FE 401 FOOD TECHNOLOGY FRUIT AND VEGETABLE PROCESSING TECHNOLOGIES
Prof. Dr. Mustafa BAYRAM University of Gaziantep, Faculty of Engineering Department of Food Engineering 27310-Gaziantep-TÜRKİYE Rev3-Nov 23, 2014
CONTENT • Main titles – Fruits – Vegetables • Sub-titles – For fruits and vegetables • Economy • Production, harvesting, consumption • Raw materials, chemical and physical properties • Processing lines & technologies • Machineries and technologies • Quality control
Classification Botanical classification Vegetable: a vegetative part of the plant including roots, stems, and leaves Fruit: a part of the plant which houses seeds including (tomatoes, cucumbers apples, etc)
Composition • Some carbohydrates –Vegetables contain primarily starch –Fruits contain primarily sugars • Little protein (except legumes) • Little fat
Why Do We Eat Fruits & Vegetables? • Essential vitamins • Essential minerals • Fiber • Some energy
RAW MATERIALS Important factors; • Varieties and types • Chemical properties • Physical properties
Physical properties Varietal Differences • Size • Shape • Flavor • Texture • Resistance to damage • Time & Uniformity of maturity
Harvesting & Processing of Vegetables/Fruits
Main stages 1. Pre-Hasvesting 2. Harvesting 3. Post-harvesting (storage, cleaning etc) 4. Receiving to process 5. Processing
1-Preharvest & Harvest Factors • Vegetables/fruits are constantly maturing in the field – must pick at ideal stage of maturity • Maturation & other changes continue after harvest, sometimes more rapidly • Rapid handling is essential • Cooling may be required to slow changes
For preharvesting Fruit Quality depends on; • Variety • Weather • Time of harvest – Flavor – Sugar/acid ratio – Color – Firmness • Harvest – hand vs. mechanical
2-Harvesting • Harvesting at the correct time is essential to the production of quality fruits. • The correct time to pick depends upon several factors; – variety, – location, – weather, – ease of removal from the tree, and – purpose to which the fruit will be put.
• Many quality measurements can be made before a fruit crop is picked in order to determine if proper maturity or degree of ripeness has developed: – Color can be checked with instruments or by comparing the color of fruit on the tree with standard picture charts. – Texture may be measured by compression by hand or by simple type of plungers. – Percentage of soluble solids, which are largely sugars, is generally expressed in degrees Brix, which relates specific gravity of a solution to an equivalent concentration of pure sucrose. The concentration of soluble solids in the juice can be estimated with a refractometer or a hydrometer. The refractometer measures the ability of a solution to bend or refract a light beam, which is proportional to the solution’s concentration. A hydrometer is a weighted spindle with a graduated neck, which floats in the juice at a height related to the juice density. – The acid content of fruit changes with maturity and affects flavor. Acid concentration can be measured by a simple chemical titration on the fruit juice. For many fruits the tartness and flavor are affected by the ratio of sugar to acid. In describing the taste of tartness of several fruits and fruit juices, the term sugar to acid ratio or Brix to acid ratio is commonly used. The higher the Brix the greater the sugar concentration in the juice, the higher the Brix to acid ratio the sweeter and less tart is the juice.
Some correct time: • Oranges change with respect to both sugar and acid as they ripen on the tree: sugar increases and acid decreases. • The ratio of sugar to acid determines the taste and acceptability of the fruit/vegetable. • sugar–acid ratio !!!!!!.
• Ripe fruits/vegetables should be avoided because it will continue to ripen in storage. • If harvested before they have matured, fruits will be more susceptible to storage disorders.
• Harvesting methods: – -by hand by worker – By Mechanical harvesting • For proper harvesting: – the fruit should be picked by hand and placed carefully in the harvesting basket, in order to avoid any mechanical damage; – the harvesting basket and the hands of the harvester should be clean; – the fruit should be picked when it is ready to be processed into a quality product.
