Texturisation of dehydrated snacks
Posted: 18 August 2016 | Clara Talens, Food Researcher, / Izaskun Pérez, Senior Researcher / Raquel Rodríguez Senior Researcher, AZTI | No comments yet
The texture of food is mainly perceived in the mouth but also visually, through touch, or even through sound. Regardless of individual texture preferences, certain foods are instinctively associated with certain textures. Conforming to these expectations often determines the product’s acceptability. Well-known examples of food–texture association are aperitifs and snacks of crunchy texture. Such snacks are usually made of dehydrated vegetable products (potatoes, corn, pellets or flour dough, etc.) of low moisture content and aerated appearance acquired during dehydration. The crispness of these products is due to their rigid, dehydrated and porous cellular structure. This structure is a consequence of several factors. Some of the decisive factors are the conditions under which the dehydration and expansion process is conducted and the composition and shape of the original substrate. The final result is mostly determined by the conditioning of the food and its preparation (cutting, moulding, etc.).
In the analysis of consumer trends, it is essential to go beyond examining patterns of behaviour. The scope of research must be broadened to include the lifestyle of consumers in order to understand their motivations and the effect of their lifestyle on consumption trends. AZTI have been extensively analysing these trends1 for some time. As such, they have been classified into nine types: Transient Food, Sustain Food, Better for Me, My Universe, Simple & Smart, Local, Eatertainment, Social & Sharing, and Emphatic/Human.
The tendencies in the consumption of dehydrated snacks are most closely related to three of these trends: Better for Me, Transient Food and Sustain Food. The Better for Me trend reflects one of the basic human desires: to achieve a high quality of life through an optimal state of health and wellness, with a clear focus on the personalisation of diet and lifestyle. The Transient Food trend is concerned with the products and services for consumption on the fly; easily accessible and efficient; such as formulas for breakfast ‘on the go’. The Sustain Food trend arises from the growing consumer awareness that every activity has a direct impact on the environment.
However, none of these trends excludes the pursuit of pleasure or satisfaction of snacking. In this sense, the texture is a key quality attribute contributing to the enjoyment of food and, therefore, directly affects the acceptability of food products.
Crunchy texture: snack-type products
The texture of food is mainly perceived in the mouth but also visually, through touch, or even through sound. Regardless of individual texture preferences, certain foods are instinctively associated with certain textures. Conforming to these expectations often determines the product’s acceptability.
Well-known examples of food–texture association are aperitifs and snacks of crunchy texture. Such snacks are usually made of dehydrated vegetable products (potatoes, corn, pellets or flour dough, etc.) of low moisture content and aerated appearance acquired during dehydration.
The crispness of these products is due to their rigid, dehydrated and porous cellular structure (Figure 1). This structure is a consequence of several factors. Some of the decisive factors are the conditions under which the dehydration and expansion process is conducted and the composition and shape of the original substrate. The final result is mostly determined by the conditioning of the food and its preparation (cutting, moulding, etc.).
The processes of dehydration and expansion
Currently snacks are mainly fried (chips, straws, etc.), extruded (puffed cornmeal snack) and baked or roasted (nuts, rice cakes, etc.). These processes of dehydration subject the food to high temperatures (usually above 180°C). Although they are suitable for generating porous and rigid structures and crunchy textures in potato or cereal snacks, they do not preserve the nutritional values, scents, colours and flavours of the original fresh materials. Furthermore, the fat content of fried products is high2,3, around 30–35%.
What are the options for the production of crunchy textures at temperatures that would reduce the loss of the nutritional and organoleptic qualities of the product?
To obtain an appropriate expansion, the evaporation of water should be fast. Such abrupt evaporation is achieved by the very rapid heating and/or pressure reduction kinetics. To preserve the colour and nutritional profile of the food, dehydration should occur at low temperatures (preferably below 60–70°C, depending on the composition of the food) or, if higher temperatures are used, the system employed should be very efficient, with a very short processing time.
Vacuum frying gives the snacks an attractive appearance, with bright colours and porous structures. The crunchy texture is generally adequate, although it might be slightly plastic due to the absorbed oil. This technology, in combination with subsequent de-oiling, delivers products with a fat content of around 10%.
In the search for an alternative to frying, dehydration techniques using hot air systems have been developed, where the product remains in a fluid bed for a short time. These systems are currently used to expand the pellets made of potato flour and various cereals. The efficiency of the process depends on the product remaining suspended in the fluid bed; this is associated with certain requirements of shape, size and weight of the food matrix to be expanded.
Lyophilisation provides the dehydrated products with a very good sensory quality. Since the kinetics of drying is low, the material does not expand, but neither does it shrink as it would do during slow drying in the air. The food dehydrates while frozen and the stiffness of the frozen structure prevents shrinkage. Freezedried products are known for their attractive appearance. They also have a pleasant texture, which, although is more brittle than crisp, fits well with the concept of a crunchy snack. However, the lyophilisation process is expensive, which is reflected in the price of the final product.
Microwave texturing is another option for obtaining crunchy textures. Microwaves excite the water molecules throughout the volume of the food, and this vibrational movement increases the temperature. At a suitable power density, the water heats rapidly, and the desired vapour is generated, causing fast expansion of the product.
DIC technology uses a very fast decompression stage after thermal pre-treatment, usually with saturated steam (typically at between 1 and 8 bar). The desired temperature and pressure is achieved within a few seconds. After this treatment (generally less than 1 min), a very rapid (some hundredths of a second) pressure drop is induced. This causes an instantaneous evaporation of the water and a change in the microstructure of the product, as well as its cooling.
