Federico Gómez Galindo

Plant Stress Physiology: Opportunities and Challenges for the Food Industry

We review and analyze the possible advantages and disadvantages of plant-stress-related metabolic and structural changes on applications in the fruit and vegetable processing industry. Knowledge of the cellular and tissue transformations that result from environmental conditions or industrial manipulation is a powerful means for food engineers to gain a better understanding of biological systems in order to avoid potential side effects. Our aim is to provide an overview of the understanding and implementation of physiological and biochemical principles in the industrial processing of fruits and vegetables.

Pulsed Electric Field Reduces the Permeability of Potato Cell Wall

The effect of the application of pulsed electric fields to potato tissue on the diffusion of the fluorescent dye FM1-43 through the cell wall was studied. Potato tissue was subjected to field strengths ranging from 30 to 500 V/cm, with one 1 ms rectangular pulse, before application of FM1-43 and microscopic examination. Our results show a slower diffusion of FM1-43 in the electropulsed tissue when compared with that in the non-pulsed tissue, suggesting that the electric field decreased the cell wall permeability. This is a fast response that is already detected within 30 s after the delivery of the electric field. This response was mimicked by exogenous H2O2 and blocked by sodium azide, an inhibitor of the production of H2O2 by peroxidases.

New insights into the dynamics of vacuum impregnation of plant tissues and its metabolic consequences.

The complex and highly interconnected intercellular air spaces of plant tissues occupied by gas or native liquid has offered the possibility for impregnation with a wide range of compounds. In food processing, the development of vacuum impregnation has allowed a controlled way to introduce these compounds to the tissue structure aiming at modifying structural, nutritional, and/or functional properties as well as improving the processability of fruits and vegetables. In the last 10 years, more than 100 research articles have been published on the topic and significant insights had been gained including improved understanding of mechanisms for mass transfer as well as the development of new, fascinating industrial applications. In the recent years, our knowledge on these aspects has increased by bringing new exploration technologies for studying the impregnation of porous materials and plant cell physiology approaches to bear on the topic. The aim of this paper is to highlight some of these exciting advances.

Investigation of the metabolic consequences of impregnating spinach leaves with trehalose and applying a pulsed electric field

The impregnation of leafy vegetables with cryoprotectants using a combination of vacuum impregnation (VI) and pulsed electric fields (PEF) has been proposed by our research group as a method of improving their freezing tolerance and consequently their general quality after thawing. In this study, we have investigated the metabolic consequences of the combination of these unit operations on spinach. The vacuum impregnated spinach leaves showed a drastic decrease in the porosity of the extracellular space. However, at maximum weight gain, randomly located air pockets remained, which may account for oxygen-consuming pathways in the cells being active after VI. The metabolic activity of the impregnated leaves showed a drastic increase that was further enhanced by the application of PEF to the impregnated tissue. Impregnating the leaves with trehalose by VI led to a significant accumulation of trehalose-6-phosphate (T6P), however, this was not further enhanced by PEF. It is suggested that the accumulation of T6P in the leaves may increase metabolic activity, and increase tissue resistance to abiotic stress.

Interactive Effects of Temperature and Water Status on Processing of Fresh Cut Carrots and Radish

Optimized packaging and storage help to maintain quality of fresh ready-to-use salad mixture. However, product keeping quality is also influenced by processing. Especially slicing should be highly optimized because it inevitably damages product tissue. The mechanical properties of a product affect the cutting resistance. Tissue toughness and stiffness are related to cell wall physical and biochemical properties. They are also influenced by tissue water status and temperature, and their interactions. Hence, these parameters also affect cutting. The aim of this investigation was to characterize the fundamental effects of produce temperature and water status on the cutting force during processing of fresh carrots and radish tubers as model products. This should improve the knowledge about the basics of the processes involved. The results provide the database for reducing tissue damage during cutting procedure thus reducing losses and improving the keeping quality of the products. Both carrot roots and radish tubers were sliced using a microtome knife adapted to a universal testing machine at a cutting speed of either 700 mm min–1 or 600 mm min-1, respectively. In fresh carrots cutting force varied with tissue temperature (in the range from 0 to 40°C) reaching highest values at 5°C. Forces changed with the cutting position in both carrots and radishes. Force rapidly increased when the knife cuts the outer tissue of the tubers and obtained a more or less constant maximum in the middle section. The force-distance curves could be analyzed using a mechanical model that assumes two specific cutting resistances that were constant for both phloem and xylem (carrot), and periderm and cortex (radish) tissue, respectively. Mean produce water potential and mean produce cutting force were positively correlated in carrots and radish although the coefficients of determination were generally low. The results provide helpful information for optimization of the cutting process.