Predicting the Quality of Pasteurized Vegetables Using Kinetic Models: A Review

A resurgence in interest examining thermal pasteurization technologies has been driven by demands for “cleaner” labeling and the need of organic and natural foods markets for suitable preventive measures to impede microbial growth and extend shelf life of minimally processed foods and ready-to-eat foods with a concomitant reduction in the use of chemical preservatives. This review describes the effects of thermal pasteurization on vegetable quality attributes including altering flavor and texture to improve consumer acceptability, stabilizing color, improving digestibility, palatability and retaining bioavailability of important nutrients, and bioactive compounds. Here, we provide kinetic parameters for inactivation of viral and bacterial pathogens and their surrogates and marker enzymes used to monitor process effectiveness in a variety of plant food items. Data on thermal processing protocols leading to higher retention and bioactivity are also presented. Thermal inactivation of foodborne viruses and pathogenic bacteria, specifically at lower pasteurization temperatures or via new technologies such as dielectric heating, can lead to greater retention of “fresh-like” properties

Storage stability of vitamin C fortified purple mashed potatoes processed with microwave-assisted thermal sterilization system

Quality changes in ready-to-eat, shelf-stable foods, during storage can be influenced by many factors, such as processing, storage conditions, and the barrier properties of the packaging. This research investigated retention of vitamin C and anthocyanin in purple mashed potatoes as influenced by packaging barrier properties and encapsulation during storage after microwave assisted thermal sterilization. Purple mashed potatoes fortified with encapsulated (EVC) or non-encapsulated vitamin C (NVC) were packaged in two high-barrier polymer pouches (TLMO and PAA), processed with a pilot-scale microwave assisted thermal sterilization (MATS) system (F0 = 10.7 min), and stored at 37.8 °C for 7 months. MATS processing caused a significant increase (P < 0.05) in the oxygen transmission rates (OTRs) of PAA pouches but did not affect the barrier properties of TLMO pouches. PAA film also had a significantly higher (P < 0.05) water vapor transmission rate (WVTRs) than TLMO films, which resulted in a significantly higher (P < 0.05) weight loss in the samples packaged in PAA pouches than TLMO pouches. Purple mashed potatoes containing encapsulated vitamin C in both TLMO and PAA pouches showed the highest retention over 2 months of storage at 37.8 °C than non-encapsulated vitamin C. Additionally, purple mashed potatoes exposed to 700 lumens light showed a significantly higher (P < 0.05) deterioration in the anthocyanin, total phenolic content, color, and vitamin C. Overall, MATS processed purple mashed potatoes in high barrier polymeric packaging can minimize the quality changes when stored in dark conditions during storage and have an extended shelf life

Glass transition and water activity of freeze-dried shark

Glass transition temperatures and water activity as a function of moisture content were determined for freeze-dried shark to further compare the two distinct criteria of food stability. The adsorption experiments were carried out at controlled water activity, at 21, 40, and 50°C using an isopiestic method and they were modeled using BET and GAB equations. Glass transition temperatures were measured by dynamic oscillation on shear. Results indicate that there is a difference in the temperature-related stability criteria predicted by the concepts of water activity (aw) and the glass phenomenon (Tg). The glass transition concept tends to accommodate higher levels of moisture within the framework of a safe storage of a dried product

The effect of pressure on the structural properties of biopolymer/co-solute. Part II: The example of gelling polysaccharides

The dependence of relaxation processes, as manifest in changes of the glass transition temperature, were examined under pressure (0.1-700 MPa) for the gelatin/co-solute system (part I of this series) and, currently, for preparations of agarose, ?-carrageenan and deacylated gellan in the presence of co-solute (part II). Structural properties were monitored using modulated differential scanning calorimetry and small-deformation dynamic spectroscopy on shear. Response curves as a function of hydrostatic pressure were treated with the combined framework of reduced variables and WLF equation/free volume theory. Shift factors derived from viscoelastic spectra and empirically treated thermograms clearly demonstrate that the effect of increasing pressure is detrimental to the stability of intermolecular polysaccharide associations. Diminishing values of the glass transition temperature with increasing pressure argue that the concept of time-temperature-pressure equivalence applicable to amorphous synthetic polymers is not operational in the structural functions of high-solid polysaccharide gels

A fundamental approach for the estimation of the mechanical glass transition temperature in gelatin

10.1016/j.ijbiomac.2005.03.010International Journal of Biological Macromolecules361-271-78IJBM

Evaluating water activity and glass transition concepts for food stability

Water activity and glass transition temperature concepts were used to investigate the connection between the two distinct criteria of food stability. The data on sorption isotherms and glass transition temperatures were obtained from the literature. Two most commonly used models i.e. GAB and Gordon-Taylor equations were used to model water activity/moisture content and glass transition temperatures/solids content relationships. The models&#039; (GAB and Gordon-Taylor) parameters were used to estimate water activity and glass transition temperature at given moisture/solids content. Results indicate that there is a considerable discrepancy in the temperature-related stability criteria predicted by the concepts of water activity (aw) and the glass phenomenon (Tg). A greater understanding of water sorption properties and Tg is required to establish a sound processing and storage stability criteria