# Techno-Functional Properties and Recent Advances in the Manufacturing of Whey Beverages: A Review
## 4. Whey-Based Beverages
### Fermented Whey-Based Beverages
The microorganisms present in kefir starter culture include _Lactobacillus kefiranofaciens_, _Lentilactobacillus kefiri_, _Lentilactobacillus parakefiri_, _Lactococcus lactis_, _Kluyveromyces marxianus_, _Saccharomyces unisporus_, and _Saccharomyces cerevisiae_. The research conducted by [PERSON] et al. [67] established that the ideal fermentation temperature for kefir starter culture is 20 \({}^{\circ}\)C. At elevated temperatures, notably 30 \({}^{\circ}\)C and 37 \({}^{\circ}\)C, the growth rate diminished, and the morphology of the kefir grains altered. Despite fermented milk, fermented whey exhibited a reduced quantity of lactic acid bacteria and an elevated quantity of yeasts. The microbial composition of the fermented whey beverage was examined in the study by [PERSON] et al. [71]. The most abundant microorganisms were yeasts _Kluyveromyces marxianus_, _Saccharomyces cerevisiae_, and _Kazachstania unispora_, along with bacteria of the _Lactobacillus_ genus. This combination of microorganisms means that kefir-fermented whey beverages can be classified as probiotics. The effect of fermentation temperature (20-30 \({}^{\circ}\)C) and the amount of kefir grains (2-8% \(w/v\)) on the phenolic content and antioxidant activity of fermented whey drinks flavoured with apple juice was investigated in a study by [PERSON] et al. [72]. Using a response surface methodology, the study suggested that the beverage exhibiting the highest antioxidant activity and total phenolic compound content would contain 7.56% (\(w/v\)) kefir grains fermented at a temperature of 24.82 \({}^{\circ}\)C.  
[PERSON] et al. [73] investigated the use of both kefir grains and water kefir grains. The study compared the physicochemical, rheological, and sensory properties of beverages fermented with either milk kefir grains or water kefir grains, with varying concentrations of carrot juice (65% (\(w/w\)), 75% (\(w/w\)), 85% (\(w/w\)), and 95% (\(w/w\)) of carrot juice). Based on the rheological analysis, a potential influence of whey content on the flow properties of the beverage was observed; however, no significant differences were found between the two starter cultures applied. Similarly, in the sensory analysis, the beverages containing 75% (\(w/w\)) carrot juice were evaluated as the most favourable, regardless of the starter culture used. The use of water kefir grains for the production of fermented whey-based beverages was also explored in a subsequent study performed by [PERSON] et al. [40], where whey-based beverages were flavoured with varying amounts of black currant juice (addition of 10 and 20% \(w/w\) blackcurrant juice). At the same time, the influence of the 0.25% (\(w/w\)) and 0.50% (\(w/w\)) hydrocolloid (furcellaran) addition on the properties of the beverage was monitored using rheology and mechanical vibration damping techniques. It was found that samples containing 0.50% (\(w/w\)) funcllaran exhibited a higher amount of sediment compared to those with 0.25% (\(w/w\)). After 48 h of fermentation, the samples contained 0.92-4.86% (\(v/v\)) ethanol. The study confirmed that all model samples exhibited non-Newtonian behaviour, and the sample containing 20% (\(w/w\)) black currant juice was rated the best.