Ilce Gabriela Medina-Meza

Advanced retorting, microwave assisted thermal sterilization (MATS), and pressure assisted thermal sterilization (PATS) to process meat products

Conventional thermal processes have been very reliable in offering safe sterilized meat products, but some of those products are of questionable overall quality. Flavor, aroma, and texture, among other attributes, are significantly affected during such processes. To improve those quality attributes, alternative approaches to sterilizing meat and meat products have been explored in the last few years. Most of the new strategies for sterilizing meat products rely on using thermal approaches, but in a more efficient way than in conventional methods. Some of these emerging technologies have proven to be reliable and have been formally approved by regulatory agencies such as the FDA. Additional work needs to be done in order for these technologies to be fully adopted by the food industry and to optimize their use. Some of these emerging technologies for sterilizing meat include pressure assisted thermal sterilization (PATS), microwaves, and advanced retorting. This review deals with fundamental and applied aspects of these new and very promising approaches to sterilization of meat products.

Kinetics of Cholesterol Oxidation in Model Systems and Foods: Current Status

In the last decades, cholesterol oxidation products (COPs) have been one of the most intense topics in food science because of their biological and pathological effects on human health. The formation of COPs during food processing is a thermodynamically governed phenomenon and, as for all chemical and biochemical reactions, this formation can be controlled through a kinetic monitoring of oxidative trends, in a manner similar to lipid oxidation. The use of kinetics modeling as a powerful predictive tool has increased recently, although its application in lipid oxidation and cholesterol is poor. Despite the abundance of data on the subject, as evidenced by the presence of numerous reviews about the content of COPs in different foods, contributions to the kinetic modeling are isolated. Moreover, the application of this mathematical approach often demonstrates numerous errors in methodology. This paper summarizes the scientific advances in kinetic modeling of thermo- and photo-induced oxidation of cholesterol. We briefly describe the reaction mechanisms of both degradative pathways, with particular attention to involucrate variables. Then, state of the art of mechanistic models that are proposed is discussed in detail. This analysis shows that it is necessary to broaden and deepen the kinetic study of cholesterol oxidative phenomenon from a mechanistic perspective with a more specific application of kinetic principles. The development of effective predictive models may help to monitor COPs during processing of the food and thus prevent their accumulation in the final products.

Kinetics of 25‐hydroperoxycholesterol formation during photo‐oxidation of crystalline cholesterol

BACKGROUND 25-Hydroxycholesterol (25-OH), a side-chain product of cholesterol oxidation, has emerged as one of the important issues in food chemistry and biochemistry, because of its involvement in several human pathologies. This oxysterol is derived from both enzymatic and non-enzymatic pathways. However, the latter mechanism has been scarcely studied in either food or model systems. In this work, a kinetic model was developed to evaluate the formation of 25-OH and its precursor 25-hydroperoxycholesterol (25-OOH) during photo-oxidation of cholesterol for 28 days under fluorescent light. 25-OOH was estimated by an indirect method, using thin-layer chromatography coupled with gas chromatography-mass spectrometry. RESULTS Peroxide value (POV) and cholesterol oxidation products (COPs) were determined. POV showed a hyperbolic behavior, typical of a crystalline system in which the availability of cholesterol is the limiting factor. Further reactions of hydroperoxides were followed; in particular, after photo-oxidation, 25-OOH (0.55 mg g(-1) ) and 25-OH (0.08 mg g(-1) ) were found in cholesterol, as well as seven other oxysterols, including 7-hydroxy and 5,6-epoxy derivatives. The application of kinetic models to the data showed good correlation with theoretical values, allowing derivation of the kinetic parameters for each oxidation route. CONCLUSIONS The results of this work confirm that cholesterol in the crystalline state involves different oxidation patterns as compared to cholesterol in solution. Moreover, the numerical fit proved that hydroperoxidation is the rate-limiting step in 25-OH formation.

