Barley β-glucan cryogels as encapsulation carriers of proteins: Impact of molecular size on thermo-mechanical and release properties

• β-Glucan cryogels are promising bioactive carries for protein controlled release.
• The elasticity of mixed β-glucans/protein cryogels decreases with β-glucan Mw.
• The thermostability and mechanical strength of cryogels increase with β-glucan Mw.
• The swelling capacity of cryogels decreases with β-glucan Mw.
• The amount and rate of protein release decrease with Mw of β-glucans and proteins.

The potential use of barley β-glucan cryogels as encapsulation carriers for delivery-controlled release of proteins was explored. For cryogel preparation, mixed β-glucan (4.2% w/w)/protein (0.8%) aqueous dispersions were subjected to 10 freezing (−23 °C/24 h) and thawing (25 °C/24 h) cycles, using three purified barley β-glucan isolates differing in molecular weight, Mp (55, 140 and 320 kDa) and four proteins, selected as model core constituents; i.e. β-lactoglobulin (18 kDa), ovalbumin (43 kDa), bovine serum albumin (67 kDa), invertase (270 kDa). Dynamic rheometry revealed that the mechanical properties of the composite cryostructurates, were significantly affected (p<0.05) by the molecular size of β-glucan and protein. With increasing polysaccharide molecular size the elastic modulus (G′) and the melting enthalpy (ΔΗ) values of the cryogels decreased, while the melting temperature (Tm) of the gels (calorimetry) increased. Incorporation of the highest Mw protein in the β-glucan cryogels also increased (p<0.05) the G′. Large deformation mechanical tests have shown an increase of compression modulus (E) and true stress (σTR) with increasing Mp of the polysaccharide, whereas the cryogel's swelling capacity, followed the reverse trend. Release kinetics of entrapped proteins was monitored spectrophotometrically in aqueous suspensions of the mixed cryogels at 37 °C. The amount and the apparent diffusion coefficient (Dm) of proteins released significantly (p<0.001) decreased with increasing molecular size of both β-glucans and proteins. Overall, the observed variation in thermo-mechanical, swelling and diffusional properties of the composite cryogels may allow the design of tailor-made delivery and controlled release systems of polymeric ingredients such as bioactive proteins.

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