Pirkko Forssell

Phase and glass transition behaviour of concentrated barley starch-glycerol-water mixtures, a model for thermoplastic starch

Abstract The effects of glycerol and water content on the thermal transitions of plasticized barley starch were examined using differential scanning calorimetry. The glycerol contents studied were 14, 20, 29 and 39% and the water content, obtained by conditioning in different relative humidities, varied in the range 1–28%. On the basis of the observed calorimetric glass transition temperatures and corresponding heat capacity increments it was inferred that a single phase system occurred at low water and glycerol contents, while in other cases phase separation occurred and the system was composed of starch-rich and starch-poor phases. Dynamic mechanical thermal analysis on a phase-separated sample showed mechanical loss peaks corresponding to the glass transitions of both phases. Amylopectin crystallization did not occur within 1 week of storage in mixtures having less than 20% water, indicating that glycerol interacted with starch, inhibiting crystallization of amylopectin.

Effect of glycerol on behaviour of amylose and amylopectin films

Abstract The effect of water and glycerol on sorption and calorimetric Tgs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the Tg. But in spite of the observed decrease in Tg under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.

In vitro fermentation of polysaccharides of rye, wheat and oat brans and inulin by human faecal bacteria

The in vitro fermentabilities of rye, wheat and oat brans and of a commercial fibre preparation, inulin, were compared. The brans were first digested enzymatically to remove starch and protein. The digested brans and inulin were then fermented with human faecal inoculum. The progress of fermentation was studied by following the consumption of carbohydrates and the production of short-chain fatty acids and gases. Inulin, a short fructose polymer, was consumed significantly faster than the more complex carbohydrates of cereal brans. Carbohydrates of oat bran (rich in β-glucan) were consumed at a higher rate than those of rye and wheat brans (rich in arabinoxylan). In all brans, glucose was consumed faster than the other main sugars, arabinose and xylose, and arabinose was degraded only slightly. The total production of short-chain fatty acids was slightly higher with oat bran than with rye and wheat brans and inulin. In the fermentation of inulin, relatively more butyric acid and less propionic acid were produced than in the fermentation of brans. The decrease in pH was also greater in the case of inulin. Wheat bran led to a slightly slower gas formation than rye and oat brans. Formation of gases was fastest and greatest in the case of inulin. In conclusion, rye, wheat and oat brans were fermented in a rather similar way. Fermentation of the brans was different from that of inulin. Cereal brans might serve as a more balanced source of dietary fibre supplement than gas-producing, readily fermentable polysaccharides such as inulin. © 2000 Society of Chemical Industry

Oxygen permeability of amylose and amylopectin films

The effects of water and glycerol contents on oxygen permeability of starch polymer films were investigated. Starch films were prepared of amylose and amylopectin by a casting technique and oxygen permeability was analysed at 20°C. Glycerol contents were 0, 10, 20 or 30% while water content varied from 8 to 36%. Under ambient humidity both amylose and amylopectin films were excellent oxygen barriers, as good as the commercial ethylene vinyl alcohol film which was studied as a reference material. It was observed that the film permeabilities were determined by water content; below 15% water both starch films were good oxygen barriers, above 20% water the barrier property was lost.

The crystallinity of amylose and amylopectin films

X-ray crystallinity of amylose and amylopectin films with 0, 10 and 30% of glycerol and stored at RH 0, 54 and 91% were studied. Films prepared of water cast dilute solutions and dried at 70°C were thin and transparent. Each fresh amylose film showed B-type crystalline structures, and depending on the glycerol and water contents the amount of crystallinity varied from 6 to 32%. No changes in the crystallinity of the amylose films were observed during storage of two months. The fresh amylopectin films were completely amorphous. After storage for two months at the highest humidity the amylopectin film with 30% glycerol showed crystalline structure (19%), but all other amylopectin films remained amorphous during ageing. The crystal formation in the highly plasticised amylopectin film was suggested to be due to its rubbery state under the storage conditions. Amylose films were stable in water unlike amylopectin films that dispersed fast in water. About 35% of the amylose films were resistant to α-amylase, whereas amylopectin films were hydrolysed wholly. Also when treated with hydrochloric acid the amylopectin films dissolved totally and fast, while one week was needed to dissolve about 50% of the amylose films. It was concluded that even if part of the amylose films were amorphous, also these amorphous regions were more resistant to hydrolysis than the amorphous amylopectin structures.

