Effects of using natural and artificial sweeteners with sucrose on product quality of fruit kefir

In this study, kefir was produced using commercial kefir culture, functionally enriched with freeze-dried strawberry tree fruit (Arbutus unedo L.) and tamarind (Tamarindicus indica L.) fruits and sweetened with stevia, monk fruit sweetener (Siraitia grosvenorii), aspartame and sucrose (sugar beet and cane sugar). Some physical, chemical, microbiological and sensory properties of kefir samples were investigated on various days of storage. The pH values of kefir samples that 3% and 4% freeze-dried and ground fruits were added were lower than plain kefir (K1) on each day of storage. The highest serum separation was detected in the control sample during storage, while the addition of sweeteners did not cause a significant difference in the samples (P > 0.05). The highest dry matter contents were determined in samples containing 5% sucrose. However, no significant differences was found in viscosity and hardness values. L*, a*, b* values of fruity and plain samples differed significantly (P < 0.05). It was determined that the fruits was the main source of phenolic components in kefir samples. Only gallic acid, protocatechuic acid, salicylic acid and caffeic acid were detected in the control sample. Among the 32 phenolic compounds investigated, 15 of them were detected at different levels in the samples. Gallic acid was the main phenolic component of kefir with A. unedo, while syringic acid and salicylic acid were determined at the highest levels in samples with tamarind. All essential amino acids were detected in plain and fruit kefir samples. Among the 42 investigated amino acids and their derivatives, 31 were detected in kefir samples. L-glutamic acid was the major amino acid in the plain control sample, and the amino acid found at the highest level is L-proline detected in kefir samples with tamarind. Acetaldehyde, diacetyl and acetoin in the samples decreased significantly on the 21st day of the storage, but an increase was observed in the amount of ethanol. Components added to kefir did not significantly effect the amounts of ethanol and acetoin (P > 0.05), but had different effects on lactic acid bacteria and yeast growth. Kefir and fruit samples showed antimicrobial activity against Bacillus cereus, Staphylococcus aureus and Escherichia coli. The samples containing tamarind, aspartame and cane sugar received the highest tastes-aroma and general acceptability scores. The highest metallic taste was detected in samples added stevia.