MATERIALS AND METHODS
2.1.4. Physicochemical properties 1. Water activity
2.1.3.8. Phenolic acid
The phenolic acid content was analyzed in terms of caffeic acid, catechin hydrate, chlorogenic acid, vanillic acid, syringic acid, sinapic acid, and 4-hydroxybenzoic acid using HPLC. The phenolic acid analysis was carried out using the detector and procedure same as that used in the analysis of β-carotene, tocopherol, and tocotrienol. For phenolic acid analysis, the mobile phase eluent A was acidified water of pH 2.64 (with the dilute hydrochloric acid), and eluent B was the mixture of acidified water and acetonitrile of 20:80 ratios. The total run time was 30 min at a flow rate of 1.5 mL/min. The phenolic acids were identified and quantified using the various phenolic acids standard.
2.1.4. Physicochemical properties
evaporating dish. The amount of dried solids recovered by evaporating the supernatant from the water absorption test was expressed as a percentage of dry solids in the 2.5 g sample and defined as the WSI.
2.1.4.5. Porosity
Porosity is the percentage of void space in the bulk sample, which is not occupied by the sample (Mahdavi et al., 2016). Porosity was calculated using the relationship between the bulk density and true density as follows
t b 100
t
(2.4)
Where, 𝜌𝑡 is true density, 𝜌𝑏 is bulk density and ε is porosity.
2.1.4.6. Hausner ratio
The Hausner ratio was determined using the standard procedure (Mahdavi et al., 2016) as follows.
Hausner ratio (HR) = t
b
v
v (2.5)
Where, 𝑣𝑡 is tap volume and 𝑣𝑏 is bulk volume.
Difference ranges for HR in defining the flowability is as below:
(i) 1.0<HR<1.1, free flowing powder (ii) 1.1<HR<1.25, medium flowing powder (iii) 1.25<HR<1.4, difficult flowing powder (iv) HR>1.4, very difficult flowing powder 2.1.4.7. Encapsulation efficiency
The encapsulation efficiency of the sample was measured using the method described by Mahdavi et al. (2016). To estimate the efficiency, total anthocyanin content (TAC) and surface anthocyanin content (SAC) of the microcapsules were measured. For the analysis, 1 mL of distilled water was added to 100 mg of sample and the microencapsulate was crushed in a mortar pestle. Then, the sample was extracted using 10 mL of ethanol. The extraction of
ethanol in a vortex within 10 s, followed by centrifugation at 3000 rpm (314.1 rad/s) for 3 min at 20 °C. After separation, both the clear supernatants were collected and filtered through 0.45 µm filter paper and used for anthocyanin determination.
( )
Encapsulation efficiency (%)= TAC SAC 100 TAC
(2.6)
2.1.4.8. Specific mechanical energy
Specific mechanical energy (SME) was determined by measuring the torque and the screw speed at a constant mass flow rate (Fang et al., 2014). The equation for specific mechanical energy is as follows:
Specific mechanical energy (kJ/kg)= 2 n T Mass flow rate
(2.7) where, n is the screw speed and T is the motor torque.
2.1.4.9. Color
Hunter Colorimeter (Make: HunterLab, Reston, Virginia, Model: ColorLab Ultrascan Vis) was used to measure the color of the sample. The L, a, and b values were recorded as the mean of three replicates. The L-value signifies the light and dark color where a low number (0-50) indicates dark and a high number (51-100) indicates light. The a-value ranges from red to green, where a positive number indicates red and a negative number indicates green. The b- values represents the yellow and blue color, where a positive number indicates yellow and a negative number indicates blue.
2.1.4.10. Cooking yield, cooking loss, and optimal cooking time
The cooking time of the sample was determined using the AACC method 66-50 (AACC, 2000). Briefly, 10 g of sample was cooked in 300 mL of boiling distilled water.
Optimum cooking time was determined when the core in the sample was still present but disappeared after squeezing between two plates.
