The Effect of Temperature and Polarity on Solubility of Substances

ABSTRACT

The differential effect of whole eggs and egg yolks on the food quality of leche flan were evaluated through the preparation of two sets of mixtures of leche flan recipes- (A) with whole eggs and (B) with pure egg yolks. Mixtures were thinly poured into molders, and were cooked under the same procedure- similar temperature and duration of cooking time. Mixture A resulted to a firm but stiffer custard with a lighter golden brown physical appearance and a pleasantly sweet yet less flavorful taste, while Mixture B resulted to a firm but tender custard with a golden yellow brown appearance and a pleasantly sweet and flavorful taste. Thus, using pure egg yolks results to a good food quality of leche flans.

Eggs from chicken are most commonly used for foods with eggs coming from turkeys, ducks and geese are most often consumed. With the rise of the existing per capita consumption of egg, this increasing figure is almost equivalent to an average of one egg per person daily (Sweetman & MacKellar, 1937).

THE STRUCTURE AND COMPOSITION OF EGG

Eggs has 3 basic parts namely the shell, the white, and the yolk. (See Figure I). The shell, which is considered to be inedible takes up almost 11 percent of the totally weight of the egg (Gates, 1976).  According to Sweetman and MacKellar (1937), eggs usually weigh from 40-60 grams with the edible portion of it ranging for about 44 grams- egg white taking up almost 28 grams and egg yolks for about 16 grams.

FIGURE

According to Gates (1976), egg whites and yolks differ in composition that this affects their use in food preparation. Egg whites, considered to be a colloidal dispersion of containing proteins, majorly albumin, in water while the yolk, although similarly distributed is mostly a fat mixture. Both the egg whites and yolk are composed of ash and vitamin constituents. (See Table I).

TABLE - THE COMPOSITION OF HEN’S EGGS

THE NUTRITIVE QUALITY OF EGGS

According to Chavez, Claudio, de Leon and Guzman (1999), eggs are important sources of vitamins, proteins, iron, phosphorus, riboflavin and trace minerals. Ranking second as a major source of Vitamin D next to fishes, eggs contain almost all vitamins except for Vitamin C which is significantly absent in its nutritive value. Eggs are also generally low in calcium which is concentrated chiefly on its shells but is the riches source of cholesterol, a substance which in excessive amounts leads to heart complications.  The nutritive contributions of whole eggs and yolks and whites are shown in Table II.

TABLE

Studies mentioned in the book written by Sweetman and MacKellar (1937) proves that the nutritive value of eggs contains sufficient amounts of nutrients essential for growth reproduction, and even lactation. Also, eggs maximize the full nutritive efficiency of other proteins such that they usually become a standard in comparing the biological value of other proteins.

EGG AS A THICKENING AGENT, AS IN CUSTARDS

Eggs are usually used as a thickening or a binding agent in cookery with such property varying from yolk to white. EGG whites thicken at 60 degrees Celsius and will not flow at 70 degress celsisus while yolks at 65 and 70, respectively.Such property as a thickening agent is commonly used in custard making such as in pudding, masapan, and leche flan which is of focal attention into this paper  (Chavez, Claudio, de Leon and Guzman, 1999).

LECHE FLAN: BRIEF HISTORY

As discussed by Chavez, Claudio, de Leon and Guzman (1999), Leche flan or the pilippine custard is known to be a successful custard rendition of the classic dessert crème caramel which is European in origin.

As defined in The Oxford Companion to Food, Crème caramel is a sweet dish which is essentially a custard is often served in France such that a caramel syrup is poured first into the molder before putting the custard into the container, thus, creating a more appealing appearance and flavor. Crème caramel can also be interchanged with flan, which is specifically used in Spain which is considered to be a dessert as well.

FACTORS AFFECTING THE COOKING PROCESS OF LECHE FLAN

As mentioned by Chavez, Claudio, de Leon and Guzman (1999) in their book Basic Food for Filipinos, there are certain factors that greatly affects the cooking process of leche flan. The temperature, amount of sugar, and egg parts used affects the coagulation of proteins in custard making. The higher molecular weight of sugar increases the cooking temperature of the flan, while higher concentration of eggs tends to toughen the custard due to its thickening capacity.