Chitosan is a cationic biopolymer that has many potential applications in the food industry because of its unique nutritional and physicochemical properties. Many of these properties depend on its ability to interact with anionic surface-active molecules, such as surfactants, phospholipids, and bile acids. The purpose of this study was to examine the influence of pH (3 and 7), ionic strength (0-200 mM NaCl), and temperature (10-50 degrees C) on the interactions between a model anionic surfactant (sodium dodecyl sulfate, SDS) and chitosan using isothermal titration calorimetry, selective surfactant electrode, and turbidity measurements. At pH 3 and 30 degrees C, SDS bound strongly to chitosan to form an insoluble complex that contained about 4-5 mmol of SDS/1 g of chitosan at saturation. When SDS and chitosan were mixed at pH 7 they did not interact strongly, presumably because the biopolymer had lost most of its positive charge at this pH. However, when SDS and chitosan were mixed at pH 3 and then the solution was adjusted to pH 7, the SDS remained bound to the chitosan. The presence of NaCl (0-200 mM) in the solutions decreased the critical micelle concentration (cmc) of SDS (in both the absence and the presence of chitosan) but had little influence on the amount of SDS bound to chitosan at saturation. The cmc of SDS and the amount of SDS bound to the chitosan at saturation were largely independent of the holding temperature (10-40 degrees C). Nevertheless, the enthalpy changes associated with micelle dissociation were highly temperature-dependent, indicating the importance of hydrophobic interactions, whereas the enthalpy changes associated with SDS-chitosan binding were almost temperature-independent, indicating the dominant contribution of electrostatic interactions. This study provides information that may lead to the rational design of chitosan-based ingredients or products with specific nutritional and functional characteristics, for example, cholesterol lowering.

Chitosan is a cationic biopolymer that has many potential applications in the food industry because of its unique nutritional and physiochemical properties. Many of these properties depend on its ability to interact with anionic surface-active molecules, such as phospholipids, surfactants, and bile acids. The purpose of this study was to characterize the interaction between chitosan and a model anionic surfactant (sodium dodecyl sulfate, SDS) using isothermal titration calorimetry (ITC), surfactant-selective electrode (SSE), and turbidity measurements. ITC and SSE indicated that SDS bound strongly to chitosan via a highly exothermic interaction. The turbidity measurements indicated that chitosan formed insoluble complexes with SDS that strongly scattered light. The chitosan bound approximately 4 mM of SDS per 0.1 wt % chitosan before becoming saturated with surfactant. The SDS-chitosan interaction was weakened appreciably by the presence of 100 mM NaCl, which suggested that it was electrostatic in origin. This study provides information about the origin and characteristics of molecular interactions between chitosan and anionic surface-active lipids that may be useful for the rational design of chitosan-based food ingredients with specific nutritional and functional characteristics, e.g., cholesterol lowering or fat replacement.

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The objective of this study was to investigate the effect of soy protein isolate on functional properties and consumer acceptance of gluten-free rice spaghetti (GFRS) made from rice flour. Dry-milled high-amylose (Chai Nat 1) rice flour was premixed with dry-milled waxy (RD 6) rice flour at a ratio of 90:10 (w/w) with the soy protein isolate (SPI) concentration varying between 0, 2.5, 5.0, 7.5, 10.0 %, db. The GFRS formulation was processed using a co-rotating twin-screw extruder up to 95 °C with a screw speed of 220 rpm, 32 % moisture content, and then dried at 40 C. The GFRS samples were analyzed by differential scanning calorimetry (DSC), X-ray diffraction, scanning electron microscopy (SEM) and texture parameters. Increasing SPI decreased the starch retrogradation of GFRS, whereas the enthalpy change of the amylose-lipid complex increased and crystallinity decreased. SEM revealed that the surface of GFRS containing SPI was much more porous than that of GFRS without SPI. The cooked GFRS containing 5.0 % SPI showed the best eating quality with increased firmness and tensile strength, and decrease stickiness. The GFRS samples were evaluated on the bases of cooking qualities and sensory evaluation. The results showed that the GFRS containing 5.0 % SPI decrease the cooking time from 17.6 to 13.7 min and cooking loss from 25.4 to 17.0 %. Overall acceptability of cooked GFRS containing 5.0 % SPI was the highest among all GFRS samples.

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Selected plant extracts including cinnamon, clove, ginger, green tea and thyme were investigated for their antioxidant activity by using both -carotene-linoleate bleaching agar well diffusion and -carotene-linoleate bleaching broth assays, and for radical scavenging activity against free radicals using a 2,2-diphenyl-1picrylhydrazyl assay. Undiluted plant extracts (except ginger oil) showed a yellow zone of -carotene ranging from 15.3 to 38.2mm in diameter. At a concentration of 50LmL -1 , thyme yielded the highest antioxidant activity (260%), followed by ginger (254%), cinnamon (108%), clove (106%) and green tea (101%), respectively. Conversely, at a plant extract concentration of 0.39mL mL -1 solution in ethanol, green tea yielded the highest radical scavenging activity (94.3%), followed by clove (93.4%), cinnamon (91.1%), thyme (30.4%) and ginger (8.29%), respectively. The minimum oxidative bleaching inhibitory concentrations (MOBICs) of these plant extracts were determined using a b-carotene-linoleate bleaching broth dilution assay ranging from 0.195 to 50mLmL -1 . The MOBICs of plant extracts in a range of 0.195-1.56mLmL -1 could reveal an ability to inhibit the oxidation of b-carotene-linoleate broth. Cellulose-based film containing cinnamon, clove or green tea showed positive activity against b-carotene-linoleate oxidation and 2,2-diphenyl-1-picrylhydrazyl radicals. Protective effects of plant extracts incorporated in cellulose-based pouches in stabilizing soybean oil were tested by measuring their peroxide values and free fatty acid contents during accelerated storage. Green tea-incorporated cellulose-based pouches exhibited stronger antioxidant properties in soybean oil than do butylated hydroxyanisole-incorporated cellulose-based pouches. This study showed the potential use of plant extracts as antioxidants for food packaging application.Free radical scavenging activity using DPPH scavenging method. Cellulose-based films containing cinnamon oil, clove oil or green tea extract also showed positive radical scavenging activity against DPPH radicals (Table 3). Their relative activity was cloveÀ>cinnamonÀ>green teaÀcellulosebased film. It is interesting to note that all plant extract cellulose-based films were more effective against DPPH radicals in comparison with the b-carotene-linoleate bleaching assay. 132P. PHOOPURITHAM ET AL.