| Summary: | 碩士 === 國立臺灣大學 === 畜產學研究所 === 88 === Spicy chicken nugget sold by street vendors around the metropolitan Taipei area as well as those produced by poultry processing plants are the subject of this study which includes documentation of methods of production, evaluation of consumer satisfaction and examination of microbial conditions. In addition, physical, chemical and microbial changes of diced chicken breast, raw vs. seasoned, are examined during cold storage.
Street vendors generally prepare the food from scratch and use their own spices. Skinless diced chicken breast with or without bone, in bite size, were seasoned then stored with refrigeration. At the beginning of the workday, vendors breaded the seasoned chicken pieces and deep-fried them at 200℃ for one minute then let stand at room temperature. As soon as the customer placed an order, the product was refried at 180℃ for one minute, sprinkled with custom-made salt-pepper and placed in a paper bag. Products made by the poultry processing plants, on the other hand, were mass-produced mechanically: chicken breast was diced with a dicer and seasoned in a tumbler then kept at 5 to 8℃ for 4 to 24 hours. Batter and bread were added with a coating machine and deep-fried at 180℃ for 1 to 2 minutes and frozen immediately with an individual quick freezer. The final product was packaged and sold at the supermarket freezer section.
Survey of 299 customers from 23 vendors indicated "favorable" to "fair" ratings regarding the overall acceptability, color, size, flavor, crispiness and tenderness. Negative attributes included oiliness (69.2%), rancidity (46.9%) and sourness (19.4%). Quality in order of its importance to the consumers is flavor and texture, clean equipment and utensil, freshness of raw ingredients and sound sanitation habit of the vendor. Majority of the consumers (80.3%) rated the hygiene condition of the vending stands as "clean" or "fair": the reasons being clean environment, frequent changes of frying oil, usage of smoke exhausting fan and wearing gloves and apron. Fewer consumers (3.0%) rated the hygiene condition as "not clean": the reasons being mixed usage of cutting board for both raw and cooked food, dirty environment, darkened frying oil, and poor personal hygiene of the vendor.
No contamination of Salmonella, Escherichia coli or Staphylococcus aureus was found in samples of nugget and salt-pepper from all 22 vendors studied. Total plate count of all nugget samples also met the Chinese Agricultural Standard. Bacillus cereus was found in 6 nugget samples and 7 salt-pepper samples, but the numbers found in the former group were within the limit set by the Food Sanitation Law. Coliform counts of 2 nugget samples and 17 salt-pepper samples, however, exceeded the limits. Total plate counts of all salt-pepper samples from vendors also exceeded limits set for spice-importing countries. Washing raw chicken was effective in reducing the total plate counts when vendors'' methods of preparation were compared. Microbial loads of seasoned chicken were similar to those found in raw ones. Deep-Fry significantly reduced total plate counts and eliminated indicator bacteria including coliform, E. coli and S. aureus. Refry did not further reduce microbial load.
Studies of nugget samples from two poultry processing plants indicated the presence of E. coli, though the total plate counts were within the legal limits. Coliform count in one of the samples exceeded the legal limit. E. coli was also detected in the salt-pepper sample pre-treated with surface-radiation. Irradiated salt-pepper did lower total plate count, which was less than those detected in vendors'' samples but still exceeded the limit imposed for spice-importing countries. Coliform count of this sample was over the legal limit as well.
Further studies were made on diced, raw and seasoned chicken breast during cold storage. After 3 days'' storage at 7℃ (6 days after slaughter), raw chicken was slightly slimy and had weak putrid odor. Significant increases of microbes, including Pseudomonas, E. coli, psychrophilic bacteria, lactic acid bacteria, coliform and total plate counts were detected. Though pH values remained unchanged, the level of volatile basic nitrogen increased while the extract release volume decreased, both significantly. Walkiewicz reaction was found to be a poor indicator test since it failed to correlate with the above mentioned test results and early signs of spoilage. Seasoned chicken seemingly remained unchanged, with no detectable odor or taste during the first three days of cold storage. In addition, total plate counts and pH values were comparable to those found with raw chicken on day 0. Sourness was detected in seasoned chicken on day 5 of cold storage in which significant increases in total plate counts, lactic acid bacteria counts and the level of volatile basic nitrogen were detected. Drops in pH value was also quite significant. Growth of coiform and E. coli appeared to be retarded, however. In the case of seasoned chicken, increased microbial loads and/or a lowered pH can be used as an assessment for the degree of freshness and spoilage. The significant increase in the level of volatile basic nitrogen indicated the incipient spoilage of the chicken. Although seasoned chicken was found to have longer shelf life than that of raw chicken, it still should be cooked and consumed within 3 to 4 days of cold storage or, 6 to 7 days after slaughter before perceptible sign of spoilage was detected.
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