Sucrose energy content

Carbohydrate accounts for about 40% of the energy content of a normal meal. In the UK, the daily intake is typically 60 g starch, 120 g sucrose, 30 g lactose, 10 g of glucose... 

Although different sugars have different sweetness factors relative to sucrose they are all identical in energy content, on a dry basis. Thus to achieve a high energy content without cloying sweetness, sugars or carbohydrates of low sweetness must be used. This is illustrated in Table 13.2. 

As a result of widespread concern about weight control, the production of lipid materials with reduced or zero calories has been of special interest recently. The lipid-based fat replacers are esters that resist enzymatic hydrolysis, are poorly absorbed, have relatively low-energy content, or have different modes of metabolism. Many of these materials can be made from soybean oil or contain soybean oil fatty acids. Sucrose polyester or other synthetic esters and diacylglycerol oils are examples of these low-calorie fat substimtes (268-274). 

Tl ie energy content of food carboliydrate and food protein is J7 kj/g, whereas that of food fat is 38 kj/g. The energy content of ethanol is 3 kJ/g. Though fairly accurate, these values are only generalizations. For example, consider the energies of different carbohydrates 17,2 kJ/g of starch, 16.6 kJ/g of sucrose, 15,9 kJ/g of glucose. 

Conforming to the concept of activation introduced by Arrhenius, the energy content of molecules is not constant but is continually changing. Certain molecules, the activated molecules, have an energy higher than the other molecules, and only they are capable of entering into a reaction. In a solution of sucrose, for example, the number of activated molecules is extremely small but if the temperature is increased by 10 their number is increased two or three times. These activated molecules travel faster and are more labile. 

Figure 16.5. Supersaturation behavior, (a) Schematic plot of the Gibbs energy of a solid solute and solvent mixture at a fixed temperature. The true equilibrium compositions are given by points b and e, the limits of metastability by the inflection points c and d. For a salt-water system, point d virtually coincides with the 100% salt point e, with water contents of the order of 10-6 mol fraction with common salts, (b) Effects of supersaturation and temperature on the linear growth rate of sucrose crystals [data of Smythe (1967) analyzed by Ohara and Reid, 1973],...

This argument does indeed support the contention that on a per-mole basis PEG is much more effective than sucrose at increasing protein chemical potential. And for cases where relatively high concentrations of PEG (e.g., >1% wt/vol) are needed to confer cryoprotection, the Timasheff mechanism may be applicable. However, it seems unlikely that a PEG concentration of 0.01% (wt/vol) would have a significant effect on the thermodynamics of the system. This is because the actual parameter of interest is the transfer free energy of the native versus denatured protein from water into cryoprotectant solution. The difference between the values for the two states determines the magnitude of the effect on the free energy... 

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