Evaluation of a post-lethality treatment against Listeria monocytogenes on Ricotta salata cheese

Sustainable Approaches in Whey Cheese Production: A Review

Whey cheeses have been produced from the very early steps of cheesemaking practices as a sustainable way to utilize whey, which is the main by-product of cheesemaking. Traditional whey cheeses, manufactured with similar processes, are Ricotta, Ricotta salata or Ricottone, and Ricotta fresca in Italy; Anthotyros, Myzithra, Manouri, Xynomyzithra, and Urda in Greece; Urda in Serbia and Romania as well as in other countries such as Israel; Lor in Turkey; Anari in Cyprus; Skuta in Croatia and Serbia; Gjetost and Brunost in Norway; Mesost and Messmör in Sweden; Mysuostur in Iceland; Myseost in Denmark; Requeijão in Portugal; and Requesón in Spain and Mexico. The production of whey cheese is based on the denaturation of whey proteins by heating to 88–92 °C. The specific processing conditions and aspects of the microbiology of whey cheeses are discussed. The special characteristics of whey cheeses, which are high pH and high moisture content, make them susceptible to microbial growth. Due to the limited shelf life of these products, extended research has been carried out to extend the shelf life of whey cheese. The sustainable preservation approaches, such as modified atmosphere packaging, addition of herbs and/or plant extracts, and bio-preservation methods are reviewed. Moreover, novel whey cheeses focused on functional properties have developed during the last 10 years.

Assessment of the Spoilage Microbiota during Refrigerated (4 °C) Vacuum-Packed Storage of Fresh Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P-Containing Extract

Although fresh whey cheeses are prone to rapid deterioration, mainly by psychrotrophic Gram-negative bacteria and lactic acid bacteria (LAB), data on the specific spoilage species in traditional Greek whey cheeses are scarce. Therefore, this study quantified growth and characterized the primary spoilage bacteria in fresh Anthotyros whey cheeses stored at 4 °C in a vacuum for 40 days, without or with an added 5% (v/w) of an enterocin A-B-P crude extract (CEntE). Psychrotrophic Pseudomonas spp., Aeromonas spp., Hafnia spp. and Serratia spp. grew faster than LAB during early storage. However, LAB outgrew the Gram-negative bacteria and prevailed by mid to late storage in all cheese batches, causing a strong or milder batch-dependent natural acidification. Two major non-slime-producing and two minor biotypes of Leuconostoc-like bacteria, all identified as Leuconostoc mesenteroides by 16S rRNA sequencing, dominated the LAB association (76.7%), which also included four subdominant Carnobacterium maltaromaticum biotypes (10.9%), one Leuconostoc lactis biotype (3.3%) and few Lactococcus (1.6%), mesophilic Lactobacillus (0.8%) and Enterococcus (0.8%). Growth and distribution of LAB and Gram-negative species were strongly batch-dependent and plant-dependent. The CEntE neither retarded growth nor altered the whey cheese spoilage association but enhanced LAB growth and the declines of Gram-negative bacteria by late storage.

Inactivation of Listeria monocytogenes using Water Bath Heat Treatment in Vacuum Packed Ricotta Salata Cheese Wedges

Ricotta salata cheese is frequently contaminated on the surface with Listeria monocytogenes. Water bath heat treatment in vacuum packed whole ricotta salata cheese wheels demonstrated to be effective in inactivating L. monocytogenes. However, the risk of cross-contamination in ricotta salata wedges is increased during cheese cutting. Therefore, the effectiveness of heat treatment in ricotta salata wedges has to be demonstrated conducting a new validation study. In this study, 9 different time temperature combinations, 75, 85, and 90 °C applied for 10, 20, and 30 min each, were tested on artificially contaminated ricotta salata cheese wedges. The extent of the lethal effect on L. monocytogenes was assessed 1 and 30 d after the application of the hot water bath treatment. Five of 9 combinations, 75 °C for 30 min, 85 °C for 20, and 30 min, and 90°C for 20 and 30 min, demonstrated to meet the process criteria of at least 5 log reduction. Sensory analyses were also conducted in order to account for the potential impact on sensory features of ricotta salata wedges, which showed no significant differences between treatments.

PRACTICAL APPLICATION

This study allowed to select water bath heat treatments of vacuum packed ricotta salata wedges effective to reduce L. monocytogenes contamination. Such treatments can be successfully applied by food business operator to meet compliance with microbiological criteria through the designated shelf-life.