Total amino acids concentration as a reliable predictor of free chlorine levels in dynamic fresh produce washing process.

We establish the total amino acids (AA) concentration in wash water as an alternative indicator of free chlorine (FC) levels, and develop a model to predict FC concentration based on modeling the reaction kinetics of chlorine and amino acids. Using single wash of iceberg lettuce, green cabbage, and carrots, we report the first in situ apparent reaction rate ß between FC and amino acids in the range of 15.3 - 16.6 M-1 s-1 and an amplification factor γ in the range of 11.52-11.94 for these produce. We also report strong linear correlations between AA levels and produce-to-water ratio (R2 = 0.87), and between chemical oxygen demand (COD) and AA concentrations (R2 = 0.87). The values of the parameters γ and ß of the model were validated in continuous wash experiments of chopped iceberg lettuce, and predicted the FC (R2 = 0.96) and AA (R2 = 0.92) levels very well.

Chlorine inactivation of Escherichia coli O157:H7 in fresh produce wash process: Effectiveness and modeling.

Inactivation rate constant or inactivation coefficient (specific lethality) quantifies the rate at which a chemical sanitizer inactivates a microorganism. This study presents a modified disinfection kinetics model to evaluate the potential effect of organic content on the chlorine inactivation coefficient of Escherichia coli O157:H7 in fresh produce wash processes. Results show a significant decrease in the bactericidal efficacy of free chlorine (FC) in the presence of organic load compared to its absence. While the chlorine inactivation coefficient of Escherichia coli O157:H7 is 70.39 ± 3.19 L/mg/min in the absence of organic content, it drops by 73% for a chemical oxygen demand (COD) level of 600-800 mg/L. Results also indicate that the initial chlorine concentration and bacterial load have no effect on the chlorine inactivation coefficient. A second-order chemical reaction model for FC decay, which utilizes a proportion of COD as an indicator of organic content in fresh produce wash was employed, yielding an apparent reaction rate of (9.45 ± 0.22) × 10-4 /µM/min. This model was validated by predicting FC concentration in multi-run continuous wash cycles with periodic replenishment of chlorine.

Synthesis and secretome release by human bone marrow mesenchymal stem cell spheroids within three-dimensional collagen hydrogels: Integrating experiments and modelling.

Myocardial infarction results in loss of cardiac cell types, inflammation, extracellular matrix (ECM) degradation, and fibrotic scar. Transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) is being explored as they could differentiate into cardiomyocyte-like cells, integrate into host tissue, and enhance resident cell activity. The ability of these cells to restore lost ECM, remodel the inflammatory scar tissue, and repair the injured myocardium remains unexplored. We here elucidated the synthesis and deposition of ECM (e.g., elastin, sulfated glycosaminoglycans, hyaluronan, collagen type III, laminin, fibrillin, lysyl oxidase, and nitric oxide synthases), matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), and other secretome (cytokines, chemokines, and growth factors) in adult human BM-MSC spheroid cultures within three-dimensional collagen gels. The roles of species-specific type I collagen and 5-azacytadine were assessed over a 28-day period. Results revealed that human collagen (but not rat-derived) suppressed MSC proliferation and survival, and MSCs synthesized and released a variety of ECM proteins and secretome over the 28 days. Matrix deposition is at least an order of magnitude lower than their release levels at every time point, most possibly due to elevated MMP levels and interleukins with a concomitant decrease in TIMPs. Matrix synthesis over the 28-day period was fitted to a competitive inhibition form of Michaelis-Menten kinetics, and the production and decay rates of ECM, MMPs, and TIMPs, along with the kinetic model parameters quantified. Such an integrated experimental and modelling approach would help elucidate the critical roles of various parameters (e.g., cell encapsulation and delivery vehicles) in stem cell-based transplantation therapies.

Modeling of Free Chlorine Consumption and Escherichia coli O157:H7 Cross-Contamination During Fresh-Cut Produce Wash Cycles.

Controlling the free chlorine (FC) availability in wash water during sanitization of fresh produce enhances our ability to reduce microbial levels and prevent cross-contamination. However, maintaining an ideal concentration of FC that could prevent the risk of contamination within the wash system is still a technical challenge in the industry, indicating the need to better understand wash water chemistry dynamics. Using bench-scale experiments and modeling approaches, we developed a comprehensive mathematical model to predict the FC concentration during fresh-cut produce wash processes for different lettuce types (romaine, iceberg, green leaf, and red leaf), carrots, and green cabbage as well as Escherichia coli O157:H7 cross-contamination during fresh-cut iceberg lettuce washing. Fresh-cut produce exudates, as measured by chemical oxygen demand (COD) levels, appear to be the primary source of consumption of FC in wash water, with an apparent reaction rate ranging from 4.74 × 10 - 4 to 7.42 × 10 - 4 L/mg·min for all produce types tested, at stable pH levels (6.5 to 7.0) in the wash water. COD levels increased over time as more produce was washed and the lettuce type impacted the rate of increase in organic load. The model parameters from our experimental data were compared to those obtained from a pilot-plant scale study for lettuce, and similar reaction rate constant (5.38 × 10-4 L/mg·min) was noted, supporting our hypothesis that rise in COD is the main cause of consumption of FC levels in the wash water. We also identified that the bacterial transfer mechanism described by our model is robust relative to experimental scale and pathogen levels in the wash water. Finally, we proposed functions that quantify an upper bound on pathogen levels in the water and on cross-contaminated lettuce, indicating the maximum potential of water-mediated cross-contamination. Our model results could help indicate the limits of FC control to prevent cross-contamination during lettuce washing.