16 Neutral fats II

Prof. M. N. Gupta

Objectives

•  To learn about the composition and utility of various vegetable oils.
•  To learn about oils/fats derived from land animals and poultry
•  To learn about fish oils
•  To learn about milk fat

Concept Map

3. Description

In the last module, we discussed some general information about fats/oils. In this module, we will focus on oils/fats from specific and diverse sources.

Plants undoubtedly constitute the source for most diverse kinds of oils. Invariably, their seeds are the main source but in some cases, other parts are also important sources.

As fats/oils are major dietary components, their fatty acid composition has attracted considerable attention.

Land animals/poultry has also been important sources of fats. Fish oils, specially as source of ὠ-3 fatty acids, are also important.

Soybean Oil

Whole beans contain about 40% protein, 34% carbohydrate and 21% oil. The key fatty acids in the oil are 53% linoleic, 23% oleic, 11% palmitic, 8% linolenic and 4% stearic acids. This makes it low in saturated and rich in PUFA.

However, higher PUFA content is both a plus as well as a negative feature! It is good from the health point of view but has poor oxidative stability.

Degumming of soybean oil produces lecithin as a valuable by-product. Soybean lecithin is a major lecithin which is industrially available. Lecithin is a good grade surfactant and finds huge application as such.

Soybean is suitable as frying oil, salad oil, for margarine, shortening, mayonnaise and salad dressing.

In USA, 86% of food lipids are based upon soyabean oil.

Palm Oil

The oil palm tree produces two major oils: palm kernel oil and palm oil. The palm oil is obtained from the mesocarp of the fruit which is quite fleshy. Palm kernel oil is derived from the stony seed. Palm oil has two fractions; palm olein and palm stearin. In terms of the total production, it is second to soybean oil. As a traded oil, it is second to none!

With the average production of palm oil as 3.5 tons/hectare and palm kernel oil as 0.4 tons/hectare; oil palm is considered as the most productive source. Hence, it is not surprising that its production has seen rapid rise over the decades.

The major triglycerides in palm oil are 29% POP; 23% POO, 10% PLO and 9% PLP. An unusual feature is the presence of ~5% Diacylglycerols. It has roughly equal % of saturated and unsaturated triglycerides.

Malaysia and Indonesia are two major producers and exporters of palm oil. Its fatty acid composition and presence of some minor components results in palm oil having high oxidative stability. Palm oil contains 500-700 ppm of a mixture of α and β-carotenes.

Refined-Bleached-Deorderized (RBD) palm oil has lost its carotenes. Red palm oil, refined in such a way so as to retain ~80% of the carotene is also marketed. Even refined palm oil retains high % of its tocols.

Palm oil can be used for frying, in shortening and in spreads. Palm stearin is used to create fat blends without any trans fatty acids.

Palm kernel oil and coconut oil have similar fatty acid compositioncid (12:0) and hence are sometimes referred to as lauric oils. They also have good amount of caprylic acid (C8: 0) and capric acid (C10:0).

Palm kernel oil has higher level of oleic acid. The content of tocopherols is low in both oils. Production of palm kernel oil has overtaken that of coconut oil. Both oils are used for creating blends with oils with more conventional C16/C18 composition.

Rapeseed and canola oils refer to the oils extracted from seeds of Brassica species such as B.napus, B.rape and B.juncea. The oil is rich in erucic acid (22:1) and seed meal has high level of glucosinolates. Breeding techniques have eliminated presence of both and this rapeseed is called double zero or canola.

The FA composition is 4% palmitic, 2% stearic, 62% oleic, 22% linoleic and 10% linolenic acids. It has unusually high levels of MUFA and PUFA and least amount of saturated fatty acids than any other commodity oil.

High erucic rapeseed is still grown for producing erucamide which is required for making “clingfilms”. Canada and Australia are major exporters. The oil is used in China, India and EU countries. It is useful as frying oil, as a salad oil, salad dressing, mayonnaise, margarine and spreads. As a commodity oil source, rapeseed/canola rank third after soyabean and palm.

Sunflower Oil

Sunflower (Helianthus anuus) seed oil ranks fourth according to production levels. The traditional oil is rich in linoleic acid but two varieties with high oleic acid and mid-level oleic acid have been produced by breeding techniques.

The aim is to enhance oxidative stability. The mid-level oil is NaSun™ by National Sunflower Association of USA and is the most common variety used in USA.

Sunflower has high level of α-tocopherol, it is also an oil richest in selenium and in fact richer than even many nuts. At one time, it was a leading oil for margarines but lately soybean oil competes with it for this application.

Sunflower oil has light colour, bland flavor, high smoke point and good nutritional value. The crude oil is light amber in colour, refined oil still retains pale yellow colour.

