Starch digestibility and predicted glycemic index of fried sweet potato cultivars.
Odenigbo, A., Rahimi, J., Ngadi, M., Amer, S. & Mustafa, A. (2012). Functional Foods in Health and Disease, 2(7), 280-289.
Background: Sweet potato (Ipomoea batatas L.) is a very rich source of starch. There is increased interest in starch digestibility and the prevention and management of metabolic diseases. Objective: The aim of this study was to evaluate the levels of starch fractions and predicted glycemic index of different cultivars of sweet potato. Material and Method: French fries produced from five cultivars of sweet potato (‘Ginseng Red’, ‘Beauregard’, ‘White Travis’, ‘Georgia Jet clone #2010’ and ‘Georgia Jet’) were used. The level of total starch (TS), resistant starch (RS), digestible starch (DS), and starch digestion index starch digestion index in the samples were evaluated. In vitro starch hydrolysis at 30, 90, and 120 min were determined enzymatically for calculation of rapidly digestible starch (RDS), predicted glycemic index (pGI) and slowly digestible starch (SDS) respectively. Results: The RS content in all samples had an inversely significant correlation with pGI (-0.52; P<0.05) while RDS had positive and significant influence on both pGI (r=0.55; P<0.05) and SDI (r= 0.94; P<0.01). ‘White Travis’ and ‘Ginseng Red’ had higher levels of beneficial starch fractions (RS and SDS) with low pGI and starch digestion Index (SDI), despite their higher TS content. Generally, all the cultivars had products with low to moderate GI values. Conclusion: The glycemic index of these food products highlights the health promoting characteristics of sweet potato cultivars.
Synthesis and characterization of enzyme–magnetic nanoparticle complexes: effect of size on activity and recovery.
Park, H. J., McConnell, J. T., Boddohi, S., Kipper, M. J. & Johnson, P. A. (2011). Colloids and Surfaces B: Biointerfaces, 83(2), 198-203.
The influence of particle size on the activity and recycling capabilities of enzyme conjugated magnetic nanoparticles was studied. Co-precipitation and oxidation of Fe(OH)2 methods were used to fabricate three different sizes of magnetic nanoparticles (5 nm, 26 nm and 51 nm). Glucose oxidase was covalently bound to the magnetic nanoparticles by modifying the surfaces with 3-(aminopropyl)triethoxysilane (APTES) and a common protein crosslinking agent, glutaraldehyde. Analysis by Transmission Electron Microscopy (TEM) showed that the morphology of the magnetic nanoparticles to be spherical and sizes agreed with results of the Brunauer, Emmett, and Teller (BET) method. Magnetic strength of the nanoparticles was analyzed by magnetometry and found to be 49 emu g-1 (5 nm), 73 emu g-1 (26 nm), and 85 emu g-1 (51 nm). X-ray photoelectron spectroscopy (XPS) confirmed each step of the magnetic nanoparticle surface modification and successful glucose oxidase binding. The immobilized enzymes retained 15–23% of the native GOx activity. Recycling stability studies showed approximately 20% of activity loss for the large (51 nm) and medium (26 nm) size glucose oxidase-magnetic nanoparticle (GOx-MNP) bioconjugate and about 96% activity loss for the smallest GOx-MNP bioconjugate (5 nm) after ten cycles. The bioconjugates demonstrated equivalent total product conversions as a single reaction of an equivalent amount of the native enzyme after the 5th cycle for the 26 nm nanoparticles and the 7th cycle for the 51 nm nanoparticles.
Development of antimicrobial packaging materials with immobilized glucose oxidase and lysozyme.
Hanušová, K., Vápenka, L., Dobiáš, J. & Mišková, L. (2013). Central European Journal of Chemistry, 11(7), 1066-1078.
Packaging based on immobilization of antimicrobial enzymes provides a promising form of active packaging systems applicable in food processing. Glucose oxidase and lysozyme were immobilized by the Ugi reaction with cyclohexyl isocyanide and glutaraldehyde on polyamide and ionomer films partially hydrolysed by hydrochloric acid. The immobilization of the enzymes on the surface of films was confirmed by FT-IR spectroscopy and the films were characterized by the specific activity of the immobilized enzymes. The enzyme migration into model solutions and the effect of pH, temperature and storage time on the activity of immobilized enzyme were also evaluated. Immobilization of lysozyme onto polyamide and ionomer films resulted in the loss of enzyme activity. The polyamide and ionomer films with immobilized glucose oxidase inhibited the growth of bacteria Escherichia coli CNCTC 6859, Pseudomonas fluorescens CNCTC 5793, Lactobacillus helveticus CH-1, Listeria ivanovii CCM 5884 and Listeria innocua CCM 4030 on agar media.
