Shelf life extension of ricotta cheese through the use of edible coatings of galactomannans from nonconventional sources incorporating nisin against Listeria monocytogenes

Abstract

Soft, white, fresh cheeses subjected to minimal processing are highly perishable and thus have a short shelf-life. Cheese is a ready-to-eat type of food that has been associated with foodborne listeriosis. Due to the fact that Listeria monocytogenes is psychrotropic and can grow at refrigeration temperatures, contamination by this organism could lead to a high risk factor at pre- and especially at post-production stages. The use of edible films helps to preserve food quality and safety and to improve its sensory properties. The incorporation of antimicrobials such as nisin into these packaging materials can further enhance their preservation effects. The present work evaluated the antimicrobial activity of coatings of galactomannans from Gleditsia triacanthos incorporating nisin against L. monocytogenes during storage of Ricotta cheese at 4 ºC. Three different treatments were tested: a control with no coating added; a sample with coating but without nisin added, and 50 IU/g nisin added to the coating solution. Samples of cheese (20 g) were immersed in 0.5 % w/v galactomannan solution containing glycerol (as plasticizer) (1.5 % v/v) whose concentrations were previously evaluated based on the surface properties of the cheese. The surface of cheese was inoculated with a suspension of L. monocytogenes. Microbiological and physical-chemical analysis (e.g., color measurements) of the cheese samples were performed at different times during 28 days. Cheese coated with galactomannans films added with nisin showed a smaller Listeria population than the control throughout storage. Within 2 days of storage, L. monocytogenes on the surface of cheese coated with nisin decreased whereas cheese without coating allowed the growth of the microorganism. In terms of color, cheese coated with nisin showed a lower color difference (E) during storage as compared to the cheese without coating. This research exhibits an alternative to control L. monocytogenes post-contamination on cheese products during storage.