| dc.description.abstract | Throughout the world there is a demand for more convenient, fresh, and healthier foods, and ready-to-eat (RTE) foods are becoming more sought-after. Retail sushi is a product that falls in under these categories. Although the demand for sushi has declined slightly the last years, it is still one of the most popular seafood products. As consumers are getting less time to prepare healthy and palatable meals, retail sushi is a convenient savior. Nevertheless, it is a product that is susceptible to microbiological hazards, both pathogens and specific spoilage organisms, and quality deteriorations, e.g., starch retrogradation of the sushi rice. This thesis aimed for better solutions regarding the microbiological stability and quality of retail sushi, by utilization of active packaging techniques, viz. modified atmosphere packaging (MAP) and edible chitosan coating. In addition, the effect of low versus high pH of the sushi rice was investigated. Physicochemical properties, specifically pH, water activity (aw), and color were examined. The retrogradation of starch was analyzed by differential scanning calorimetry (DSC), to investigate the phenomenon in sushi rice and develop a method of analysis. While the DSC analysis provided results, it did not however provide sufficient results for interpretation of retrogradation in sushi rice. The approach produced more questions than answers, although beneficial for further research. The microbiological analyzes of the maki sushi in the first experiment did not provide significant insight on the effect of neither MAP nor coating, and the low initial pH (4.8 ± 0.05) was thought to be a major inhibitor of bacterial growth. Samples stored at 4 °C had a final bacterial count of 2 ± 0.79 log CFU/g , while the samples stored at 8 °C had a final count of 1.6 ± 0.75 log CFU/g, after eight days of storage. Consequently, all samples were below the critical limit of total viable bacterial count of 6 log CFU, and no coliforms or LAB were detected. This provided insight for the second experiment, where the initial pH was higher (5.5 ± 0.07 and 5.1 ± 0.06, uncoated and coated resp.), and a clear effect of both low-CO2 MAP and chitosan coating were observed. The coating showed inhibiting effect on bacterial growth (t38.736 = 3.538, p = 0.001) between all groups, and when the coated control was tested against the uncoated control, disregarding MAP (t20.351 = 3.074, p = 0.006). Low-CO2 MAP did also significantly inhibit bacterial growth (t40.145 = 2.829, p = 0.006). The key findings of this thesis are the effectiveness of the edible chitosan coating, especially in combination with low-CO2 MAP, on bacterial inhibition. Particularly, this combination could work as a safety measure against temperature abuse in the food cold chain, as the results from storage at 8 °C revealed. | |