A survey of rheological behaviour and antioxidant efficiency in comestible oils [ ( ]
In the nutrient industry, rheological behaviour and thermic debasement is the of import parametric quantities required to find the quality and stableness of nutrient system. In this paper, the rheological behaviour and thermic debasement of rice bran and maize oil, is investigated. Redwood viscosimeter is used to mensurate viscousness at a scope of temperature. A 16F88 microcontroller based temperature accountant is designed to mensurate and to maintain the temperature of the oil at the coveted temperature. The rice bran and maize oil exhibit Newtonian behaviour during warming and chilling in the temperature scope 30 & A ; deg ; to 90 & A ; deg ; C. The oils besides exhibit Newtonian behaviour even after heating to the frying temperature.
A non-Newtonian feature is observed in sunflower oil due to rancidity that changes the complex chemical composing of oil. To qualify the cookery oils the structural alteration is carried out utilizing FTIR spectra analysis and it is observed that the antioxidant activity is stronger in rice bran oil. The public presentation of Microcontroller based temperature accountant is studied.Keywords: rheology, Newtonian, non-Newtonian, thermic debasement, redwood viscosimeter, kinematic viscousness, FTIR, microcontroller.
Rheology is defined as the survey of the alteration in the signifier and the flow of viscousness, snap and malleability. Rheologic measuring is much utile behavioural and prognostic information for merchandise consistence and quality [ 1 ] . It besides has of import applications in technology, geophysical sciences, pharmacies and physiology.
In peculiar, hemorheology, the survey of blood flow, has an tremendous medical significance. In technology, rheology has had its prevailing application in the development and usage of polymeric stuffs. Temperature is an of import parametric quantity in the survey of rheological behavior [ 2 ] . In the nutrient industry, viscousness is one of the most of import parametric quantities required to find the quality and stableness of nutrient system.
Edible oils represent one of the primary components in the preparation and industry of merchandises by nutrient industry [ 3 ] . Viscosity means the opposition of one portion of the fluid to travel relation to another one and hence it is closely correlated with the structural parametric quantities of the fluid particles [ 1 ] . The oil viscousness has a direct relationship with some chemical features of the liquids, such as the grade of unsaturation and the concatenation length of the fatty acids that constitute the triglycerides [ 4 ] .
Viscosity somewhat decreases with increased grade of unsaturation and quickly additions with polymerisation that led to the development of the thought to utilize comestible oils as bio-diesel fuel [ 1 ] . When the oil is heated to the frying status the unsaturation decreases and it becomes saturated due to oxidization. Edible oils are complex mixtures of many triglycerides with different concatenation lengths [ 4 ] .Oxidation is accelerated by exposure of heat, visible radiation, sum of O available and humidness. The intense sauteing of oils causes an oxidising thermic debasement with the formation of decomposition, such as aldehydes, ketones, free fatty acids and hydroxyl compounds that in high degrees can be harmful to human wellness [ 5 ] .
When the oil is heated to the frying status the unsaturation decreases and it becomes saturated due to oxidization. Mid FT-IR spectra have been used to qualify comestible oils and fats because it differentiates the strength and the exact frequence at which the maximal transmittal of the sets appears, harmonizing to the nature and composing of the sample [ 5 ] . Furthermore infra ruddy spectra show differences in the profile, maximal strength and place of transmittal sets harmonizing to the oil composing.High dietetic consumption of polyunsaturated fatty acids increases the oxidization of lipoproteins that leads to Atherosclerosis, Hypertension, Coronary arteria disease, shot, etc. , saturated fatty acids are converted into diacyl glycerin which alter colonic epithelial cells taking to colon malignant neoplastic disease.
The rheological behavoiur of oil based liquid has assorted application such as lubrication engineering, insularity intent and bio Diesel. Hence in this work the survey of Newtonian and non-Newtonian nature of oils which determines the thermic debasement and its oxidative stableness on warming is studied. An FTIR Spectroscopic method is employed to measure efficiency of antioxidants in oils subjected to intense heat.
Sample readying for FTIR analysis:
Rice bran and maize oils are purchased in local commercialism.
Perkin Elmer Fourier transform infrared spectrometer with deuterated triglycin sulfate ( DTGS ) as a sensor is used for the analysis. The liquid sample is placed between two KBr pellets with the aid of capillary tubing.