Ingredients most commonly used for preparing expanded snacks
A large variety of ingredients is currently used for the production of snacks. The process used depends on the type of ingredients. Selection of these ingredients depends on the process used. In the expansion processing, the most used ingredients are cereals, particularly maize, wheat and rice. The germ of these grains (and other particles) is excluded; only starch is used. In general, starches with an amylose content of 5–20% improve the expan sion and the texture of the expanded food4.
Cornmeal comes in different grain sizes: fine for obtaining products with a fine texture and soft bite, and in larger grain sizes for a crunchy texture. Corn starch granules are of medium size (5–20µm) and have very good expansion properties. The function of starch is to generate different textures that can be modified by changing the ratio of amylose to amylopectin. Starches with high amylose content are used when a hard and crunchy texture is desired. However, to enhance the expansion starches with high amylopectin content are used (waxy starch).
Wheat can be classified into two types: hard and soft. Durum wheat is rich in protein and produces strong flours, suitable for making bread. Common wheat contains less protein and is more suitable for general baking. In the snack industry wheat is used for baked or fried snacks, flavoured biscuits, rolls, etc.
Wheat starch granules are quite large (20–40µm) in comparison with other cereal granules. On average, they contain 20–25% amylose, giving a good expansion during extrusion. Wheat has a higher protein content than other cereals, which can reduce expansion due to the presence of gluten. However, gluten provides high nutritional value as well as crunchiness and texture.
Rice is more expensive than other cereals and is not often used in the manufacture of snacks.
The rice starch grains are small (2–8µm) and are easily digested. Their technological properties are very different from those of wheat or corn, especially in terms of the amylose–amylopectin ratio.
The physicochemical properties of rice starch differ depending on the variety of rice. For example, the long grain varieties (containing 22–23% amylose) can increase the snack crunchiness while the waxy rice flour (containing <1% amylose) provides a more creamy texture. The rice is also used as a vehicle for other flavours as it has a neutral taste and requires high temperatures to be cooked during extrusion.
In addition, ‘chips’ made from 100% rice starch have the nutritional advantage of absorbing 20–30% less oil during frying than other types of chips.
The potato is used in several different forms as an ingredient in snacks (granules, flakes, flours and starches). Potato starch is generally used to provide extra expansion. This starch contains 20–25% amylose and has a low fat content. It requires low cooking temperatures since the granules are easily degraded.
Tapioca granules vary greatly in shape and size (5–35µm) and have an amylose content of 17%. The grains develop a very high viscosity and are a highly potent cohesion agent. Tapioca also provides a neutral taste, is low in calories and requires moderate temperatures during cooking.
Recently, given the trends discussed above, new raw materials and ingredients have been introduced in the snack sector to develop new, innovative products. These products are designed to meet the demand of consumers concerned about their health (favouring low fat, high protein, lack of preservatives or additives, etc.), convenience (ration packs) and the environment (ecology).
Ingredients for innovative snacks
Some new sources of raw materials suitable for the expansion and development of innovative snacks are:
Fruit and vegetables
Owing to their nutritional and sensory profiles, fruit and vegetables are an ideal source for developing natural, convenient and healthy snacks. Such snacks can be produced without additives, using ecological raw materials. Vegetable snacks are increasingly becoming a healthy alternative to the more traditional products. Over the last three years these innovative fruit and vegetable snacks have outperformed the new potato snacks.
Millet, buckwheat, quinoa, chia seed and amaranth seed are gluten-free ingredients suitable for celiac disease sufferers. They are also a rich source of protein. The application of these grains in snacks is still under development. Some of these grains, such as amaranth, show good expansion properties during dehydration.
Pulses are another source of protein and gluten-free raw materials, which have been recently used to improve the nutritional profile of low-fat snacks. The starch of legumes (lentils, chickpeas, beans, etc.) has potential as an ingredient of expanded snacks. The optimisation of the expansion processes of this ingredient is still in progress. The consumer perception of the products containing pulse starches is also under examination.
Meat snacks are becoming increasingly popular with consumers looking for convenient high protein sustenance. Most of the nutritional properties of meat – particularly its protein content – remain unchanged by drying. However, the animal fat is prone to oxidation. Therefore, it is advisable to use lean meat (i.e., chicken, beef and buffalo), to obtain high-protein and ‘low/no/reduced fat’ products5.
There are other raw materials with high potential for the healthy snack industry. However, it is still necessary to research the processes that mask the flavour, as in the case of fish and by-products of food processing (fruit fibres). Insects are another new, environmentally friendly, alternative source of protein. However, research into the applications of this material is still in its infancy. In this field, it is not only necessary to develop the appropriate processing methods but also affect the cultural and perceptual changes among consumers6.
One of the main lines of research in AZTI is the development of formulas and dehydration processes for texturing these new ingredients. Our aim is simple: to develop new healthy snacks, with original textures; that are convenient for consumers; and employ environmentally friendly methods.
- Eat Tendencias by AZTI, https://issuu.com/aztitecnalia/docs/eatendencias2016_by_azti, (visited 15th June 2016)
- Mintel GNPD. Healthy Snack Trends, 2014
- Mintel GNPD. Health and Wellness, Focus on Snacking, 2015
- Hui, Y.H. Handbook of Food Science, Technology, and Engineering, Taylor & Francis, 2006
- Mintel GNPD. Meat snacks targeting the sports occasion, 2016
- Nielsen, Snack attack what consumers are reaching for around the world, 2014.