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Fruit and Vegetable Processing Its more than putting peas in a can! Dr. Steve Talcott Professor, Food Chemistry

Fruits and Vegetables – Living systems Postharvested Fruits and Vegetables: l Breathe, Eat, Sleep, Tired, Sick, Die l Enzymes still very active l Softening, color change, etc. l Respiration continues long after harvest l Production of water, heat »Glucose + oxygen => CO 2 + H 2 O + Heat l Transpiration continues »Loss of water (wilting) due to evaporation

Quality of fresh commodities when presented to the consumer depends on: l 1. Initial quality at harvest. l 2. Care exercised in physical handling. l 3. Length of time since harvest. l 4. Storage environment.

l Proper temperature management is the single most important tool in maintaining product quality and shelf life. l “It’s the temperature, stupid”.

COOLING BENEFITS l 1. Removes field heat. l 2. Reduces respiration rate and ethylene production. l 3. Decreases the rate of deterioration. l 4. Reduces rate of water loss. l 5. Limits growth of decay organisms.

PREPARATION FOR PROCESSING

A. WASHING AND CLEANING l For removal of: l 1. dirt and dust l 2. surface bacteria l 3. molds l 4. insects l 5. other unwanted filth or debris

BLANCHING Blanching is a hot water or steam treatment that is used to: l 1. Inactivate enzymes that cause deterioration or loss of quality during storage of frozen products. eg. off flavor due to peroxidase and lipoxygenase enzymes impart earthy, hay, grassy, sour, bitter flavors during storage. l 2. Remove air in intercellular spaces, will retard oxidative reactions during storage. Also makes the vegetable more compact. l 3. Reduces the number of surface microorganisms, but is not adequate for food preservation.

BLANCHING VEGETABLES l Blanching vegetables helps to maintain color, texture, and flavor during storage since it inactivates deteriorative enzymes eg. peroxidase and catalase. l When cells are frozen decompartmentalization of E & S occur, which leads to deteriorative changes. l Peroxidase and catalase- are used as indicator enzymes to ensure the adequacy of the blanching treatment. l Typically used for vegetables that are to be frozen or dried. l Blanching time and temp depends upon the thickness of the product and the amount of enzyme present.

PRINCIPLES OF FOOD PRESERVATION

MAJOR CAUSES OF FOOD DETERIORATION l 1. Growth of microorganisms l 2. Biochemical processes (oxidation, chemical and enzymatic reactions) OBJECTIVES OF FOOD PRESERVATION: l Retard growth of microorganisms l Inactivate enzymes present in the food product l Slow and/or prevent undesirable chemical rxns.

BIOCHEMICAL DETERIORATION l ENZYMES- are proteins that catalyze biochemical rxn's. Enzymatic changes can be desirable or undesirable. In food preservation, steps are taken to inactivate or retard enzymatic rxn's that cause deleterious effects.

EXAMPLES OF DETERIORATIVE ENZYMES PEROXIDASE l H 2 O 2 + 2AH AH + 2H 2 O------HAAH (polymers) l catalyzes several different reactions l substrates are phenolic compounds l can cause browning and off flavors l Is heat stable, may regenerate after blanch treatments l Fairly thermo-stable, so is a good blanching indicator enzyme

CATALASE l 2H 2 O H 2 O + O 2 l reduces levels of hydrogen peroxide l oxidizes pigments and flavor compounds POLYPHENOLOXIDASE (PPO) l catalyzes the oxidation and polymerization of phenolic compounds when plant tissues are disrupted and exposed to air. l causes rapid browning EXAMPLES OF DETERIORATIVE ENZYMES

PROCESSING OF FRUIT JUICES

FRUIT JUICES MAY BE PRESERVED BY A NUMBER OF METHODS : 1. Hot-fill 2. Post-fill pasteurization 3. Aseptic packing (HTST) sterilization and sterilized containers eg. Tetrapak system 4. Juice concentration by evaporation or RO 5. Pasteurize and freeze