Apart from for extracting oil, sunflower seed is often recommended as a healthy “nut” as it is higher in protein (42% in decorticated seeds) as compared to fat (10%). The protein has all essential amino acids except lysine and is highly digestible. The seeds have 1-4% chlorogenic acid and weak trypsin inhibitor activity. Both are antinutritional factors so excess consumption of seeds is not advised.

Safflower Oil

In India, safflower oil was introduced in refined form under the brand name of Saffola. Safflower is also an oil seed crop with compositae as the family.

The oil contains 76% linoleic acid, 16% oleic acid and 1% stearic acid + 7% palmitic acid. The high PUFA content has led the oil to be labeled as very healthy oil. In India, the variety with 30% oil content is used as it is highly adaptable.

Unlike edible oils which have been discussed so far, linseed oil is an industrial oil. Linseed (Linum usitatissimium L.) has been grown from early times as its fibre (flax) is obtained from its stem part.

Linseed seed has 30-55% oil, ~22% protein, 25% carbohydrate, 8% fibre and 4% minerals. Linseed oil is a drying oil and forms hard films upon exposure to air. The film is resistant to acids and alkali and has glossy appearance.

Hence, linseed oil is used in paints, printing inks, wood products. Its oxidation in air to form films is due to high % of linolenic acid. The oil composition is 4-7% palmitic acid, 2-4% stearic acid, 14-18% oleic acid, 7-8% linoleic acid and 35-66% linolenic acid.

High PUFA content makes it go rancid very fast. The oil has laxative property due to high mucilage in the seed coat. The seed meal contains phytic acid (as an antinutritional factor) but worse, it contains a glucoside linamarine which on hydrolysis produces CN-.

Castor Oil

If linseed oil finds very limited use as edible oil or as blending oil, castor oil is another oil which is classified as a non –edible oil. Both linseed and castor oils are sometime called technical oils.

Castor (Ricinus communis L.) has seeds which produces oil with a unique fatty acid called Ricinoleic acid present with 85-90% content. The fatty acid (C18) has a –OH group on C12.

Other fatty acids are ~1% each of stearic and palmitic, ~3% oleic acid and ~3% linoleic acid. The seed is pressed at 32-38 °C to produce pale yellow oil. The oil content in seed is 45%.

The oil is useful as a lubricant. It remains liquid even at -32 °C. Its viscosity is ~18 times more than other vegetable oils.

Castor oil is also blended with sesame oil and coconut oil in hair oils. The oil also is credited with some medicinal properties and used in eye inflammation etc. as a pharmaceutical preparation.

Esters of castor oil are used as high grade lubricants in jet engines and turbines. The castor seed cake cannot be used as either food or feed material as it contains an extremely poisonous lectin called ricin. It is generally used as a fertilizer. Luckily, ricin does not get extracted in oil.

Castor oil is a subject of extensive research to convert it into products which may have more diversified applications. At the same time, efforts have been made to reduce the ricin content.

While cotton is grown largely for the textile fibre, the seed is also a valuable source of oil. Crude cotton seed oil is reddish brown and contains gossypol and other pigments. However, the oil has useful Vit B and Vit E contents.

The seed oil has ~50% linoleic acid and ≥20% oleic acid. Even though it is ≥70% unsaturated fatty acids, it has a good shelf life. Its nutritional quality is considered comparable to even olive oil

Gossypol is a toxic phenolic compound and cotton seeds contain 0.6-2.5% of it by weight. Such toxic compounds often form part of the plant defense systems. Reducing Gossypol content makes cotton plants more vulnerable to pests.

Refined cottonseed oil does not contain any Gossypol. Hence, it is used as edible oil in many countries like USA, Egypt, China and some West European countries.

Groundnut Oil

While groundnut or peanut oil is not among the oils which have contributed to major increase in world oil production, it is undoubtedly among the major edible oils. It is cultivated in more than 80 countries.

Peanut, as it is more often called in India, has about 45-50% oil and 20-30% protein. It is rich in B-complex vitamins but most of its minerals are tied up with phytates.

The oil is obtained by hydraulic pressing, expeller pressing and solvent extraction. It is rich in oleic acid (35-56%) and linoleic acid (16-38%). Palmitic acid is the saturated fatty acid present in highest amount at ~10-16%. About 10% are other fatty acids like myristic acid, stearic acid, arachidic acid (2-10%), behenic acid, lignoceric acid and eicosenoic acid (20:1, 0.7-2%).

The discussion so far illustrated the diversity of fats/oils from some well known plants. While the focus was on edible oils, two technical oils linseed and castor oils were also covered.

One plant oil which has attracted considerable attention is Jatropha oil. It was chosen by the Indian government as a part of the mission project on biodiesel. Along with some other oils such as Mahua (Madhuca longifolia), it represents non edible oils which were thought to be promising for conversion into biodiesel and biolubricants. We will cover those in a later module when we discuss biotechnological applications of lipases. Here we will now discuss the fats/oils of fish origin.

