The Mechanical Glass Transition Temperature Affords a Fundamental Quality Control in Condensed Gels for Innovative Application in Functional Foods and Nutraceuticals

Abstract

A subject of increasing fundamental and technological interest is the techno- and bio-functionality of functional foods and nutraceuticals in high-solid gels. This encompasses the diffusion of natural bioactive compounds, prevention of oxidation of essential fatty acids, minimization of food browning, and the prevention of malodorous flavour formation in enzymatic and non-enzymatic reactions, to mention but a few. Textural and sensory considerations require that these delivery/encapsulating/entrapping vehicles are made with natural hydrocolloids and co-solutes in a largely amorphous state. It is now understood that the mechanical glass transition temperature is a critical consideration in monitoring the performance of condensed polymer networks that incorporate small bioactive compounds. This review indicates that the metastable properties of the rubber-to-glass transition in condensed gels (as opposed to the thermodynamic equilibrium in crystalline lattices) are a critical parameter in providing a fundamental quality control of end products. It appears that the "sophisticated synthetic polymer research" can provide a guide in the design of advanced biomaterials for targeted release or the prevention of undesirable byproducts. Such knowledge can assist in designing and optimizing functional foods and nutraceuticals, particularly those including vitamins, antioxidants, essential fatty acids, stimulants for performance enhancement, and antimicrobials.

Keywords: condensed hydrocolloid gels; delivery vehicles; encapsulating agents; functional foods; mechanical glass transition temperature; nutraceuticals.

Figure 1

Formation mechanism of food gels.

Figure 2

(a) Diffusion coefficient (D) of 1% linoleic acid in 79% solid matrix comprising whey protein isolate with percent substitution of the protein with glucose syrup 0% (◆), 20% (☐), 30% (▲), 40% (×), 60% (○), and 100% (●) as a function of T − T_g, (b) the coupling parameters, ξ, of 1% linoleic acid release from 79% whey protein/glucose syrup matrices as a function of co-solute concentration (%), and the fractional free volume (●, right y-axis) and diffusion coefficient (D) of 1% nicotinic acid (○, left y-axis) from matrices of (c) 25% bovine gelatin with 59% glucose syrup and (d) 25% fish gelatin with 59% glucose syrup. Reprinted from [72,99,146] with permission from Elsevier.

Figure 3

(a) Rate constant of ROOH formation (k_f) (○, left yaxis) and decomposition (k_d) (●, right y-axis) in the propagation phase of 20% bovine gelatin/64% polydextrose/0.75% linolenic acid/0.25% lecithin/0.5% genipin, with reference to both mechanical (T_gm) and calorimetric (T_gc) glass transition temperatures; (b) the relative inhibition of lipid oxidation (RLO) in bovine gelatin/polydextrose/linolenic acid/lecithin matrices as a function of genipin concentration was recorded at various temperatures: −10 (●), 0 (△), 10 (▲), 20 (☐), 30 (■), 40 (○), and 50 °C (◆); and (c) oxidation resistance (A) measured for different κ-carrageenan concentrations in a glucose syrup/linoleic acid/lecithin system (○, left y-axis) and for varying genipin concentrations in a bovine gelatin/polydextrose/linolenic acid/lecithin system (▲, right y-axis). Reprinted from [26,29] with permission from Elsevier.

Figure 3

(a) Rate constant of ROOH formation (k_f) (○, left yaxis) and decomposition (k_d) (●, right y-axis) in the propagation phase of 20% bovine gelatin/64% polydextrose/0.75% linolenic acid/0.25% lecithin/0.5% genipin, with reference to both mechanical (T_gm) and calorimetric (T_gc) glass transition temperatures; (b) the relative inhibition of lipid oxidation (RLO) in bovine gelatin/polydextrose/linolenic acid/lecithin matrices as a function of genipin concentration was recorded at various temperatures: −10 (●), 0 (△), 10 (▲), 20 (☐), 30 (■), 40 (○), and 50 °C (◆); and (c) oxidation resistance (A) measured for different κ-carrageenan concentrations in a glucose syrup/linoleic acid/lecithin system (○, left y-axis) and for varying genipin concentrations in a bovine gelatin/polydextrose/linolenic acid/lecithin system (▲, right y-axis). Reprinted from [26,29] with permission from Elsevier.