Effect of hydrostatic pressure on starch gelatinisation

Samples of wheat and potato starches, mixed with water to four concentrations were subjected to preselected hydrostatic pressures (in the range 200–1500 MPa) and temperatures. Subsequent examination in a polarising microscope revealed that the effect of high hydrostatic pressure was to lower the gelatinisation temperature. With the exception of the low water content samples, the samples did not appear to be greatly affected in any other way by hydrostatic pressure (as evidenced by staining behaviour, appearance in the polarising microscope and subsequent gelatinisation behaviour at ambient pressure). Reduction in gelatinisation temperature was a non-linear function of pressure, being greatest at high pressure. The effect was also more pronounced at the higher water contents. The significance of these results with respect to thermodynamic models of starch gelatinisation is discussed.     

The effect of lintnerisation on wheat and potato starch granules

Wheat and potato starches were hydrolysed with 2·2 n hydrochloric acid at 35°C for a period of time up to 15 days. The residues (lintnerised starches) were washed and freeze dried, and studied by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle light scattering (SALS), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques showed that profound changes took place in the first day of hydrolysis (during which time the extent of hydrolysis was 7·7% for potato starch and 12·5% for wheat starch). In particular, the gelatinisation enthalpy (ΔH) decreased, the X-ray crystallinity increased and the SANS and SAXS peaks (indicative of a regular spacing between crystalline and amorphous regions) virtually disappeared. The reduction in ΔH is surprising and is discussed at length. It was also shown that freeze drying results in a considerable lowering of the gelatinisation temperature of potato starch (and also of ΔH) while that of wheat starch is only slightly affected.     

Gelatinisation of sago starch in the presence of sucrose and sodium chloride as assessed by differential scanning calorimetry

The inhibitory effect of sucrose and sodium chloride on sago starch gelatinisation was investigated by differential scanning calorimetry (DSC). The temperature of gelatinisation of starch in the presence of low levels of water and high levels of sucrose was found to increase in the presence of sucrose, whereas the gelatinisation enthalpy was unaffected. The gelatinisation temperature range was not as broad in the presence of sucrose as without sucrose. Furthermore, the shape of the gelatinisation endotherm was changed by the addition of sucrose. The double endotherm obtained in limited water:starch systems was changed into a single endotherm, similar to the endotherm obtained in excess water:starch systems at a higher temperature. DSC was also used to examine the effects of water and sodium chloride content on the phase transitions of sago starch. Samples were adjusted to starch:water ratios of 2:3 and 3:2 in sodium chloride concentrations of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 M. The gelatinisation temperatures of sago starch increased and then decreased as the sodium chloride concentration increased. Sodium chloride created similar effects on the endotherms in excess water content and on the first endotherm with limited water content. In the presence of sucrose and sodium chloride, gelatinisation shifted to higher temperatures, and enthalpy associated with the endothermic process decreased. The extent of temperature shift and enthalpy change was dependent on the water to starch to solutes ratios.     

Effect of temperature on gelatinization and retrogradation in high hydrostatic pressure treatment of potato starch-water mixtures

The effect of temperature (20-70 °C) on the gelatinization and retrogradation of potato starch-water mixtures (10-70%, w/w) treated with high hydrostatic pressure (HHP) (400-1000 MPa) was investigated. Gelatinization enthalpy change (ΔH_gel) and re-gelatinization enthalpy change of retrograded crystalline part (ΔH_retro) of the HHP-treated starch were evaluated using differential scanning calorimetry. The value of ΔH_gel of 10-20% (w/w) mixtures decreased with increased pressure and temperature, while ΔH_gel of 30-50% (w/w) mixtures decreased to certain values with increased pressure and the values depended on treatment temperature. With higher temperature and pressure conditions, ΔH_gel of 10-40% (w/w) mixtures reached zero, but ΔH_gel of 50-70% (w/w) mixtures did not. Retrogradation was observed with HHP-treated 20-60% (w/w) mixtures and the value of ΔH_retro depended on the starch content, pressure, and temperature. The value of ΔH_retro trended to increase with increase in starch content. In addition, retrogradation was promoted by HHP treatment at low temperature. Gelatinizaiton and retrogradation behaviors of HHP-treated (400-1000 MPa) potato starch-water mixtures (10-70%, w/w) at 20-70 °C were summerized in a series of state diagrams.     

