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Case study III (Ice cream)

4 important questions on Case study III (Ice cream)

You first investigate whether it would be possible to replace sugar (sucrose) in ice cream by other components, to decrease the calorie intake and/or the raw material cost.
You first suggest to replace sucrose with aspartame, an artificial sweetener (MW 294, ~ 200 times sweeter than sucrose, for the same mass). However, a colleague warns you that it may impact the texture of the ice cream. Which defects can indeed be expected, and why?

You will need a much lower amount of aspartame as compared to sucrose to reach the same sweet taste. You will have then a lower solute mass concentration and molality. The freezing point depression increases with the number of molecules in solution, so the amount of ice in the ice cream will be higher, and the ice cream will be hard. Besides, you have to think which component you will use to replace the “bulking” properties of sugar.

Next, you are asked to explore whether alternative lipid sources could be used instead of milk fat, to improve the nutritional quality of ice cream. The focus should be on increasing the amount of polyunsaturated fatty acids (PUFAs).

On Figure 5 of this article (Goh et al., 2006), the emulsion droplet diameters in melted ice cream are shown. Explain why there is a difference for some samples depending on whether SDS/EDTA was added to the samples before measurement.

SDS/EDTA is used to dissociate flocculated fat droplets (if any) before droplet size measurement. SDS is a strongly surface-active molecule, and also negatively charged. It can replace the emulsifiers initially adsorbed onto the fat globules, providing electrostatic repulsion between droplets. Also, EDTA binds calcium, which can disrupt calcium bonds between fat globules covered with caseins. Therefore, when the measured particle size, for a given sample, is different without and with SDS/EDTA, it means that the fat globules were non-irreversibly flocculated (at least to some extent).

Next, you are asked to explore whether alternative lipid sources could be used instead of milk fat, to improve the nutritional quality of ice cream. The focus should be on increasing the amount of polyunsaturated fatty acids (PUFAs). Can you think of two other strategies that could allow for incorporation of PUFAs in ice cream, while ensuring that no texture or stability defects are encountered? Motivate your suggestions.

Hint: you may be interested in having a look at this paper: Zulim Botega et al. (2013), J. Food Sci. 78(9), C1334.

Use oleogels as the oil phase (i.e., a solid-like fat phase made from liquid (unsaturated) oil in the presence of structuring agents); see for instance the paper of Zulim Botega et al. (2013), J. Food Sci. 78(9), C1334.
Use unsaturated lecithins as the low molecular weight emulsifier.

Segall & Goff (2002) published a paper that has caught your attention: they suggest that ice cream with a good stability and texture can be obtained, through a re-design of the process, without using low-molecular weight emulsifiers. If this actually works, that could substantially decrease the raw material costs, which would make your boss very happy!

Explain what is the role of low-molecular weight emulsifiers in ice cream made through conventional processes. You may use a scheme to support your explanation.

During homogenization of the ice cream mix, fat droplets are formed and stabilized by proteins (available in large amounts). Thereby, a thick protein layer forms around the droplets. During ageing, low molecular weight emulsifiers (e.g., polysorbates, monoglycerides) will progressively replace part of the adsorbed proteins, because they are more surface-active. This “weakens” the interfacial layer surrounding the droplets, and favours the protrusion of fat crystals at the droplet surface, and hence partial coalescence.