This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Strong concentrated acids decompose all the sugars producing humus or caramel substances. The weak acids, malic and citric in fruits, lactic in sour milk, acetic acid, and salts with an acid reaction like cream of tartar, affect, the sugars in different degrees, depending on the particular acid used, the strength of the acid, whether it is heated, and the length of time of heating.
The monosaccharids, dextrose and levulose, are not affected to any appreciable extent by weak acids. When sucrose is cooked with weak acids it is partially hydrolyzed to dextrose and levulose, but since the invert sugars are not affected by the acid practically no other change takes place.
Lactose is only very slowly hydrolyzed by acid to dextrose and galactose.
Maltose is less readily affected by acid than sucrose, but is slowly hy-drolyzed to two molecules of dextrose.
Sucrose and fondant. Sucrose is very easily hydrolyzed, even by very weak acids, though the addition of water to the sugar molecule cannot be brought about by mixing sugar and water, but may be brought about by enzymes as well as acids. The weak acids used in cookery - lemon juice, vinegar, fruit juices, or the acid salt cream of tartar - all cause sucrose to combine with water forming dextrose and levulose. Hydrolysis takes place more rapidly if the solution is heated. In making fondant with cream of tartar, if the sirup is boiled slowly for a long time, more inversion may take place than when the sirup is boiled quickly with a larger amount of cream of tartar. Compare the length of time required to bring about crystallization in Experiments 7C, 1, and 7C, 2. Hydrolysis of fondant containing cream of tartar occurs during storage though the rate is slow at the storage temperature. Fondant made with cream of tartar and stored in a fairly tight container becomes softer than fondant of the same consistency before storage, but without the addition of cream of tartar. The amount of the acid salt to bring about this softening at room temperature imparts a slightly sour taste to the fondant. To many persons this slight acidity improves the flavor. In fondant made with a larger amount of cream of tartar (Experiment 7C, 4), considerable hydrolysis may occur with short storage.
To determine the effect of salts found in hard water upon the decomposition of dextrose in fondant, some fondants were made with 10 per cent of dextrose added to sucrose and distilled water. To the solution different salts similar to those found in water were added, the fondants made and stored in a heavy glass container, with a tight-fitting lid. They were kept for two years. Acid calcium phosphate was added to some of the fondant to compare an acid-reacting salt containing calcium with the other calcium salts used. At the end of one year the fondants made with calcium acid phosphate were plastic and kneadable, whereas those made with magnesium sulfate, calcium sulfate, and other salts, as well as the control with no salt, were too hard and dry to be kneaded. Here slow hydrolysis from the calcium acid phosphate probably occurred over a long period, but drying out of the fondant was also prevented, which was due to the hygroscopic property of the levulose. If fondant is to be stored for some time before it is molded the fondant made with an acid salt remains soft and plastic, or Keeps better than fondant made without an acid or acid salt.
Hydrolysis of sucrose is often spoken of as inversion and the resulting sugar as invert sugar. The reason for this name is found in the effect of invert sugar upon a beam of light. If a straight beam of light is allowed to pass through a solution of sucrose in an instrument called a polariscope, the beam of light is rotated to the right and the sucrose is called dextro-rotary. After the sucrose is hydrolyzed, the ray of light is rotated to the left and the invert sugar is levo-rotary. Because of this inversion of a beam of light, hydrolyzed sucrose is called invert sugar. Dextrose is dextro-rotary and sucrose is levo-rotary. It is due to the fact that levulose rotates the beam of light further to the left than dextrose rotates it to the right that the rotation of invert sugar is opposite to that of sucrose.
Hydrolysis of sugars by enzymes. Enzymes also bring about hydrolysis of the disaccharid sugars. Since heat destroys enzymes the reaction must occur at a low temperature. The enzyme invertase causes hydrolysis of sucrose to dextrose and levulose. Maltose is prepared from corn by using an enzyme.
Hydrolysis in chocolate creams. Jordan states that the liquefied centers of chocolate creams and other confections are brought about by acids, acid salts, or enzymes. The substance bringing about the hydrolysis is added when the fondant is fairly hard and the softening due to the hydrolysis occurs during storage. Paine states that the amount of the acid or acid salt required to bring about inversion imparts a perceptible acid taste to the fondant. Evaporation of liquid from the fondant must be prevented, or the fondant loses water and becomes dry. Then some moisture is necessary for hydrolysis to occur. The enzyme, invertase, may be added when the fondant is beaten or when it is molded before dipping. The proper amount of invertase is added for the inversion of the fondant, and according to Paine this inversion takes place more readily at pH 4.4 to 4.6. To give this acidity citric acid is added in small quantities. Invertase may be used in fondant for chocolate creams, in confections with fruit like cherries and pineapple, and in bonbons. The fat of chocolate prevents the confections dipped in it from losing moisture by evaporation. The bonbons dry out more rapidly than the chocolate-covered candies. Paine states that the addition of a small amount of egg albumen or egg white lessens evaporation from the fondant.
Hydrolysis of starch. Starch, like sucrose, is very readily hydrolyzed by acids, and the reaction takes place more rapidly at a high temperature. When starch is used with acid fruit juices, a larger proportion of starch is required to thicken the mixture to a definite consistency than is needed for an equal quantity of water or milk. Fillings for lemon or cherry pie, because of the hydrolysis by acid during cooking, need a larger proportion of starch for thickening than fillings like chocolate cream.