Methods of preparation of egg and therapeutic uses:a review perspective of Persian Medicine

Fatemeh Moradi ,Malihe Tabarrai ,Fatemeh Nejatbakhsh

1Department of Persian Medicine,School of Persian Medicine,Tehran University of Medical Sciences (TUMS),Tehran,Iran

Abstract Background:The nutrients in eggs play an important role in the health of different body organs like the brain,cardiometabolic system,musculoskeletal system,skin and eyes and so the eggs can be considered as functional foods.In order to maintain the highest nutrient content of an egg,it is recommended to cook it properly,but no specific clinical research has been carried out yet on the role that the cooking of an egg plays in its food and health properties.For this reason,this study has collected and discussed the topics related to a variety of methods of cooking eggs,based on the texts of Persian Medicine,and conducted a comparison with modern sources of nutrition.Methods:The present study is a review in which sources of Persian Medicine (PM)were searched in software JamiTib (Version 1.5)and Persian electronic banks,sites of PubMed,Google Scholar,ScienceDirect,and Embase and websites of health reference of American food and water.Finally,the results obtained were classified and a content analysis was carried out.Results:In the PM books,in addition to referring to the different properties of eggs,different effects of different egg preparation have been investigated.The wise men of the school of medicine have proposed at least five methods of egg preparation,including very soft boiled,soft-boiled,hardboiled,fried,and omelet.In the texts,the healing properties of each case and the quality of digestion in the body were separately investigated.Among the five main methods of preparation eggs,the therapeutic and digestive effects of soft-boiled eggs are emphasized to a greater extent,because easy digestion leads to more beneficial effects of the yolk of the eggs.Conclusion:Though the wise men of Persian Medicine have proposed a variety of methods to cook eggs,ease of digestion is one of the most important factors in their decision-making while proposing the type of cooking method for therapeutic prescriptions.In contrast,in modern nutrition research,regardless of the method of cooking eggs,the effect of its use on diseases like heart disease or diabetes has been studied.Owing to the fact that many cases of eggs,as mentioned,have been confirmed in PM texts during modern scientific surveys,it appears that clinical studies on the relevant issues of eggs in this context are useful in better understanding therapeutic effects.

Keywords:Eggs,Cooking,Preparation,Food,Nutrients,Persian Medicine

Introduction

At present,eggs are known as a natural resource that is rich in vitamins,essential minerals,high-quality or first class protein,and antioxidants,which can be included in a healthful diet.This,despite the fact that all the material inside an egg has only 82 kcal [1,2].The economy and varieties of cooking methods of this nutrient—containing unique compounds—have made it a recommended food for one’s lifetime,from a healthy pregnancy to childhood growth and development as well as maintaining muscle mass and its functions in the elderly.Over 40 years of research have shown that all healthy adults can consume one egg daily without worrying about its risks of heart diseases and dietary cholesterol is not related to serum cholesterol concentration [3-5].The presence of antioxidants in the diet is very important,since it reduces oxidative damage to cells and thereby improves human health.Egg white has significant levels of B vitamins.Egg yolk also contains all fat-soluble vitamins and is one of the few natural and food sources of vitamin D and its metabolites [1,6]:The amount of vitamin D in the yolk of eggs raised outdoors is more than in any other egg [7].Clinically,this nutrient has been known to be effective on the maintenance of health of many organs,including the cardio-metabolic system,weight management,the strengthening of muscles,safe pregnancy,proper functioning of the brain,and eye health [8].For these reasons,eggs have been introduced as a functional foods [9].

The process of cooking eggs like other kinds of food causes some of its nutrients to be partially lost.Vitamins such as riboflavin,thiamine and folic acid are more sensitive to heat than other materials.Hence,by choosing the appropriate method of preparation eggs,most of its nutrient content can be retained [10].In the survey of new sources and papers,despite the numerous properties for eggs that have been noted,adequate studies have not been conducted on cooking methods,and the effect of each on the nutritive and therapeutic role of eggs.

