Screening And Identification Of Acid Reducing Yeast Strains From Wild Berries And Their Characteristics Of Organic Acid Degradation

Wild berries are rich in nutrients,in which anthocyanins,flavonoids,polyphenols and organic acids are the main components.However,the content of organic acids is usually high,which affects the taste of products and limits the market.The main wild berries are Rubus idaeus,Lonicera edulis,Hippophae rhamnoides,Schisandra chinensis,Actinidia arguta and Vitis amurensis.The main organic acids are malic acid,citric acid and tartaric acid.The organic acid content in wild berries can be effectively degraded by biological acid reducing method,so as to improve the product quality and meet the market demand.Yeast strains A3 and B5,which can degrade malic acid,citric acid and tartaric acid,were screened from wild berries Rubus idaeus,Lonicera edulis,Hippophae rhamnoides subsp.Sinensis Rousi,Schisandra chinensis and Vitis amurensis.The growth and physicochemical tolerance of acid reducing strains were determined,and the content of organic acids in wild berries was determined by high performance liquid chromatography(HPLC),so that yeast can degrade organic acids in fruits.This method can be more widely used in wild berry products in the future.The specific conclusions are as follows:(1)Screening and identification of acid reducing yeast strains.Strains A3 and B5 were screened from wild Rubus idaeus and Lonicera edulis by acid reducing rate,and their acid reducing effect was analyzed.The strains were identified by 26S r DNA.The results showed that:according to the acid-base titration method,the acid reducing rates of strain A3 and B5 to malic acid,citric acid and tartaric acid were 29.76±0.08%?29.67±0.12%?7.42±0.04%and42.60±0.10%?18.28±0.15%?13.09±0.07%respectively;the mass concentrations of three main organic acids in wild berries decreased gradually within 5 days,especially malic acid and citric acid.A3 and B5 were identified as Hanseniaspora uvarum and Zygosasaccharomyces bisporus,respectively.The results showed that yeast strains A3 and B5 played an important role in microbial degradation of organic acids.(2)Study on the growth and acid reducing characteristics of acid reducing yeast strain.The growth curves of acid reducing yeast strains A3 and B5 were determined to study the optimal culture time,inoculation amount,growth temperature,growth speed and tolerance to glucose,organic acid,alcohol and SO₂.The results showed that the optimal culture time of strain A3 and B5 were 20?28 h,the optimal inoculum size were 3%and 2%,the optimal growth temperature and rotation speed were 30?,150 r/min,the tolerance to glucose and organic acid concentration were 250 g/L and 25 g/L,the tolerance to alcohol was 18%vol,and the tolerance to SO₂ concentration were 500 mg/L and 400 mg/L,respectively.Through the determination of the growth and acid reducing characteristics of acid reducing yeast strains A3 and B5,we can determine the most suitable conditions for the growth of strains,so as to enhance the potential of acid reducing strains in the field of wild berry products.(3)Study on the acid reducing effect of acid reducing yeast strain on wild berry juice.The two selected acid reducing yeast strains were inoculated into the juice of Rubus idaeus,Lonicera edulis,Hippophae rhamnoides,Schisandra chinensis and Vitis amurensis,respectively.The acid reducing rate and sensory evaluation of the five wild berries were determined by high performance liquid chromatography(HPLC).The results show that the separation of organic acid mixed standard solution is good,and it almost corresponds to the peak time of main organic acids in the sample.The content of citric acid in Rubus idaeus and Schisandra chinensis was higher than that in other two organic acids,the content of malic acid in Lonicera edulis and Hippophae rhamnoides was higher than that in other two organic acids,the content of tartaric acid in Vitis amurensis was very high,and no tartaric acid was detected in Hippophae rhamnoides and Schisandra chinensis.After adding acid reducing strains A3 and B5 respectively,the peak areas of the three main organic acids decreased to varying degrees compared with the corresponding samples before acid reducing,and malic acid and citric acid were the most obvious.It can be seen that the degradation effect of yeast strains A3 and B5 on malic acid and citric acid in wild berries was the best,and tartaric acid was also slightly degraded.According to the linear regression equation,the acid reduction rates of malic acid,citric acid and tartaric acid were 27.35±0.05%,28.14±0.03%and 7.03±0.25%respectively before and after adding A3to Rubus idaeus,Lonicera edulis,Hippophae rhamnoides,Schisandra chinensis and Vitis amurensis 30.13±0.13%,18.11±0.07%,12.94±0.09%,36.57±0.05%,9.59±0.10%,0%,26.31±0.17%,25.42±0.04%,0%,36.62±0.08%,24.62±0.03%,5.13±0.02%;After B5was added,the acid reduction rates of malic acid,citric acid and tartaric acid were 31.36±0.06%,26.11±0.02%,7.15±0.03%,36.47±0.26%,17.33±0.02%,11.57±0.17%,40.31±0.10%,16.98±0.30%,0%respectively 32.69±0.26%,19.93±0.01%,0%,31.19±0.12%,21.88±0.03%,9.25±0.05%;Sensory evaluation showed that Rubus idaeus and Lonicera edulis juice were the most popular,followed by Hippophae rhamnoides and Schisandra chinensis,and Vitis amurensis juice was the lowest.The comprehensive results showed that strain A3 and B5 had obvious acid reducing ability,and could effectively alleviate the sour taste of wild berries,so as to improve the quality of wild berries after biological acid reducing.