Fats/oils of Land animals/poultry

Land animals provide fats/oils in two ways. Early hominids used animal body tissues of animals as a source of energy by scavenging and hunting. Milk is another valuable source of lipids. While eggs do have fat especially with very long chain PUFAs, in terms of total fat intake, these do not contribute much.

It is believed that in those days arachidonic acid (ARA), and docosahexanoic acid (DHA) accessed via animal fat played a role in evolutionary development of brain.

Animal fat or meat fat is the fat in adipose tissues of land animals. Celts made soap by boiling animal; fat with ashes and passed on the soap making skill to Romans. Thus, apart from nutrition, animal fat was used for soap, lubricant, torches and candles and cosmetics.

Tallow is derived from ruminant species including sheep and goat, lard is obtained from pigs and poultry fat is obtained from poultry offal.

Tallow has higher proportion of saturated, branched and odd-chain fatty acids than lard and has fewer PUFA. This is due to ruminal hydrogenation and microbial function. Fatter animals have more saturated and MUFA as endogenously synthesized fats overtake dietary fat containing PUFA.

Leaner animals, thus, have higher PUFA contents in their fat. Peripheral fats (subcutaneous) contain less saturated fatty acids as compared to internal fats like intermuscular fats. In modern pigs, PUFA of dietary origin increase in the fat upto 20% in lean fat.

Poultry fat is higher in PUFA and lower in saturated fatty acids as compared to pork fat. It should be pointed out that nevertheless, lard has >50% saturated fatty acid and poultry fat is generally <30%.

Horse is not a ruminant but a hind-gut fermentor. Hence, it has higher amount of linolenic acid derived from green forage.

Milk

Equine milk has only 1.4% fat, milk of seals has 54%. Neolithic phase started the animal domestication and sheep, goats and cattle were reared for milk as early as 5000 B.C. Sumerian documents from 3200 B.C. indicate that butter oil was the earliest processed food. It is a microbiologically stable product to a fair extent.

In a 2004 FAO release, global milk production was 84% from cows, 12.5% from buffalo. 1.3% from sheep, 2% from goat and 0.2% from camel.

Milk contains 97% TAG and small amounts of phospholipids and sterol. Over 400 different fatty acids have been described in milk fat! More than 220 TAG structures have been characterized, their actual number is several thousands. Fatty acid chain length varies from C4-C28, includes odd and branched fatty acids, UFA and PUFA (upto 6 double bonds). Milk fat melts over a wide range of -30 °C to 37 °C. It has tendency to crystallize in β’ form.

Milk fat globule membrane prevents coagulation of this colloidal substance. Milk is a very complex substance. The various processed foods based upon milk cover a wide range of well known products.

Lipids from marine sources

Marine sources are considered renewable sources and are likely to play ever increasing role in human’s life in coming decades. Fish oils have been used by Icelandic and Scandanavian people for centuries at various times in indoor lamps, lighting street lamps, household remedies for malnutrition and nightblindedness.

Eicosapentenoic acid (EPA) and docosahexanoic acid (DHA) and few other ὠ-3 PUFA are found in marine fat and fish oil is an important source of these nutritionally valuable fatty acids.

Epidermiological studies indicate that ὠ-3 PUFA are helpful in preventing cardiovascular diseases. In patients with Alzheimer dementia, the concentration of DHA is lower than in control population of similar ages.

In cases of acute depression, the level of EPA has been found to be lower. It is well established that ὠ-PUFA are critical in brain development and healthy vision in infants.

Table 3: Fatty acids found in fish oil

Fish oil contains >50 different fatty acids. The ὠ-3 PUFA are present in lipids of photosynthetic micro-algae part of the phytoplankton. Fish get this from zooplankton.

Contrary to some reports, α-linolenic acid of flax seed oil is not converted to EPA and DHA to any significant level. So, flax seed oil cannot replace fish oil as a source of EPA and DHA.

Oils from different fish species differ in the fatty acid composition. Composition of fish oils in wild fish and farmed fish is different as the feed dictates the fatty acid composition of the oil. ὠ-3 fatty acid can also be obtained from oil rich algae. A U.S. company Martek continues to be the market leader for DHA.

Hence, we see that some oils can be synthesized by us. For others we are dependant upon the dietary intake of fats/oils as sources. Unfortunately dietary recommendations especially available from internet and popular print media have been frequently revised and offer oversimplified picture. Not all fats with saturated fatty acids are bad, saturated fatty acids are also necessary. Just like the concept of balanced diet, we have to be balanced about our fat intake. Some fatty acids like ὠ-3 fatty acids seem to be beneficial as supplements especially in case of infants.

Summary

In this module we learnt about:

•  The composition and utility of various vegetable oils.
•  Oils/fats derived from land animals and poultry
•  Fish oils
•  Milk fat