Marianna Giannoglou

Kinetic study of the combined effect of high hydrostatic pressure and temperature on the activity of Lactobacillus delbrueckii ssp. bulgaricus aminopeptidases.

The effect of high hydrostatic pressure (HHP) (100 to 700 MPa) combined with temperature (20 to 40 degrees C) on the activity of 5 aminopeptidases (PepN, PepX, PepY, PepC, and PepA) of Lactobacillus delbrueckii ssp. bulgaricus ACA-DC 0105, used as starter culture for feta cheese production, was studied. Aminopeptidases PepN, PepX, and PepA were activated at pressures up to 200 MPa, at temperatures up to 40 degrees C. PepY and PepC appeared to be more sensitive to pressure and temperature treatment leading to inactivation for pressures above 100 and 200 MPa, respectively, combined with temperature above 30 degrees C. A multi-parameter equation was used for predicting the activation of PepN, PepX, and PepA aminopeptidases in the pressure and temperature domain. Overall, processing at 200 MPa and 20 degrees C may be selected as the optimum conditions for maximum activation of 4 out of 5 aminopeptidases of L. delbrueckii ssp. bulgaricus. A 20-min treatment at these conditions leads to an average 3-fold increase in activity, which could lead to better and faster maturation of white cheese.

Shelf-life prediction models for ready-to-eat fresh cut salads: Testing in real cold chain

The aim of the study was to develop and test the applicability of predictive models for shelf-life estimation of ready-to-eat (RTE) fresh cut salads in realistic distribution temperature conditions in the food supply chain. A systematic kinetic study of quality loss of RTE mixed salad (lollo rosso lettuce-40%, lollo verde lettuce-45%, rocket-15%) packed under modified atmospheres (3% O2, 10% CO2, 87% N2) was conducted. Microbial population (total viable count, Pseudomonas spp., lactic acid bacteria), vitamin C, colour and texture were the measured quality parameters. Kinetic models for these indices were developed to determine the quality loss and calculate product remaining shelf-life (SLR). Storage experiments were conducted at isothermal (2.5-15°C) and non-isothermal temperature conditions (Teff=7.8°C defined as the constant temperature that results in the same quality value as the variable temperature distribution) for validation purposes. Pseudomonas dominated spoilage, followed by browning and chemical changes. The end of shelf-life correlated with a Pseudomonas spp. level of 8 log(cfu/g), and 20% loss of the initial vitamin C content. The effect of temperature on these quality parameters was expressed by the Arrhenius equation; activation energy (Ea) value was 69.1 and 122.6kJ/mol for Pseudomonas spp. growth and vitamin C loss rates, respectively. Shelf-life prediction models were also validated in real cold chain conditions (including the stages of transport to and storage at retail distribution center, transport to and display at 7 retail stores, transport to and storage in domestic refrigerators). The quality level and SLR estimated after 2-3days of domestic storage (time of consumption) ranged between 1 and 8days at 4°C and was predicted within satisfactory statistical error by the kinetic models. Teff in the cold chain ranged between 3.7 and 8.3°C. Using the validated models, SLR of RTE fresh cut salad can be estimated at any point of the cold chain if the temperature history is known. Shelf-life models of validated applicability can serve as an effective tool for shelf-life assessment and the development of new products in the fresh produce food sector.

Food Cold Chain Management and Optimization

The main shelf life determining post-processing parameter for chilled and frozen food products is temperature. Possible temperature fluctuations and even unexpected, out of specifications, temperature conditions throughout the cold chain should be considered when developing a cold chain management and quality/safety assurance system. This chapter describes the use of two different approaches for an effective cold chain management and optimization.