Densely packed matrices as rate determining features in starch hydrolysis

To aid in the design of starch-containing foods with slow and/or incomplete digestion in the upper gastrointestinal tract, the starch structural factors which control the rate of action of alpha-amylase are reviewed. It is concluded that local starch molecular density has the major influence on amylase digestion kinetics, and that density sufficient to either limit enzyme binding and/or slow down catalysis can be achieved by either crystallization or dense amorphous packing

Effect of biscuit baking conditions on the stability of microencapsulated 5-methyltetrahydrofolic acid and their physical properties

Among the folate compounds, 5-methyltetrahydrofolic acid (5-CH3THF) is regarded as one of the most bioactive forms of folate. It is regarded as the better source of folate to humans as compared to folic acid, a synthetic form of folate, which is used for fortifying foods to prevent the incidence of neural tube defects in the new born babies. The use of 5-CH3THF as an alternative fortificant, in place of folic acid, has been explored by various researchers. However, fortification of 5-CH3THF is problematic due to its lower stability. This study investigated the stability of microencapsulated 5-CH3THF in biscuits baked at various temperatures and times as well as changes in their physical properties. Microcapsule with pectin and alginate ratio of 80:20, prepared by spray drying, gave the highest retention (68.6%) of the 5-CH3THF, therefore, chosen for fortification. The encapsulated and unencapsulated 5-CH3THF were mixed separately with flour and biscuit ingredients and baked at 180°C, 200°C and 220°C, each for 5, 9 and 12 min. The inclusion of encapsulated and unencapsulated 5-CH3THF in the biscuit formulation and subsequent baking at various temperatures and times resulted in retention of 5-CH3THF from 19.1% to 1.7%. Microencapsulation of 5-CH3THF slightly improved the retention of 5-CH3THF over unencapsuated biscuits at 180°C for 5 min, but almost no such effect was achieved under baking temperatures of 200°C and 220°C. Physical analysis showed darker colour, harder texture and lower moisture content for biscuits baked at higher test temperatures. It seems intense heating condition that caused “over baking” of the biscuit likely to be responsible for the loss of the vitamin as well as less desirable physical properties of the biscuits

Amylase binding to starch granules under hydrolysing and non-hydrolysing conditions

Although considerable information is available about amylolysis rate, extent and pattern of granular starches, the underlying mechanisms of enzyme action and interactions are not fully understood, partly due to the lack of direct visualisation of enzyme binding and subsequent hydrolysis of starch granules. In the present study, α-amylase (AA) from porcine pancreas was labelled with either fluorescein isothiocyanate (FITC) or tetramethylrhodamine isothiocyanate (TRITC) fluorescent dye with maintenance of significant enzyme activity. The binding of FITC/TRITC-AA conjugate to the surface and interior of granules was studied under both non-hydrolysing (0 °C) and hydrolysing (37 °C) conditions with confocal microscopy. It was observed that enzyme binding to maize starch granules under both conditions was more homogenous compared with potato starch. Enzyme molecules appear to preferentially bind to the granules or part of granules that are more susceptible to enzymic degradation. The specificity is such that fresh enzyme added after a certain time of incubation binds at the same location as previously bound enzyme. By visualising the enzyme location during binding and hydrolysis, detailed information is provided regarding the heterogeneity of granular starch digestion

Encapsulation of Lactobacillus plantarum in porous maize starch

This study investigated the survival of probiotic Lactobacillus plantarum 299v microencapsulated in native maize starch or partially hydrolyzed maize starches after acid, bile and heat treatments. Scanning electron microscopy and confocal scanning laser microscopy confirmed that naturally present cavities and channels in native maize starch were enlarged by enzymatic hydrolysis allowing them to be filled with probiotics. The formulations using the modified starches had significantly higher initial viable cells compared to native starch after freeze-drying. Compared to free cells, the microencapsulated probiotic bacteria showed a significant improvement in acid tolerance. When comparing unmodified and modified starches, the enzymatic treatments did not significantly improve relative survival, but did result in significantly higher total probiotic numbers after exposure to acid (pH = 2.0, 1 h), bile salt (3% w/v, 4 h) and heat (60 °C, 15min). These results demonstrate that porous maize starch granules allow for a high probiotic loading efficiency and provide enhanced protection to various stressful conditions compared to free cells

The interplay of α-amylase and amyloglucosidase activities on the digestion of starch in in vitro enzymic systems

In vitro hydrolysis assays are a key tool in understanding differences in rate and extent of digestion of starchy foods. They offer a greater degree of simplicity and flexibility than dynamic in vitro models orin vivo experiments for quantifiable, mechanistic exploration of starch digestion. In the present work the influence of α-amylase and amyloglucosidase activities on the digestion of maize and potato starchgranules was measured using both glucose and reducing sugar assays. Data were analysed through initialrates of digestion, and by 1st order kinetics, utilising logarithm of slope (LOS) plots. The rate and extent of starch digestion was dependent on the activities of both enzymes and the type of starch used. Potatorequired more enzyme than maize to achieve logarithmic reaction curves, and complete digestion. The results allow targeted design of starch digestion experiments through a thorough understanding of the contributions of α-amylase and amyloglucosidase to digestion rates

Influence of abnormal potassium levels on mortality among hospitalized heart failure patients in the US: data from National Inpatient Sample.

