Yogurt is the most popular fermented milk product in the world, and its consumption has increased due to consumer concern for healthier foods. Although yogurt is an alternative to preserving milk, its shelf life is still short compared to other dairy products such as some types of cheese, and its nutritional value also makes this product suitable for the growth of some spoilage microorganisms.
In dairy production, drying is usually associated with the maintenance of live microorganisms and various drying methods are used, such as fluidized bed, vacuum, convective drying, blown bed, and microwave processes. However, freeze-drying and spray-drying are identified as the most efficient methods that lead to good-quality products. In this context, drying is introduced as a process to preserve yogurt. freeze drying and spray drying are the most used drying processes due to maintaining the sensory and nutritional characteristics of the product.
Drying process
Freeze-drying
Freeze-drying involves the sublimation of water from a frozen product under reduced pressure (vacuum) at temperatures typically below 30°C, resulting in a product with a moisture-free porous structure that can be reconstituted by adding water. However, this process keeps the sensory, biological, and nutritional characteristics of the dried product close to those of the fresh product. High costs of the process are a major drawback of freeze drying, so spray drying can be a lower-cost alternative to freeze drying.
Spray drying
In a spray dryer, the transformation of fluid products into dried particles through a centrifugal or high-pressure system occurs, so that the very fine droplets immediately encounter a stream of hot air, resulting in the immediate evaporation of water and preventing thermal effects that endanger biological and sensory properties.
Drying with a spray dryer and freeze dryer to produce yogurt powder helps preserve yogurt for a long time and facilitates its transportation and storage without the need for a refrigerator. Freeze drying has the advantage of preserving the microflora of yogurt because this process is done at low temperatures.
Yogurt powder has a shelf life of one to two years in a dry and temperate place, which makes it easier to transport and store than fresh yogurt.
Yogurt powder application
Yogurt powder can be used as a substitute for fresh yogurt for drinks and dips. The taste of this product is sour and like yogurt, which is used in many products that we are not able to use fresh yogurt. For example, confectionery coatings, dairy drinks, and nutritious snacks such as protein bars, dried fruits, and cereals can be made from yogurt which is made of yogurt powder. Yogurt powder creates a sour and yogurt-like flavor that appeals to yogurt consumers. It can also be used in powder drink mixes in which the taste and sourness of yogurt are desired. In addition, it can replace powder milk in the formulation, thus increasing the nutritional value and functional properties of these products.
Packaging and stability of yogurt powder
During the storage of yogurt powder, oxygen content, temperature, pH, water activity and high solute concentration can affect the survival of microorganisms. Various studies have shown that temperature is an important parameter for the survival of bacteria during storage. In one study, it was shown that the stability of spray-dried samples decreased during storage, and low storage temperature contributed to higher survival rates.
The main purpose of yogurt powder production is to keep the product stable and easy to use. Yogurt powder is becoming an interesting dairy ingredient for a wide variety of food applications due to its unique taste and nutrients. Yogurt powder is produced by fermenting skim milk using yogurt culture with the usual yogurt starter cultures (Lactobacillus and Streptococcus) until reaching the desired pH and then drying it. Mixed yogurt powder may contain other cultured dairy products such as fermented whey, whey protein concentrate, nonfat milk powder, whey powder, lactic acid, and natural/artificial flavors. The difference between yogurt powder and yogurt mix powder in terms of taste and functional properties depends on the starter culture and the pH of the yogurt before drying.
Commercial yogurt powder contains 3-5% moisture, 1-2% fat, 33-36% protein, 51.5-50% lactose, and 7-8% ash.
Currently, yogurt powder is commercially produced using the spray drying method, but some factors should be considered. First, yogurt concentration should be done at 50-60°C before drying. Second, the drying conditions must be balanced to ensure the number of viable cells in the yogurt culture. The number of lactobacilli in commercial yogurt powder is 7×105 CFU/g.
Reference:
Santos, G.D., Nunes, T.P., Silva, M.A.A.P., Rosenthal, A. and Pagani, A.A.C., 2018. Development and acceptance of freeze-dried yogurt” powder yogurt“. International Food Research Journal, 25(3), pp.1159-1165.
Santos, G.D., Nogueira, R.I. and Rosenthal, A., 2018. Powdered yoghurt produced by spray drying and freeze drying: a review. Brazilian Journal of Food Technology, 21. DOI: 1590/1981-6723.12716
