Authors: Dr. Ulrike Fischer-Nägele, Yvonne Haslauer*
Cappuccino (espresso with milk foam), latte macchiato (espresso with foamed milk and warm milk layers) and Asian bubble tea (tea with pearls and topping) are becoming more and more popular as new lifestyle products. The resulting coffee and tea-based beverages use aerated/foamed toppings, which must develop a fine, smooth foam with substantial volume and satisfactory stability over time. These food products are made either fresh in food service restaurants, by the consumer at home or in vending machines; nearly all types of these applications involve the use of either liquids or powder premixes. In addition to resistance to drainage, coarsening and foam collapse, another highly valuable property in toppings such as these is a smooth, creamy mouthfeel. While research aimed at understanding and optimizing the corresponding mechanisms in dairy foams has a long history, increasing demand for vegan diets requires the same properties for plant-based toppings as well.
The Technical Service Unit of the Nutrition Team at WACKER has explored the beneficial impact of alpha-cyclodextrin (ACD) on various foam properties in different model systems (Figure 1).
Figure 1: Model systems tested, foaming processes and foam properties
Dairy powder: powdered dairy and non-dairy toppings varying in fat content; milk: UHT milk varying in fat content; plant milk:(in this case almond milk with 2.5% almond content). Foam was produced either by infusing steam through a coffee machine or through the use of a milk frother. Various properties of the resulting foam were then analyzed.
Alpha-cyclodextrin is a ring-shaped oligosaccharide based on 6 glucose units, which is produced by WACKER BIOSOLUTIONS in a patented fermentative process based on starch, a renewable raw material. WACKER markets ACD under the brand name CAVAMAX® W6. Its unique molecular structure and three-dimensional interactions give the molecule an internal lipophilic area (referred to as the “cavity”) and an external hydrophilic area (Figure 2).
Figure 2: Typical molecular structure data of ACD
a) Molecular structure; b) The molecular structure results in a bucket shape with a hydrophilic exterior (blue) and a lipophilic cavity (yellow).
Due to this highly unique molecular structure, ACD has a huge variety of properties (Figure 3) that can be used in multiple food applications. The hydrophobic inner cavity of ACD allows other lipophilic molecules to form host-guest inclusion complexes through non-covalent interactions. The spontaneous interaction of ACD with triglycerides at the oil-water interface of food systems gives ACD-TG complexes emulsifying properties (“emulsifier-in-situ”). Hydrogen bonds between the exterior part of ACD and long-chain molecules, such as proteins or polysaccharides in food ingredients, make the system more viscous and therefore positively influence the foaming/whipping properties of the food matrix. As an additional beneficial consequence, the various interactions of ACD also stabilize the desired food matrix.
Figure 3: Multifunctional properties of ACD in food systems
Regarding the specific application of barista toppings, an evaluation of various examples of the model systems in this study shows that ACD significantly improves foaming capacity, i.e., the amount of foam achieved in such systems could be increased substantially, as shown in Figure 4.
Figure 4: Foaming capacity of different barista formulations:
The foam volume of a reconstituted, medium-fat dairy powder system (4 g powder in 100 g water, fat content: 20 – 25%) was analyzed either on its own, with 1.4% maltodextrin or with 1.4% alpha-cyclodextrin (ACD) (n = 3).
The addition of 1.4% ACD nearly doubled the overrun. The same amount of an inert linear oligosaccharide (maltodextrin) was used as a direct comparison. Maltodextrin caused only a slight increase in the overrun, due to the increase of dry matter – not comparable to the significant increase in foaming capacity achievable by the presence of ACD.
Adding ACD to barista toppings not only improved foaming capacity – the stabilizing effect of CAVAMAX® W6 in the foam also retarded foam degradation reactions (Ostwald ripening, drainage, coalescence, deformation and bubble creaming) and therefore positively influenced foam stability in these toppings.
Figure 5: Foam stability and foam half-life-time in the presence of ACD
Reconstituted, high-fat dairy powder (4 g powder in 100 g water, fat content: 50 – 60%) was analyzed either on its own, with maltodextrin or with ACD (n = 3).
Figure 5 shows the increase in foam stability for the model dairy and non-dairy powders (fat content 50-60%) reconstituted from 4 g powder in 100 g water: the addition of ACD increased foam stability even at low dosage rates, extending the foam half-life-time (the time it takes for the foam volume to shrink by half) from 3 to 15 minutes – this will enable a longer serving time with appropriate foam appearance.
Barista products are luxury lifestyle products. This means that, in addition to the volume and stability of the foamed topping, consumers also place a great deal of importance on the overall impression: the appearance of the foam should be nicely creamy and homogenous. Figure 6 demonstrates the positive effect of 1% ACD in an almond milk foam (UHT almond milk with 2.5% almond content). For the consumer, this homogenous, creamy pore structure correlates to a full-bodied beverage and an improved mouthfeel – especially in plant-based barista toppings, which often need an additional boost in that regard.
Figure 6: Almond milk foam
UHT almond milk (2.5% almond) was foamed by infusion – plain almond milk without ACD (left) and with ACD (right).
Figure 7: Sensory evaluation of almond milk, with and without 1.0% ACD
Cyclodextrins are also known for their potential to mask undesired flavors in various matrices. As part of this study on the influence of ACD in barista toppings, this masking effect was demonstrated to either balance the cooking off-taste of dairy liquid systems and to cover/trap the rancid off-notes of the vegetable fat fraction of non-dairy powder systems. It also reduced the partial astringent or bitter note of almond milks – for other plant-based milks (those based on legumes such as soy or pea), the typical “beany” profile is a major concern and has to be balanced for consumer acceptance.
* Technical Service, Nutrition, Wacker Chemie AG, firstname.lastname@example.org