In the U.S., water immersion chilling (WC) is commonly used to chill poultry while other regions of the world, such as the European Union (E.U.), prefer air chilling (AC). Water chilling is accomplished by submerging eviscerated carcasses in chilled water, while air chilling utilizes forced air in a cool room to chill carcasses. Water chilling is typically faster than traditional AC and antimicrobials can be incorporated directly into the water. But concerns over retained water on carcass, cross-contamination and wastewater disposal exist. Air chilling also comes with concerns over decreased yield because of evaporative loss as well as other concerns such as surface drying. A potential benefit of AC, however, would be an increase in the U.S. poultry export market. The E.U. currently bans U.S. poultry over concerns about the addition of chlorine to water during chilling. The U.S. is currently the largest poultry producer in the world and the second-largest exporter. As demand for poultry continues to rise, poultry products with longer shelf life and less food waste will be needed. Meanwhile, widespread efforts to reduce natural resource and energy expenditures, such as water, as a means of enhancing sustainability, exist across the meat industry, including the poultry industry. Therefore, the objective of this study was to compare the impact of WC and AC on the shelf life and meat quality of bone-in and boneless chicken breast.
A total of 256 eviscerated non-chilled chicken carcasses were obtained from a commercial processing facility in California and transported to the UC-Davis meat laboratory within two hours. Carcasses were randomly and evenly assigned to either WC or AC, then were evenly assigned to be fabricated into bone-in (BI) or boneless (BL) breast. Carcass weight was taken pre- and post-chilling. The breast samples were subsequently packaged onto polystyrene trays, overwrapped and placed into cardboard boxes for dark storage at 4 degrees Celsius for either seven days (phase 1) or 14 days (phase 2). Then breast samples were placed into a retail display case maintained at 4 degrees Celsius for three days. Instrumental and subjective color measurement was performed every 12 hours during retail display. For instrumental color, the lean color of the boneless samples and the skin color of the bone-in samples were measured using a portable spectrophotometer. For subjective color, a panel of eight untrained participants were asked to evaluate the color (desirable, acceptable and unacceptable) and their willingness to purchase (would purchase, would not purchase would purchase at a discounted price) every 12 hours during retail display. Microbial analysis was conducted for samples collected upon arrival, post-chilling, post-fabrication, after dark storage at 4 degrees Celsius for seven or 14 days and after three days of retail display (n=10 per sampling point per treatment). The psychrotrophic and mesophilic bacterial counts were determined using direct plating method.
The WC chicken possessed lower psychrotrophic bacterial counts (1.05 log CFU/g) pre-fabrication than the AC chicken (2.12 log CFU/g), indicating WC may remove a portion of the psychrotrophic bacteria. No difference in mesophilic bacterial counts was observed, however, between the two treatments for pre-fabrication samples. The WC chicken and AC chicken, regardless of fabrication type, reached the end of shelf life (7 log CFU/g) at 14 days. The BL samples, regardless of chilling method, had lower total microbial counts throughout storage and display than the BI samples, because the removal of the skin physically removed the general microbial population as well. On average, WC chicken gained 5 percent of its pre-chilling weight while AC chicken lost 1.6 percent. In terms of objective color, the a* and b* values were higher for AC breast, suggesting that AC breast was more red and yellow than WC breast through the display time. Chilling method did not have an impact on subjective color measurement. During phase 1, untrained panelists considered the color of BL chicken breasts more desirable than the BI breasts. During phase 2, regardless of chilling method or fabrication type, the desirability of color by untrained panelists decreased as display time increased.
The results indicate chilling method had a minimal impact on the shelf life in terms of the microbial counts. Both AC and WC breast reached the end of shelf life at the same time when the microbial population reached to 107 CFU/g as the indication of microbial spoilage. After chilling, WC breast had lower bacteria counts. But for this study, only one batch of chicken carcasses were chilled in a tank of fresh water, which may not reflect commercial settings, where multiple batches of carcasses would be cooled using the same water. Additionally, the use of antimicrobials in the water for WC is common a practice. For this study, no antimicrobials were added to the water. The reuse of the water to chill multiple batches of carcasses and the addition of antimicrobials could potentially yield different microbial results. In our study, AC chicken breast tended to be more yellow-based on objective color measurement. This color difference could be caused by the evaporative moisture loss drying the surface of the chicken. Consumers during phase 1 may have found the BL chicken breast to be more desirable due to the skin being removed. Because yellow is not the dominant color of the chicken breast, the removal of the skin may have made this harder for consumers to discern the difference in yellow between boneless breast.
Based on this study, there is a potential for U.S. producers to move from WC to AC method from a microbial standpoint because chilling had a minimal impact on shelf life; however, there are many other factors that must be considered to determine the viability of this production shift and further research is needed. Factors such as resource and energy expenditure still need to be evaluated as well as determining the cost and economic viability associated with a change in chilling systems. Further research needs to evaluate the reuse of water in chilling multiple batches, the incorporation of antimicrobials and comparison with other novel chilling methods such as evaporative air chilling. NP