Abnormalities in serum potassium levels have been associated with variable mortality risk among hospitalized patients with heart failure (HF). We aim to use a large database study to further characterize risk of mortality, demographic factors, and associated comorbidities among heart failure inpatients. Methods: Our sample population was from the US National Inpatient Sample database from the year 2009-2011. The inclusion criteria used to identify patients was those with a diagnosis of heart failure as per ICD-9 classification. Other demographic factors considered in data collection included income, and cardiac risk factors. Taking these factors into consideration, a univariate association of potassium level and mortality was performed, as well as multivariable logistic regression controlling for demographic factors and associated conditions. Results: Of the 2,660,609 patients who were discharged with a diagnosis of heart failure during this time period, patients with hypokalemia during hospitalization had increased mortality risk (OR: 1.96, 95% CI: 1.91-2.01) when compared with those with hyperkalemia who had decreased inpatient mortality risk OR: 0.94,95% CI: 0.91-0.96) versus those not coded for potassium abnormalities. This finding was significant even regardless of the etiology of the hypokalemia while the hyperkalemic patients were noted to have no difference or a decreased risk in all subtypes and groups. Conclusion: Unlike heart failure patients with hyperkalemia, those with hypokalemia are at an increased inpatient mortality risk. Whether our mortality findings translate to longer-term outpatient settings where significantly less monitoring is possible is a matter for further study

Isolation of wheat endosperm cell walls: effects of non-endosperm flour components on structural analyses

We report the isolation of a pure form of cell walls from wheat endosperm ‘popped’ out from the whole, enzyme deactivated and soaked grain, and compare them with cell walls isolated from milled flours of extraction rates from 45% to 75%, at physiological (37 °C) and elevated (70 °C) temperatures. Cell walls isolated from flours all contained non-endosperm walls whereas walls from popped endosperm were apparently pure. The monosaccharide composition of ‘popped’ cell walls was different to that of cell walls isolated from flour, particularly glucose and mannose contents (34 and 7% for ‘popped’ cf 29 and 3% for flour respectively) and arabinose to xylose ratios (0.45 for ‘popped’ cf 0.58 for flour). Total phenolic contents of popped endosperm cell walls were three to four times lower than for cell walls from flour. Elevated isolation temperature also had a solubilising effect, altering the cell wall composition. This study provides a novel method of isolating pure wheat endosperm cell walls, and demonstrates how contaminating (thick cell walled) non-endospermic material in milled flours can have a major influence on cell wall compositional analyses

Extrusion induced low-order starch matrices: enzymic hydrolysis and structure

Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing

Tribology of swollen starch granule suspensions from maize and potato

The tribological properties of suspensions of cooked swollen starch granules are characterised for systems based on maize starch and potato starch. These systems are known as granule 'ghosts' due to the release (and removal) of polymer from their structure during cooking. Maize starch ghosts are less swollen than potato starch ghosts, resulting in a higher packing concentration and greater mechanical stability. In a soft-tribological contact, maize ghost suspensions reduce friction compared to the solvent (water), generate bell-shaped tribological profiles characteristic of particle entrainment and show a marked concentration dependence, whereas potato ghost suspensions exhibit lubrication behaviour similar to water. Microscopy analysis of the samples following tribological testing suggests that this is due to the rapid break-up of potato ghosts under the shear and rolling conditions within the tribological contact. A reduction in the small deformation moduli (associated with a weak gel structure) is also observed when the potato ghost suspensions are subjected to steady shear using parallel plate rheometry; both microscopy and particle size analysis show that this is accompanied by the partial shear-induced breakage of ghost particles. This interplay between particle microstructure and the resultant rheological and lubrication dynamics of starch ghost suspensions contributes to an enhanced mechanistic understanding of textural and other functional properties of cooked starches in food and other applications

Structural and physicochemical properties of granular starches after treatment with debranching enzyme

The present study modified maize and potato granular starches by partial debranching treatment below the gelatinization temperature, and investigated their structural and physicochemical properties. Pullulanase was much effective (more than three times) on hydrolyzing potato starch compared to maize starch as measured from total carbohydrate values in the supernatant. The pullulanase hydrolysis decreased the amount of double helices as observed from DSC measurement. These effects were dependent upon the time of enzyme hydrolysis (24 h > 8 h > 1 h) as well as type of starch (potato > maize). The pullulanase hydrolysis decreased the peak viscosity of the potato starch paste, whereas the effect was very less pronounced for maize starch. The current results showed that it is possible to achieve the starches with desired physicochemical properties by varying the starch type as well as modification process