Abstract
Chitosan coating is a promising method for food preservation. This study aims to fill the data gap regarding the application of chitosan (1% and 2%) on vacuum-packed fresh pork stored at 4 °C for 28 days, with particular attention on the effect on Listeria monocytogenes, inoculated as a cocktail of three strains. Chitosan at both concentrations was able to significantly reduce L. monocytogenes counts by more than 1.5 Log CFU/g with respect to control; moreover, it inhibited the growth of mesophilic bacteria and was particularly effective on lactic acid bacteria and yeasts. The beneficial effects on shelf life were demonstrated by both panel test and pH evolution. In fact, panellists did not detect any sensory difference between samples treated with 1% chitosan and control up to 14 days of storage, while after 28 days, a pungent flesh odour was perceived in control samples only. Interestingly, at aw values of fresh meat (0.984), the chitosan coating exhibited a liquid behaviour, with a dynamic viscosity of 229.4 ± 4.2 mPa/s. Chitosan coating applied on vacuum-packed pork loins contained L. monocytogenes growth and improved the microbiological characteristics of the product, with a beneficial effect on product shelf life.
Highlights
Fresh meat is a rich nutrient matrix that is highly prone to spoilage caused by different microorganisms, with subsequent biochemical and enzymatic deteriorations
The evaluation of the antimicrobial effects of chitosan against L. monocytogenes was carried out in accordance with European guidelines produced by the European Reference Laboratory ANSES [20], using a cocktail of one type strain and two strains isolated from meat products
The application of chitosan on vacuum-packed pork loins stored at 4 ◦ C was effective in improving the safety of the product by containing L. monocytogenes growth
Summary
Fresh meat is a rich nutrient matrix that is highly prone to spoilage caused by different microorganisms, with subsequent biochemical and enzymatic deteriorations. Vacuum-packaging and modified atmosphere are traditionally used to control microbial growth, improve safety, and delay spoilage [1]. Vacuum-packaging, which is generally more economical than modified atmosphere, is frequently used for primary cuts, while modified atmosphere packaging (MAP) is more suitable for retail displays of meat [2]. Vacuum-packaging is frequently used in restaurants for temporary storage of meat slices. The exclusion of oxygen in vacuum-packaging inhibits aerobic bacteria, such as Pseudomonas species [2], allowing the growth of anaerobic and facultative anaerobic bacteria. Vacuum-packaging of chilled meat does not inhibit the development of Listeria monocytogenes, the presence of which, in meat products, is a particular food safety concern as it can cause listeriosis with serious effects, especially in elderly adults and immune-compromised people, causing meningitis, and in pregnant women, spontaneous abortion or stillborn babies [3]. An increase in the notified incidence rate of listeriosis in Europe has been reported during the years 2008–2015, with meat and meat products being often responsible of outbreaks [4]; in particular, this Gram-positive rod has the highest scores of risk for pork consumers [5]
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