3-Post-Harvesting stage • Fruits/vegetables are living tissues and they continue to respire even after they have been harvested. • After harvesting, the organoleptic and nutritional properties of fruits/vegetables deteriorate in different degrees. • (Note:Usual storage life of fruits is between 1 and 7 days at 21 C if proper measures are not taken)
Causes of deterioration include: – the growth and activity of microorganisms, – the activities of the natural food enzymes, – the action of insects and rodents, – changes in temperature and water content, and – the effect of oxygen and light.
Some changes during storage • a) loss of sugars due to their consumption during respiration or their conversion to starch; losses are slower under refrigeration but there is still a great change in vegetable sweetness and freshness of flavour within 2 or 3 days FE 401 Food Techn.-Vegetable Dr. M. BLG arge Co.
• b) production of heat when large stockpiles of vegetables are transported or held prior to processing. • (At room temperature some vegetables will liberate heat at a rate of 127,000 kJ/ton/day; this is enough for each ton of vegetables to melt 363 kg of ice per day. Since the heat further deteriorates the vegetables and speeds micro- organisms growth, the harvested vegetables must be cooled if not processed immediately.) FE 401 Food Techn.-Vegetable Dr. M. BLG arge Co.
• c) the continual loss of water by harvested vegetables due to transpiration, respiration and physical drying of cut surfaces results in wilting of leafy vegetables, loss of plumpness of fleshy vegetables and loss of weight of both. FE 401 Food Techn.-Vegetable Dr. M. BLG arge Co.
• Chemical Treatments for post-harvesting – Harvested fruits are often treated with chemicals to inhibit storage disorders. Dip or spray treatments
Important points for post-harvesting stage: • In case of aerobic respiration, – refrigeration is not enough to retard ripening and foods may not develop desired flavor/texture. • Firmness and the level of soluble solids – are good indicators of maturity in determining picking time. • Fruits/vegetables are normally transported and stored – in bulk boxes (bins) kept in the orchard. • Bins should not be allowed to sit for extended periods – in direct sunlight, nor for more than a few hours before cooling is started
Important points for post- harvesting stage • Simple stores should be covered, fairly cool, dry and well ventilated but without forced air circulation which can induce significant losses in weight through intensive water evaporation; air relative humidity should be at about 70-80%.
• A major economic loss occurs during transportation and/or storage of fresh fruits/vegetables due to the effect of respiration. USE REFRIGERATION (COOLING) TO REDUCE RATE OF RESPIRATION • (For example:Apples, respire and degrade twice as fast at 4.5 C as at 0 C. – At 16 C they will respire and degrade more than six times faster. Note: Refrigerated trucks are not designed to cool fresh commodities. They can only maintain the temperature of previously cooled products.
• fruits/vegetable require humidity to preserve, which may be reached by adding water vapor to the air in the storage room with one or more humidifiers. • Maintaining the humidity within this range will also reduce weight loss. • Humidity near the saturation point will promote the growth of bacteria and fungi.
Optimal conditions for fresh vegetable storage Vegetables Storage conditions Temperature, °C Relative humidity, % Potatoes +1…+3 85-90 Carrots 0 … +1 90-95 Onions 0 … +1 75-85 Leeks 0 … +0.5 85-90 Cabbage -1 … 0 90-97 Garlic 0 … +1 85-90 Beets 0 … +1 90-95 FE 401 Food Techn.-Vegetable Dr. M. BLG arge Co.
• During post-harvesting, there are some methods: – Cooling – Special methods – (controlled atmosphere and Modified atmosphere)
• Cooling: • Proper postharvest cooling is advisable to: – suppress enzymatic degradation (softening) and respiratory activity; – slow down or inhibit water loss (wilting); – slow down or inhibit the growth of decay- producing microorganisms (molds and bacteria); – reduce the production of ethylene (a ripening agent) or minimize the commodity’s reaction to ethylene.
