. Solubility, water hydration capacity (WHC), surface hydrophobicity, foaming and emulsifying properties of unmodified, alkali‐treated, and papain‐modified soy protein (PMSP) were compared. PMSP exhibited higher solubility (100% at pH > 7.0), WHC (3.13) and hydrophobicity (40.8) than unmodified soy protein which had solubility 68.5%, WHC 0.21, and hydrophobicity 8.1. The PMSP had foaming capacity (22.0 mL) similar to egg white (21.2 mL) at pH 7.0; and enhanced foam stability (36.4) compared to the unmodified control (32.9). In general, alkali‐treated soy had lower functional properties. Emulsifying properties of PMSP and alkali treated soy were unchanged by the modification. PMSP could be used as an egg white substitute in foaming applications at neutral pH.

Survival of alginate-entrapped cells of Azospirillum lipoferum during dehydration and storage in relation to water properties

Survival of alginate-entrapped cells of Azospirillum lipoferum was studied during dehydration using a dry air stream and during prolonged storage at various constant water activity values (aw). During the drying operation, the viability loss remained almost constant from the initial water content to 0.35 g water/g dry weight (DW) corresponding to a 98.5% water removal, strongly increased until a water content of 0.25 g/g DW and then stopped until the end of the drying operational (final aw 0.18). A water content of 0.25 g/g DW (aw=0.55) corresponded to the critical point of the moisture sorption isotherm curve from which water became restricted to the dry material. A high drying rate (5 g/g DW per hour) was shown to be more detrimental for cell viability than a low drying rate (1.18 g/g DW per hour). When the product was stored in a closed chamber with a regulated aw (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product aw stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by aw values in the range 0–0.55. Above aw=0.55, the higher the aw and the storage duration, the lower the residual survival percentage. The influence of the drying and storage conditions on the cell death rate are discussed with regard to both the mechanisms generally involved in viability loss and the hydration properties of water.