Abstract
The effect of the addition of microbial TGase to milk on selected physical properties of the final product and the viability of lactic acid bacteria cultures during storage at 6 °C for 56 days was studied. Three types of set-style yogurt were made with varying parameters. Weekly analyses included the determination of syneresis and water-holding capacity, texture, pH, and the lactic acid bacteria population. Our research has confirmed that mTGase may be used to stabilize yogurts, although the syneresis, the water-holding capacity of yogurts, and the textural features of yogurts were dependent on the step in the production process at which mTGase was added to milk. The presence of mTGase had no relevance with regard to the acidity of yogurts stored under refrigerated conditions. The addition of mTGase had no effect on lactobacilli, but had a variable effect on Streptococcus thermophilus, depending on the duration of enzymatic activity.
Highlights
Lactic acid fermentation is a process that forms the basis for the production of fermented drinks, including yogurts
Analyses included the determination of syneresis and waterholding capacity, texture, pH, and the lactic acid bacteria population
No correlation was seen between the populations of lactic acid bacteria or pH values and the textural attributes that were measured
Summary
Lactic acid fermentation is a process that forms the basis for the production of fermented drinks, including yogurts. The physical and structural properties of the resulting gels are determined by both, process parameters (temperature; time; mechanical factors such as stirring, pumping, and aeration) and changes in milk proteins in the stages preceding and following the fermentation (Lucey, 2004) Each of these factors can contribute to a reduction of the stability of the curd in the finished products. Some investigators recommend heating milk prior to the addition of TGase, because milk may have TGase inhibitors, and heat treatment may improve the reactivity of whey proteins similar to that of milk after termination of mTGase activity for enzyme inhibition (Abou-Soliman et al, 2017; De Jong et al, 2003; Neve et al, 2001) This does not mean, that the enzyme does not subsequently affect the final product. This study was conducted to determine the effect of the addition of microbial TGase to milk, either before fermentation (with or without heat treatment at 80 °C prior to fermentation) or concurrently with the starter culture (immediately prior to fermentation) on selected physical properties of the final product and the viability of starter cultures (S. thermophilus and L. delbrueckii subsp. bulgaricus) during storage at 6 °C for 56 days
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