Cooling Methods for post-harvesting – room cooling, – forced-air cooling, – vacuum cooling, – hydrocooling, – package icing, – top icing. • One of the common and least expensive methods for cooling fruits is room cooling
• Hydrocooling is one of the quickest methods for removing field heat from fruits. (Cooling with cold spray/pool water)
Special methods: (1-Controlled and 2-Modified atmosphere) 1. Controlled atmosphere (CA) storage prolongs product life by lowering the oxygen concentration and increasing the carbon dioxide concentration in the storage atmosphere. • The effects of CA are based on the often-observed slowing of plant respiration in low O2 environments.
• As the concentration of O2 falls below about 10%, respiration starts to slow. • This suppression of respiration continues until O2 reaches about 2–4%. • (Details:Depending on product and temperature, if O2 gets lower than 2–4%, fermentative metabolism replaces normal aerobic metabolism; and off-flavors, off-odors, and undesirable volatiles are produced. Similarly, as CO2 increases above the 0.03% found in air, a suppression of respiration results for some commodities. Reduced O2 and elevated CO2 together can reduce respiration more than either alone. These concentrations of oxygen and carbon dioxide also reduce the ability of the ethylene produced by ripening fruits to further accelerate fruit ripening.)
• CA storage facilities are specially constructed, airtight cold storage rooms with auxiliary equipment to monitor and maintain specific gaseous atmospheres. • Oxygen, carbon dioxide, and ethylene levels should be monitored daily and controlled within narrow limits.
2- Modified atmosphere • Due to respiration of vegetables and fruits, permeable film/package can be used to oxygen and carbondioxide permeate. • If the packaging film is semipermeable O2 and CO2 equilibrium concentration of both gases is established the package is equal to the rate of respiration.
The main disadvantages are: • cost increase • need of temperature control • different gas formulations for each product type • special equipment and personnel training • product safety.
• The three main gases used commercially in MAP are oxygen, nitrogen, and carbon dioxide. Details: • Carbon dioxide is important because of its biostatic activity against many spoilage organisms that grow at refrigeration temperatures. • Oxygen inhibits the growth of anaerobic pathogens, but in many cases does not directly extend shelf life. • Nitrogen is used as a filler gas to prevent pack collapse, which may occur in high CO2-containing atmospheres. • The package must be made from a suitable material. PVC and LDPE are the most commonly used films.
4-5) Receiving and Processing • Receiving/acceptance • Washing • Skin removal –Lye peeling –Pressure steam peeling –Flame peeling –Mechanical
• Cutting & trimming –stemming –pitting –coring • Blanching – heating to deactivate enzymes –Steam –Hot water • Canning
• Freezing • Juice Extraction – may use peeling (citrus) and heating (grapes) prior to pressing • Clarification • Deaeration • Pasteurization • Concentration • Essence add-back
During Processing DETERIORATION BY BROWNING !!! • ENZYMATIC BROWNING • NONENZYMATIC BROWNING (sugar+a.a.)
Some important processing steps
1- RAW MATERIAL RECEPTION TECHNIQUES
2- Washing • Washing is used not only to remove field soil and surface micro-organisms but also to remove fungicides, insecticides and other pesticides, since there are laws specifying maximum levels of these materials that may be retained on the vegetable; and in most cases the allowable residual level is virtually zero. • Washing water contains detergents or other sanitisers that can essentially completely remove these residues.
• The washing equipment, like all equipment subsequently used, will depend upon the size, shape and fragility of the particular kind of vegetable: – flotation cleaner for peas and other small vegetables; – rotary washer in which vegetables are tumbled while they are sprayed with jets of water; this type of washer should not be used to clean fragile vegetables
3-SORTING This step covers two separate operations: a) removal of non-standard vegetables (and fruit) and possible foreign bodies remaining after washing; b) quality grading based on variety, dimensional, organoleptical and maturity stage criterion.
