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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: Breathe, Eat, Sleep, Tired, Sick, Die Enzymes still very active Softening, color change, etc. Respiration continues long after harvest Production of water, heat

» Glucose + oxygen => CO2 + H2O + Heat Transpiration continues

» Loss of water (wilting) due to evaporation

Quality of fresh commodities when presented to the consumer depends

on:

1. Initial quality at harvest. 2. Care exercised in physical handling. 3. Length of time since harvest. 4. Storage environment.

Proper temperature management is the single most important tool in maintaining product quality and shelf life.

“It’s the temperature, stupid”.

COOLING BENEFITS

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

PREPARATION FOR PROCESSING

A. WASHING AND CLEANING

For removal of:

1. dirt and dust 2. surface bacteria 3. molds 4. insects 5. other unwanted filth or debris

BLANCHING

Blanching is a hot water or steam treatment that is used to:

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.

2. Remove air in intercellular spaces, will retard oxidative

reactions during storage. Also makes the vegetable more compact.

3. Reduces the number of surface microorganisms, but is not adequate for food preservation.

BLANCHING VEGETABLES

Blanching vegetables helps to maintain color, texture, and flavor during storage since it inactivates deteriorative enzymes eg. peroxidase and catalase.

When cells are frozen decompartmentalization of E & S occur, which leads to deteriorative changes.

Peroxidase and catalase- are used as indicator enzymes to ensure the adequacy of the blanching treatment.

Typically used for vegetables that are to be frozen or dried.

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

1. Growth of microorganisms 2. Biochemical processes (oxidation, chemical and

enzymatic reactions)

OBJECTIVES OF FOOD PRESERVATION:

Retard growth of microorganisms Inactivate enzymes present in the food product Slow and/or prevent undesirable chemical rxns.

BIOCHEMICAL DETERIORATION

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 H2O2 + 2AH2 ------ 2AH + 2H2O------HAAH (polymers)

catalyzes several different reactions substrates are phenolic compounds can cause browning and off flavors Is heat stable, may regenerate after blanch treatments Fairly thermo-stable, so is a good blanching indicator

enzyme

CATALASE 2H2O2 ------ 2H2O + O2

reduces levels of hydrogen peroxide oxidizes pigments and flavor compounds

POLYPHENOLOXIDASE (PPO) catalyzes the oxidation and polymerization of phenolic

compounds when plant tissues are disrupted and exposed to air.

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 Pasteurization

» Refrigerated or non-refrigerated» Milk, orange juice, pickles, salsa

Retort processing» Standard cook at 250°F» Metal cans» 12-D “bot” cook

Fully pasteurizedShelf stable

Commerc. sterile

Lightly pasteurizedKeep 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

Cloudy juices are pasteurized immediately after extraction to prevent microbial and enzymatic breakdown.

Cloud stabilization is due to inactivation of PME and prevention of Ca-pectate formation.

CLEAR JUICES

Juices are not heated immediately after expression

Enzymes are allowed to activate Ascorbic acid may be added to control

browning. Gelatin or bentonite may be added to

precipitate tannins, and control haze formation (fining step).

MINIMALLY PROCESSED FRUITS AND VEGETABLES

DEMAND FOR CONVENIENCE

For fruits and vegetables, high quality usually implies fresh-like quality characteristics of flavor, texture, and appearance.

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

Convenience is an attribute that is usually associated with some type of processing, such as peeling, coring, trimming, and slicing.

Demands for fresh-like quality and convenience » "lightly processed“» "minimally processed“» "value added"

CHEMICAL CHANGES ASSOCIATED WITH MINIMAL PROCESSING

Processing should be as gentle as possible» Avoid bruising and cellular damage.

Damage or wounding results in “decompartmentalization” of enzyme and substrate (results in deleterious changes).

CAT-POD-PPO oxidize vitamins, pigments, and phenolics

REDUCING CELLULAR DAMAGE

Use of very sharp knives Chelate pro-oxidant metal ions (iron and copper) Use a very mild surface heat treatment Lower the pH Controlled/modified storage atmosphere Surface wash TEMPERATURE control

» Being mindful of chill-sensitive products

Modified Atmospheres

CONTROLLED ATMOSPHERES/MODIFIED

ATMOSPHERE

“Controlled Atmosphere” (CA) and “Modified Atmosphere” (MA) The atmospheric composition surrounding produce is

different from that of normal air » 78.08% N2, 20.95% O2, and 0.03% CO2

Usually this involves reduction of O2 levels and/or elevation of CO2 levels.

CA is used in bulk storage of produce MA or MAP (package) is a retail-ready product

GAS PRODUCTION AND DIFUSSION

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)

Barriers to gas diffusion include

» Produce’s natural dermal layers» Bulk packages (boxes)» Wax coatings» Plastic films» Food packaging systems

MODIFYING O2 and CO2

Gas composition also influences respiration rates» Reducing O2 levels to ~8% greatly decreases respiration rates

However, there are limits. » Too low of O2 or» Too high of CO2» Results in toxic environments and gives off-flavors

Elevated CO2 also reduces respiration rate, but ~20% will result in anaerobic products such as acetaldehyde and ethanol.

COMMODITY GENERATED MA

Most MAP systems are generated by the commodity through respiration

The package is sealed in normal air and respiration reduces O2 and increase CO2

Respiration is controlled by temperature and degree of minimal processing

Packaging must be used to allow for GAS EXCHANGE» CO2 must escape the package» O2 must enter the package

Packages are commonly 3-5 times more permeable to CO2 than O2 to prevent anaerobic respiration.