FRUITS AND VEGETABLES CONTINUE METABOLIC PROCESSES AFTER BEING HARVESTED. IN SOME PRODUCE, MAINLY CLIMACTERIC FRUITS, THESE PROCESSES CAUSE DETERIORATION OF THE PRODUCE DURING STORAGE. TO REDUCE THE DETERIORATION RATE, SEVERAL STRATEGIES HAVE BEEN IMPLEMENTED FOR POSTHARVEST HANDLING. ONE OF THESE PRESERVATION STRATEGIES IS MODIFIED ATMOSPHERE PACKAGING (MAP). IN THIS TECHNOLOGY, THE RESPIRATION RATE OF THE PRODUCE AND THE GAS PERMEABILITY OF THE STORAGE FILM ARE THE TWO FUNDAMENTAL KINETIC PROCESSES ACCOUNTED FOR IN DESIGNING THE PACKAGING SYSTEM. TO UNDERSTAND THE RELATIONSHIP OF THESE TWO KINETIC PROCESSES DURING PACKAGING IN MODIFIED ATMOSPHERES, TWO MAJOR TECHNIQUES HAVE BEEN PRESENTED FROM THE STANDPOINT OF MATHEMATICAL MODELING: THE CLASSIC RESPIRATION RATE MODELS AND THE REACTION-DIFFUSION MODEL. IN THE CLASSIC MODEL OF RESPIRATION RATE, FOUR TYPES OF BLACK BOX MODEL APPROACHES HAVE BEEN PROPOSED: LINEAR, POLYNOMIAL, EXPONENTIAL, AND THE MICHAELIS?MENTEN KINETIC MODELS. FOR THE LAST BLACK BOX MODEL, FOUR TYPES OF INHIBITION APPROACHES ARE CONSIDERED: COMPETITIVE, UNCOMPETITIVE, NONCOMPETITIVE, AND, FINALLY, A COMBINATION OF COMPETITIVE AND UNCOMPETITIVE INHIBITION. IN THE REACTION-DIFFUSION MODEL, IT HAS BEEN CONSIDERED THAT THE TRANSPORT OF A SPECIES IN MODIFIED ATMOSPHERE PACKAGING (MASS TRANSPORT IN THE HEADSPACE AND THE FILM USED AS PACKAGING) OBEYS STRICTLY DIFFUSIVE TRANSPORT MODELS. FOR THIS REASON, THE MAIN OBJECTIVE OF THIS REVIEW IS TO SHOW THE ADVANCES IN THE TWO MAJOR TECHNIQUES (CLASSIC RESPIRATION RATE MODELS AND THE REACTION-DIFFUSION MODEL) IMPLEMENTED TO DESCRIBE THE MAP OF FRUIT AND VEGETABLES, AS DESCRIBED IN SPECIALIZED LITERATURE.

DIFFERENT STUDIES HAVE EMPHASIZED THE IMPORTANCE OF COOLING IN OIL ABSORPTION AFTER FRYING, SUGGESTING THAT THE LARGEST PROPORTION OF OIL IS SUCKED INTO THE CRUST AFTER THE PRODUCT IS REMOVED FROM THE OIL. MICROSCOPY HAS BEEN A POWERFUL TOOL TO SUPPORT THESE DETERMINATIONS, BUT, DIRECT OBSERVATION OF FLUXES HAS NOT YET BEEN POSSIBLE. THE AIM OF THIS RESEARCH WAS TO DEVELOP AN EXPERIMENTAL PROCEDURE BASED ON THE USE OF GLASS MICROMODELS TO GET DIRECT EVIDENCE OF TRANSPORT PHENOMENA DURING OIL IMMERSION FOR THE FIRST TIME. TO DO SO, MICROMODELS WERE SATURATED WITH WATER AND IMMERSED IN OIL AT 190 °C. FLUIDS DISPLACEMENTS WERE MONITORED USING VIDEO-MICROSCOPY AS WELL AS FLUORESCENCE MICROSCOPY. RESULTS SHOWED THAT ONLY A SMALL FRACTION OF OIL PENETRATED DURING THE IMMERSION PERIOD, DUE TO THE VIGOROUS ESCAPE OF BUBBLES. ONCE THE RELEASE OF STEAM STOPPED, AFTER SOME INITIAL COOLING, OIL-UPTAKE BEGAN ABRUPTLY AND OIL MOVEMENT INTO THE PORES COULD BE CLEARLY IDENTIFIED. OIL ABSORPTION ENDED AS SOON AS THE OIL FILM LOST CONTINUITY, DUE TO AIR PENETRATION. OVERALL, THE DEVELOPED TECHNIQUE ILLUSTRATES HOW GLASS MICROMODELS MAY BE USED TO VISUALIZE AND PROVIDE VALUABLE INFORMATION TO UNDERSTAND KEY TRANSPORT PHENOMENA DURING PROCESSING.

THE RELATIONSHIP BETWEEN WATER CONTENT AND CAPILLARY PRESSURE AND THE MICROSTRUCTURAL CHANGES IN APPLES (GRANNY SMITH) DURING DRYING WAS STUDIED. APPLES WERE DRIED IN A PILOT TRAY DRYER AND SAMPLES, WITH DIFFERENT MOISTURE CONTENTS, WERE PUT IN LIQUID NITROGEN. THE REMAINING WATER WAS ELIMINATED BY THE CRITICAL POINT METHOD TO AVOID STRUCTURAL CHANGES AND SAMPLES WERE THEN OBSERVED BY SCANNING ELECTRON MICROSCOPY (SEM). IT WAS POSSIBLE TO CHARACTERIZE THE INTERNAL SPACE OF THE APPLES DURING DRYING AND FIND A RELATIONSHIP BETWEEN THE DRYING RATE AND MICROSTRUCTURAL CHANGES. WE POSTULATE THAT SHRINKAGE DURING DRYING IS MAINLY DUE TO CHANGES IN CAPILLARY PRESSURE.