• Manual peeling only use when the other methods are impossible or sometimes as a completion of the other three ways. Losses at vegetable peeling, in % Peeling methods Vegetables Manual Mechanical Chemical Potatoes 15-19 18-28 – Carrots 13-15 16-18 8-10 Beets 1416 13-15 9-10 Mechanical peeling • a machine with abrasion device (potatoes, root vegetables); • equipment with knives (apples, pears, potatoes, etc.); • equipment with rotating sieve drums (root vegetables). Sometimes this operation is simultaneous with washing (potatoes, carrots, etc.) or preceded by blanching (carrots).
5- Extraction (juice)
9- Blanching. • The special heat treatment to inactivate enzymes (peroxidase and catalase as indicator due to their resistivity) is known as blanching. – Blanching is not indiscriminate heating. – Too little is ineffective, and too much damages the vegetables by excessive cooking, especially where the fresh character of the vegetable is subsequently to be preserved by processing. • This heat treatment is applied according to and depends upon the specificity of vegetables, the objectives that are followed and the subsequent processing / preservation methods.
Blanching parameters for some vegetables Vegetables Temperature, °C Time, min. Peas 85-90 2-7 Green beans 90-95 2-5 Cauliflower Boiling 2 Carrots 90 3-5 Peppers 90 3 FE 401 Food Techn.-Vegetable Dr. M. BLG arge Co.
On-line simplified methods for enzyme activity check • Two of the more heat resistant enzymes important in vegetables are catalase and peroxidase. – If these are destroyed then the other significant enzymes in vegetables also will have been inactivated. The heat treatment to destroy catalase and peroxidase in different vegetables are known, and sensitive chemical tests have been developed to detect the amounts of these enzymes that might survive a blanching treatment. – Small vegetables may be adequately blanched in boiling water in a minute or two, large vegetables may require several minutes.
• Peroxidase test – The contents of the test tube is shaken well. The gradual appearance of a weak pink colour indicates an incomplete peroxidase inactivation – reaction slightly positive. If there are no tissue colour modifications after 5 minutes, the reaction is negative and the enzymes have been inactivated. • Catalase test – These tests are of a paramount importance in order to determine the vegetable blanching treatments (temperature and time); incomplete enzyme inactivation has a negative effect on finished product quality. • For all other vegetables and for potatoes, both tests MUST be negative, for catalase and for peroxidase.
10-Drying/dehydration 1)Dryers with plates under vacuum are equipped with plates heated with hot water. » Stainless steel plates containing the purée to be dried are placed on them. » Process conditions are at low residual pressure (about 10-20 mm Hg) and a product temperature of 50-70° C. » This equipment is discontinuous but easy to operate.
2)Drum dryers have one or two drums heated with hot water or steam as heating elements. » Feeding is continuous between the two drums which are rotating in reverse direction (about 2-6 rotations per minute) and the distance of which is adjustable and determines the thickness of layer to be dried. he product is dried and removed by mechanical means during rotation. 3) Drying installations by spraying in hot air; the product is introduced in equipment and sprayed by a special device in hot air. » Drying is instantaneous (1/50 s) and therefore can be carried out at 130- 15O° C.