Structural and physicochemical characterisation of rye starch

The gelatinisation, pasting and retrogradation properties of three rye starches isolated using a proteinase-based procedure were investigated and compared to those of wheat starch isolated in a comparable way. On an average, the rye starch granules were larger than those of wheat starch. The former had very comparable gelatinisation temperatures and enthalpies, but slightly lower gelatinisation temperatures than wheat starch. Under standardised conditions, they retrograded to a lesser extent than wheat starch. The lower gelatinisation temperatures and tendencies of the rye starches to retrograde originated probably from their higher levels of short amylopectin (AP) chains [degree of polymerisation (DP) 6–12] and their lower levels of longer chains (DP 13–24) than observed for wheat starch. The rapid visco analysis differences in peak and end viscosities between the rye starches as well as between rye and wheat starches were at least partly attributable to differences in the levels of AP short chains and in average amylose molecular weight. The AP average chain lengths and exterior chain lengths were slightly lower for rye starches, while the interior chain lengths were slightly higher than those for wheat starch.     

The effect of pre-harvest pruning on the quality of cassava starch

Two cassava cultivars CMC 40 and MPer 245 were grown at the Centro Internacional de Agricultura Tropicale (CIAT) in Colombia. Specimens were pruned by the removal of aerial growth 4 weeks prior to harvest and starch granules were isolated from the roots of pruned and control plants after harvest. The glassiness and hardness of cooked roots from the pruned plants showed an increase of 60–70% and 40–60% respectively compared with the controls. Although there was some reduction in the size of the starch granules derived from the pruned roots as compared with the control, pruning had negligible effects upon X-ray crystallinity, amylose/amylopectin contents, the elution patterns of the isoamylase debranched starch, the susceptibility of the granules to enzyme digestion, their swelling power and solubility, the temperature and enthalpy of gelatinisation and their behaviour in the Rapid Visco Analyser. Minor differences were observed when pruned and control samples were examined in the Brabender amylograph.     

Oxidized and acid thinned starch derivatives of hybrid maize: functional characteristics, wide-angle X-ray diffractometry and thermal properties

Starch isolated from hybrid maize (8535-23) was subjected to oxidation and acid thinning. Proximate analyses revealed that moisture, ash, protein, fat, fibre, and pH reduced after oxidation and acid thinning. Percentage amylose content reduced from 20.42% in native starch to 18.76 and 17.65% in oxidised and acid thinned starch derivatives, respectively. Wide-angle X-ray diffraction patterns indicated strong peaks at 15.9 degrees, 17.2 degrees, 18.8 degrees, and 25.0 degrees 2theta. No significant difference was observed between the X-ray pattern of the native and modified starches. Both swelling power and solubility increased with increase in temperature. Oxidation and acid thinning reduced swelling power and increased solubility starch. At all pHs, both oxidation and acid thinning reduced the swelling capacity of the native starch. Oxidation increased water and oil absorption capacity of the native starch, while both hydrophilic and hydrophobic properties reduced following acid thinning. Least gelation concentration reduced in acid thinned starch but increased in oxidised derivative. Pasting temperature (Tp), peak viscosity (Pv), hot paste viscosity (Hv), and viscosity after 30 min holding at 95 degrees C (H(v30)) reduced following both modifications. However, values for cold paste viscosity (Cv) and setback (SB) reduced in oxidised derivative and increased in acid thinned starch. Light transmittance of the starch pastes reduced with increase in storage days, however, reduction was more pronounced in native and acid thinned starches. Onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc) of gelatinisation reduced in modified starches compared with native hybrid maize starch. Also, gelatinisation enthalpy reduced after oxidation and acid thinning. Enthalpy of regelatinisation increased as days of storage of starch paste increased.     

