Abstract
Shredded cabbage is widely used in much ready-to-eat food. Therefore, rapid methods for detecting and monitoring the contamination of foodborne microbes is essential. Short wavelength near infrared (SW-NIR) spectroscopy was applied on two types of solutions, a drained solution from the outer surface of the shredded cabbage (SC) and a ground solution of shredded cabbage (GC) which were inoculated with a mixture of two bacterial suspensions, Escherichia coli and Salmonella typhimurium. NIR spectra of around 700 to 1100 nm were collected from the samples after 0, 4, and 8 h at 37 °C incubation, along with the growth of total bacteria, E. coli and S. typhimurium. The raw spectra were obtained from both sample types, clearly separated with the increase of incubation time. The first derivative, a Savitzky–Golay pretreatment, was applied on the GC spectra, while the second derivative was applied on the SC spectra before developing the calibration equation, using partial least squares regression (PLS). The obtained correlation (r) of the SC spectra was higher than the GC spectra, while the standard error of cross-validation (SECV) was lower. The ratio of prediction of deviation (RPD) of the SC spectra was higher than the GC spectra, especially in total bacteria, quite normal for the E. coli but relatively low for the S. typhimurium. The prediction results of microbial spoilage were more reliable on the SC than on the GC spectra. Total bacterial detection was best for quantitative measurement, as E. coli contamination could only be distinguished between high and low values. Conversely, S. typhimurium predictions were not optimal for either sample type. The SW-NIR shows the feasibility for detecting the existence of microbes in the solution obtained from SC, but for a more specific application for discrimination or quantitation is needed, proving further research in still required.
Highlights
Public concern about the safety of fresh produce consumption has been continuously growing
Samples were collected from the shredded cabbage (SC) and GC solutions mixed with a bacteria suspension of E. coli and S. typhimurium at 0, 4, and 8 h during the incubation period at 37 ◦C
At 0 h, the total bacteria detected in the SC solution was at 2.88 log CFU·mL−1 and in the GC mixture solution at 3.15 log CFU·g−1, while E. coli or S. typhimurium were not detected
Summary
Public concern about the safety of fresh produce consumption has been continuously growing. Many foodborne disease outbreaks in fresh and fresh-cut produce are still being reported [1]. Fung et al [2] found that Staphylococcus, Salmonella, Clostridium, Campylobacter, Listeria, Vibrio, Bacillus, and Escherichia coli accounted for 90% of global food poisoning illnesses. E. coli and Salmonella are two pathogenic bacteria mainly concerned with fresh-cut produce [3,4,5,6]. This report agrees with the food poisoning statistics from the Japanese Ministry of Health, Labour, and Welfare about the most common causes of foodborne disease in Japan in 2011 [7]. For fresh and fresh-cut producers, assuring the safety of the produce to the consumer is inescapable
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