OVERALL FLOWCHART FOR FRESH CLEANED/PACKED FRUITS AND VEGETABLES 1. Pre-Hasvesting 2. Harvesting 3. Post-harvesting (storage, cleaning etc) 4. Receiving to process 5. Processing
TO GO only cleaned and packaged fruits/vegetables lines)
only cleaned and packaged fruits/vegetables lines)
Process: Fruit Juice/Pulps/Puree/Semi
FRUIT JUICE PROCESSING JUICE AND CONCENTRATE
APPLE JUICE CONCENTRATE PROCESSING (a) Alternative 1 (b) Alternative 2
PROCESS: Technological flow-sheet for vegetable canning in salt solution (brine) Storage silo (1) Sorting (2) Washing (3) Grading (4) Preliminary operations Cleaning (5) Cutting (6) Blanching (7) or steaming (8) Cooling (9) Receptacle filling (10) Preheating (11) Hermetic sealing (12) Sterilisation (13) Cooling (14) Labelling (15) Storage (16)
Orientative technical data for canned vegetables in salt brine
PROCESS: Flow-sheet for vegetable canning in vegetable oil Reception (1) Sorting (2) Cleaning/peeling (3) Washing (4) Cutting (5) —————————— Frying (6) or Blanching (7) Cooling (8) Filling and adding of vegetable oil, sauce or tomato concentrated juice (9) —————————— Sealing (10) Sterilisation (11) Cooling (12) Labelling (13) Storage (14)
BRIEF INFORMATIONS FOR SOME PRODUCTS 1- Canned products
2- Frozen products
3- Dried products
4- Juice products
5- Marmalade products
Tomato juice • The modern technological flow-sheet covers the following main operations: • PRE-WASHING is carried out by immersion in water, cold or heated up to 50° C (possibly with detergents to eliminate traces of pesticides). This operation is facilitated by bubbling compressed air in the immersion vessel/equipment. • WASHING is performed with water sprays, which in modern installations have a pressure of 15 at or more. • SORTING/CONTROL on rolling sorting tables enables the removal of non-standard tomatoes – with green parts, yellow coloured, etc.
• CRUSHING in special equipment. • PREHEATING at 55-60° C facilitates the extraction, dissolves pectic substances and contributes to the maintaining of vitamins and natural pigments. In some modern installations, this step is carried out under vacuum at 630-680 mm Hg and in very short time. • EXTRACTION of juice and part of pulp (maximum 80%) is performed in special equipment / tomato extractors with the care to avoid excessive air incorporation. In some installations, as an additional special care, a part of pulp is removed with continuous centrifugal separators.
• DE-AERATION under high vacuum of the juice brings about its boiling at 35-40° C. • HOMOGENISATION is done for mincing of pulp particles and is mandatory in order to avoid future potential product “separation” in two layers. • FLASH Pasteurization at 130-150° C, time = 8-12 see, is followed by cooling at 90° C, which is also the filling temperature in receptacles (cans or bottles). • ASEPTIC FILLING • CLOSING OF RECEPTACLES is followed by their inversion for about 5 to 7 minutes. • COOLING has to be carried out intensely.
Receptacle size Pre-heating Time of pasteurization 0.33 1 60° C 40 minutes 0.501 60° C 45 minutes 0.66 1 60° C 55 minutes 0.751 60° C 60 minutes 1.0 litre 60° C 70 minutes
Carrot juice • This product represents an important dietetic product due to its high soluble pectin content. Technological flow-sheet is oriented to the maintaining of as high as possible a pectin content and covers the following steps: • PRE-WASHING • CLEANING • WASHING • BLANCHING in steam for 20 minutes
• GRATING • PRESSING • JUICE In the pressed juice will then be incorporated 25% of grated carrot (non pressed) • HOMOGENISATION in colloidal mills • ACIDIFICATION with 0.25% citric or tartric acid • DE-AERATION • FILLING in receptacles (bottles or tinplate cans) • AIRTIGHT SEALING Pasteurization at 100° C for 30 minutes.
• The main characteristics of a good quality carrot juice: • uniformity (no separation in layers occurs during storage); • good orange colour; • pleasant taste, close to fresh carrot taste; • total soluble solids: 12 %; • total sugar content: 8%; • beta-carotene: 1.3 mg/100 ml; • soluble pectin: 0.4 %.
Red beet juice • The product is obtained following this technological flow-sheet: washing, cleaning, steam treatment / steaming (30-35 min at 1050 C), pressing, strain through small hole sieve, filling in receptacles, tight sealing / closing, sterilisation (25 min at 1 15° C). • In order to improve taste, the juice is acidified with 0.3% citric or tartric acid.