Starch pastes thinning during high-pressure homogenization

High-pressure homogenization induced thinning of potato and cassava starch paste was investigated. The starch slurries at a concentration of 2.0 wt.% were heated at 90 °C for 1 h and then rapidly cooled in tap water. The cooled starch pastes were homogenized at various pressures ranging from 0 to 100 MPa using a lab-scale high-pressure homogenizer. The influence of homogenizing pressure on the temperature, apparent viscosity, electrical conductivity, and percent light transmittance of homogenized starch pastes were determined. Temperatures of homogenized starch pastes increased linearly with the increase of the applied pressure, and the rate was 0.177 °C/MPa and 0.186 °C/MPa for potato and cassava starch pastes, respectively. After high-pressure homogenization, the apparent viscosities of the starch pastes decreased, while the percent light transmittances of them increased. However, the electrical conductivities of starch pastes were not affected by homogenization.     

Consequences of antisense RNA inhibition of starch branching enzyme activity on properties of potato starch

Antisense constructs containing cDNAs for potato starch branching enzyme (SBE) were introduced into potato (Solanum tuberosum L.). A population of transgenic plants were generated in which tuber SBE activity was reduced by between 5 and 98% of control values. No significant differences in amylose content or amylopectin branch length profiles of transgenic tuber starches were observed as a function of tuber SBE activity. Starches obtained from low SBE activity plants showed elevated phosphorous content. ³¹P n.m.r. analysis showed that this was due to proportionate increases in both 3- and 6-linked starch phosphates. A consistent alteration in starch gelatinisation properties was only observed when the level of SBE activity was reduced to below ˜5% of that of control values. Starches from these low SBE activity plants showed increases of up to 5 °C in d.s.c. peak temperature and viscosity onset temperature. Studies on melting of crystallites obtained from linear (1 → 4)-- -glucan oligomers suggest that an average difference of double helix length of about one glucose residue might be sufficient to account for the observed differences in gelatinisation properties. We speculate that the modification of gelatinisation properties at low SBE activities is due to a subtle alteration in amylopectin branch patterns resulting in small changes in double helix lengths within granules.     

The distribution of covalently bound phosphate in the starch granule in relation to starch crystallinity

Five selected starches with a 60-fold span in their content of monoesterified starch phosphate were investigated with respect to distribution of glucose 6-phosphate and glucose 3-phosphate residues, amylopectin chain length distributions and gelatinisation properties. The distribution of starch phosphate in the starch granules was determined by preparation of N?geli dextrins followed by quantitative 31P-nuclear magnetic resonance spectroscopy. Total starch phosphate content was positively correlated to the unit chain lengths of the amylopectin as well as to the chain lengths of the corresponding N?geli dextrins. The major part (68-92%) of the total starch phosphate content was partitioned to the hydrolysed (amorphous) parts. Starch-bound glucose 6-phosphate per milligram of starch was 2-fold enriched in the amorphous parts, whereas phosphate groups bound at the 3-position were more evenly distributed. The gelatinisation temperatures of the native starches as determined by differential scanning calorimetry were positively correlated (R(2)=0.75) to starch phosphate content, while crystallinity (gelatinisation enthalpy) and crystal heterogeneity (endotherm peak width) showed no correlations to starch phosphate content. The relations between starch molecular structure, architecture and functional properties are discussed.     

Catalytic activity of beta-amylase from barley in different pressure/temperature domains

The depolymerization of starch by beta-amylase during exposure to hydrostatic pressure up to 700 MPa and within a temperature range from 20 to 70 degrees C has been investigated. Inactivation of the enzyme as well as alterations in conversion speed in response to combined pressure-temperature treatments were assessed by analyzing the kinetic rate constants. At 200 MPa a significant stabilization of the enzyme against heat inactivation was observed. However, high pressure also impedes the catalytic reaction and a progressive reduction of the conversion rate constants with increasing pressure was found at all temperatures investigated. For the overall reaction of maltose liberation from soluble starch in ACES buffer at pH 5.6 an optimum was identified at 106 MPa and at 63 degrees C, which is approximately 7 degrees C above the local maximum at ambient pressure (0.1 MPa). Gelatinization of nonsoluble starch granules in response to pressure-temperature (p-T) treatment has been inspected by phase-contrast microscopy and yielded circular curves of identical effect in the p-T plane.     