Each pellet is made of 0.2mm thickness and it is placed in the way of the sample beam. The spectra are recorded from 4000 to 450cm-1, the figure of scans being 256 at a declaration of 4cm-1. Scan velocity is 0.20cm/s.
The Redwood viscosimeter manufactured by Associated Instrument makers India Private limited ; New Delhi ( India ) is used for the measurings. Redwood viscosimeter specification No.
1 and flow clip of 30 to 2000sec is selected as the standard viscousness measuring device to supply the existent kinematic viscousness of comestible oil at different temperature. Kinematic viscousness ( ? ) is defined as the ratio of absolute viscousness ( ? ) to mass denseness. Redwood viscosimeter is based on the rule of laminar flow through capillary tubing. The viscosimeter consists of an oil cup furnished with a arrow, which ensures a changeless caput and opening at the centre of the base of interior cylinder. The opening is closed with a ball, which can be lifted to let the flow of oil during the experiment. The cylinder, is filled up to a fixed tallness with liquid whose viscousness is to be determined.
The cylinder is surrounded by a H2O bath. To keep the H2O bath at the coveted temperature a dedicated PIC16F88 microcontroller based temperature accountant is designed for the measuring and to command of temperature.The Block diagram for the temperature accountant is shown in Fig 1. The Temperature control hardware consists of K- type thermocouple, signal conditioning circuit, solid province power accountant and PIC 16F88 microcontroller. The PIC16F88 microcontroller ( 18 pin DIP ) in Block B is the bosom of the measuring system that is a low power, high public presentation RISC CPU 8-bit microcontroller with 4 K Words of flash programmable and effaceable memory and 368 bytes of RAM and 256 bytes of EEPROM. It has two 8-bit and one 16-bit timer/counters, two gaining control, comparators and pulse breadth transition ( PWM ) faculties, a full semidetached house consecutive port, 2 analogue ports, an on-chip oscillator, a programmable codification protection, and a 7 channel 10- spot A/D convertor.
To mensurate the temperature of the sample a chromel alumel thermocouple in Block A is used. The voltage generated by the thermocouple is amplified ( derive 250 ) by an operational amplifier [ Block A ] . The parallel temperature in the signifier of electromotive force is digitized by the built-in A/D convertor in the microcontroller. Port A is used to acquire linear input electromotive forces from the temperature detector and to trip temperature control circuit. The solid-state power accountant in block C is built with optocoupler ( MOC3040 ) , Triac ( BT136 ) and other constituents are used to command the power of the electric warmer in Block D. An LCD show is interfaced with the microcontroller through Port B to expose the mensural temperature.
Keies are provided to give informations to microcontroller. Software is developed in C linguistic communication to initialise the ports, to read fit temperature, to mensurate temperature, to expose the temperature and to command the temperature of the sample liquid.The Cu cup in the viscosimeter is washed with CCl4 after each observation.
The sample is taken in the Cu cup and after the coveted temperature is maintained the opening is opened and the clip required for roll uping 50cc of oil is measured. The experiment is repeated and the norm of three tests is taken for measuring of clip and kinematic viscousness is calculated utilizing the undermentioned relation:( ? ) = ( A* t – B/t ) x 10-4 m2/s.T = redwood clip which measure the rate of flow in seconds.A & A ; B are invariablesA = 0.
0026 & A ; B = 1.175 when, t & lt ; 34 andA = 0.26 & A ; B = 172 when, t & gt ; 34To analyze the Newtonian behaviour and non-degradation of oil, the sample is kept at assorted temperatures ( in stairss of 10 & A ; deg ; C from 30 & A ; deg ; C to 90 & A ; deg ; C ) and the viscousness is measured during warming and chilling. To analyze of thermic debasement and non-Newtonian behaviour, the sample is kept at 210 & A ; deg ; C ( frying temperature ) for the continuance ( 1, 2, 3, 4 & A ; 5hrs. ) . After heating to coveted clip, viscousness of the sample is measured at 30 & A ; deg ; C
RESULTS AND DISCUSSION
Rheologic parametric quantity
ourier transform spectrometry is a measuring technique whereby spectra are collected based on measurings of the temporal coherency of an irradiative beginning.
It provides a speedy and accurate manner of measuring thermic debasement of comestible oil subjected to intense heat, tantamount to that used in the readying of nutrient. The finding of unsaturation in oils makes it possible to sort them and measure their oxidative impairment which is straight related with the debasement of polyunsaturated fatty acids in the lipoids.
