Chemical composition and sensory analysis of cheese whey-based beverages using kefir grains as starter culture : Chemical and sensory analysis of CW-based kefir beverages

Cheese whey, the main dairy by-product, is increasingly recognized as a source of many bioactive valuable compounds. Nevertheless, the most abundant component in whey is lactose (ca. 5% w/v), which represents a significant environmental problem. Due to the large lactose surplus generated, its conversion to bio-ethanol has long been considered as a possible solution for whey bioremediation. In this review, fermentation of lactose to ethanol is discussed, focusing on wild lactose-fermenting yeasts, particularly Kluyveromyces marxianus, and recombinant Saccharomyces cerevisiae strains. The early efforts in the screening and characterization of the fermentation properties of wild lactose-consuming yeasts are reviewed. Furthermore, emphasis is given on the latter advances in engineering S. cerevisiae strains for efficient whey-to-ethanol bioprocesses. Examples of industrial implementation are briefly discussed, illustrating the viability of whey-to-ethanol systems. Current developments on strain engineering together with the growing market for biofuels will likely boost the industrial interest in such processes.

In an investigation of the changes in the microflora along the pathway: kefir grains (A)-->kefir made from kefir grains (B)-->kefir made from kefir as inoculum (C), the following species of lactic acid bacteria (83-90%) of the microbial count in the grains) were identified: Lactococcus lactis subsp. lactis, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus helveticus, Lactobacillus casei subsp. pseudoplantarum and Lactobacillus brevis. Yeasts (10-17%) identified were Kluyveromyces marxianus var. lactis, Saccharomyces cerevisiae, Candida inconspicua and Candida maris. In the microbial population of kefir grains and kefir made from them the homofermentative lactic streptococci (52-65% and 79-86%, respectively) predominated. Within the group of lactobacilli, the homofermentative thermophilic species L. delbrueckii subsp. bulgaricus and L. helveticus (70-87% of the isolated bacilli) predominated. Along the pathway A-->B-->C, the streptococcal proportion in the total kefir microflora increased by 26-30% whereas the lactobacilli decreased by 13-23%. K. marxianus var. lactis was permanently present in kefir grains and kefirs, whereas the dominant lactose-negative yeast in the total yeast flora of the kefir grains dramatically decreased in kefir C.

An extract from a dry young wine from Maccabeo was studied by aroma extract dilution analysis (AEDA), quantitative gas chromatography, and different sensory studies. In a first study, 53 different aroma compounds were quantified and used to prepare aroma models. 2-Methyl-3-furanthiol (FD = 16) and 4-methyl-4-mercaptopentan-2-one (FD = 2), could not be quantified and were not included in those models, which were not very similar to the original wine. Omission tests did not show the existence of impact compounds. In another set of experiments, selected aroma chemicals were added to the original wine, but in only in two cases (isoamyl acetate and gamma-nonalactone) was a positive effect noted, on banana and citric notes, respectively. After these discouraging results, 4-methyl-4-mercaptopentan-2-one and 2-methyl-3-furanthiol were quantified and included in the models. The concentration of the former was as low as 5 ng x L(-)(1) (odor threshold = 0.8 ng x L(-)(1)); however, its inclusion in the synthetic mixture had a significant effect, making it very close to the original wine. Its role was confirmed by omission tests. Results are briefly discussed.