Concentrated tomato products Tomato paste • The product with highest production volumes among concentrated products is tomato paste which is manufactured in a various range of concentrations, up to 44% refractometric extract. • Tomato paste is the product obtained by removal of peel and seeds from tomatoes, followed by concentration of juice by evaporation under vacuum. • In some cases, in order to prolong production period, it may be advisable or possible to preserve crushed tomatoes with sulphur dioxide as described under semi-processed fruit “pulps”.
• Technological flow-sheets run according to equipment/ installation lay-outs, which are especially designed for this finished product. • Manufacturing steps fall into three successive categories: • obtaining juice from raw materials; • juice concentration and • tomato paste pasteurization.
• a) Obtaining juice from raw material. – Preliminary operations (pre-washing, washing and sorting / control) are carried out in the same conditions as for manufacturing of “drinking” tomato juice described above. – Next operation is removal of seeds from raw tomatoes: tomato crushing and seed separation with a centrifugal separator. – Tomato pulp is pre-heated at 55-60° C and then passed to the equipment group for sieving: pulper, refiner and superrefiner with sieves of 1.5 mm, 0.8 mm and 0.4-0.5 mm respectively in order to give the smoothest possible consistency to the tomato paste.
• b) Juice is concentrated by vacuum evaporation, a technological step which in modern installations runs continuously, tomato paste from the last evaporation step being at the specified concentration. – In continuous installations with three evaporation steps (evaporating bodies), the juice is submitted in step / body I to pasteurization at 85- 90 C for 15 min and this will determine the microbiological stability of finished product. Vacuum degree corresponding to this temperature is 330 mm Hg. – In evaporating bodies II and III, temperatures are around 42-46° C and vacuum at 680-700 mm Hg.
General technological flow-sheet for vegetable dehydration in belt dryers
Moisture and shipping factors for some dehydrated vegetables Product Form/cut Moisture % Weight kg/m³ Bean (green) 20 nun cut 5 1.6 Bean (lima) 5 3.3 Beet 6 mm strips 5 1.6-1.9 Cabbage 6-12 mm shreds 4 0.7-0.9 Carrots 5-8 mm strips 5 3-5 Celery Cut 4 Garlic Cloves 4 Okra 6 mm slices 8 Onion Slices 4 0.4- 0.6 Pea (fresh) Whole 5 3.4 Pepper (hot) Ground 5 Pepper (sweet) 5 mm strips 7 Potato (Irish) 5-8 mm strips 6 2.9-3.2 Diced 5 3.3-3.6 Tomato 7-10 mm slices 35
Dehydrated products potential defects and means to prevent them
Technical data for vegetable dehydration in tunnels
Technology for vegetable/fruit powder processing • This technology has been developed in recent years with applications mainly for potatoes (flour, flakes, granulated), carrots (powder) and red tomatoes (powder). • In order to obtain these finished products there are two processes: • a) drying of vegetables down to a final water content below 4% followed by grinding, sieving and packing of products; • b) vegetables are transformed by boiling and sieving into purées which are then dried on heated surfaces (under vacuum preferably) or by spraying in hot air.
Technological data for vegetable powders
(DETAILS-HOME STUDY) • SPECIAL APPLICATIONS • EQUIPMENTS
• 1- Chemical preservation may be carried out with sulfur dioxide, sodium benzoate, formic acid, and, on a small scale, with sorbic acid and sorbates. • 2- Heat treatment. As fruits have a low pH, preservation of semiprocessed fruit products by heat treatment step at maximum temperature of 100 C, can be done (pasteurization). – This treatment results in a more hygienic process, thereby assuring long-term preservation. – However, air-tight containers are needed and pectic substances could deteriorate if the thermal treatment is too long. • 3- Freezing. Freezing is applied to semiprocessed fruit products with a very high quality and cost. – This can be done with or without sugar addition. – The obvious advantages of this process are the absence of added substances, a very good preservation of quality of fruit constituents (pectic substances, vitamins, etc.), and good preservation of organoleptic properties. – Freezing is done at about 20 to 30 C and storage at 10 to 18C