RESUMEN
The need to improve the structure of components to create a new system compacter and cheaper, but still ensuring the system's consistent operation is always necessary and urgent. This study found the consistent of a new integrated freezer construction in the tubular ice machine by experimental study. The measuring instruments were been set for this air-cooled experimental model to validate the system stability when integrating the freezer, accumulator and heat exchanger into an integrated freezer. At a typical experiment 50 Hz inverter control, the R404a refrigerant used to evaporate at -15 °C, achieved the duration of total ice production cycle is around 29.5 min whereas the duration of ice production process takes around 24.5 min (rated 2.88 min/°C) and the defrost takes 5 min. The experimental coefficient of performance decreases from 1.77 to 1.51 and gets averagely 1.55 in the ice production process. From three others experimental results, coefficient of performance, the duration of ice production process, and saturation temperature of refrigerant in freezer change corresponding to the supplied power by inverter control for compressor.
RESUMEN
Pediocin PA-1 is a bacteriocin that shows strongly anti-microbial activity against some Gram-positive pathogens such as Listeria monocytogenes, Staphylococcus aureus, and Enterococcus faecalis. With the broad inhibitory spectrum as well as high-temperature stability, pediocin has a potential application in the food preservation and pharmaceutical industry. Pediocin has been studied to express in many heterologous expression systems such as Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris as a free peptide. Here we showed in this study a new strategy by using yeast surface display system to produce the anchored pediocin PA-1 on the cell surface of Saccharomyces cerevisiae, which could be used directly as a pediocin resource. We had successfully constructed a recombinant S. cerevisiae W303 strain that could express pediocin PA-1 on the cell surface. The pediocin-expressing yeast could inhibit the growth of Shigella boydii and Shigella flexneri, which have never been reported before for pediocin activity. Besides, the pediocin expression level of the recombinant S. cerevisiae strain was also evaluated in three different media: synthetic defined (SD), basic medium (BM), and fermentation medium (FM). BM medium was shown to give the highest production yield of the recombinant yeast (4.75 ± 0.75 g dry cell weight per 1 L of culture) with the ratio number of the pediocin-expressing cells of 93.46 ± 2.45%. Taken together, the results clearly showed that pediocin can be displayed on yeast cell surface as anchored protein. The application of yeast cell surface system enables a new door of pediocin application on either food or feed industries. Graphical abstract.