Changes in antioxidant quantity and bioavailability of sour cherry, black grape and pomegranate juices fermented with water kefir grain

Fermentation is one of the most economic and easy bioprocess widely used for thousands of years in food protection and production of novel functional food products. Dairy products fermented with lactic acid bacterias take the most important place among the fermented foods. Milk kefir is the primary probiotic beverage which is fermented with milk kefir grains or culture. For every passing day new researches and developments coming up interested with positive health effects of kefir and considerable increase in total antioxidant capacity and total phenolic content of milk products after fermentation with kefir grains is demonstrated by several reports. On the other hand, water kefir grains are different kefir cultures that‟s similar with respect to visual characteristics but with different microorganism content. On the other hand, water kefir is produced by water kefir grains fermented in sugar solution. Researches related with water kefir are focused on the microbiological properties of the grain and there is lack of information on its health effects, antioxidant capacity and phenolic profile. Besides there is no study investigating in vitro bioaccesibility of water kefir or fruit juices fermented with water kefir grains. In this study changes in quantity and in vitro bioaccesibility of antioxidants in sour cherry, pomegranate and black grape juices fermented with water kefir grains are investigated. Water kefir was prepared with two sugar concentration as 6% (w/v) and 12% (w/v). Fruit juices were prepared with added sugar as 6% (w/v) and without adding sugar. Fermantation took 72 hours in total and sampled in every 24 hours. By the way, it was aimed to investigate the effect of sugar concentration, fermentation time, and fruit type on total antioxidant capacity, total phenolic and flavonoid content of the samples and in vitro bioaccessibilities. Total antioxidant capacities, total phenolic and flavonoid contents of the samples were determined by spechtrophotometric methods and in vitro bioaccessibility was analyzed by simulated gastrointestinal digestion sistem for oral, gastric and intestinal phases. Also, Layne Eynon method was applied to fruit juices and after 72 hours samples for investigating the amount of consumed sugar during fermentation. As the results of the DPPH assay, values of 6% (w/v) and 12% (w/v) sugar concentration and 0-24-48-72 hours samples of water kefirs are 2.8±0.9, 8.5±1.9, 12.1±1.0, 13.8±1.0, 3.8±0.5, 11.0±1.0, 11.6±0.8, 14.7±2.8 mg TE/100 ml, respectively. Maximum values are obtained on the first day of sugar free sample and on the second day of %6 (w/v) sugary sample of sour cherry kefir. As compared this values with sour cherry juice there is 4% decrease in antioxidant capacity of sugar free sample and 8% decrease of sugary sample. Sugar addition has decreasing effect on the antioxidant capacity of pomegranate kefir. During the fermentation of day xx maximum level of antioxidant capacity is obtained on the first day from sugar free sample and on the second day from sugary sample. When these values are compared with pomegranate juice there are 1% and 6% increases for sugar free and sugary samples, respectively. For grape juices for either sugar free and sugary samples the maximum levels of total antioxidant capacity is obtained on first day. When comparing these values with grape juice there are 13% an 10% increases for sugar free and sugary samples, respectively. As the results of the CUPRAC assay antioxidant capacity of water kefir prepared with 6% (w/v) and 12% (w/v) sugar concentration, values of 0-24-48-72 hours samples are obtained as 12.0±8.2, 30.8±3.4, 46.9±16.4, 49.1±14.0, and 6.9±0.9, 27.3±5.2 401.0±4.5, 60.1±8.6 mg TE/ 100 ml, respectively. When comparing the sugar free and 6% (w/v) sugary samples of fruit kefir; There are decreases in both sugar free and sugary samples of sour cherry kefir. The decrease in antioxidant capacity was 13% when the data for sour cherry juice and maximum value obtained for the samples with sugar was compared and it was found to be 10% when the comparison was done for the samples without sugar addition. There is loss