In recent years,the use of Complementary and Alternative Medicine has become prevalent in the world.One of these medical schools,which is referred in papers as Arabic-Unani medicine,Humoral medicine,Iranian Traditional Medicine etc.according to texts such as Harrison's Principles of internal medicine is derived from "Persian Medicine" [11,12].From the perspective of Persian Medicine, eggs are a valuable source of nutrients,which,despite their small size,have high boosting,and nutritive properties [13].Doctors of this medical school have,in several cases,prescribed different parts of eggs,including the egg yolk,white,lime shell and layer sticking to the shell,in oral and topical forms to patients.They believe that eating egg yolk has high nutritive potential,produces good blood,and plays a role in strengthening the body,heart,and brain.Half-cooked yolk was recommended for cough and shortness of breath,and eating egg white was prescribed to stop bleeding [13-15].In many of these recommendations,special emphasis has been placed on the type of cooking eggs.With regard to the special properties of eggs and the effect of preparation methods on its therapeutic and digestive effects,there is extensive material in this medicine—to the extent that the Muslim scholar in traditional medicine Ibn Nafis(Qarshi;1210–1288 AD),in the book al-Shamel,has written about 45 pages on eggs’ properties.He said,“A lot can be said about eggs,because there are rules and principles,and these certainly do not fit in one paper”[14].In the present paper,we decided to address the different methods of egg preparation and the clinical and gastrointestinal effects of each from the perspective of PM.

1 Materials and methods

The present study is a review in which valid PM resources were studied.In addition to the detailed study of chapters related to the methods of the use of eggs,the abovementioned resources were searched with the following keywords:“Tokhm-e Morq,Khagineh,Bayz,Nayei,Mosakhkhan,Nim-beresht,Maslouq,Ajjeh,Bayaz-al-bayz”in the software JamiTib (Version 1.5).After that,the Persian electronic banks—consisting of Jihad Scientific Information Database (SID),publication database (Magiran),Institute for Iran Scientific Information and Documentation (IranDoc)and specialized bank of medical literature (Medlib)—were used.The contents of the sites of PubMed,Google Scholar,ScienceDirect and Embase were searched and studied with the following keywords:“eggs,cooking,hen egg,chicken egg,egg dishes,scramble egg,pancake,egg soldiers,poached and coddle egg,omelet,very soft boiled,soft-boiled,hard-boiled and fried eggs.”

In the next step,the word“egg”was searched in the Krause’s Food &the Nutrition Care Process—14th ed.and all the relevant subjects was snapped [1].Two reputable websites:“U.S.Poultry and Egg Association”[16]and“American Egg Board”[17]and subsidiaries[8,18]introduced in Krause’s Textbook were also searched for as food and water safety resources by the same keywords.Finally,a classification of the findings obtained and a content analysis were carried out.

2 Result

After the survey of Persian Medicine reference books,six methods of using eggs were finally extracted.In the first type,eggs are used as a raw material,and in the remaining five types,eggs are cooked by various methods.In other words,the scholars have proposed at least five cooking methods for the oral therapy with eggs,which contain very soft boiled,soft-boiled,hardboiled,and fried eggs and Khagineh [19].All these methods of preparing eggs—prescribed in PM texts—are separately described below:

2.1 Raw eggs

In this method,eggs are used raw,and not cooked at all.According to the wise men of traditional medicine,the speed of nutrition in raw eggs is slower than in verysoft-boiled eggs.In other words,the conversion speed of eggs to nutritive components in the body depends on whether eggs are cooked or not cooked,and because of the lack of heat,this kind of eggs is not converted to blood and components of organs [14].Hence,raw eggs are more prescribed in topical treatments to eliminate swelling and boils [14,15].Meanwhile,PM physicians consider a high degree of consumption of raw egg yolk as the cause for the formation of kidney stones and some types of skin hyperpigmentation [13].In the old medical books,slow drinking of raw eggs was considered useful for patients suffering from snakebite[13].

2.2 Very soft-boiled eggs

This method of egg preparation—very soft boiled eggs— is known by the term“Mosakhkhan”in the original texts of Persian Medicine.In some books,softboiled eggs and Mosakhkhan are considered equivalent to each other [20].

