Comparative transcriptomic analysis of the flavor production mechanism in yogurt by traditional starter strains.

The synergistic fermentation of milk by Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus is one of the key factors that determines the quality of yogurt. In this study, the mechanism whereby yogurt flavor compounds are produced by a mixture of S. thermophilus SIT-20.S and L. delbrueckii ssp. bulgaricus SIT-17.B were investigated by examining the flavor production, growth, and gene transcription of these strains. The results showed that yogurt produced by a 10:1 mixture of the aforementioned strains had the highest abundance of acetoin, whereas yogurt produced by a 1:1 mixture had the highest abundance of diacetyl and acetaldehyde. In addition, the growth of S. thermophilus SIT-20.S was enhanced in the 10:1 mixture. Transcriptomic analysis revealed differentially expressed genes in the flavor-compound-related pathways of S. thermophilus SIT-20.S and L. delbrueckii ssp. bulgaricus SIT-17.B in yogurts produced by 10:1 and 1:1 mixtures compared with those produced by either strain alone. Mixed fermentations regulated the expression of genes related to glycolysis, resulting in an increase of pyruvate, which is an important precursor for diacetyl and acetoin synthesis. The gene encoding the acetoin reductase (SIT-20S_orf01454) was decreased in S. thermophilus SIT-20.S, which ensured the accumulation of acetoin. In addition, the gene encoding the acetaldehyde dehydrogenase (SIT-20S_orf00949) was upregulated in S. thermophilus SIT-20.S, and the expression of alcohol dehydrogenase (SIT-20S_orf01479; SIT-17B_orf00943) was downregulated in both strains, maintaining the abundance of acetaldehyde. In addition, the gene encoding the NADH oxidase (SIT-17B_orf00860) in L. delbrueckii ssp. bulgaricus SIT-17.B were upregulated, which promoted the accumulation of diacetyl and acetoin. Overall, we characterized the mechanism by which S. thermophilus and L. delbrueckii ssp. bulgaricus synergistically generated yogurt flavor compounds during their production of yogurt and highlighted the importance of appropriate proportions of fermentation starters for improving the flavor of yogurts.

[Collection, processing and cryopreservation of placental cord blood hematopoietic stem cells].

OBJECTIVE: To establish methods of collection, processing and cryopreservation of placental cord blood units. METHODS: Between July 1997 and July 2000, 3,744 placental cord blood (CB) units were stored in Beijing Cord Blood Bank. All of CB units had been HLA-typed with molecular (sequence specific primer/sequence specific oligonucleotide, SSP/SSO) and serological methods. CB units were collected by trained midwives while the placentas remained in utero. Collected CB units were temporarily stored at room temperature and processed within 18 hours after collection. Depletion of red blood cells was performed using hydroxythyl starch with one time centrifuge. CB units were cryopreserved with DMSO and hydroxythyl starch. RESULTS: The mean volume collected from 3,744 CB units was (93 +/- 22) ml (mean +/- s, range 45-198 ml). The mean total nucleated cell count per unit was 11.2 x 10(8) +/- 5.3 x 10(8) (rang 4.5 x 10(8)-45.1 x 10(8)). After depletion of red blood cells, the mean nucleated cell count was 9.7 x 10(8) +/- 4.6 x 10(8) (rang 3.1 x 10(8)-30.5 x 10(8)) with mean nucleated cell recovery of 79%. Forty CB units were thawed for testing, and trypan blue viability of nucleated cells was 88.2%. The recoveries of CFU-GM and CD34+ cells (ProCOUNT) were 97.6%, 86.4% respectively. CONCLUSION: We have established a CBB, and have shown that our system of the whole procedure and methods is functional for supplying qualified cord blood units in transplantation.

[Study on non-programmed process using dimethyl sulfoxide and hydroxyethyl starch as cryoprotectants in cryopreservation of cord blood hematopoietic cells].

This study was aimed to search for effective cryoprotectants and freezing methods used in cord blood bank (CBB) for cryopreservation of cord blood hematopoietic stem cells. The non-programmed group using 8% final concentration of dimethyl sulfoxide (DMSO) and 5% final concentration hydroxyethyl starch (HES) (molecular weight 120,000) as protectants and group of conventional of programmed controller method using 10% DMSO only as cryoprotectant in cryopreservation of cord blood hematopoietic stem cells were compared. In each of the two groups, 15 cord blood units were used. In non-programmed group, cord blood units put in -80 degrees C refrigerator for 24 hours as a transitional step before deep-freezing in liquid nitrogen, when both of DMSO and HES had been added. The recoveries of the nuclear cells number, the yield of granulocyto-macrophage colony forming units (CFU-GM) and the cells viability in cord blood units before preservation and after thawing were tested for both methods. The results showed that no significant difference was found in above assays between two groups. The clinical application results also showed that hematopoietic engraftment rates after infusion were similar in both groups. It is concluded that the non-programmed method by -80 degrees C refrigerator as a transitional step and using the combined two protectants seems simple in operation and effective in clinical transplantation as well as the conventional programmed method.