of antioxidant capacity of sugar free and sugary of pomegranate kefirs. For both sugar free and sugary sample of grape kefir maximum antioxidant capacity is obtained on first day and it is improved by sugar adding. When comparing the maximum levels with grape juice for sugar free samples 9%, and for sugary sample 5% increases are obtained. Total phenolic content of water kefir samples is increased by fermentation time and amount of added sugar. Increase in total phenolic content for 6% (w/v) sugar and 12% (w/v) sugar samples are obtained as 110%, 170%, 7% and 65%, 248%, 29%. When comparing the fruit juice kefirs maximum levels with fruit juices, for both sugar free and sugary sour cherry kefir samples there is 7% of decrease in total phenolic content. For pomegarante kefir samples there is increase in both sugar free and sugary kefir. When comparing the maximum levels with pomegranate juice, total phenolic content of sugar free samples 16% and sugary samples 12% increased. For both sugar free and sugary grape kefir samples there is decrease in total phenolic content. When comparing with maximum levels, with sugar free sample 6% and with sugary sample 5% decreases are obtained. Total flavonoid content values of 6% (w/v) and 12% (w/v) sugar concentration of water kefirs, 0-24-48-72 hours samples, are obtained as respectively 7.3±2.4 9.5±1.5, 12.8±0.7, 10.7±3.3, 7.3±1.6, 8.7±2.3, 10.5±4.5, 8.5±3.3 mg KE/ 100 ml. When comparing the fruit juice kefirs maximum levels with fruit juices; for both sugar free and sugary sour cherry kefir samples there is of decrease in total flavonoid content up to third day. When comparing the maximum levels of sugar free and sugary sour cherry samples there is decrease in total flavonoid content as repectively 15% and 13%. When comparing the pomegranate samples with pomagranete juice there is 2% decrease in total flavonoid content for both sugar free and with sugar samples. When comparing the grape kefir sample with grape juice total flavonoid content is reached to maximum level on the second day for the sample with sugar and it is decreased up to third day for sugar free samples. Loss of the total flavonoids are obtained as 18% for sugar free sample and %9 for samples with sugar. On the contrary to water kefir by the fermentation of all sour cherry, pomegranate and grape juice, there is considerable amount of decrease in total flavonoid conte xxi After the in vitro digestion of water, sour cherry, pomegranate and grape kefirs significant amount of loss is obtained in antioxidant capacities. Maximum recovery is provided in %12 (mg/ml) sugary sample of water kefir by CUPRAC assay as 11%, 16%, 18% respectively. By both DPPH and CUPRAC assays three days fermented sugar free sour cherry kefir sample showed the maximum level of antioxidant capacity as 5%, 12%, 19% and 14%, 18%, 25%, repectively. For the pomegranate kefir one day fermented sugar free sample has the maximum recovery of antioxidants by both DPPH and CUPRAC assays as 4%, 7%, 10% and 6%, 10%, 12%, respectively. Grape kefir showed minimum recovery of antioxidant, by the DPPH method it is obtained as 5%, 9%, 10%, respectively. Kefir with 12% (mg/ml) sugar concentration has the maximum phenolic content after the oral, gastric and intestinal digestion. Maximum recovery from sour cherry kefir is obtained with two days fermented sugar free and with sugar samples as 10%, 14%, 16% and 11%, 15%, 22%, respectively. Three days fermented sugary sample of pomegranete kefir also show the good recovery after the digestion as 9%, 16% ve 18% and one day fermented grape samples‟ recovery as 11%, 19%, 12% and 12%, 18%, 18%. After oral, gastric and intestinal digestion maximum total flavonoid content of water kefir is obtained with three days fermented samples with sugar as 46%, 27%, 26%, respectively. Maximum recovery of flavonoid from sour cherry kefir is obtained with three days fermented sugar free and sugary samples as 41%, 33%, 53% and %11, %15, %22 respectively. Three days fermented sample (with sugar) of pomegranate kefir also showed good recovery after the digestion with the values as 20%, 41%, and 39%. Maximum recovery is obtained with three day fermented sugar free and grape samples with sugar as 48 %, 34%, 30% and 37%, 6%, 2%, respectively.