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Test tube containing an inverted Durham tube resting on top of a 60-mm-long capillary tube so as to increase volume beneath the Durham tube from which gas could be collected.
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Gas production by obligatory heterofermentative lactic acid bacteria such as Paucilactobacillus wasatchensis is a sporadic problem in Cheddar cheese and results in undesired slits and cracks in the cheese. Growth of Pa. wasatchensis is not rapid, which makes investigations of gas production difficult to consistently execute. A primary objective of...
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Context 1
... stock cultures were frozen and stored at −80°C until needed. Working cultures were prepared by inoculating thawed stock solution into MRS+R broth, incubating at 23°C for 72 h, and then diluting to an optical density at 600 nm (OD 600 ) of 1.3, which had been determined to be the OD 600 indicating a cell concentration of 10 9 cfu/ mL (Supplemental Figure S1, https: / / doi .org/ 10 .6084/ m9 .figshare ...
Context 2
... solutions containing 1% (wt/vol) sugars were prepared by adding ribose and galactose to CR-MRS broth at levels of 0.5% ribose + 0.5% galactose, 0.4% ribose + 0.6% galactose, 0.3% ribose + 0.7% galactose, 0.2% ribose + 0.8% galactose, and 0.1% ribose + 0.9% galactose. Half of the test tubes contained a Durham tube (Fisher Scientific) inverted onto a 6-cm-long capillary tube (Drummond Scientific Company; Figure 1) that was added before autoclaving. Test solutions (with and without Durham tubes) were inoculated with Pa. ...
Context 3
... Pa. wasatchensis WDC04 was grown using the GPT, exponential growth was observed through 4-d incubation at 23°C and then slower growth over the next 4 d to an OD ~1.5, followed by a slight decrease (Figure 3). Based on prior correlations of OD 600 , the cell numbers would be predicted to be 10 9 cfu/mL (see Supplemental Figure S1). Gas bubbles were observed in the Durham tube starting on d 6 (Table 2) and at least by d 8, when growth appeared to reach a plateau. ...
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Citations
... It has been reported that class Bacilli was also the dominant bacteria except for producer Streptomyces in oxytetracycline fermentation residue, via clone libraries of 16S rRNA gene ( Liu et al., 2012 ). Species of Bacilli class and Lactobacillaceae family, or evolutionary similar species, had fermentation function ( Green et al., 2021 ). Bins from stored penicillin and erythromycin fermentation residues carried β-lactams and macrolide resistance genes, respectively. ...
Antibiotic fermentation residue (AFR) is nutrient-rich solid waste generated from fermentative antibiotic production process. It is demonstrated that AFR contains high-concentration of remaining antibiotics, and thus may promote antibiotic resistance development in receiving environment or feeding farmed animals. However, the dominate microorganisms and antibiotic resistance genes (ARGs) in AFRs have not been adequately explored, hampering understanding on the potential antibiotic resistance risk development caused by AFRs. Herein, seven kinds of representative AFRs along their production, storage, and treatment processes were collected, and multiple methods including amplicon sequencing, metagenomic sequencing, and bioinformatic approaches were adopted to explore the biological characteristics of AFRs. As expected, antibiotic fermentation producer was found as the predominant species in raw AFRs, which were collected at the outlet of fermentation tanks. However, except for producer species, more environment-derived species persisted in stored AFRs, which were temporarily stored at a semi-open space. Lactobacillus genus, classified as Firmicutes phylum and Bacilli class, became predominant bacterial taxa in stored AFRs, which might attribute to its tolerance to high concentration of antibiotics. Results from metagenomic sequencing together with assembly and binning approaches showed that these newly-colonizing species (e.g., Lactobacillus genus) tended to carry ARGs conferring resistance to the remaining antibiotic. However, after thermal treatment, remaining antibiotic could be efficiently removed from AFRs, and microorganisms together with DNA could be strongly destroyed. In sum, the main risk from the AFRs was the remaining antibiotic, while environment-derived bacteria which tolerate extreme environment, survived in ARFs with high content antibiotics, and may carry ARGs. Thus, hydrothermal or other harmless treatment technologies are recommended to remove antibiotic content and inactivate bacteria before recycling of AFRs in pharmaceutical industry.
... When ribose is present, galactose can be co-utilized for other cellular needs such as cell wall growth (Ortakci et al., 2015a) without any CO 2 being produced while still enabling cell multiplication. In a model system, if all the galactose was consumed before ribose was depleted then gas production was not observed (Green et al., 2021). Rather, gas production was observed after the presence of ribose had promoted growth of Pa. ...
