Elucidation for mechanism of discoloration of meat induced by cold atmospheric pressure plasma and its application

Abstract

The objective of present experiments were 1) to investigate the bactericidal effect of cold atmospheric pressure plasma (APP) on raw chicken meat and to observe quality changes and genotoxicological safety after the APP treatment, 2) to elucidate the mechanism and control the APP-induced green discoloration of raw meat using myoglobin, 3) to confirm the possibility of red color development in pork by APP treatment and to evaluate the physiochemical properties and microbiological safety of pork jerky made with APP as a substitute method of sodium nitrite, and 4) to compare the quality of injected loin ham cured with sodium nitrite and plasma-treated water (PTW).

Experiment I. Evaluation of the microbiological safety, quality changes, and genotoxicity of chicken breast treated with flexible thin-layer atmospheric pressure plasma The microbiological safety, changes in quality, and genotoxicity of raw chicken breasts treated with flexible thin-layer atmospheric pressure plasma (APP) were investigated. Following 10-min APP treatment, the numbers of Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium were reduced by 2.14, 2.73, and 2.71 Log CFU/g, respectively. L* (lightness) and b* values (yellowness) increased whereas a* value (redness) decreased following plasma treatment with increasing exposure duration. Lipid oxidation was unaffected by APP treatment. There was also no significant difference in the texture properties between the APP-treated sample and non-treated control. No genotoxicity was detected in APP-treated chicken breast using the Salmonella mutagenicity assay. Therefore, it can be concluded that APP is applicable since it is able to improve microbiological safety with minimal changes in color properties of the chicken breast.

Experiment II. Elucidation of the mechanism of APP-inducted green discoloration of myoglobin Meat color is an important factor that influences product acceptability by consumers. The most responsible factor for meat color is a myoglobin. Thus, the aim of this experiment was to elucidate the mechanism and control measure of APP-induced green discoloration of myoglobin. Generally, it is known that green-colored pigments derived from myoglobin are in the forms as sulfmyoglobin, choleglobin, verdoheme, nitrihemin or nitrimyoglobin. When myoglobin dissolved in phosphate buffer was exposed to APP for 20 min, L* and a* values were significantly decreased whereas b* value was increased. In the UV absorption spectrum, APP-treated myoglobin showed absorption peak at 503 and 630 nm, which is not a spectrum of sulfmyoglobin or choleglobin. With evidences that the secondary structure and molecular weight of myoglobin were not changed by APP treatment, we excluded the possibility of the form of verdoheme or nitrihemin in APP-treated myoglobin solution. Nitrite, hydrogen peroxide, and hydroxyl radical were produced in myoglobin solution by APP treatment, which provide a positive environment that nitrimyoglobin could be formed. When 0.1% sodium dithionite, a strong reducing agent, was added to myoglobin solution, green discoloration was slightly prevented after APP treatment. Moreover, addition of 0.5% sodium dithionite in myoglobin solution induced red color, not green color, after APP treatment for 20 min. Red color development in myoglobin was resulted in nitrosomyoglobin formation. Consequently, occurrence of green color in APP-treated myoglobin is due to ntrimyoglobin formation. Addition of sodium dithionite prevents green discoloration and induced red color in myoglobin solution after APP treatment.

Experiment III. Color development, physiochemical properties, and microbiological safety of pork jerky manufactured with APP Generally, synthetic nitrite including sodium nitrite is used in the production of cured meat products. Nitrites added in meat products reduced to nitric oxide then interact with myoglobin to produce nitrosomyoglobin, which is responsible for characteristic red color of cured meat. Nitrite can also inhibit the lipid oxidation and growth of food-borne pathogens. However, increasing number of consumers avoids synthetic additives for their cured meat products. In persent experiment, possibility of red color development in pork was confirmed with addition of ascorbic acid and APP treatment. Then, applicability of APP as an alternative to sodium nitrite in pork jerky manufacturing was investigated. Pork marinated with or without sodium nitrite was prepared, and the latter was exposed to APP. As APP-treatment time increased, the a* value, nitrosoheme pigment content, and residual nitrite content increased, while lipid oxidation decreased (all P<0.05). Similar quality properties, particularly color, were observed in jerky applied by APP for 40 min compared to jerky made with sodium nitrite. After inoculation of marinated pork with Staphylococcus aureus and Bacillus cereus, the amounts of both pathogens in jerky applied by APP for 40 and 60 min were significantly lower than in jerky made with sodium nitrite. Consequently, APP can be applied for manufacturing even potentially safer pork jerky without added sodium nitrite.

Experiment IV. An innovative curing process with plasma-treated water for production of loin ham and for its quality and safety To extend industrial utilization of APP, plasma treated water (PTW) was investigated as an alternative to synthetic sodium nitrite in loin ham manufacturing. Loin ham is a cured meat product manufactured by injecting brine into raw meat (loin) without chopping, mixing or emulsifying process. For curing of loin ham, two brine solutions made of sodium nitrite were compared against PTW. In comparison to chemical brining PTW resulted in increased a* value, while allowing to maintain low residual nitrite content and total bacterial counts. No significant differences were found in b* and L* value, and lipid oxidation among the treatment groups. Furthermore, the loin ham manufactured using PTW showed no genotoxicity by Salmonella mutagenicity assay. Therefore, PTW could be considered as an effective and innovative substitute for synthetic nitrite in cured meat manufacturing without compromising on quality changes.