A small-angle X-ray scattering study of the absorption of water into the starch granule

Analysis of the shape of the small-angle X-ray scattering (SAXS) intensity profiles obtained from suspensions of wheat starch granules in water gives information on the amount of absorption into the different regions of the granule. At room temperature, less water is absorbed into the granules the higher the starch concentration. At 51°C, the beginning of the gelatinisation region, lower amounts of water are absorbed when the concentration of starch is high and there is less loss of crystalline order. In an excess of water, co-operative melting occurs, whereas, with less water, the absorption is insufficient to destabilise the crystalline order. The beam damage at room temperature is reflected in a slight increase in order, possibly due to rearrangement after chain scission.     

Effect of pressure and temperature on the gelatinization of starch at various starch concentrations

The effects of pressure, temperature, and treatment time on the degree of gelatinization were determined with differential scanning calorimetry measurements for wheat starch-water mixtures with starch concentrations varying between 5 and 80 w/w %. Although simple models could be used to describe the degree of starch gelatinization as a function of pressure or temperature, a more complex model based on the Gibbs energy difference had to be used to describe the degree of gelatinization as a function of both pressure and temperature. The experimental and model data were used to construct a phase diagram for 5, 30, and 60 w/w % wheat starch-water mixtures. Data obtained from literature were in accordance with our phase diagrams. These phase diagrams can be used to estimate the degree of gelatinisation after applying a certain pressure and temperature on a starch-water mixture with starch concentrations in the range of 5 and 60 w/w %.     

Links in the histamine metabolism in the brain of rats with sequential exposure to low- and high-pressure oxygen

Histamine content and diamine oxidase activity in rat brain under hyperbaric oxygenation have been studied. Under 0,3 MPa histamine level decreases in brain of more sensitive rats, but it does not change in brain of more resistant animals in comparison with the control ones. High oxygen pressure (0,7 MPa) causes a significant increase of histamine concentration. Diamine oxidase activity decreases under hyperoxia. Under the consequent action of high and low pressure (0,3 MPa during 1 h and 0,7 MPa) convulsions in rats begin later and alterations of histamine content in brain are less than under 0,7 MPa oxygen action only. The role of histamine at compensate reaction and cause of increasing resistance of animals to hyperoxia are discussed.     

SANS study of the distribution of water within starch granules

This study describes contrast variation small angle neutron scattering (SANS) experiments which focus on the role which the intra-granular room temperature distribution of water and carbohydrate plays in determining the native structure and subsequent functionality of starch. It is shown that variations in botanical origin and amylose content do not correlate with significant differences in room temperature composition of A-type starch granules. In turn, variations in the gelatinisation behaviour of A-type starches do not correlate with variations in room temperature water distribution. In contrast, the room temperature water content is found to differ significantly between granules of potato (B-type) and a range of A-type starch cultivars. A correlation is found between these compositional differences and variations in crystal structure, which has implications for biological growth conditions and gelatinisation behaviour.     

Efficiency of high pressure treatment for destruction of Listeria monocytogenes in fruit juices

The objective of this study was to compare high pressure resistance of Listeria monocytogenes strains at 25 degrees C and 50 degrees C at 350 MPa and to use high pressure (250 MPa and 350 MPa) at 30 degrees C and 40 degrees C for the inactivation of the relatively most pressure resistant strain inoculated in pasteurized apple, apricot, cherry and orange juices. L. monocytogenes CA was found to be the relatively most pressure resistant strain and increasing pressurization from 250 MPa to 350 MPa at 30 degrees C had an additional three to four log cycle reduction in viability, still leaving viable cells after 5 min. When 350 MPa at 40 degrees C for 5 min was applied more than eight log cycle reduction in cell population of all fruit juices was achieved. This study demonstrated that low temperature (40 degrees C) high pressure (350 MPa) treatment has the potential to inactivate relatively pressure resistant L. monocytogenes strains inoculated in different fruit juices within 5 min.     