... wasatchensis to high numbers and there was still some galactose remaining. Extensive gas pro-duction appears to occur as the cells transition from exponential growth into a stationary phase (Green et al., 2021). If the same observations apply in cheese then the observed gas production would indicate both growth of Pa.wWDC04 to high numbers and concomitant depletion of ribose in the cheese. ...
Paucilactobacillus wasatchensis can use gluconate (GLCN) as well as galactose as an energy source and because sodium GLCN can be added during salting of Cheddar cheese to reduce calcium lactate crystal formation, our primary objective was to determine if the presence of GLCN in cheese is another risk factor for unwanted gas production leading to slits in cheese. A secondary objective was to calculate the amount of CO2 produced during storage and to relate this to the amount of gas-forming substrate that was utilized. Ribose was added to promote growth of Pa. wasatchensis WDC04 (P.waWDC04) to high numbers during storage. Cheddar cheese was made with lactococcal starter culture with addition of P.waWDC04 on 3 separate occasions. After milling, the curd was divided into six 10-kg portions. To the curd was added (A) salt, or salt plus (B) 0.5% galactose + 0.5% ribose (similar to previous studies), (C) 1% sodium GLCN, (D) 1% sodium GLCN + 0.5% ribose, (E) 2% sodium GLCN, (F) 2% sodium GLCN + 0.5% ribose. A vat of cheese without added P.waWDC04 was made using the same milk and a block of cheese used as an additional control. Cheeses were cut into 900-g pieces, vacuum packaged and stored at 12°C for 16 wk. Each month the bags were examined for gas production and cheese sampled and tested for lactose, galactose and GLCN content, and microbial numbers. In the control cheese, P.waWDC04 remained undetected (i.e.
We compared the effects of two waste-based culture media (M1 and M2) on the technological properties of Lacticaseibacillus paracasei 90 (L90) for its application as a secondary culture in Cremoso cheese. The following parameters were studied at different ripening times: pH (7, 20, and 40 d), microbiological counts, carbohydrates and organic acids (7 and 40 d), moisture, fat, protein and volatile compounds (40 d). The viability and the metabolic performance of the strain in cheeses were also verified along ripening. Lactobacilli counts in experimental cheeses manufactured with L90 were ~8 log CFU/g at 40 d, meanwhile adventitious lactobacilli reached ~4 log CFU/g in the control cheese (made without L90). The levels of lactic acid, citric acid and pyruvic acid were similar among cheeses at 40 d, reaching levels of ~1433 mg/100 g, ~172 mg/100 g, and 7 mg/100 g, respectively. However, the concentration of lactic acid showed numerical differences between experimental and control cheeses. The cheeses made with the adjunct culture showed lower residual galactose (< 588 mg/100 g) in comparison with the control cheese (836 mg/100 g), highlighting the potential of L90 to play a bioprotective role. In the same vein, orotic and hippuric acids were metabolized at different degrees in cheeses made with L90, reaching levels of < 3.7 mg/100 g and < detection limit, respectively, at 40 d. In general, volatile compounds profiles were not negatively affected by the culture media used. On the contrary, the production of key aroma compounds (diacetyl and acetoin) was positively affected by the growth of L90 in these alternative media. The results demonstrated that the L90 strain could be used as an adjunct culture in Cremoso cheese, regardless of the culture media employed for its growth.
Lactic acid bacteria (LAB) comprise a wide range of genera. LAB have been isolated from various sources such as raw and fermented foods, human and animal intestinal tracts, and mucus membranes. LAB also play an important role as a probiotic culture, usually belonging to Lactobacillus, Enterococcus, and Bifidobacteria genera. This chapter summarizes the isolation and identification steps widely used in LAB strains.
Lactobacillus helveticus is a homofermentative, thermophilic starter bacterium commonly used in dairy processing to produce cheese and fermented milk. It is known for enhancing flavor and texture and improving the final products' health benefits. L. helveticus has a number of characteristic features that differentiate it from commonly used starter cultures, including the ability to metabolize galactose, high acidification rate, and strong proteolytic activity. This article aims to review the key features of L. helveticus relevant to the dairy industry, i.e., technological advantages, health effects, current applications, and future trends in dairy fermentation. It provides an overview of the health benefits associated with the consumption of L. helveticus-fermented dairy products, which are enriched in bioactive components. The review covered some important strains, bioactive peptides, and their health advantages. L. helveticus is characterized by strong proteolytic activity that leads to the production of technologically- and physiologically active peptides that contribute to products’ flavor and health benefits. The consumption of L. helveticus-fermented dairy products was shown to contribute bioactive compounds with antimicrobial, antioxidant, antihypertensive, anticarcinogenic, gut-wellness, psychobiotic, and immunostimulatory effects. L. helveticus is, thus, a potential bacterium for use in future starter cultures designed for the production of functional dairy products.