Nevertheless,some savants,such as Ibn Sina(Avicenna;980–1037 AD),have proposed these as two separate cooking methods and have separately spoken about the properties of each [21].This means that though the two preparation methods are different,their nutritional effects are relatively similar [15,21].Wise/Hakim Qarshi has said Mosakhkhan—as compared with soft-boiled eggs—has slower digestion,but more diluted blood is produced,which is caused by being more watery and less hardened than soft-boiled eggs.Therapeutic applications of the slow drinking of very soft boiled eggs have a positive effect on the cessation of bleeding,including urinary tract bleeding [14].

2.3 Soft-boiled eggs

In PM books,the word“Nim-beresht”is more widely known,and the egg with such a yolk is called“halfboiled”[21].Galen has identified a limit for softboiling an egg,saying:“Whenever (you)put it in boiled water and count a hundred,or put it in cold water and count to 300,it becomes half-boiled”[13].Poached eggs are now cooked by this method [10].

The best method to cook soft-boiled yolk is to stir the egg yolk in a bowl,put this bowel in a pot full of water,and stir and boil the yolk till it becomes softboiled [13].It seems with this method,the egg’s softboiled yolk can be better controlled.

Nim-beresht egg—in terms of temperament—is known as the most moderate food,tending toward warmth [14].This leads to the rapid digestion and absorption of the egg in the gastrointestinal tract,and the conversion into the body’s nutritive components[14].Hence,soft-boiled egg results in a rapid and severe strength;it is suitable for those who are weak or have bleeding,and require fast and facilitated feeding[14].

In Persian medical resources,many properties of“soft-boiled yolk”have been addressed more than the rest of the egg components or cooking methods.For example,it has been mentioned that because it is tenderer and less compressed,the yolk components are hardened,and more dilute blood is produced.Such comparatively diluted blood causes the patient to be strengthened robustly and speedily.In addition,eggs cooked by this method penetrate more easily into skin layers:This gives the person a good face coloring [14].

In addition,soft-boiled egg yolk is considered a good substitute for milk for children [13].This is because from the perspective of the medical school,in addition to rapid and easy digestion,the egg yolk has many nutrients.For this reason,it has been created to feed the chickens [14,15].

Meanwhile,from the perspective of PM,some foods and drugs have a property named“Ghabz,”which strengthens the body tissues [13,15].Soft-boiled egg also has this property,and its presence is greater in the“yolk”.Therefore,its important effects are strengthening the heart as well as boosting mental vitality [14].

2.4 Hard-boiled eggs

In this method,the egg is boiled in water until both the white and yolk become hardened [14].According to the scholars,hard-boiled eggs—compared with soft-boiled eggs—are responsible for greater nutrition [14,15].But the components of the eggs are compressed to a greater degree by this cooking method,and,as a result,its digestion and passage in the gastrointestinal tract prove to be slower and more difficult.Finally,the resultant nutrients only slowly infiltrate the body’s cells,and provide for them.Owing to the slow intestinal passage and greater retention,pain and other intestinal symptoms also result more from the consumption of such eggs [14].

Therefore,it is recommended that boiled eggs should not be boiled and hardened too much,since a longer pause in the stomach leads to further disruptions in digestion.It is also recommended that people with weak stomachs should not consume overcooked hardboiled eggs and,if they do want to consume them,they should eat these with salt,olive oil,as pepper or vinegar,which would speed up digestion [14].

2.5 Fried eggs

According to PM texts,fried eggs are a relatively heavy food for the digestive system and pass too late from the stomach.In addition,it should be noted that the consumption of fried eggs is preferred more from overcooked hard-boiled eggs [14].

In addition,the consumption of fried eggs by those whose stomachs have a“hot temperament”may producing inappropriate materials and headaches.Since a cool stomach is also unable to digest such eggs,the wise believe consuming such eggs is only good for those whose temperament is a little hot and,in fact,tends to heat.Moreover,it should be noted that fried eggs can cause constipation [14].

2.6 Khagineh/omelet

The Persian word“Khagineh”is used to describe the omelet and if vegetables are used in its cooking,the word“KuKu”is used instead [13].To prepare Khagineh,usually flour,oil and sometimes sugar,honey or grape molasses are be added to the egg.The use of eggs with dates or onions or vegetables is also common[22].Of course,the exact method of preparation of this food item is not mentioned in traditional medical books or,if mentioned,there are differences between the texts,which is probably because of differences in cooking methods during the year.In general,it can be said that when any material is added to eggs and cooked together,it can be called Khagineh,so that all kinds of omelets have similar properties.

