Topic 5 Flashcards
Composition of fruits and vegetables
Water – usually 80%, can be at 95%, starchy vegetables around 50%.
Carbohydrates from 2% to 40%.
Protein between 1 to 5%. Vegetables generally higher than fruits.
Lipids usually 1% or less, olives and avocados are 15 and 20%.
Organic acids – around 3%. Citric, malic, tartaric, oxalic. Usually higher in unripe fruits.
Vitamins and minerals – 90% of dietary vitamin C from fruits and vegetables. Good sources of vitamin A and folic acid. Calcium and iron present.
Volatile compounds – in low concentrations, Important for aroma in fruit.
Physiological development of fruit and vegetables
Major stages: germination, growth, maturation, senescence.
Ripening: commences at last stage of maturation and first stage of senescence. Maybe on or off the planet.
Ripening of fruits: marks completion of development, fruits undergo many physical, physiological, biochemical changes – respiration rate, rate, ethylene production, colour, texture, tissue permeability, carbohydrates, composition, acidity, aroma profiles.
Transform inedible plants issue into attractive product.
Respiration of fruit
Two typical respiratory patterns obtained:
Climacteric – Increase in respiration: coincident with ripening. Commences when fruit has attained maximum size. All other changes associated with the ripening occur.
Non-climacteric – No increase in respiration during ripening. Lower respiration rate in general, ripening changes proceed at slower rates.
Effects of ethylene
Higher production in climacteric fruits, internal concentration is very widely. Non climacteric show little change.
Is known to accelerate ripening of climacteric fruits. Non climacteric only increase rate of respiration.
Other changes during ripening of fruits
Colour – loss of green colour. Fruit attains best eating quality. Carlos is due to degradation caused by pH changes, oxidation, action of chlorophyllases. Loss of chlorophyll is accompanied by appearance of carotenoids.
Breakdown of carbohydrates – degradation of fibrous substances.
Organic acids – the client during ripening, respired or converted to sugars.
Aroma– Production of volatile compounds. Ethylene predominant compound, 50 to 75% of total volatiles produced, does not contribute to aroma.
Factors affecting and metabolic activity and storage life of post harvest produce
Temperature – enzymatic reactions increase exponentially with increases in temperature. Reductions in storage temperature delay on set of ripening of fruits. Ripening occurs only usually between 10 to 30°C, best at 20°C.
Methods of cooling produce – room cooling, forced air calling, hydro cooling, contact icing, vacuum cooling.
Storage atmosphere – gas composition changes rate of restoration of produce, referred to as controlled atmosphere storage or modified atmosphere storage. These: reduced rate of ethylene production, lowest rate of chlorophyll degradation, inhibits breakdown of pectin substances, retention of flavour, inhibit growth of decay organisms. Oxygen in less than 10%.
Ethylene – Kept a low levels, good ventilation, destroyed by ozone, destroyed by potassium permanganate.
Causes of post harvest losses
Physical and mechanical injury
Moisture loss – water loss is a direct loss of sellable weight, produce appears wilted or shrivelled, loss of crispness, undesirable colour changes. Lost by evaporation and transpiration. Determined by ratio of surface area/volume, natural surface coatings, rate of transpiration, temperature, relative humidity, velocity of air.
Physiological disorders: low temperature disorders (accumulation of substrates or deficiency of products, ceased reactions) - chilling injury, physiological disorders; mineral deficiency disorders.
Pathogens – usually fungi, bacteria lack enzymes,
Factors influencing development of microbial decay of produce
Environmental conditions – high temperature and humidity, moisture condensation.
Modified atmosphere storage with increased carbon dioxide and reduced oxygen retards development of decay.
Control of microbial decay of produce
Spray produce with chemical fungicides.
Careful handling it during harvest.
Low temperature storage.
High temperature treatment – brief hot water dip.
Treatment of produce with chemical antimicrobial agents.
Other measures for reducing post harvest losses (not microbial) and improving quality of produce.
Controlled ripening – harvested, transported, ripened to optimum quality under controlled conditions of temperature, relative humidity, application of ethylene.
Controlled degreening - treatment with ethylene under controlled conditions hastens degradation of chlorophyll. Cosmetic treatment.
Sprout inhibitors – sprouting of potato and onion inhibited by the use of several chemicals.
Waxing – artificial application of wax to products that lack waxy skins can prevent or reduce water loss.
Disinfection – fumigation with gas sterilants, storage low temperatures, brief exposure to high temperatures.
Irradiation – Low doses of ionising radiation, not permitted in Australia
Packaging – convenient units for handling, protects produce during storage transport and marketing.
Reasons for processing of fruit and vegetables
To preserve produce so it’s available in off season
Cook produce
Increase variety of produce based products and all the flavours of certain commodities
To destroy or reduce the content of plant toxins: phytohaemagglutinins cause lumping and destructing of red blood cells; lathyrogen cause spastic paralysis; glucosinolates cause goitre enlargement; enzyme inhibitors inhibit digestion and absorption of proteins; cyanogens; oxalates interfere with absorption of calcium in spinach; toxic phenolic
Preparation of fruits and vegetables for processing
Receiving – good quality suitable for intended processing
Cleaning and washing – aspiration, gravity separators, washing procedures, brush washer, high-pressure water jet.
Inspection and sorting – to remove unwonted materials and substandard fruit or vegetables from production line. Detectors based on visible light or infrared radiation, x-rays, TV image analysis.
Trimming and peeling – mechanical, thermal, chemical
Slicing and dicing –
Blanching - inactivates enzymes, kills plant tissues. Advantages shrinks fruit or vegetables, prevents discolouration, cleaning a fact and reduces microbial load. Adequacy checked by measuring residual activity of heat resistant enzymes, peroxidase. Commonly used methods – water blanching, steam blanching, vacuum steam blanching, in can blanching.
Canning operations
Preparation
Feeling
Exhaustion of container – creates a partial vacuum after cooling, removal of oxygen minimises chance of oxidation and corrosion. Achieved by hot filling, vacuum sealing, steam flashing.
Sealing – formation of double seam. Accomplished in vacuum.
Thermal processing and cooling – batch retorts or continuous,
Cooling
Types of freezers
Blast air freezers – tunnel type, spiral belt.
Fluidised bed freezers
Plate freezers
Freezers using cryogenic liquid
Storage of frozen vegetables
Temperature fluctuations – during storage, transport, retailing, leads to growth of ice crystals in product, may damage structure of the tissue and reduce firmness.