Cooking loss of the sample was determined according to the AACC 66-50 method (AACC, 2000). Drain the cooked sample for 15 min and the weight was measured. The sample was weighed individually before and after cooking. The drained water was then poured in petri-dish of a known weight and dried at 105 °C to obtain the dried sample in the cooking water.
The cooking yield was calculated as follows:
Weight of cooked extrudate
Cooking yield (%)= 100
Weight of fresh dry extrudate (2.8) The cooking loss was calculated as follows:
Weight before cooking-Weight after cooking
Cooking loss (%)= 100
Weight before cooking (2.9) 2.1.4.11. Thermal properties
A Differential scanning calorimetry instrument (Make: NETZSCH, Selb, Germany;
Model: DSC 214) was used to determine the thermal properties of the sample. The temperature varied from 30 to 250 °C with 10 °C/min rate. The onset, endset, and peak temperature of the powder were measured and analysed using the DSC instrument’s software.
2.1.4.12. X-Ray diffraction
The crystallinity of the microencapsulated powder was studied at 35 kV and 20 mA Cu-Ka radiation in an X-ray diffractometer (Make: Bruker Axs, Karlsruhe, Germany; Model:
D8 FOCUS). Data were recorded over an angular range of 2° to 50° (2θ) with a scanning rate of 2° /min.
2.1.4.13. FT-IR analysis
The FT-IR spectra of powders were recorded using a spectrometer (Make: NICOLET, Wisconsin, USA; Model: IMPACT 410). The absorbance spectra of the samples were recorded in the range of 4000 to 400 cm-1 with a resolution of 4 cm-1. All the experimental data were analysed using OMNIC E.S.P.5.0 software.
2.1.4.14. Morphological properties
The morphological properties of samples were investigated using scanning electron microscope (Make: JEOL Akishima, Tokyo, Japan; Model: JSM 6390 LVSingapore). The powdered samples were coated with gold after attaching with the tape stubs. The sample were analyzed under 20 kV energy with 5000X magnification.
2.1.4.15. Steady-shear rheology
The effect of microencapsulate incorporation on rheological properties of rice dough was investigated in terms of steady-shear rheology. The flow properties of dough were evaluated using a controlled shear stress rheometer (Make: Antron Paar, Graz, Austria; Model:
Physical MCR 72) with a plate and plate attachment having a 50 mm diameter. For the analysis, various amount of microencapsulated powder (5, 10, 15, and 20 % w/w) was incorporated in rice flour dough with a moisture content of 35 % w/w. For the test, the shear rate varied from 0.1 to 100 /sand the temperature was 25 ± 1 °C. The experimental data were fitted with Herschel–Bulkley, and Mizrahi-Berk model as follows,
H
H OH
k
(2.10)0.5 M
M OM
k
(2.11) Where, σ shear stress, 𝜎0𝐻 and 𝜎0𝑀 are yield stress, 𝑘𝐻 and 𝑘𝑀 are consistency index, 𝜂𝐻 and𝜂𝑀 are flow behavior index, and γ is shear rate.
2.1.4.16. Oscillatory rheological properties
The effect of microencapsulated powder incorporation on rheological properties of rice dough was investigated in terms of oscillatory rheological properties. The oscillatory rheological properties of dough were assessed using a Rotational Rheometer (Make: Antron Paar, Graz, Austria; Model: Physical MCR 72) with a plate and plate geometry of 50 mm diameter. For the analysis, various amount of microencapsulate (5, 10, 15, and 20 % w/w) was incorporated in rice flour dough with a moisture content of 35 % w/w. The dough was placed on the plate and the excess sample was removed carefully by using a sharp razor blade. A thin layer of oil was used on the exposed surface of the sample to prevent drying during testing.
Frequency sweep tests from 0.1 to 100 /s were performed at 25 °C. The storage modulus (G′), and loss modulus (G″) were calculated for each dough sample. The data was analysed using Rheoplus version 3.61 software.