Heat Preservation Degree of preservation l Pasteurization »Refrigerated or non-refrigerated »Milk, orange juice, pickles, salsa l Retort processing »Standard cook at 250°F »Metal cans »12-D “bot” cook Fully pasteurized Shelf stable Commerc. sterile Lightly pasteurized Keep Cold Not commerc. sterile

FRUIT JUICES MAY BE CLASSIFIED AS: 1. CLEAR JUICES eg. grape apple, cherries and berries 2. CLOUDY JUICES containing ISS eg. pineapple, orange 3. PULPS containing fibrous and other insoluble materials eg. tomato

CLOUDY JUICES l Cloudy juices are pasteurized immediately after extraction to prevent microbial and enzymatic breakdown. l Cloud stabilization is due to inactivation of PME and prevention of Ca-pectate formation.

CLEAR JUICES l Juices are not heated immediately after expression l Enzymes are allowed to activate l Ascorbic acid may be added to control browning. l Gelatin or bentonite may be added to precipitate tannins, and control haze formation (fining step).

MINIMALLY PROCESSED FRUITS AND VEGETABLES

DEMAND FOR CONVENIENCE l For fruits and vegetables, high quality usually implies fresh-like quality characteristics of flavor, texture, and appearance. l In addition to desire for fresh-like quality, changes in consumers life-styles have led to an increased demand for convenience in food products.

Minimally Processed Products l Convenience is an attribute that is usually associated with some type of processing, such as peeling, coring, trimming, and slicing. l Demands for fresh-like quality and convenience »"lightly processed“ »"minimally processed“ »"value added"

CHEMICAL CHANGES ASSOCIATED WITH MINIMAL PROCESSING l Processing should be as gentle as possible »Avoid bruising and cellular damage. l Damage or wounding results in “decompartmentalization” of enzyme and substrate (results in deleterious changes). l CAT-POD-PPO oxidize vitamins, pigments, and phenolics

REDUCING CELLULAR DAMAGE l Use of very sharp knives l Chelate pro-oxidant metal ions (iron and copper) l Use a very mild surface heat treatment l Lower the pH l Controlled/modified storage atmosphere l Surface wash l TEMPERATURE control »Being mindful of chill-sensitive products

Modified Atmospheres

CONTROLLED ATMOSPHERES/MODIFIED ATMOSPHERE l “Controlled Atmosphere” (CA) and l “Modified Atmosphere” (MA) l The atmospheric composition surrounding produce is different from that of normal air »78.08% N 2, 20.95% O 2, and 0.03% CO 2 l Usually this involves reduction of O 2 levels and/or elevation of CO 2 levels. l CA is used in bulk storage of produce l MA or MAP (package) is a retail-ready product

GAS PRODUCTION AND DIFUSSION l The gas composition in plant tissue (or food package) is controlled by respiration »Pre-harvest (CO2 in and O2 out) »Post-harvest (O2 in and CO2 out) l Barriers to gas diffusion include »Produce’s natural dermal layers »Bulk packages (boxes) »Wax coatings »Plastic films »Food packaging systems

MODIFYING O2 and CO2 l Gas composition also influences respiration rates »Reducing O2 levels to ~8% greatly decreases respiration rates l However, there are limits. »Too low of O2 or »Too high of CO2 »Results in toxic environments and gives off-flavors l Elevated CO2 also reduces respiration rate, but ~20% will result in anaerobic products such as acetaldehyde and ethanol.

COMMODITY GENERATED MA l Most MAP systems are generated by the commodity through respiration l The package is sealed in normal air and respiration reduces O2 and increase CO2 l Respiration is controlled by temperature and degree of minimal processing l Packaging must be used to allow for GAS EXCHANGE »CO2 must escape the package »O2 must enter the package l Packages are commonly 3-5 times more permeable to CO2 than O2 to prevent anaerobic respiration.