1. Determination of antioxidant capacity and total polyphenols
Josip Juraj Strossmayer University of Osijek
Faculty of Food Technology Osijek
Determination of antioxidant capacity and total polyphenols
in pasta enriched with hull-less barley flour
Indira Kosović, Ante Lončarić, Antun Jozinović, Marko Jukić, Daliborka Koceva Komlenić
Josip Juraj Strossmayer University of Osijek, Faculty of Food Technology Osijek, Franje Kuhača 20, HR Osijek, Croatia
Introduction
Results
Barley (Hordeum vulgare L.) is considered as a functional grain because it contains β-glucan, B-complex vitamins, tocotrienols, tocopherols and bioactive compounds. It has greater antioxidant activity than wheat and rice and contains many phenolic compounds that are concentrated in the outer layer of barley grain. Hull-less barley is usually richer in phenolic compounds compared to hulled. Intake of dietary phenolics can reduce the risk imposed by free radicals and oxidation products that cause various forms of cancer and cardiovascular disease. Therefore, the total content of the phenolic compounds is an important quality indicator for evaluation of barleys and wheats. The aim of this study was to determine antioxidant capacity and total polyphenols of pasta enriched with hull-less barley flour by using various solvents and extraction methods.
Materials and Methods
Sample preparation
Barley grain was milled on IKA laboratory mill (sieve size 1 mm) and after that passed through Braun kitchen coffee blender. Pasta was produced by replacing durum semolina (DS) with 10, 20, 30, 40 and 50% whole grain barley flour (BF) on laboratory extruder (Brabender 19/20 DN, 3:1 screw, 7x2 mm die, temperature profile 35/40/40 ˚C). Water content of DS and BF blends was set to 34% (w/w). Samples were dried in cooling incubator with controlled humidity (Climacell MMM) on 90 ˚C until water content of dried pasta was below 13%. Samples were stored in plastic containers at room temperature for a minimum of ten days to stabilize moisture movement before further analysis.
Extraction of polyphenols
The samples (1 g) were extracted at room temperature in two ways, with magnetic stirring (1 h) and assisted with ultrasounds (15 minutes) in order to obtain the pasta extract. Solvents used for extraction were as follows: 70% acetone, 70% methanol, 1% HCl in methanol, and 1:80:10 (HCl/methanol/water, v/v/v).
Total phenolic content (TPC)
TPC was measured by using a modified colorimetric Folin-Ciocalteu method. A volume of 2 mL of the pasta extract was mixed with 10 mL of (1:10 v/v with water) Folin-Ciocalteu reagent and 8 mL of 7.5% solution of sodium carbonate. The colour was developed in 120 min, and the absorbance was read at 765 nm by spectrophotometer. The measurements were performed in triplicates for each sample and the average value was interpolated on a gallic acid calibration curve and expressed as g of gallic acid equivalents per kg of sample (g GAE/kg).
Antioxidant activity (AOA)
Antioxidant activity was measured by 2,2-diphenyl-1-picrylhydrazil (DPPH) method. The 0.2 mL of extract was mixed with 2.8 mL of DPPH solution (0.5 mM) to the final volume of 3 mL. After 15 min the absorbance was measured at 517 nm. The results of antioxidant activities were expressed as of sample. Additional dilution was needed if the measured values were over the linear range of the standard curve of the methods. For each sample, the measurements were performed in triplicates and the average value was interpolated on a gallic acid calibration curve and expressed as µmol of trolox per 100 g of sample (µmol trolox/100ml).
Fig. 1. Total phenolic content in dried pasta samples (g GAE/kg)
DS – durum semolina, BF – barley flour, US – ultrasounds, MS – magnetic stirrer
*Different letters for each extraction method used (US and MS) correspond to significant differences by Fisher LSD test (p = 5%). Values are means of three determinations
Fig. 2. Antioxidant activity in dried pasta samples (µmol trolox/100ml)
DS – durum semolina, BF – barley flour, US – ultrasounds, MS – magnetic stirrer
*Different letters for each extraction method used (US and MS) correspond to significant differences by Fisher LSD test (p = 5%). Values are means of three determinations
Literature
Biney K. and Beta T. (2014): Phenolic profile and carbohydrate digestibility of durum spaghetti enriched with buckwheat flour and bran. LWT - Food Science and Technology 57,
Sharma P. and Gujral H.S. (2010): Antioxidant and polyphenol oxidase activity of germinated barley and its milling fractions. Food Chemistry 120, 673–678
Thondre P.S., Ryan L., Henry C.J.K. (2011): Barley β-glucan extracts as rich sources of polyphenols and antioxidants. Food Chemistry 126, 72–77
Conclusions
40 and 50% BF addition significantly increased total phenolic content and antioxidant activity in pasta samples
70% acetone and 70% methanol showed as superior solvents, for TPC and AOA determination, to other two solvents
MS showed superior against US extraction in TPC determination, and for AOA determination both US and MS in combination with 70% acetone and 70% methanol showed good results
Acknowledgements
This work has been supported in part by Croatian Science Foundation under the project 1321