Cholesterol photo-oxidation: A chemical reaction network for kinetic modeling

In this work we studied the effect of polyunsaturated fatty acids (PUFAs) methyl esters on cholesterol photo-induced oxidation. The oxidative routes were modeled with a chemical reaction network (CRN), which represents the first application of CRN to the oxidative degradation of a food-related lipid matrix. Docosahexaenoic acid (DHA, T-I), eicosapentaenoic acid (EPA, T-II) and a mixture of both (T-III) were added to cholesterol using hematoporphyrin as sensitizer, and were exposed to a fluorescent lamp for 48h. High amounts of Type I cholesterol oxidation products (COPs) were recovered (epimers 7α- and 7β-OH, 7-keto and 25-OH), as well as 5β,6β-epoxy. Fitting the experimental data with the CRN allowed characterizing the associated kinetics. DHA and EPA exerted different effects on the oxidative process. DHA showed a protective effect to 7-hydroxy derivatives, whereas EPA enhanced side-chain oxidation and 7β-OH kinetic rates. The mixture of PUFAs increased the kinetic rates several fold, particularly for 25-OH. With respect to the control, the formation of β-epoxy was reduced, suggesting potential inhibition in the presence of PUFAs.

Impacts of Scarification and Degermination on the Expansion Characteristics of Select Quinoa Varieties during Extrusion Processing

Extrusion of 2 quinoa varieties, Cherry Vanilla and Black (scarified and unscarified) and a mixed quinoa variety, Bolivian Royal (scarified and degermed) were studied for their extrusion characteristics. A corotating twin-screw extruder with a 3 mm round die was used. Feed moisture contents of 15%, 20%, and 25% (wet basis) were studied. The extruder barrel temperature was kept constant at 140 °C and screw speeds were varied from 100, 150, and 200 revolutions per minutes. Process responses (specific mechanical energy, back pressure, and torque) and product responses (expansion ratio, unit density, and water absorption index/water solubility index) were evaluated. The degermed Bolivian Royal showed the highest expansion in comparison to all other varieties, attributed to its significantly low levels of fat, fiber, and protein. The scarified Cherry Vanilla resulted in the lowest expansion ratio. This was attributed to the increase in the protein content from the removal of the outer layer. The results indicate that all the varieties performed differently in the extrusion process due to their modification processes as well as the individual variety characteristics.

Enhancement of Fruit Technological Maturity and Alteration of the Flavonoid Metabolomic Profile in Merlot (Vitis vinifera L.) by Early Mechanical Leaf Removal

Removal of basal leaves near blooms inevitably affects grapevine balance and cluster microclimate conditions, improving fruit quality. Mechanization of this practice allows growers to save time and resources, but to our knowledge, it has not yet been compared with the manual application of this practice in a cool-climate region where seasonal temperatures frequently limit fruit technological maturity and phenolic ripening in red Vitis vinifera cultivars. In our research, berry sugar concentration was highest with prebloom mechanical treatment (PB-ME). Furthermore, metabolomics analysis revealed that PB-ME favored the accumulation of significantly more disubstituted anthocyanins and flavonols and OH-substituted anthocyanins compared with manual application. Given that vine balance was similar between treatments, increased ripening with PB-ME is likely due to enhanced microclimate conditions and higher carbon partitioning through a younger canopy containing basal leaf fragments proximal to fruit. This information provides an important strategy for consistently ripening red Vitis vinifera cultivars in cool climates.

The role of cholesterol oxidation products in food toxicity

Food consumption can lead to the accumulation of certain chemical compounds able to exert toxic activities against humans. Of mayor interests are those molecules generated during food processing and handling, since their occurrence and distribution depend of many intrinsic and extrinsic factors. Cholesterol - a lipid constituent of mammalian cells - is the precursor of several toxic molecules known as cholesterol oxidation products (COPs). In the last decades, it has been demonstrated that food processing can dramatically trigger COPs accumulation in meats, eggs, dairy products, fish and poultry. On the other hand, countless scientific evidences have pointed out the highly toxic and pathogenic activities of COPs, from cancer stimulation to neurodegenerative disorders, via molecular mechanisms that are largely unexplored. The aim of this review is to merge the evidence on COPs accumulation in foods and their toxic activities through dietary intake, as from in vivo and in vitro studies. We consider that it is imperative to systematically monitor the formation of COPs to bridge these quantitative efforts with a risk exposure assessment on sensitive populations.