Effects of annealing on the polymorphic structure of starches from sweet potatoes (Ayamurasaki and Sunnyred cultivars) grown at various soil temperatures

Starches extracted from the sweet potato cultivars Sunnyred and Ayamurasaki grown at 15 or 33 degrees C (soil temperature) were annealed in excess water (3 mg starch/mL water) for different times (1, 4, 8 or 10h) at the temperatures 2-3 degrees K below the onset melting temperature. The structures of annealed starches, as well as their gelatinisation (melting) properties, were studied using high-sensitivity differential scanning calorimetry (HSDSC). In excess water, the single endothermic peak shifted to higher temperatures, while the melting (gelatinisation) enthalpy changed only very slightly, if any. The elevation of gelatinisation temperature was associated with increasing order/thickness of the crystalline lamellae. The only DSC endotherm identified in 0.6 M KCl for Sunnyred starch grown at 33 degrees C was attributed to A-type polymorphic structure. The multiple endothermic forms observed by DSC performed in 0.6M KCl for annealed starches from both cultivars grown at 15 degrees C provided evidence of a complex C-type (A- plus B-type) polymorphic structure of crystalline lamellae. The A:B-ratio of two polymorphic forms increased upon annealing due to partial transformation of B- to A-polymorph, which was time dependent. Long heating periods facilitated the maximal transformation of B- to A-polymorph associated with limited A:B ratio.     

Effect of high hydrostatic pressure on chicken myosin subfragment-1

Hydrostatic pressure-induced structural changes in subfragment-1 (S1) of myosin molecule were studied. ATP-induced emission spectra of S1 were used to detect global structural change of S1 by pressure treatment. The fluorescence intensity of unpressurized S1 increased by addition of ATP. The increment of fluorescence of pressurized S1 up to 150 MPa was almost the same as control, whereas it became smaller above 200 MPa. ATP binding ability of S1 examined using 1, N⁶-ethenoadenosine 5′-diphosphate (-ADP) indicated that the binding of -ADP to S1 decreased in the range of 250–300 MPa. S1 pressurized below 250 MPa and unpressurized S1 similarly bound to F-actin, although binding of S1 pressurized above 250 MPa decreased. Electron microscopic observation revealed arrowhead structure in control acto-S1, while disordered arrowhead structure was observed in acto-S1 prepared from pressurized S1 at 300 MPa. S1 pressurized below 250 MPa retained the same actin activated ATPase activity as the control, whereas the activity decreased to 60% at 300 MPa. Pressure treated S1 was easily cleaved by tryptic digestion into three domains, i.e. 27 kDa (N-terminal), 50 and 20 kDa (C-terminal) fragments, which were the same as those in unpressurized one. It is concluded that pressure-induced global structural changes of S1 begin to occur about 150 MPa, and the local structural changes in ATPase and actin binding sites followed with elevating pressure to 250–300 MPa.     

High-pressure potato starch granule gelatinization: synchrotron radiation micro-SAXS/WAXS using a diamond anvil cell

Potato starch granules have been examined by synchrotron radiation small- and wide-angle scattering in a diamond anvil cell (DAC) up to 750 MPa. Use of a 1 microm synchrotron radiation beam allowed the mapping of individual granules at several pressure levels. The data collected at 183 MPa show an increase in the a axis and lamellar period from the edge to the center of the granule, probably due to a gradient in water content of the crystalline and amorphous lamellae. The average granules radius increases up to the onset of gelatinization at about 500 MPa, but the a axis and the lamellar periodicity remain constant or even show a decrease, suggesting an initial hydration of amorphous growth rings. The onset of gelatinization is accompanied by (i) an increase in the average a axis and lamellar periodicity, (ii) the appearance of an equatorial SAXS streak, and (iii) additional short-range order peaks.