Oil The onset temperature Tonset DSC and Tonset

Oil was extracted from plant source using conventional extraction methods like soxhlet extraction, reflux extraction and non-conventional extraction methods like ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), supercritical fluid extraction (SFE). The conventional methods were compared with novel extraction methods based on numerous parameters such as extraction times, consumption of organic solvents, and extraction yield. The non-conventional methods were superior to conventional methods because they need less time, consume less solvent, and produce more yield. Many methods can be used to measure thermal as well as the oxidative stability of plant oil. The oxidative stability of plant oil was studied using classical methods such as active oxygen method (AOM), schaal test, rancimat method based on conductometric measurements and thermoanalytical methods like differential scanning calorimetry (DSC) and thermogravimetry (TG). The onset temperature Tonset DSC and Tonset TG can be measured from dynamic DSC and TG curves, respectively.

Keywords: edible oil, extraction methods, oxidative analysis, thermal analysis.

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INTRODUCTION

Plant oil is a prime source of raw materials like fat, carbohydrate, protein with possible application in nutraceuticals as well as functional foods. Essential fatty acids (EFAs) are macronutrients which are essential for the human body but can’t be produced and hence must be acquired from dietary source and nutritional supplements. It is of two types: ?-3 series and ?-6 series. Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the third carbon atom from the end of the carbon chain. Omega-3 fatty acids which are involved in human physiology are of three types: ?-linolenic acid (ALA) is widely distributed in plant oils, eicosapentaenoic acid (EPA), and docohexaenoic acid (DHA) both generally found in marine oils. One of the most important ?-3 fatty acids is ?-linolenic acid (ALA). ALA is one of the essential fatty acids and is found in seeds (chia, flaxseed, hemp), nuts and many vegetable oils. Omega-3 fatty acids (ALA) have been reported to show a protective effect and even maximize the effect in the treatment of various diseases. Due to their anti-carcinogenic, glucose metabolism controlling effect and anti-hypercolesterolemic, this component help prevents or minimize the risk of a variety of diseases including diabetes, lupus nephritis, hormone-dependent type of cancer, cardiovascular diseases, eczema, and Sjogren’s syndrome. Thus it is crucial for maintaining the overall body’s health. Intake of sufficient amount of ALA is important in daily life (2.22g/day). 19

Fatty acid of oils obtained from plants is usually classified as saturated and unsaturated fatty acid. Unsaturated fatty acid includes oleic, linoleic acid, EPA, DHA and their content is always high as compared to saturated fatty acids. In Sunflower oil, unsaturated fatty acid content is >90%. 2, poppy and safflower oil have a high content of linoleic acid (omega-6) 74.5% and 70.5% respectively 14.  A Major component of flax oil and camelina oil is ALA containing 45-58.3% and 35-36% of total fatty acid, respectively.3,14

 

Oils are extracted from plant source in a variety of ways: ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, and conventional extraction (maceration, solvent extraction, reflux extraction, press extraction).

FOOD OILS

SERVING SIZE

KCALS

OMEGA-3

Canola oil

1 tbsp.

124

1302

Perilla oil

1 tbsp.

120

8960

Flaxseed oil

1 tbsp.

120

7980

Mustard oil

1 tbsp.

124

826

Walnut oil

1 tbsp.

120

1414

Soybean oil

1 tbsp.

120

925

Sunflower oil

1 tbsp.

124

27

Peanut oil

1 tbsp.

119

0

Coconut oil

1 tbsp.

117

0

Grapeseed oil

1 tbsp.

120

14

Cottonseed oil

1 tbsp.

120

27

Olive oil

1 tbsp.

119

81

 

Edible oils can undergo lipid oxidation leading to the rancidity of the products. It is a severe problem in the food industry. Plant oil having a high concentration of ALA is highly susceptible to oxidation, leading to rapid deterioration of quality. It must be stored in an amber colored bottle. According to ICH, Stability testing is to provide indication on how the quality of a substance or a product varies with time under the influence of a variety of environmental factors such as temperature, humidity, light, and storage etc., set to establish a retest period and to promote their shelf life, to optimize the product storage conditions stability indicating study is a promising tool. Historically, classic methods for determining oxidative stability of oils in the edible oil industry are active oxygen method (AOM) or swift method and Schaal test. The stability of oils and fats can be assessed by various accelerated stability tests. Maximum of the accelerated tests are aimed to accelerate the oxidation process by exposing the oil samples to high temperature in the presence of surplus quantity of air or oxygen. Presently, oxidative stability of oils and fats can be measured by rancimat and oxidative stability instrument (OSI). A method for determining the thermal stability of oil is differential scanning calorimeter (DSC). Currently, thermoanalytical methods are used for the characterization of fats and oils along with the investigation of their thermal auto-oxidation process. DSC provides unique profile information which specifically measures the temperatures and heat flows associated with material transitions as a function of time and temperature.

Isolation and purification methods are used to acquire fractions which are rich in unsaturated fatty acid from plant seed oil. It generally depends on the difference in polarity and/or geometrical configuration of fatty acids present in the extract. These differences are usually correlated with the number of double bonds in the carbon chain. Fatty acids can be separated on the basis of the degree of unsaturation.

Precise determination and quantification of ALA can be achieved by using several analytical techniques in which most are based on gas chromatography (GC) and few on high performances liquid chromatography (HPLC). HPLC can be coupled with numerous detection methods such as refractive index (RI), fluorescence (FD), mass spectroscopy (MS), flame ionization detector (FID), evaporative light scattering (ELSD), electrochemical detection and UV being most frequently used.