Khagineh has many nutrients,but takes very long to digest [13].Like fried eggs,it is heavy and is removed from the stomach slowly,especially if it is prepared with ghee (the oil extracted from cow or sheep milk).In the case of cooking with olive oil,its digestion is easier and lighter.In addition,it is recommended that the only egg yolk be used to prepare Khagineh [14].

PM scholars have prescribed the use of an egg as Khagineh for the sexual drive booster;of course,the eggs of all birds and even fish are used for the sexual drive booster.For this purpose,the most popular way of preparing Khagineh is by cooking egg yolk with ghee and onion [14],prescribed with various spices like cinnamon [13].

3 Discussion

As mentioned above,despite a variety of egg cooking methods around the world and various opinions on different nutritional effects of egg on human health,no clinical research has been conducted on therapeutic uses of different egg preparation yet.Cross-sectional and population-based studies only report consumption or not consumption of egg,or describe methods of egg preparation.As an example,Bermúdez-Millán and her colleagues (2009)identified cultural beliefs of low-income pregnant Latinas about egg consumption during pregnancy and methods of egg preparation with food frequency questionnaire and a single 24-hour dietary recall.Egg consumers had higher intakes of protein,fat,vitamin K,vitamin E,selenium,betacarotene,lutein and zeaxanthin,cholesterol,total polyunsaturated fatty acids,and docosahexaenoic acid.Finally,they concluded that egg consumption in these women significantly contribute to their overall nutrient intakes and nutrient density of their diets [23].Song et al.(2000)conclude that daily nutrient intake in people who consume egg is significantly greater than that of non-consumers,too [4].In addition,in most interventional clinical trials on eggs,the number of eggs was studied and the researchers did not mention preparation methods and their details.Katz et al.,in a study conducted in 2015,found that daily consumption of two eggs for 6 weeks did not have an effect on endothelial function in adults with CAD [24].Woo et al.study in 2016 showed that consuming more eggs(more than 3 eggs per week)would reduce the risk of metabolic syndrome [25].In neither of these studies,the type of eggs cooking did not matter [24,25].This is while in Persian medical texts,the differences between nutritional and therapeutic properties have been studied separately and,in various diseases,there is a great variation in prescribing eggs.

Some people believe that raw eggs are more nutritious and healthy than cooked eggs [26],But according to modern nutritional advice,the consumption of raw egg entails risks such as infection of Salmonella enteritidis (one in 20,000 eggs may contain the bacteria).Hence,those who tend to consume raw eggs in homemade ice cream or salad are recommended to use pasteurized eggs.In addition,the athletes who consume eggs because of high-quality protein should know that the egg cooking process not only does not cause any reduction in the quality or bioavailability of protein in the egg,but also actually increases its protein digestibility [27].For example,avidin is one of the active proteins in raw egg white,which,in combination with biotin,makes the latter unattainable.However,by cooking the egg white,avidin becomes inactive,and biotin is absorbed during digestion [10].This is strictly in accordance with PM content on the relationship of egg conversion speed to the body’s nutritive components by cooking,and,for this reason,raw egg is prescribed more for topical treatments [14].

However,with egg cooking,some of its nutrients such as folic acid [28],antioxidants [29-31],and free amino acids [31]decrease,but Remanan et al.,concluded that (simulated)digestion increased the antioxidant activity of eggs,due to the production of new antioxidants (free amino acids and peptides)[30].

The“Egg Safety Center”in America provides safety tips on the extent to which eggs should be cooked.When preparing a variety of foods containing eggs,the egg white should be quite hardened,and the egg yolk should be a little hardened—there is no need for it to be hardened completely.To prepare soft-boiled eggs properly,these should be slowly put in half-boiled water (i.e.less than 70°C)until no white remains in liquid form and the yolk begins to get hardened.Also,pre-cooking or reheating soft-boiled eggs should be avoided [32].Therefore,the use of soft-boiled eggs(i.e.Nim-beresht,not Mosakhkhan)is safe because,as in Persian medical texts,it is complete hardened white and“soft-boiled”yolk [21]:The school of medicine prefers the use of soft-boiled egg to very-soft-boiled egg,because it is easier to digest [14].

