Evaluating the utilization of organic compounds by certain lactic acid bacteria including starter culture candidates in the cucumber fermentation
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- Tez No: 716348
- Danışmanlar: DR. ILENYS M. PEREZ-DíAZ
- Tez Türü: Yüksek Lisans
- Konular: Gıda Mühendisliği, Food Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2018
- Dil: İngilizce
- Üniversite: North Carolina State University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 153
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Özet (Çeviri)
Carbohydrate utilization by lactic acid bacteria (LAB), defines the extent of cucumber fermentations, quality and long-term stability. Aside from glucose and fructose, alternate energy sources such as citrulline, trehalose, cellobiose, xylose, lyxose, gentiobiose, and furfural were detected in cucumber fermentations using metabolomics. These compounds remain present in cucumber fermentations after glucose and fructose are utilized. We hypothesize the removal of alternate energy sources by starter cultures during the most active period of the bioconversion is to prevent the proliferation of spoilage associated microbes, such as L. buchneri. The content of the alternate energy sources in fresh and fermented cucumbers was corroborated using HPLC. The presence of putative pathways for the utilization of alternate energy sources in the LAB listed above was investigated using the publically available genome sequences and the KEGG Orthology and Integrated Microbial Genomes tools. The ability of starter or adjunct culture candidates, including Lactobacillus plantarum, L. pentosus, L. brevis, L. buchneri and Pediococcus pentosaceous to utilize alternate energy sources in a fermented cucumber juice model system (FCJM) simulating conditions post-fermentation was studied. The influence of oxygen availability and pH on the metabolism of some of the targeted compounds was also studied in FCJM. The metabolic conversion of the targeted substrates was monitored using HPLC analysis as well. While the presence of gentiobiose, cellobiose, and lyxose was unconfirmed in fresh cucumber juice and fermentation cover brines collected on day 3 and 38 of commercial fermentations trehalose and xylose were sporadically detected to 15.5 ± 1.6 and 36 mM in the fresh fruits, respectively, and citrulline was consistently found in fresh cucumbers to 1.6 ± 0.6 mM and in lower concentrations in fermentations. Even though, the putative metabolic potential of the selected LAB to utilize alternate energy sources was clearly delineated by the bioinformatics analysis, limited correlation was found with the phenotypes observed suggesting strain level differentiation for all the species studied. L. plantarum and L. pentosus were able to utilize cellobiose, gentiobiose and trehalose in FCJM, but not citrulline, furfural or xylose. L. brevis was found able to only utilize gentiobiose, xylose and furfural in FCJM at pH 4.7. P. pentosaceous utilized trehalose in FCJM at pH 4.7, and it is still uncertain if this species can utilize the other compounds. L. buchneri was able to utilize all the compounds tested in FCJM and was unique in converting citrulline to ammonia and ornithine in the presence of limiting glucose. The presence of excess glucose in the FCJM prevented the production of the biogenic amine, ornithine by L. buchneri. Additionally, L. plantarum, L. pentosus and L. brevis were able to produce citrulline presumably from arginine in FCJM. Differences were observed in the ability of specific L. plantarum and L. pentosus strains to convert cellobiose or gentiobiose to lactic acid. Inoculation of L. brevis and L. buchneri in a fresh cucumber juice medium (FrCJ) supplemented with 18.25 ± 0.49 mM trehalose, 51.97 ± 1.30 mM xylose, and 4.23 ± 0.61 mM citrulline resulted in a complete removal of the alternate energy sources prior to reaching a pH inhibitory for the fermentation itself (pH 3.3). Inoculation of unsupplemented FrCJ with a tripartite starter culture of L. pentosus, L. brevis and L. buchneri resulted in the removal of citrulline between days 10 and 30 of the fermentation and a stable pH and lactic acid and acetic acid concentrations for 55 days of long-term storage under anaerobiosis. Further studies are needed to determine if the use of a tripartite starter culture can aid in achieving a complete cucumber fermentation that is microbiologically stable as a function of time.
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