AVOCADO BYPRODUCTS ARE A RICH SOURCE OF HEALTH-PROMOTING BIOMOLECULES. THE PURPOSE OF THIS WORK IS TO STUDY THREE GROUPS OF STATISTICALLY DIFFERENT AVOCADO FRUIT SIZES (PERSEA AMERICANA MILL.) (SMALL (S), MEDIUM (M), AND LARGE (L)), AND THEIR RELATIONSHIP WITH TOTAL PHENOLIC AND FLAVONOID CONTENTS (TPC AND TFC, RESPECTIVELY), DPPH (2,2-DIPHENYL-1-PICRYLHYDRAZYL) SCAVENGING CAPACITY AND INDIVIDUAL PHENOLICS, AND THE ACTIVITIES OF PHENYLALANINE AMMONIA-LYASE (PAL), CHALCONE SYNTHASE (CHS), AND POLYPHENOL OXIDASE (PPO) IN AVOCADO PEEL EXTRACT (APE). THE RESULTS INDICATED THAT TPC, TFC, AND ANTIOXIDANT AND ENZYMATIC ACTIVITIES WERE HIGHER IN THE APE OF THE S GROUP (P < 0.05). THE FLAVONOIDS (FLAVANOLS AND FLAVONOLS) AND PHENOLIC ACIDS WERE ALSO SIGNIFICATIVELY CONCENTRATED IN S GROUP?S APE. OVERALL, THE PHENOLIC CONTENT WAS SIGNIFICANTLY LOWER IN THE L GROUP. POSITIVE CORRELATIONS (P < 0.0001 AND P < 0.05) WERE OBSERVED BETWEEN TPC, TPF, DPPH, AND ENZYMATIC ACTIVITY, AND NEGATIVE CORRELATIONS RESULTED FOR AVOCADO WEIGHT AND VOLUME. THE OUTSTANDING PHENOLIC CONTENT AND ENZYMATIC ACTIVITY OF AVOCADO PEELS FROM LOW-COST AVOCADO BYPRODUCTS ARE IDEAL FOR BIOREFINERY APPLICATIONS, THEREBY INCREASING THE BIOECONOMY OF THE AVOCADO INDUSTRY.

VACUUM IMPREGNATION IS A PROCESS METHOD IN WHICH AIR AND NATIVE SOLUTION ARE REMOVED FROM THE POROUS SPACE OF A GIVEN POROUS MATERIAL AND REPLACED BY AN EXTERNAL SOLUTION. VACUUM IMPREGNATION IS DIVIDED INTO TWO STEPS: FIRSTLY, THE POROUS MATERIAL IS IMMERSED IN A LIQUID SOLUTION AND EXPOSED TO SUBATMOSPHERIC PRESSURE FOR A GIVEN TIME TO ENSURE THAT AIR TRAPPED IN THE POROUS MATERIALS WILL BE REMOVED; SECONDLY, ATMOSPHERIC PRESSURE IS RE-ESTABLISHED AND THE EXTERNAL SOLUTION PENETRATES THE PORE STRUCTURE OF THE POROUS MATERIAL. THE OBJECTIVE OF THIS STUDY WAS TO DESCRIBE THE HYDRODYNAMIC MECHANISMS INVOLVED IN VACUUM IMPREGNATION OF POROUS MATERIALS AS A FUNCTION OF CAPILLARY NUMBER AND VISCOSITY RATIO. TO ACHIEVE THE OBJECTIVES PROPOSED IN THE PRESENT STUDY, A TRANSPARENT GLASS MICROMODEL 7.7 CM × 7.4 CM WAS FIRST CONSTRUCTED USING THE PHOTOLITHOGRAPHIC TECHNIQUE. IN ADDITION, A STAINLESS STEEL VACUUM TANK WAS BUILT. THE TANK TOP WAS COVERED WITH A TRANSPARENT REINFORCED GLASS PLATE. THE WHOLE SYSTEM WAS CONNECTED TO A VACUUM PUMP, AND A CONVENTIONAL VIDEO CAMERA WAS ADAPTED TO RECORD THE EXPERIMENTS. LIQUID SATURATION WAS DETERMINED THROUGH THE IMAGE ANALYSIS PROCESS. CAPILLARY NUMBER AND VISCOSITY RATIO WERE DETERMINED FOR THE DRAINAGE AND IMBIBITION PROCESSES. FOR THE SYSTEMS STUDIED, WE CONCLUDE THAT TRANSPORT MECHANISMS RANGED BETWEEN STABLE DISPLACEMENT AND CAPILLARY FINGERING DURING THE VACUUM STEP (DRAINAGE) WHILE TRANSPORT MECHANISMS RANGED BETWEEN CONTINUOUS CAPILLARY AND DISCONTINUOUS CAPILLARY DOMAINS DURING THE ATMOSPHERIC STEP (IMBIBITION). EARLIER WORK INDICATED THAT OUR PROPOSED PROCESS SHOULD BE EVEN MORE EFFICIENT FOR REALISTICALLY LARGE SYSTEMS.