Antioxidant and Starch-Hydrolyzing Enzymes Inhibitory Properties of Striga-Resistant Yellow-Orange Maize Hybrids

Most of the health benefits derived from cereals are attributed to their bioactive compounds. This study evaluated the levels of the bioactive compounds, and the antioxidant and starch-hydrolyzing enzymes inhibitory properties of six pipeline Striga-resistant yellow-orange maize hybrids (coded AS1828-1, 4, 6, 8, 9, 11) in vitro. The maize hybrids were grown at the International Institute of Tropical Agriculture (IITA), Nigeria. The bioactive compounds (total phenolics, tannins, flavonoids, and phytate) levels, antioxidant (DPPH• and ABTS•+ scavenging capacity and reducing power) and starch-hydrolyzing enzymes (α-amylase and α-glucosidase) inhibitory activities of the maize hybrids were determined by spectrophotometry. At the same time, carotenoids were quantified using a reverse-phase HPLC system. The ranges of the bioactive compounds were: 11.25–14.14 mg GAE/g (total phenolics), 3.62–4.67 mg QE/g (total flavonoids), 3.63–6.29 mg/g (tannins), 3.66–4.31% (phytate), 8.92–12.11 µg/g (total xanthophylls), 2.42–2.89 µg/g (total β-carotene), and 3.17–3.77 µg/g (total provitamin A carotenoids). Extracts of the maize hybrids scavenged DPPH• (SC50: 9.07–26.35 mg/mL) and ABTS•+ (2.65–7.68 TEAC mmol/g), reduced Fe3+ to Fe2+ (0.25 ± 0.64–0.43 ± 0.01 mg GAE/g), and inhibited α-amylase and α-glucosidase, with IC50 ranges of 26.28–52.55 mg/mL and 47.72–63.98 mg/mL, respectively. Among the six clones of the maize hybrids, AS1828-9 had the highest (p < 0.05) levels of tannins and phytate and the strongest antioxidant and starch-hydrolyzing enzymes inhibitory activities. Significant correlations were observed between total phenolics and the following: ABTS•+ (p < 0.01, r = 0.757), DPPH• SC50 (p < 0.01, r = −0.867), reducing power (p < 0.05, r = 0.633), α-amylase IC50 (p < 0.01, r = −0.836) and α-glucosidase IC50 (p < 0.05, r = −0.582). Hence, the Striga-resistant yellow-orange maize hybrids (especially AS1828-9) may be beneficial for alleviating oxidative stress and postprandial hyperglycemia.

Colour analysis of syrup from malted and unmalted rice of different varieties

The colour of rice syrup produced from flours of malted and unmalted rice of different varieties treated with a combination of starch hydrolyzing enzymes were analysed using CIE-LAB Spectrophotometric colorimeter after being filtered and/or centrifuged. The resulting syrups were processed as filtered unmalted hydrolyzed rice (FUHR), filtered malted hydrolyzed rice (FMHR), centrifuged unmalted hydrolyzed rice (CUHR) and centrifuged malted hydrolyzed rice (CMHR). Results showed that L* ranged from 60.16 to 68.57, a* ranged from 10.49 to 11.13 and b* ranged from 55.34 to 64.56. The magnitude of the colour values was an indication of the intensity of the rice syrup colour. Hue angle (oH*) ranged from 79.08o to 80.36o indicating less yellow in the CIE-LAB colour space and brown colour spectrum in the visible region of opponent colour chart. Total colour difference (ΔE) of syrups ranged from 0.50 to 1.72 for ΔEunmalted while ΔEmalted ranged from 0.49 to 1.76. However, the ΔEfiltered ranged from 5.89 to 11.19 while ΔEcentrifuged ranged from 5.54 to 9.47 indicating that filtration and centrifugation contributed to non-significant difference (p&gt;0.05) in colour attributes (ΔE) of the rice syrup, whereas very distinct colour difference (ΔE) was observed between rice syrups from malted and unmalted samples.

ENZYMATIC AND AFLATOXIN PRODUCTION POTENTIAL OF ASPERGILLUS FLAVUS

Fungi especially Aspergillus species are potential candidates for production of mycotoxins and industrially important enzymes. Aspergillus flavus isolates (129) recovered from soil mixed with animal rations (n=145) had aflatoxins (17.82%) and Enzymes (10.37%) production potential. Quantity of detected Aflatoxins varied for different isolates i.e., 3.25 to 11622.24ng, 21.34 to 194.47ng and 3.36 to 40.12ng per mL of Sabouraud’s dextrose broth in case of AFB1, AFB2 and AFG1 as determined by High performance liquid chromatography. Optimization of non-toxigenic starch hydrolyzing A. flavus was carried out at different incubation temperatures (22, 30 and 37°C), pH (4.5, 6 and 7.5) and substrates including maize, wheat bran and rice husk (1, 3 and 5% each) for incubation period of 7 days. In optimization experiments for starch hydrolysis, most of the A. flavus (86%) produced highest enzyme (IU) at 37°C and pH 6 quantified by Dinitrosalicylic method. Most of the isolates were able to produce enzymes using rice husk followed by maize. The highest quantity of enzyme was produced by A. flavus (179.88+1.71IU) using one percent of maize at pH 6 and 37°C. It was concluded that indigenous non-toxigenic A. flavus can be used in food industry as biological source of starch hydrolyzing enzymes.

Sugar Profile of Syrups from Malted and Unmalted Rice of Different Varieties

Rice syrup was produced from ten varieties of locally available rice in Nigeria. Flours of malted and unmalted rice from different varieties were treated with a combination of starch hydrolyzing enzymes (Amyloglucosidase, Bacterial &alpha;-amylase and Fungal &alpha;-amylase); and the starch hydrolysates were either filtered and/or centrifuged at the end of hydrolysis. The resulting rice syrup was evaluated for sugar compositions (maltose, glucose, maltotriose, sucrose, raffinose and stachyose) using HPLC. The results showed that syrups from malted rice had significantly higher (p&lt;0.05) maltose and maltotriose concentration than syrups from unmalted rice. The resultant syrup is a &lsquo;High Maltose Syrup&rsquo; since maltose was found to be the predominant sugar in the rice syrup with concentration of above 50% especially for malted samples. Rice syrup can be widely applied as a potential raw material in beverage and confectionery industries as well as a good adjunct for brewing since the sugar profile of the rice syrup was similar to that of barley wort.

Purification and characterization of a novel α-glucosidase from an Antarctic yeast Dioszegia fristingensis isolate

Starch hydrolyzing enzymes, amylases, are important commercial enzymes used in several productive areas. A current tendency is to find amylases with high catalytic activity at 20-40°C, to generate products that work well at low temperatures, such as detergents, and for energy saving resources in industrial processes. In this work, an α-glucosidase secreted by the cold-adapted yeast Dioszegia fristingensis was purified and biochemically characterized. The effect of physicochemical parameters on the enzyme activity was evaluated. According to our results, the amylolytic enzyme secreted by D. fristingensis is a monomeric α-glucosidase of about 30 kDa that displayed the highest activity at 37-40°C and at pH 5.5-6.5,in the presence of 10 mM CaCl