关键词：
Douchi fermentation;GC-TOF/MS;metabolic characterization;orthogonal partial least squares-discriminant analysis;principal components analysis
摘要：
Intensive study of the metabolome during the Douchi fermentation can provide new knowledge for optimizing the fermentation process. In this work, the metabolic characterization throughout the fermentation of Mucor racemosus Douchi was investigated using gas chromatography with time-of-flight mass spectrometry. A total of 511 peaks were found, and 114 metabolites were identified. The fermentation process was clearly distinguished into two main phases by principal components analysis and orthogonal partial least squares-discriminant analysis. All the samples in the score plots were within the 95% Hotelling T (2) ellipse. Two separated clusters can be seen clearly in the score plot, which represents the two stages of fermentation: koji-making (within 48 hr) and postfermentation (after 48 hr). Besides, clear separation and discrimination by both methods were found among different fermentation time within 15 days, while the discrimination cannot be found with more than 15 days of fermentation, indicating that the fermentation of Douchi was finished in 15 days. Due to the synergistic effect of protease and hydrolase accumulated in the early stage, proteins and other big molecular substances are rapidly hydrolyzed into a large number of small molecule components. However, the activity of enzymes decreased with the further fermentation, and some free amino acids were consumed in Maillard reaction. Therefore, there was no significant change in the content of small molecular substances after 15 days of fermentation. Furthermore, the levels of some metabolites such as alanine and lysine involved in the fermentation varied significantly throughout the processes. This study provides new insights for the metabolomics characteristics of Douchi fermentation.
摘要：
It is difficult to produce southern stinky tofu, a famous traditional Chinese snack, at industry scale due to the complex composition of its brine. In this study, the fingerprints of organic volatile flavor compounds in the southern stinky tofu brine samples from five manufacturers were studied using headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) with the aid of chemometric methods. The fingerprints were obtained by HS-SPME/GC-MS and analyzed with the time shift alignment method, Shannon entropy, correlation coefficient, and principal component analysis. The results show that the time shifts in the samples can be accurately corrected by the time shift alignment method despite unexpected interferences. The fingerprint information was evaluated by Shannon entropy, while the similarities and differences in the fingerprints were investigated by correlation coefficient. Moreover, the identification of stinky tofu manufacturers can be achieved by principal component analysis. The predominant volatile compounds in southern stinky tofu brines were indole, 3-methylindole, phenol, and 4-methylphenol. Therefore, the established fingerprinting of volatile compounds for the brines by combining HS-SPME/GC-MS with chemometric methods was a simple and reliable method.
作者机构：
[郭红英; 姚荷; 刘楚岑; 王锋; 周红丽; 谭兴和; 刘宗敏] College of Food Science and Technology, Hunan Agricultural University, Changsha, 410128, China;[严钦武; 徐永兵] Hunan Chaqi Vegetables Industry Co. Ltd., Yueyang, 414000, China;[王栏树] Hunan Jiayan Food Co. Ltd., Changsha, 410000, China
关键词：
植物乳杆菌;发酵;萝卜干;亚硝酸盐;品质
摘要：
为加快发酵速率,降低产品亚硝酸盐含量,并提高产品品质,本研究以萝卜干为原料,分别接种植物乳杆菌L4(Lactobacillus plantarum L4)和植物乳杆菌B5(L. plantarum B5),并以自然发酵为对照,萝卜干发酵时间为56 d,研究L4和B5对萝卜干品质的影响。结果表明:L4、B5和自然发酵pH值降低的速率依次为: L4>B5>自然发酵。亚硝酸盐含量随着发酵时间的延长先增加后减小,其中L4发酵在22 d左右出现亚硝酸盐峰,峰值为(3.23±0.17)mg/kg,B5和自然发酵在33 d左右出现亚硝酸盐峰,峰值分别为(2.04±0.12)mg/kg和(3.79±0.25)mg/kg(P<0.05)。挥发酯含量、游离氨基酸含量都随着发酵时间的延长呈上升趋势。L*、b*随着发酵时间的延长呈下降趋势,而a*随着发酵时间的延长呈上升趋势。发酵结束时,L4、B5和自然发酵感官评分别为88.7±2.56、81.8±1.49和74.1±3.88。由此表明,植物乳杆菌L4和B5可以缩短萝卜干的发酵周期,提高萝卜干安全性和品质,其中L4表现比B5好。
通讯机构：
College of Food Science and Technology, Hunan Agricultural University, Changsha, China
关键词：
内生细菌;发酵;菌种鉴定;保鲜;辣椒
摘要：
从辣椒果实中分离、筛选出了一株对辣椒炭疽病菌具有拮抗作用的内生细菌P5,通过菌体、菌落形态观察、生理生化测定及16S r DNA序列分析,鉴定P5为枯草芽孢杆菌。以辣椒炭疽病作为指示菌,测定其发酵滤液理化性质。用发酵滤液处理辣椒进行采后保鲜研究,测定品质指标:质量损失率、腐烂率、可滴定酸含量、Vc含量、总糖含量、叶绿素含量等品质指标。结果表明,发酵滤液热稳定性良好,在p H 8.0以下,40100℃范围内,抑菌活性稳定无变化,121℃处理30 min活性有所下降,为对照组的85%;对p H稳定,在室温下,p H 2.012范围内,抑菌活性不发生变化;对紫外线稳定,经紫外光照射12 h,其活性仍为对照的89.87%。发酵滤液处理过的辣椒保鲜效果明显优于无菌水对照组,显著降低了辣椒失重率和腐烂率,并有效抑制了果实中可滴定酸、Vc、总糖、叶绿素等含量的减少,对辣椒有显著的保鲜效果。
作者机构：
[程远渡; 易有金; 夏菠; 周红丽; 曹熙; 罗程印] Hunan Provincial Key Laboratory of Food Science and Biotechnology, College of Food Science and Technology, Hunan Agricultural University, Changsha, 410128, China
