ItemPhenotypic and genomic characterization of Klebsiella pneumoniae subsp. pneumoniae and Rahnella inusitata strains reveals no clear association between genetic content and ropy phenotypeLucija Princic, Renato H. Orsi, Nicole H. Martin, Martin Wiedmann, Aljosa Trmcic (Journal of Dairy Science, 2023-10)Ropy defect of pasteurized fluid milk is a type of spoilage which manifests itself by an increased viscosity, slimy body, and string-like flow during pouring. This defect has, among other causes, been attributed to the growth, proliferation and exopolysaccharide production by coliform bacteria, which are most commonly introduced in milk as post-pasteurization contaminants. As we identified both Klebsiella pneumoniae subsp. pneumoniae and Rahnella inusitata that were linked to a ropy defect, the goal of this study was to characterize three K. pneumoniae subsp. pneumoniae strains and two R. inusitata for (i) their ability to grow and cause ropy defect in milk at 6 and 21°C and to (ii) probe the genetic basis for observed ropy phenotype. While all K. pneumoniae subsp. pneumoniae and R. inusitata strains showed net growth of >4 log10 over 48 h in UHT milk at 21°C, only R. inusitata strains displayed growth during 28-day incubation period at 6°C (>6 log10). Two out of three K. pneumoniae subsp. pneumoniae strains were capable of causing the ropy defect in milk at 21°C, as supported by an increase in the viscosity of milk and string-like flow during pouring; these two strains were originally isolated from raw milk. Only one R. inusitata strains was able to cause the ropy defect in milk; this strain was able to cause the defect at both 6 and 21°C, and was originally isolated from a pasteurized milk. These findings suggest that the potential of K. pneumoniae subsp. pneumoniae and R. inusitata to cause ropy defect in milk is a strain-dependent characteristic. Comparative genomics provided no definitive answer on genetic basis for the ropy phenotype. However, for K. pneumoniae subsp. pneumoniae, genes rffG, rffH, rfbD, and rfbC involved in biosynthesis and secretion of enterobacterial common antigen (ECA) could only be found in the two strains that produced ropy defect, and for R. inusitata a set of two glycosyltransferase and flippase genes involved in nucleotide sugar biosynthesis and export could only be identified in the ropy strain. While these results provide some initial information for potential markers for strains that can cause ropy milk, the relationship between genetic content and ropiness in milk remains poorly understood and merits further investigation. ItemLeveraging milk permeate fermentation to produce lactose-free, low-in-glucose, galactose-rich bioproducts: optimizations and applicationsRivera Flores, Viviana K.; Fan, Xingrui; DeMarsh, Timothy A.; deRiancho, Dana L.; Alcaine, Samuel D. (2023-07-29)Previous studies have highlighted Brettanomyces claussenii OYL-201 as a versatile yeast that can produce ethanol or acetic acid from lactose or selectively metabolize glucose while leaving behind galactose, depending on a variety of operational conditions. This flexibility enables the production of multiple galactose-rich bioproducts from liquid dairy residues. The purpose of this study is two-fold: (i) optimize this partial anaerobic fermentation of milk permeate (MP) by B. claussenii to maximize the yields of galactose and ethanol and minimize leftover glucose, and (ii) combine this optimized process with distillation and freeze-drying to characterize multiple products resulting from this approach. To achieve this, response surface methodology via central composite design was used to create the optimization models. Three fermentation parameters were chosen as input factors: temperature (25°C - 35°C), inoculation level (7.0 - 8.5 log cfu/mL), and time (4 – 40 days), with three metabolites as responses: galactose, glucose, and ethanol. The optimal combination of parameters found was temperature, 28°C; inoculation level, 7.6 log cfu/mL; and time, 33 days. These were used to run an 18-L fermentation followed by distillation and freeze-drying. As a result, four product streams were obtained and characterized for relevant physicochemical and nutritional attributes. Our results show that the partial fermentation of MP by B. claussenii can be used as the first step to develop lactose-free, low-in-glucose, galactose-rich bioproducts, which improve the value of this residue and broaden its applications in the food supply chain. ItemCheese whey permeate as a precursor of lactose-free, galactose-rich bioproducts: an approach for optimization and applicationRivera Flores, Viviana K.; DeMarsh, Timothy A.; Fan, Xingrui; Alcaine, Samuel D. (2023-03) ItemSelective survival of protective cultures during high-pressure processing by leveraging freeze-drying and encapsulation Supplementary InformationMcGillin, Meghan R.; deRiancho, Dana L.; DeMarsh, Timothy A.; Hsu, Ella D.; Alcaine, Samuel D. (2022) ItemFermentation of dairy-relevant sugars by Saccharomyces, Kluyveromyces, and Brettanomyces Part II_Supplemental MaterialRivera Flores, Viviana K.; DeMarsh, Timothy A.; Gibney, Patrick A.; Alcaine, Samuel D. (2022-05-06) ItemData from: Whole genome sequencing-based characterization of Listeria isolates from produce packinghouses and fresh-cut facilities suggests both persistence and re-introduction of fully virulent L. monocytogenesSullivan, Genevieve; Orsi, Renato H; Estrada, Erika; Strawn, Laura; Wiedmann, Martin (2022-03)Whole genome sequencing of Listeria isolates from produce packinghouses and fresh-cut facilities ItemDevelopment of a Monte Carlo simulation model to predict pasteurized fluid milk spoilage due to post-pasteurization contamination with gram-negative bacteria_Supplemental MaterialLau, Samantha; Trmcic, Aljosa; Martin, Nicole; Wiedmann, Martin; Murphy, Sarah (2021-12-08) ItemFermentation of dairy-relevant sugars by Saccharomyces, Kluyveromyces, and Brettanomyces_Supplemental MaterialRivera Flores, Viviana K.; DeMarsh, Timothy A.; Gibney, Patrick A.; Alcaine, Samuel D. (2021-09-24) ItemData from: Survival of Escherichia coli O157:H7 during moderate temperature dehydration of plant-based foodsRana, Yadwinder Singh; Eberly, Philip M.; Suehr, Quincy J.; Hildebrandt, Ian M.; Marks, Bradley P.; Snyder, Abigail B. (2021-09-13)data in support of research: The effect of moderate-temperature (≤60 ◦C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product- matrix, aw, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to aw 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 ◦C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and aw level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of aw was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing aw in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 ◦C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 ◦C as a microbial kill step.