Quantification of starch in plant tissues.
Smith, A. M. & Zeeman, S. C. (2006). Nature Protocols, 1(3), 1342-1345.
This protocol describes a simple means of measuring the starch content of plant tissues by solubilizing the starch, converting it quantitatively to glucose and assaying the glucose. Plant tissue must initially be frozen rapidly to stop metabolism, then extracted to remove free glucose. Starch is solubilized by heating, then digested to glucose by adding glucan hydrolases. Glucose is assayed enzymatically. The method is more sensitive and accurate than iodine-based protocols, and is suitable for tissues that have a wide range of starch contents. Measurements on multiple samples can be completed within a day.
Free nonimmobilized ligands as a tool for purification of proteins.
Patchornik, G. & Albeck, A. (2005). Bioconjugate Chemistry, 16(5), 1310-1315.
Purification of proteins on a large scale is a complex multistep process, and alternative economic strategies are required. This study presents a novel approach (Affinity Sinking, AS) for purification of native proteins utilizing nonimmobilized modified ligands. The nonimmobilized state of the ligand circumvents the need for immobilizing ligands to polymeric supports. Therefore, purification from large volumes can be accomplished without the use of industrial-scale affinity columns. The mechanism of product capture is formation and precipitation of a specific [target-protein/modified-ligand] complex by using a soluble interconnecting entity that generates an insoluble [target-protein/modified-ligand/interconnecting entity] sediment containing the target protein. Rabbit IgG and two glycoproteins were purified accordingly, utilizing free avidin (as the interconnecting entity) and either desthiobiotinylated-protein A (DB-ProA) or desthiobiotinylated-concanavalin A (DB-ConA) as the modified ligand. The recovery yields for the IgG and the two glycoproteins were 80−86% and 70−75%, respectively. Target proteins are eluted from the generated pellet nearly without disrupting the [modified-ligand/interconnecting entity] macro-complex, thus enabling a practical procedure of recovering target proteins. Leaching of the DB-ProA ligand under eluting conditions (pH 3) was found to be lower than 1%. The two modified ligands, DB-ProA and DB-ConA, were regenerated without any chromatographic procedure in 80% and 85%-89% yield, respectively. The advantage of excluding the polymeric component from the purification process and obtaining highly purified proteins has been demonstrated, and it implies that other contaminants (e.g. endotoxins, prions, host DNA) could be excluded as well, thereby reducing the number of purification steps in a typical downstream process.
On the relationship between jetted inks and printed biopatterns: Molecular-thin functional microarrays of glucose oxidase.
Arrabito, G., Musumeci, C., Aiello, V., Libertino, S., Compagnini, G. & Pignataro, B. (2009). Langmuir, 25(11), 6312-6318.
Arrays of circular spots of glucose oxidase have been obtained on functionalized silicon oxide by piezoelectric inkjet printing and the enzymatic activity toward glucose recognition has been monitored. The addition of glycerol to the molecular ink allows to obtain high spot definition and resolution (tens of micrometers wide; one molecule tall), but in spite of its well-known structural stabilizing properties, in dynamic conditions it may lead to increased protein stresses. The jetting voltage and pulse length have been found to be critical factors for both activity retention and pattern definition. High voltages and pulse lengths results in stress effects along with the loss of activity, which, at least in our experimental conditions, has been found to be recovered in time.
Starch fraction profiles of milled, nonparboiled rice varieties from Nigeria.
Odenigbo, A. M., Ngadi, M., Manful, J. & Danbaba, N. (2013). International Journal of Food Science & Technology, 48(12), 2535-2540.
This study determined the levels of nutritionally important starch fractions in selected milled, nonparboiled rice cultivated in Nigeria. Five improved varieties (FARO 52, FARO 57, FARO 44, FARO 60 and FARO 61) and four local varieties (Kwandala, Yardass, Jeep and Jamila) were evaluated. There were significant differences in starch fractions among varieties. Resistant starch (RS) ranged between 1.43% and 3.13%. Rapidly digestible starch (RDS) was lowest in Jamila (27.70%) and highest in FARO 61 (39.26%). Generally, the local varieties had significant higher RS (2.71%) with a lower RDS (32.82%) compared with improved varieties (RS; 1.88% and RDS; 36.07%). RS was inversely related to RDS and starch digestion index (SDI). The SDI had a highly significant positive correlation with RDS (r = 0.879, P < 0.01). These results highlight the need for further work in the identification of milled, nonparboiled rice varieties with less rapid digestion for its associated health benefits to consumers.