The rheological behavior of wheat starch preparations at intermediate moisture contents (25–60%, w/w) was studied by dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) and electron spin resonance (ESR) experiments were also performed in parallel. Upon heating wheat starch preparations from 25 to 85°C, DMTA showed first a slight decrease in storage modulus (G′) to 45–60°C, then an increase of the shear modulus (predominant effect of swelling) to 68–74°C, followed by a decrease (predominant effect of melting‐softening) to 85°C. In this 25–85°C temperature range, the initial swelling and subsequent softening were less pronounced with decreasing moisture content. The 45% moisture content level appeared critical, since there was a radical change in the thermomechanical behavior below this concentration. DSC showed that gelatinization did not appear as a single endotherm but as two endotherms. Whatever the moisture content, the melting started within a quite narrow temperature range, while the end of melting shifted progressively to higher temperatures as moisture content was decreased. ESR showed first a slight decrease in the water‐soluble probe (Tempol) mobility as temperature was increased to 47–50°C, followed by a pronounced decrease to 57–60°C. Then, a progressive increase in probe mobility was observed to 85°C. These changes in probe mobility suggest some modifications of the kinetic and thermodynamic properties of the aqueous phase associated with changes in the starch physical state. For the lowest moisture contents, the probe mobility was quite stable during heating.

Cereal Chem. 77(4): [414][415][416][417][418][419][420] Gluten solubility was improved by enzymatic proteolysis at moderate acidic pH level. Reversed-phase HPLC analysis of gluten hydrolysates with a degree of hydrolysis (DH) in the range of 0-5% showed that both hydrophilic and hydrophobic soluble peptides were released. Emulsifying and foaming properties of hydrolysate dispersions at 3.75 mg/mL decreased with the increasing DH at all pH levels and salt conditions investigated.On the other hand, the soluble fractions separated from those hydrolysate dispersions exhibited good functional properties, independently of the initial DH. The proportion of hydrophilic and hydrophobic peptides in the soluble fractions depended on DH, pH level, and salt concentration. Nevertheless, these soluble fractions were characterized by an excellent capacity to stabilize both oil-water and air-water interfaces.The solubility properties of proteins, which depend on intrinsic physicochemical characteristics and on the pH level and salt conditions of the medium, sometimes limit their use in formulated food systems (Panyam and Kilara 1996). The improvement of the functional properties of proteins by enzymatic or chemical modifications has been extensively studied (Hardwick and Glatz 1989, Hamada 1992, Guillerme et al 1993, Guéguen et al 1995, Chobert et al 1996.Wheat gluten, a by-product of the wheat starch industry, is a typical water-insoluble protein. Much research focused on chemical or enzymatic modifications has resulted in the enhancement of its solubility, foaming, and emulsifying properties (Yang and McCalla 1968, Batey 1985, Bollecker et al 1990, Thébaudin 1990, Kato et al 1991, Mannheim and Cheryan 1992, Mimouni et al 1994, Babiker et al 1996. Adler-Nissen (1986) reported that extensive protein hydrolysis produced short peptides unable to form stable films at the oil-water or air-water interfaces. Thébaudin (1990) showed that limited hydrolysis of wheat proteins by various proteases improved solubility and that gluten hydrolysates with a degree of hydrolysis (DH) in the range of 1-2% exhibited good emulsifying and foamforming properties. However, the foam-stabilizing properties of gluten hydrolysates were very limited (Thébaudin 1990, Mannehein andCheryan 1992). Proteolysis of gluten by several enzymes (pepsin, neutrase, alcalase) confirmed these results (Mimouni et al 1994). According to this author, a pepsin hydrolysate with 1.25% DH exhibited a solubility of 80% but poor foam-stabilizing properties at pH 7. This showed that high solubility is not the only requirement to improve other functional properties. It is important to note that many studies were performed with total hydrolysates characterized by high solubility but only a few reported the effect of the insoluble fraction. Only Velev et al (1993) compared the emulsifying properties of tomato seed protein isolate with its water-soluble fraction and noted a positive effect of the insoluble fraction.The objectives of this research were 1) to study the hydrolysis of gl...

A glassy model of freeze-dried maltodextrin was developed for the encapsulation of flaxseed oil. Kinetics of lipid oxidation have shown that the matrices efficiently protected lipids from oxidation for a moisture content corresponding to the monolayer value. An NMR method based on the 2nd moment, M 2, was used to study the molecular mobility and physical state of the freeze-dried maltodextrin and water mixtures. Physical state transitions were observed at temperatures very close to the glass transition temperature (Tg) determined from the equation of Vuataz (1999), suggesting a relationship between glass transition and proton relaxation behavior. No apparent relation between molecular mobility and oxidation rate were observed whatever the DE of maltodextrins. Food Engineering and Physical PropertiesEncapsulation of flaxseed oil . . . 0 (P 2 0 5 ) and 0.8. Water activity was controlled using a hygrometer (FA-st/1, GBX Scientific Instruments, France).