Improvement of food safety design of cook-chill foods

Effect of High Hydrostatic Pressure Processing on the Microbiological Quality and Bacterial Diversity of Sous-Vide-Cooked Cod

High hydrostatic pressure (HP) is a promising method to improve the microbiological quality of sous-vide foods. Monitoring the composition and behavior of the microbial communities in foods is of most importance for the production of high-quality and safe products. High-throughput sequencing (HTS) provides advanced approaches to determine food’s microbial community composition and structure. The aim of the present study was to determine the impact of different HP treatments on the microbial load and bacterial diversity of sous-vide Atlantic cod. Sous-vide cooking at 57.1 °C for 30 min followed by HP treatment at 500 MPa for 8 min reduced viable cell counts (total aerobic mesophiles) in the cod samples below detectable levels for 45 days of storage under refrigeration. In a second trial with cod cooked sous-vide at 52 °C for 20 min followed by HP treatments at 300 or 600 MPa (with HP treatment temperatures of 22 °C or 50 °C for 4 or 8 min, depending on treatment), only the treatments at 600 MPa delayed bacterial growth for at least 30 days under refrigeration. The optimal HP conditions to improve the microbiological quality of sous-vide cod cooked at low temperatures were obtained at 600 MPa for 4 min at a pressurization temperature of 50 °C. Bacterial diversity was studied in cod cooked sous-vide at 52 °C for 20 min by HTS. In the absence of HP treatment, Proteobacteria was the main bacterial group. A succession of Pseudomonadaceae (Pseudomonas) and Enterobacteriaceae was observed during storage. Firmicutes had low relative abundances and were represented mainly by Anoxybacillus (early storage) and Carnobacterium (late storage). The HP-treated sous-vide cod showed the greatest differences from controls during late storage, with Aerococcus and Enterococcus as predominant groups (depending on the HP conditions). The application of HTS provided new insights on the diversity and dynamics of the bacterial communities of sous-vide cod, revealing the presence of bacterial genera not previously described in this food, such as Anoxybacillus. The significance of Anoxybacillus as a contaminant of seafoods should be further investigated.

Control Paramethers for Sous-vide Cook-chill Processing of Swiss Chard (Beta vulgaris) Stems

Within the various stages involved in the preparation of swiss chart stems (Beta vulgaris) as a `V gamme' product, this work concentrated on heating and subsequent cooling, since these are the stages which cause the most drastic changes in the quality parameters of the product. For the detailed analysis, a 3D finite-difference conductive heat transfer model has been developed. This model takes into account vegetal physico-chemical properties (humidity, density, thermal conductivity) as well as their thermoresistance. The texture is one of the parameters that most influences the organoleptic quality of this product, both as an indicator of the extent of cooking and for reflecting the level of homogeneity. Its temperature dependence has been determined by means of a texturometer, confirming a first-order Arrhenius type behavior. Assuming a pasteurization level corresponding to the absence of Listeria monocytogenes in its vegetative form with a margin of 7 logarithmic units as appropriate, the solution of the model enables the establishment of the time necessary for each processing temperature (from 65 to 95 °C). Given the marked temperature gradients observed, various geometric configurations of the stems have been simulated in order to find the most homogenous product.

Surface pasteurization of vacuum-sealed precooked ready-to-eat meat products

Pathogens may contaminate ready-to-eat meat products after cooking but before packaging. Listeria monocytogenes is a formidable contaminant in the food processing environment and is relatively heat resistant compared with other non-spore-forming pathogens. As a consequence, this microorganism is commonly chosen for evaluation in postpackage pasteurization studies. The aim of this study was to review information on the thermal surface pasteurization of vacuum-sealed precooked ready-to-eat meat products, bearing in mind the conditions of commercial production lines, and to formulate a guideline for pasteurization intensity. Review of the literature revealed that fewer microorganisms were killed at the product surface than would be expected based on the results of volumetric thermal resistance studies. Mathematical modeling studies indicated that this low kill might be due to surface imperfections that shield bacteria from the heat. More information on contamination with L. monocytogenes (and other possible pathogens) in process lines and their potential migration into product surface irregularities is urgently required. Studies involving destructive sampling (surface shaving) methods and inoculation with pathogens, both at realistic and inflated levels, should be performed with various product types. Published reports suggest that postpackage pasteurization of fully cooked meat products (weighing up to 9 kg) by water submersion (96 degrees C) for about 10 min should achieve a 2- to 4-log destruction of L. monocytogenes on the product surface. If heating at this temperature and duration is not feasible for product quality or logistic reasons, the inherent bacteriological stability of the product should be increased so that the intensity of surface pasteurization can safely be reduced.

Technological developments and the need for technical competencies in food services

The growing scale of institutional and commercial food services poses a technological challenge of producing large quantities of high quality meals in terms of their safety, sensory and nutritional attributes. Developments in food service technology and systems (cook-freeze, cook-chill and others) allow the replacement of fast food with the service of cooked meals, which are often nutritionally superior. Reliance on equipment, packaging and technological 'know-how' makes food service operations more complex. Operators have to minimise the impact of the numerous steps in the production process, the fundamental weaknesses of cook-chill food safety design, coupled with the practical limitations of Hazard Analysis Critical Control Points management, the potential unevenness of temperature distribution and product deterioration during storage. The fundamental knowledge of food science and microbiology, engineering and packaging technologies is needed. At present, the 'high tech' options, which can improve a product's nutritional value, such as natural preservation hurdles or functional meals, are not used in practice.