Abstract
This study aimed to evaluate the physical-chemical characteristics and the viability of lactic acid bacteria during the fermentation process of the yogurt and after the freeze-dried process, in addition to testing three thickener formulations for the rehydration of the yogurt powder. During the fermentation process, the production of lactic acid and the growth of lactic acid bacteria were accompanied. Before and after freeze-dried process, yogurt was analyzed for pH, titratable acidity, carbohydrates, proteins, lipids and viable lactic acid bacteria. After lyophilization, three thickener formulations were tested to evaluate the rehydration of powdered yogurt. At the end of the fermentation process, it was verified that the lactic acid bacteria grew to reach 7.8.107 UFC.g-1 and the acidity obtained was 9.27 g.L-1. The viable lactic acid bacteria count of freeze-dried and non-freeze-dried yogurt was 5.6.107 CFU.g-1 and 7.8.107 CFU.g-1, respectively. Non-freeze-dried and freeze-dried yogurts showed a content of 20.8% and 21.0% carbohydrates, 4.0% and 3.6% protein and 3.7% and 2.7% lipids, respectively. The combination of thickeners that provided viscosity similar to commercial yogurts was the guar gum, pectin and maltodextrin mix. Thus, it was possible to verify that the freeze-drying process maintains the physical-chemical characteristics and viability of lactic acid bacteria. In addition, the developed yogurt presented easy reconstitution at the time of consumption.
Highlights
The knowledge of the beneficial effects of dairy products allows the production of a range of yogurts with different flavors, textures, and consistencies in response to consumer preferences (Morell et al, 2015)
According to the Codex Alimentarius Commission (FAO/WHO, 2011), yogurt is defined as a fermented milk with symbiotic yeasts of lactic bacteria such as Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus, which must remain viable in the product until the end of its useful life
The yogurt is rich in protein, calcium, phosphorus and vitamins and lactic acid bacteria present may exert beneficial effects to the organism (Saad, 2006)
Summary
The knowledge of the beneficial effects of dairy products allows the production of a range of yogurts with different flavors, textures, and consistencies in response to consumer preferences (Morell et al, 2015). The lactic bacteria incorporated into milk are responsible for the acidification of the product until it reaches pH close to 4.0, necessary to avoid the development of undesirable bacteria, to provide specific sensorial characteristics, by modifying flavor, texture, aroma and protein content (Dias & Pulzatto, 2009; Piard et al, 2011). To preserve the nutritional characteristics of the yogurt and to keep the lactic acid bacteria viable, the drying process can be applied by freeze-dried. According to Mata et al (2005) and Yamaguchi et al (2017), the freeze-dried process comprises the removal of water from the product by sublimation, allowing the maintenance of biological, nutritional and sensory characteristics similar to its matrix. The objective of this study was to evaluate the physical-chemical characteristics and the viability of lactic acid bacteria during the fermentation process of the yogurt and after the freeze-dried process, in addition to testing three thickener formulations for the rehydration of the yogurt powder
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