FTIR spectrum of maize oil
FTIR Spectrum of rice bran oil
Fig 4 shows the FTIR spectra of unwarmed maize oil.
To analyze the thermic debasement the oil is heated for one hr and the procedure is repeated 5 timed and it is shown in fig.5. From the figures it is observed that the transmittal at 3008, 2924, 2854, 1463, 1378, 1237, 1163, 1099, 722 centimeter -1 exist. The presence of the same wavelength in both instances reveal that most of the compounds can keep stableness due to the presence of antioxidants Besides it is observed from the fig 5 that the transmittal 1417 centimeter -1 1746 centimeter -1, 3471 centimeter -1 are changed due to partial thermic debasement of oil. The presence of transmittal 1417 centimeter -1 in Fig 5 may be due to swaying quivers of – CH bonds of Commonwealth of Independent States disubstituted alkenes [ 9 ] .
Besides the widening of transmittal at 1746 centimeter -1 in fig.5 is due to the production of concentrated aldehydes functional groups or other secondary oxidization merchandises that cause a transmittal at 1728 centimeter -1 that overlaps with the stretching quiver at 1746 centimeter -1 of the ester carbonyl functional group of the triglycerides. This consequences correlate with the earlier mention [ 9 ] . When new carbonyls are formed from initial aldehydes and ketones compounds, the maximal optical density is in the part between 1700 and 1726 centimeter -1 ensuing in a widening of carbonyl part [ 9 ] . The 1651.57cm-1 set show C=C stretching quiver of cis-olefins [ 10 ] . It is besides observed that the vale between 2925 and 2854 centimeter -1 has found to be deepened during warming. This may be due to the alteration in the feature of marjoram [ 11 ] .
Shift in transmittal from 3448 centimeter -1 to 3471 centimeter -1 has been observed. Hamed and Mousa A.Allam ( 2006 ) have mentioned that hydroperoxide set of the sample without antioxidant is much higher than that of sample incorporating antioxidants. In our present survey, the hydroperoxide set showed increased transmittal while heating. This perchance will be due to the loss of assorted antioxidants during warming.
The transmittal 915 centimeter -1 has been formed due to – CH=CH2 ( in unsaturated fatty acids ) out of plane flexing [ 11 ] .
Figures 6 and 7 show the FTIR spectra of unwarmed and het rice bran oil [ RBO ] . Almost all the transmittals are found to be the same.
The lessening in transmittal from 3465cm -1 ( fig.5 ) to 3432cm -1 ( fig.7 ) reveals the deficiency of formation of hydroperoxide [ 10 ] . This might be due to the presence of 2417ppm of antioxidants in RBO [ 8 ] . Transmission at 3008 centimeter -1 shows the higher presence of Linoleic and linolenic acyl groups [ 5 ] . 2854 centimeter -1 has been formed due to symmetric and asymmetric stretching of -CH 2 group [ 12 ] . The widening of 1743 to 1744 centimeter -1 may be due to production of concentrated aldehydes functional groups [ 9 ] .
Shows the fluctuation of kinematic viscousness of rice bran and maize oils with temperature and it is observed that the viscousness of oils lessenings as the temperature increases. This is due to the high thermic motions among molecules reduces intermolecular forces, doing flow among them easier and cut downing viscousness. The presence of dual bonds in fatty acid that exist in Commonwealth of Independent States constellation signifier, produces “ cricks ” in the geometry of the molecules [ 1 ] .
This prevents the ironss coming near together to organize intermolecular contacts, ensuing in an increased capableness of the oil to flux. The flow of oil is related to the concentration of polyunsaturated ironss than monounsaturated ironss because of p bonds, which makes adhering more stiff, diminishing rotary motion between C-C bonds [ 6 ] . For low viscousness of the oil it has appreciable sum of polyunsaturated fatty acids. A more drawn-out concatenation makes flow easier and viscousness smaller. It is observed that the fluctuation of viscousness of the oils between the temperatures range 30 & A ; deg ; C to 90 & A ; deg ; C is same for warming and chilling and is found that there is no debasement and the oil has Newtonian behavoiur in this temperature scope. The temperature is maintained by temperature accountant [ 7 ] .