Effect of Relative Humidity on Oxidation of Flaxseed Oil in Spray Dried Whey Protein Emulsions

Flaxseed oil was emulsified in whey protein isolate (WPI) and spray-dried. Powder characteristics and oxidative stability of oil at relative humidities (RH) from RH approximately 0% to RH 91% at 37 degrees C were analyzed. Oil droplets retained their forms in drying and reconstitution, but the original droplet size of the emulsion was not restored when the powder was dispersed in water. The particles seemed to be covered by a protein-rich surface layer as analyzed by electron spectroscopy for chemical analysis (ESCA). Oxidation of flaxseed oil dispersed in the WPI matrix was retarded from that of bulk oil but followed the same pattern as bulk oil with respect to humidity. A high rate of oxidation was found for both low and high humidity conditions. The lowest rate of oxidation as followed by peroxide values was found at RH 75%, a condition that is likely to diverge significantly from the monolayer moisture value. A weak baseline transition observed for the WPI matrix in a differential scanning calorimetry (DSC) thermogram suggested a glassy state of the matrix at all storage conditions. This was not consistent with the observed caking of the powder at RH 91%. Scanning electron microscopy (SEM) images revealed a considerable structural change in the WPI matrix in these conditions, which was suggested to be linked with a higher rate of oxygen transport. Possible mechanisms for oxygen transport in the whey protein matrix under variable RHs are discussed.

Effect of enzymatic interesterification on the melting point of tallow-rapeseed oil (LEAR) mixture

To reduce the melting point of a tallow-rapeseed oil mixture, the triglyceride composition of the mixture was altered by enzymatic interesterification in a solvent-free system. The interesterification and hydrolysis were followed by melting point profiles and by free fatty acid determinations. The degree of hydrolysis was linearly related to the initial water content of the reaction mixture. The rate of the interesterification reaction was influenced by the amount of enzyme but not much by temperature between 50 and 70°C. The melting point reduction achieved by interesterification depended on the mass fractions of the substrates: the lower the mass fraction of tallow, the larger the reduction of the melting point.

Fructan Content of Rye and Rye Products

ABSTRACT The fructan content of Finnish rye grains (13 samples, seven cultivars, harvested in 1998-2000) varied at 4.6–6.6 g/100 g (db). Commercial whole grain rye flour and rye flakes had fructan content of 4 g/100 g, light refined rye flour had fructan content of 3 g/100 g, and rye bran had fructan content of 7 g/100 g. Fructan content as high as 23 g/100 g was detected in the water-extractable concentrate of rye bran. Finnish soft rye bread and rye crisp bread contained 2–3 g of fructan/100 g. According to the suggested new definition of dietary fiber, fructans are also classified as dietary fiber. This means that the dietary fiber content of some cereal foods such as rye products may be increased by as much as 20% due to the presence of fructans in the grain.

Corn starches as film formers in aqueous-based film coating.

The purpose of this study was to evaluate the film formation ability and mechanical stress–strain properties of aqueous native corn starches, using free films and film coatings applied to tablets. Free films were prepared from high-amylose corn (Hylon VII), corn and waxy corn starches, using sorbitol and glycerol as plasticizers. The tablets and pellets were film-coated using an air-suspension coater, and characterized with respect to the film coating surface topography, cross-sectional structure and thickness (SEM), and dissolution in vitro. The amylose content of the starch film formers affected both the tensile strength and the elongation. The elongations were under 5% for even the plasticized starches, and in most cases, no plasticization effect was seen by either of the plasticizers. Dissolution of native corn starch film-coated tablets (weight gain 1%) did not differ from uncoated ones. A notable delay in dissolution of the drug was found by increasing Hylon VII film coating thickness, suggesting controlled-release characteristics.

Enzymatic transesterification of rapeseed oil and lauric acid in a continuous reactor

The optimum conditions for enzymatic transesterification of rapeseed oil and lauric acid in a fixed-bed reactor were studied. No solvent was used in the reaction mixture. A small amount of water was dissolved in the substrate mixture to maintain the activity of the enzyme at as high a level as possible. For maximum yield, the transesterification was performed with a residence time of about 20 min at a water content in the range of 0.1 to 0.2% and at the lowest possible temperature.