Abstract
Chicken liver is a highly perishable meat product with a relatively short shelf-life and that can get easily contaminated with pathogenic microorganisms. This study was conducted to evaluate the behavior of spoilage microbiota and of inoculated Salmonella enterica on chicken liver. The feasibility of Fourier-transform infrared spectroscopy (FTIR) to assess chicken liver microbiological quality through the development of a machine learning workflow was also explored. Chicken liver samples [non-inoculated and inoculated with a four-strain cocktail of ca. 103 colony-forming units (CFU)/g Salmonella] were stored aerobically under isothermal (0, 4, and 8°C) and dynamic temperature conditions. The samples were subjected to microbiological analysis with concomitant FTIR measurements. The developed FTIR spectral analysis workflow for the quantitative estimation of the different spoilage microbial groups consisted of robust data normalization, feature selection based on extra-trees algorithm and support vector machine (SVM) regression analysis. The performance of the developed models was evaluated in terms of the root mean square error (RMSE), the square of the correlation coefficient (R2), and the bias (Bf) and accuracy (Af) factors. Spoilage was mainly driven by Pseudomonas spp., followed closely by Brochothrix thermosphacta, while lactic acid bacteria (LAB), Enterobacteriaceae, and yeast/molds remained at lower levels. Salmonella managed to survive at 0°C and dynamic conditions and increased by ca. 1.4 and 1.9 log CFU/g at 4 and 8°C, respectively, at the end of storage. The proposed models exhibited Af and Bf between observed and predicted counts within the range of 1.071 to 1.145 and 0.995 to 1.029, respectively, while the R2 and RMSE values ranged from 0.708 to 0.828 and 0.664 to 0.949 log CFU/g, respectively, depending on the microorganism and chicken liver samples. Overall, the results highlighted the ability of Salmonella not only to survive but also to grow at refrigeration temperatures and demonstrated the significant potential of FTIR technology in tandem with the proposed spectral analysis workflow for the estimation of total viable count, Pseudomonas spp., B. thermosphacta, LAB, Enterobacteriaceae, and Salmonella on chicken liver.
Highlights
Meat is considered as the most nutritious and energy-rich food product that can provide the human body with all the essential amino acids and micronutrients needed for growth and development (Wood, 2017; Ahmad et al, 2018)
The aerobic storage of chicken livers generally allowed the growth of microorganisms at high levels, with Pseudomonas spp. being the dominant spoilage microorganism, followed closely by B. thermosphacta, while lactic acid bacteria (LAB), Enterobacteriaceae, and yeasts/molds remained at lower levels at both isothermal and dynamic temperature conditions (Figure 1)
The yeasts/mold levels appeared to be lower than the rest of the bacterial populations, in accordance with previous studies reporting yeasts and molds to be a minor part of the microbial association of poultry products, contributing less to poultry spoilage (Dillon and Board, 1991; Ismail et al, 2000; Balamatsia et al, 2007)
Summary
Meat is considered as the most nutritious and energy-rich food product that can provide the human body with all the essential amino acids and micronutrients needed for growth and development (Wood, 2017; Ahmad et al, 2018). Chicken microbiota may harbor pathogenic species, with Salmonella being the most important zoonotic agent responsible for human gastroenteritis due to poultry meat consumption [EFSA (European Food Safety Authority) and ECDC (European Centre for Disease Prevention and Control), (2017); EFSA Panel on Biological Hazards et al, 2019]. Several reports of salmonellosis outbreaks associated with chicken liver consumption have been released worldwide, including the USA (Lanier et al, 2018) and EU [EFSA (European Food Safety Authority) and ECDC (European Centre for Disease Prevention and Control), (2017)]. Given the increased production of chicken meat in the last decade, ensuring the microbial safety and quality of chicken liver is of primary importance (Augère-Granier, 2019)
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