Biodegradable and non-retrogradable eco-films based on starch-glycerol with citric acid as crosslinking agent.

Interaction of hydrocolloids (xanthan gum, locust bean gum, guar gum, and high-methoxyl pectin) with macrocomponents of dough (water, starch, and protein) was evaluated by different techniques. (1)H spin-spin NMR relaxation assays were applied to study the mobility of the gluten-hydrocolloid-water matrix, and the amount of freezable water was determined by differential scanning calorimetry (DSC). Starch gelatinization parameters (T, enthalpy) were also analyzed by DSC. The influence of additives on the protein matrix was studied by Fourier transform (FT) Raman assays; analysis of the extracted gliadins and glutenins was performed by electrophoresis (SDS-PAGE). A significantly higher molecular mobility was found in matrices containing xanthan gum, whereas pectin led to the lowest molecular mobility. Freezable water showed a trend of increasing in the presence of hydrocolloids, particularly under conditions of water restriction. Starch gelatinization final temperature was decreased when hydrocolloids were added in the presence of enough water. In general, FT-Raman and SDS-PAGE indicated that hydrocolloid addition promoted a more disordered and labile network, particularly in the case of pectin addition. On the other hand, results obtained for dough with guar gum would indicate a good compatibility between this hydrocolloid and the gluten network.

Hydrocolloid interaction with water, protein, and starch in wheat dough.

The water binding capacities of five cereal and three tuberous starches, as well as fourteen modified wheat starches were determined using a Differential Scanning Calorimetry technique. Of the native starches, the tuberous ones had the highest moisture binding capacities. The influence of amylose/amylopectin ratio on water binding capacity was examined using waxy maize, normal maize and high amylose maize starches and increases in amylose level were found to result in reduced water binding. Chemical modification caused a reduction in the water binding capacity of wheat starch presumably as a result of blocking water binding sites on the starch molecules. Pregelatinized wheat starch showed a higher water binding capacity than wheat starch as a consequence of the disruption of the internal structure of the granule.

Water Binding Capacity of Commercial Produced Native and Modified Starches

Gelation of myosin in 0.6M KC1 at pH 7.0 and 6.0 during heating at various temperatures between 25–70°C was quantitatively measured by a simple shear modulus tester devised in our laboratory. Shear modulus data indicated that gelation occurs with a stepwise elevation of temperature from 30–60°C. Heat-treatment of the protein solution remarkably influenced the structure and water mobility in the system. Myosin gel formed by heating had a micro-network structure, which was not-present in the original myosin solution. The myosin gel had a slower value of spin-spin relaxation time compared to that of the original untreated sample, suggesting that the water mobility in the gel system was somehow restricted. The heat-induced gelation of myosin may be the result of the development of a three dimensional network structure which holds water in a less mobilized state.

Changes in shear modulus, ultrastructure and spin-spin relaxation times of water associated with heat-induced gelation of myosin

The king of fruits “Mango” (Mangifera indica L.) is very nutritious and rich in carotenes. India produces about 50% of the total world’s mango. Many researchers have reported the maturity indices and quality parameters for determination of harvesting time and eating quality. The methods currently used for determination of quality of mango are mostly based on the biochemical analysis, which leads to destruction of the fruits. Numerous works are being carried out to explore some non-destructive methods such as Near Infrared (NIR), Nuclear Magnetic Resonance (NMR), X-ray and Computed Tomography (CT), electronic nose, machine vision and ultrasound for quality determination of fruits. This paper deals with some recent work reported on quality parameters, harvesting and post-harvest treatments in relation to quality of mango fruits and reviews on some of the potential non-destructive techniques that can be explored for quality determination of mango cultivars.

Quality parameters of mango and potential of non-destructive techniques for their measurement — a review

Pulsed NMR was applied to measure the spin-lattice (T1) and the spin-spin (T1) relaxation times of the water adsorbed on sodium alginate, pectin, corn starch, casein and cellulose. T1 was determined by means of repeated 90°-90° pulse sequences and T2 by the spin-echo method. T1 relaxation time curves for all the samples studied showed simple exponential, i.e., single phase, behavior. Plots of T1 as a function of moisture content showed minima at 0.15–0.258 water/g dry matter; plots of T1 vs water activity (Aw) yielded minima at Aw of 0.65. T2 relaxation time curves for corn starch containing more than 0.56g water/g DM exhibited two-phase behavior, indicating the existence of two water fractions of different mobility. The amount of water in the bound fraction showed a remarkable consistency (0.194 ± 0.011g water/g DM) among six samples of high moisture content. T2 was found to increase with moisture content for all the macromolecules. Cellulose showed exceptionally long T2 values compared to the other materials at the same moisture content, whereas pectin and sodium alginate showed short T2 values. These results indicated that T2 value is a measure of strength of water binding. Break points were observed in the T2-moisture curve. The moisture contents at these points corresponded to the bound water content determined by freezing and to the equilibrium moisture content at Aw of 0.9. T2 increased exponentially with Aw.

H. K. Leung

Papers

Water binding of macromolecules determined by pulsed nmr