The figure 3 shows the fluctuation of viscousness with clip to analyze of thermic debasement and non-Newtonian behaviour of the samples. From the figure, it is seen that viscousness of maize and rice bran oil is about changeless with clip whereas the viscousness of sunflower oil additions. The changeless value of viscousness of maize and rice bran oil can be due to antioxidants in the oil that prevents oxidization and no impregnation occurs with clip. Antioxidants are molecules that slow or prevent the oxidization of other molecules. The addition in viscousness of helianthus with frying clip shows that unsaturated hydrocarbons become saturated as the antioxidants get evaporated.
Edible oil repeatedly used in sauteing is degraded by oxidative reaction with air and H2O. Oxidation leads to the formation H bonds that increase intermolecular forces, doing flux among molecules that increases viscousness. Sunflower oil is non suited for high temperature cookery because polyunsaturated fat would turn into trans- fats after cooking at high temperature [ 3 ] . The antioxidant third butyl hydroquinone that is added to the oil gets evaporated on consecutive warming.From the figure 3 it is observed that there is undistinguished fluctuation in the viscousness of maize oil as it has higher composing of antioxidants.
Heating to a really high temperature for long continuance causes debasement in the oil due to high per centum of polyunsaturated fatty acids. Corn oil has 13 % of unsaturated, 25.8 % monounsaturated and 61.2 % polyunsaturated fatty acids. This implies that a measure of antioxidant kernel in maize oil like propyl gallate, a-Tocopherol, & A ; szlig ; -sitosterol sterols – 1 % , sitostanyl ferulate which lowers LDL, ? -oryzanol, ester of steroid alcohol 5 – 9 % , free steroid alcohols -2.1 % [ 6 ] . Unsaturated bonds are reactive and new atoms attached without interrupting the bing skeleton of the hydrocarbon, though a big bulk of lipoids are fatty acerb tri-esters of glycerin. Thermal debasement in the oil is farther confirmed in FTIR analysis.
The viscousness rate of rice bran oil is besides changeless in fig.3, due to the big composing of antioxidants in the oil. It retains the Newtonian behavoiur of the oil. Rice bran oil is the oil extracted from the interior chaff of rice and has really high fume point of 490 & A ; deg ; F ( 254 & A ; deg ; C ) and its mild spirit, doing it suited for high-temperature cooking methods such as splash sauteing and deep sauteing. Rice bran oil contains a scope of fats, with 47 % of its monounsaturated, 37 % polyunsaturated, and 20 % saturated. The oil may besides offer some wellness benefits, as it contains oryzanol, an antioxidant that aid to forestall bosom onslaughts ; phytosterols, compounds believed to assist lower cholesterin soaking up ; and comparatively high sums of vitamin E [ 8 ] .
The per centum of polyunsaturated fatty acids is less compared to maize oil hence it shows less debasement of oil in FTIR analysis. The latest findings from Mohammad Minhajuddin, Ph.D. , and co-workers, are reported in the May 2005 Food and Chemical Toxicology diary. They show that entire cholesterin degrees in animate beings dropped by 42 per centum, and LDL or “ bad cholesterin ” degrees dropped up to 62 per centum, after their diets are supplemented with a concentrated signifier of Vitamin E called tocotrienol rich fraction isolated from rice bran oil.
Kinematic viscousness is measured for the comestible oils at different temperatures runing from 30 & A ; deg ; C – 90 & A ; deg ; C. A low cost microcontroller based temperature accountant is designed and fabricated for thermic debasement survey of oils. The mistake in measuring of temperature is found to be less than 1 % . The Study of viscousness with clip for rice bran and maize oil reveals that they are Newtonian liquids in the temperature scope ( 30 & A ; deg ; C – 90 & A ; deg ; C ) ; Thermal debasement surveies reveal sunflower is non-Newtonian at high temperature 210 & A ; deg ; C. FTIR surveies show that maize oil has more structural alteration in the composing in the oils compared to rice bran oil. From the survey of FTIR and viscousness measuring it is observed that rice bran is the best for deep-frying.
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Figure and table caption:
- Block Diagram of Temperature Controller
- Variation of viscousness with temperature
- Variation of viscousness with clip
- FTIR spectra of unwarmed maize oil
- FTIR spectra of het maize oil
- FTIR spectra of het rice bran oil
- FTIR spectra of het rice bran oil