In Persian Medicine,to brighten and improve skin coloring,the consumption of egg yolk in the softboiled form is recommended [14].Research has shown that one of the main factors preventing the skin from environmental damage is its antioxidant capacity.In Palumbo et al.’s study,for antioxidant protection,oral and topical consumption of carotenoids,lutein and zeaxanthin has been recommended:Zeaxanthin is greatly available in green leafy vegetables and the egg yolk [33,34].

The feature of strengthening the cardiovascular system in PM texts is more attributed to“soft-boiled egg yolk.”In addition,the consumption of eggs by the preparation method,which has a great effect on one’s body,has positive effects on a person’s mental and emotional happiness [14].In this respect,Chou et al.study showed that people with high dietary choline intake have lower blood homocysteine levels.High homocysteine is known to be a risk factor of coronary heart disease and choline by converting homocysteine to methionine (the body’s essential and useful amino acids),which plays a heart-protective role [35].As mentioned in nutrition resources,the egg yolk is an excellent source of choline [1].In the above mentioned study,the method of egg preparation has not been noted[35].

As noted,the scholars of PM introduce soft-boiled egg yolk for children as a good substitute for milk[13].Today,egg yolk lipids are also used as a source of unsaturated fatty acids and phospholipids in infant formula [36,37].Of course,no food except mother’s milk provides all the nutrients required by humans.But here,the egg contains a wide range of essential nutrients.For this reason,in nature,the egg has been designed to supply all the materials required to create and develop a chicken [10].

Regarding the special effects of soft-boiled eggs,there are many interesting discussions in PM texts that can be the subject of a separate paper.Some of these are noted in the Results section.Because of this method of preparation eggs,in addition to its easy digestibility,even by poor patients,many other properties have been listed.

In PM resources,the consumption of hard-boiled eggs,despite admitting its rich nutritive property,it has not been welcomed so much and is not recommended for all people,because of the difficulty in digesting it [14].Of course,the time conditions,temperature required,and cooking details have not been mentioned yet.Today,we know that the egg white is hardened at a temperature of 144–149°F and the yolk at 149–158°F.Therefore,to prepare hard-boiled eggs the temperature within an egg should be above 160°F (71°C).It is usually recommended that after cooking,the egg should be immediately cooled in water,and quickly put in the refrigerator.In this way,boiled eggs can be stored in the refrigerator for a week within their shells[32].

It should also be noted that if an egg is boiled too long and at a temperature more than what is required,a black-green ring is formed around the egg yolk.The high boiling temperature leads to increased pressure inside the egg,pushing hydrogen sulfide gas from the white into the yolk,thanks to a chemical reaction between sulfur in the white and iron in the yolk.As a result,the green ring is formed.This combination of“iron sulfide”is responsible for the hard-boiled egg odor [27].To prevent the formation of this ring,it is recommended to cook eggs in hot water,not boiling water,and immediately cool it after the completion of cooking [18].

Though it is noted that the change in the color of an overcooked egg is not deleterious to health [27],from the perspective of PM,the egg is digested in a very difficult manner and not everyone’s stomach is able to digest it [14].The wise men of this medicine school unanimously believe that the best way of preparation eggs for healthy people is“nim-beresht/soft-boiled,”to be eaten with some salt [14,15].

Conclusion and suggestions

As seen from Persian Medicine texts,the ability to digest a food for suitable use by each body organ has been the first concern of the wise.For this purpose,at the beginning of the discussion about each method of egg preparation,first the convenience and digestion rate of egg are discussed and then its useful properties are listed.Although the processes of cooking eggs reduce their nutrients [29],gastrointestinal digestion promotes antioxidant properties [30,38].

So it is suggested that clinical research be conducted on different effects of several egg-cooking methods on the human body in addition to studying the oral effects of eggs on problems such as cardio-metabolic diseases or the effect on organs’ health,such as skin,muscles and eyes.