Great Yoghurt Textures Are A Technical Triumph

Wednesday, September 13th, 2017

For the best and most stable yoghurts to captivate consumers, you need the tailored texturant that takes proteins in hand, matches your process and meets market demands. Angie Ng, regional product manager, Dupont nutrition & health, Malaysia, shares more on this.

No successful food brand has ever truly won a place in consumer hearts without having a finely tuned texture that remains unchanged right through to the end of shelf-life. If that brand carries a smooth fruit yoghurt or a flavoured yoghurt drink, careful consideration of the texturant is critical to overcoming the significant technical challenges that arise during processing and storage, and in achieving the most appealing texture for a chosen market.

Throughout Southeast Asia, consumers have many opinions on how the best stirred or drinking yoghurt should taste or feel in the mouth. But there are some overriding trends these countries share. One is a preference for fermented dairy brands that are marketed as healthy. Another is a general move in these countries towards taxation of sugar-sweetened beverages.

But more on that later. First let’s take a closer look at the challenges specifically related to a fermented dairy drink—a product that is becoming increasingly popular among consumers due to its convenience and status as a health beverage choice.

Dependent On PH

While texturants are used in stirred yoghurt to enhance viscosity and reduce syneresis, in drinking yoghurt the target is protein stabilisation. Further texturants may be added to finetune texture to the required viscosity once the proteins are fully stable. But what do you need to look out for when determining whether the proteins in your yoghurt recipe are at risk?

In a drinking yoghurt, the final pH is typically around 3.6 to 4.5—not far from the isoelectric point of protein at pH 4.6. At this point, the casein proteins in milk have a neutral charge and, left unchecked, are likely to aggregate and form sediment, resulting in a sandy, gritty texture. Whey separation will typically occur at the same time.

The risk of protein destabilisation in yoghurt is even greater in many Southeast Asian markets, where chilled distribution is limited or even non-existent, particularly in rural areas. Higher temperature processing must then be used after fermentation to achieve a longer yoghurt shelf-life at ambient temperatures. This puts protein stability under further stress.

Texturising ingredients—otherwise known as hydrocolloids—can stabilise yoghurt in several ways through their interaction with casein. As the fermentation process causes the casein to undergo a transition from negative through neutral to a positive charge, negatively charged hydrocolloids can protect the casein particles by accumulating around them and bonding to their surface.

Best For Protein Stabilisation

Of the many types of hydrocolloid that exist, pectin is the one that has proven most successful in stabilising proteins and securing a smooth, clean mouthfeel in drinking yoghurt.

Classified as a dietary fibre, pectin is a primary component of the cell walls of most fruit and vegetables. Commercial pectin products are typically produced from the peel of citrus fruits, such as lemons, limes and oranges, or from the apple pomace left over from juice processing.

Food scientists have classified them in two categories— high ester (HE) or low ester (LE)—a technical definition defined by the number of galacturonic acid groups that are esterified with a methyl ester. Galacturonic acid, which is a sugar acid, is a main component of pectin. Having a degree of esterification ranging from 50-80 percent, HE pectin is stable at pH levels of 3.0 to 4.0 and shows good heat resistance.

It is at low pH levels that HE pectin molecules are appreciated for their ability to interact with the positively charged protein via electrostatic interactions. The proteinpectin interaction primarily takes place in the smooth region shown in Figure 1. Through careful raw material selection, process technology and standardisation of acidified protein systems, it is possible to tailor the molecular structure to optimise the protein-pectin interaction.

For this reason, HE pectin is widely used for protein stabilisation and supports texture development in drinking yoghurts. It is used to obtain the light viscosity, clean texture and good flavour release that all add up to a refreshing sensory experience.

Why Does He Pectin Work?

The technical explanation for why HE pectin is so effective in protein stabilisation relates to the distribution of ester groups along the galacturonic backbone of the pectin molecule. The outcome can be illustrated by comparing the microstructures of drinking yoghurt stabilised with and without HE pectin, respectively (Figure 2).

This shows that the drinking yoghurt with HE pectin has significantly better homogeneity than the reference—in other words, fewer green clusters, which represent undesirable protein aggregation.

The reason why this works is because the HE pectin adsorbs to the protein surface via electrostatic interaction (Figure 3), resulting in steric stabilisation which protects the protein against aggregation.

Consequently, the drinking yoghurt has a low viscosity and smooth, non-grainy texture. Other texturants such as modified starch, on the other hand, can only provide a stabilising effect by increasing the viscosity of the whey phase.

While this delays protein sedimentation, the presence of protein aggregates still causes the texture to be grainy (Figure 4).

Maximum flexibility in yoghurt texture development can be achieved by using texturants in combination. Whether producing a drinking or stirred yoghurt, pectin is in general a good choice for obtaining a stable final product with a low tendency towards whey separation. However, depending on manufacturer requirements, other texturants such as carboxyl methyl cellulose (CMC), modified starch, guar and xanthan gum have potential when creating tailored blends to meet a specific textural need.

Making Up The Sugar Shortfall

Today, the value of tailored texturant solutions is being further underlined by the trend towards sugar reduction. Taking over from fat, sugar is now perceived as the dietary demon, linked to lifestyle-related health issues such as diabetes, inflammation and obesity.

As more consumers make a conscious effort to reduce the sugar content of their diet, the health authorities in several Southeast Asian countries are taking steps to encourage reduced sugar consumption by imposing a sugar tax. A tax on sugar-sweetened beverages is soon expected to be agreed by legislators in the Philippines, while a Thai proposal for a sugar tax specifically names acidified milk drinks as one of the targets.

Although a range of sweeteners are available to restore sweetness in reduced sugar yoghurts, they cannot replace viscosity and mouthfeel. This is where a customised texturant blend can make up the shortfall when sugar solids are taken out of the formulation.

For manufacturers looking for a new brand positioning, texturants provide endless opportunities to obtain anything from a creamy texture for premium snacks to a light texture for a refreshing beverage.

The Value Of An Expert Opinion

A final word of caution—successful use of texturants in any yoghurt type also requires a good understanding of the conditions during processes such as pasteurisation, homogenisation and cooling. This is especially true of the Southeast Asian region where long shelf-life yoghurt products are subject to greater stress due to higher heat treatment and ambient storage conditions.

So, this is our advice: never underestimate the expertise of a texturant specialist when identifying the best texturant solution for your yoghurt brand. It’s the fastest way to the market.