The Role of Sugar in the Food Industry 1
ROBERT H. COTTON , PAUL A. REBERS, J. E. MAUDRU, and GUY RORABAUGH
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Research Department, Holly Sugar Corp., Colorado Springs, Colo.
The role of sugar in the food industry is described here in terms of its chemical and physical properties. Studies of the chemical aspects of sugar include those on sweetness and flavor, the reactions of sucrose and invert sugar, caramel formation, antioxidant effect, and the effect of sugar on the curdling of milk, gel formation, and metal corrosion. Physical properties of sugar discussed here are osmotic pressure, crystallization and solubility, hygroscopicity, thermodynamic properties, viscosity, grain size, bulk handling, and such miscellaneous properties as stickiness and thermal and electrical conductivity.
S u g a r plays a major role i n the production of thousands of food products from cured meats through preserves and frozen fruits to confections. Sugar (sucrose) is white, colorless crystalline compound whose molecule i s composed of one molecule each of D-glucose (dextrose) and D-fructose (lévulose) w i t h the elimination of one molecule of water. Its organic chemical name is 1-D-glucopyranose β-D-fructofuranoside. P a r t of the extraordinary versatility of sugar lies i n the fact that i t can be hydrolyzed p a r t i a l l y or completely to the two simple sugars, dextrose and lévulose. W a r t i m e scarcities of sugar served to prove dramatically how basic i s sugar to this country's food supply. N u t r i t i o n a l l y , sugar produces energy. Economically, sugar i s probably the most efficient foodstuff i n terms of calories produced per acre tilled (A3). W i t h the great advances i n nutrition over the last 50 years i t may be perhaps easily forgotten that adequate calories are essential to health (66). Hockett (43) has shown that after one meets the m i n i m u m daily requirements f o r protein, fat, minerals, and vitamins, as recommended by the N a t i o n a l Research Council, there still remains approximately 1500 calories of the total 3000 considered essential to a 150-pound man. These 1500 calories can be supplied by any wholesome food of choice. Since sucrose contributes palatability to many foodstuffs rich i n proteins, minerals, or vitamins, i t also serves nutritionally i n addition to producing calories. A s an example, addition of sucrose to processed orange juice rich i n vitamin C but w i t h a low sugar-acid ratio makes the juice palatable and thus results i n utilization of a valuable food which otherwise would be wasted. Furthermore, sugar enhances the stability of canned orange juice (93) and many other foods. Thus, i t would seem that rational use of sugar is both nutritionally and economically desirable. The extent to which sugar is used is shown i n Table I . W i t h the growth of food science or technology many of the " a r t s " of food preparation and preservation yield to scientific inquiry and method. More a n d more chemists and engineers are entering food processing industries (105). These industries w i l l more and more use sugar i n light of its basic chemical a n d physical properties to produce a given result and i n accord w i t h carefully controlled tests on quality and yield. The latter approach requires both great effort and expense as i t involves carefully conducted taste panels and expert food technologists w o r k i n g i n well equipped laboratories. It may involve extensive market testing. Such work fits into the competitive A m e r i c a n scheme where emphasis on quality often means the difference between profit and loss. Such work also leads to new products (105). 1
P r e s e n t address, H u r o n M i l l i n g C o . , H a r b o r B e a c h , M i c h .
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In USE OF SUGARS AND OTHER CARBOHYDRATES IN THE FOOD INDUSTRY; Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
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The growth of the rational use of sugar calls f o r widespread knowledge of the chemical and physical properties of sucrose. I n this paper an attempt i s made to indicate some of the sources of knowledge i n this field and to give a few examples of newer food technology studies on sugar. Table I.
Sugar Deliveries, by Type of Product or Business of Buyer (United States, year ending: December 31, 1950 ) e
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Product or Business of Buyer Bakery, cereal, and allied products Confectionery and related products Ice cream and dairy products Beverages Canned, bottled, frozen foods, jams, jellies, preserves Multiple and all other food uses Nonfood products Hotels, restaurants, institutions Wholesale grocers, jobbers, sugar dealers Retail grocers, chain stores, supermarkets All other deliveries, including deliveries to government agencies
Total Sugar, 100-Lb. Units 12,723,819 14,376,515 5,074,008 15,115,929 11,009,726 4,993,283 780,019 554,051 60,775,357 23,440,775 1,758,747 150,602,224
Total deliveries
• Represents over 95% of deliveries by primary distributors in continental United States. Production and Marketing Administration, U S D A .
Data from
Chemical Aspects of Sugar
Sweetness and F l a v o r . Because the taste sensation is a subjective phenomenon, indexes of relative sweetness must always represent averages of opinion. I n spite of this difficulty Dahlberg and Penczek (27) a n d Cameron (18, 14), using improved testing methods, have been able to obtain reproducible results. Both groups have shown that the relative sweetness of the various sugars varies w i t h the concentration, as is shown i n the curve i n Fierure 1. The results of Dahlberg include values for corn sirup and corn sirup solids (Table I I ) . Table II.
I so-Sweet Sugar Solutions According to Dahlberg (27) (Concentrations i n per cent by weight)
Sucrose Dextrose Lévulose Maltose Lactose Enzyme Converted corn sirup
Solutions Equivalent to 10% sucrose 20% sucrose 10 20 12.7 21.8 8.7 16.7 21.1 34.2 20.7 33.3 ... ... 17.9 28.2
The relative sweetness of mixtures of sucrose and other sugars, as compared to sucrose, has been studied by Dahlberg (27) and Cameron (13, 14) (see F i g u r e 1). Dahlberg found that a solution containing 1 0 % sucrose and 5.3% glucose was equal i n sweetness to a solution containing 1 5 % sucrose. The flavor-enhancing power of sucrose has also been noted by other workers (16). The relative sweetness of invert sugar as compared to sucrose has been studied by Cameron (13, 14) and M i l l e r (74)- A t concentrations of 1 0 % they are equivalent i n sweetness, at concentrations below 1 0 % sucrose is sweeter, while above 10% invert is sweeter. However, because of the sweetness-enhancing power of sucrose, a solution of p a r t l y inverted sucrose w i l l be sweeter than one completely inverted. The type of sweetness varies w i t h the different sugars (27). The sweetness of sucrose is quickly perceived and promptly reaches a maximum intensity, whereas the sweetness of dextrose stimulates the taste organs more slowly a n d reaches a maximum intensity later. The p r i m a r y taste of glucose (14) is sweet but the secondary tastes are bitter, sour, or tart, while i n the case of sucrose secondary flavors are absent. The effect of temperature on sweetness i n comparing the relative sweetness of sucrose to lévulose has been made by Y a m a z a k i et al. (128). Comparing 5 and In USE OF SUGARS AND OTHER CARBOHYDRATES IN THE FOOD INDUSTRY; Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
C O T T O N , REBERS, M A U D R U , A N D
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RORABAUCH—SUGAR
10% solutions of each sugar, they found that when they had been kept at temperatures below 50° C. lévulose was sweeter, at 50° C. the sweetness was equal, a n d above 50° C. sucrose was sweeter. They explained the relative change of sweetness on the relative proportions of fructose isomers present at the various temperatures. A t lower temperatures more of the sweeter beta isomers are present. SUCROSE
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