Post-harvest behaviour of different crop categories Flashcards
Please give a categorization of crops by region?
-
Fruits from temperate zone:
pome fruits (pip fruits), stone fruits (drupes), small fruits, berries -
Subtropical fruits:
citrus fruit, avocado, persimmon, pomegranate -
Tropical:
banana, mango, papaya, pineapple others: passion fruit, lychee, rambutan,…
Please give a categorization crops by their ripening behaviour?
1. CLIMACTERIC FRUITS (apple, pear, apricot, peach, plum, kiwi, avocado..)
- mature (fully developed) fruits ripen also after beeing separated by the originating plant
- Ethylene production during ripening
- Influence of ethylene on ripening process
2. NON-CLIMACTERIC FRUITS (berries, grape, cherry, citrus, pineapple, lychee, pomegranate)
- the ripening is not continued after separation from the originating plant
- Very low ethylene production
- Ripening processes not influenced by ethylene
The optimal ripening stage for maintaining quality after harvest == compromise between: highest possible quality and best storage potential
What are negative quality effects influenced by ethylen?
- Decay: fresh produce and flower bulbs
- Russet spotting: leafy vegetables and eggplants Yellowing: cucumbers, broccoli and brussel sprouts Odor: garlic and onions
- Wilting: vegetables and cut flowers
- Scald and loss of crunch apples
- Rind breakdown: citrus
Whats is the categorization of crops according to their potential post-harvest life-span?
- Lowest temperature tolerated
- Longest life-span at ideal temperature
- Metabolic activity and fruit development duration
What are post harvest factors for quality degradadtion?
- Metabolic stress (Senescence, Physiological disorders)
- Transpiration (Water loss, weight loss, profit loss, quality loss)
- Mechanical injuries (Wounds)
- Microorganisms (facilitated by senescence, physiological disorders, wounds, hygen)
What are the HACCP Principles?
- Hazard assessment (all steps reg. biol., chem., physical. hazards)
- Defining Critical Control Points (where lack of control results in unacceptable risk)
- Compilation of Specifications (critical values and tolerances)
- Development of Procedures for monitoring & testing
- Creation of Amendment procedures
- Documentation: functionality of HACCP,
- Verification: operationality HACCP reg. whole process
What should the HACCP outcomes be?
- Surveillance of hazards and health risks
- Improvement of processes
- Control on product outage
- Waste reduction
- Cost reduction
- Consumer trust
- HACCP demand to supplier
How can we define quality?
Quality = Fulfillment of Expectations
What are the main post harvest quality criteria for consumer?
- Appearance- size, color, shape
- Freshness & perfection- Ripeness, Mechanical injuries
- Texture (The mouthfeel)- Firmness, Crunchiness, Juiciness, Mealiness
- Flavour- Taste+Aroma
- Nutritional value- Not instantly recognizable
- Safety/hygiene- Pesticide residues, Microbial contaminations
What are the two main post harvest losses?
- Quantitative losses (shrivelling, rots, mechanical injuries, physiological disorders)
- Qualitative losses (loss of taste, aroma, acidity, sweetness, color change, texture changes, nutritional value)
What are the main quality management systems?
1. Quality Assurance (QA)
- intentional Planning of all quality- and safety-related activities
- continuous Monitoring and Evaluating of all product related procedures and processes
2. Quality Control (QC)
- Definition of Quality and Safety
- by assessing: well defined criteria or specifications
- Integration of preventive measures is encouraged
What are the HACCP critical points in post harvest?
1. pH/organic acids
- C. botulinum > pH 4.5 or > 3 °C
- Yeasts, fungi < pH 4.5
2. Respiration vs. storeability
- Apple @25°C 5xhigher as @ 5°C
- Bruising increases respiration
- *3. Harvest moment
4. Post-harvest handling** - Bruising, wounds, cold chain, storage conditions
5. Hygiene and sanitation
- staff, equipment, rooms, container
What are the factors that contribute to post harvest physiological disorders?
- Developmental stage (under developed)
- Agronomical conditions (crop density)
- Nutritional supply
- Meteorological conditions
- Pedoclimatic conditions (soil, site)
- Storage conditions
What are common post harvest disorders and how are they expressed?
- Un-ripe: common scald
- Advanced ripeness: internal flesh browning, Jonathan-Spot
- Over-ripe: senescent scald, break down
- Too low temperature: flesh browning, soft scald, chilling injury
- CA (extreme O2/CO2): skin-, flesh-discoloration, tissue deformation, flavour change
- Developmental disorders: bitter pit, water core
How can the superficial sclad be prevented in post-harvest?
1. Lowest possible O2-level
- Purging, hypobaric storage
- DCA: dynamically controlled atmosphere)
2. Antioxidants treatment
- Diphenylamine
- Ethoxyquine
3. Alpha-farnesene elimination
- accumulation in ‘oil’ films
4. Ethylene-inhibition
- 1-methylcyclopropene (1-MCP)
- CO -shock
What are the causes for bitter pit?
- Lower calyx: lowest Ca supply
- K/Ca (N/Ca) ratio too high
- Ca-deficiency -> cell walls
- Water core sometimes before necroses
- Involvement of carbohydrate metabolism
- Browning phenoloxidases
How can bitter pit be prevented?
1. Forecasting-Methods
- Fruit mineral analyses (K/Ca ratio > 25)
- 2-Chlorethanphosphonsäure -> Ethylen → symptoms
- Mg-infiltration → symptoms
2. Prevention
- Pre-harvest: good supply with nutrients, irrigation
- Pre-harvest: additional Ca foliar nutrition
- Post-harvest: Ca dipping
What is bitter pit?
- Dark-green to brown, bitter spots in the fruit flesh
- necroses (3-10 mm)
- deep corky pits
- Mainly around the calyx
What is internal flesh browning?
- All disorders regarding the inner fruit tissues
- By: low temperatures
- By: anaerobic processes -> toxic compounds
- Browning ist the result of cell damage
Influencing factors:
- Over-ripeness: high metabolic activity, senescence
- Oversize: weak cell cohesion/structure, little cations
- High rainfall
- high N, little Ca
- low crop load
What are the most important storage factors?
- Temperature
- Air recirculation
- Air humidity
- Air composition (CA)
What are the main functions of the storage factor temperature?
- Temperature influences mainly: speed and intensity of metabolism
- Cooling= Heat removal
- Aim: Max. ripening inhibition WITHOUT physiological disorders
- Rapid cooling (e.g. pears) Stepwise cooling
What are the main functions of the storage factor air recirculation?
- Uniform distribution of: Temperature, Humidity and other atmosphere components (organ. compounds)
- Heat distributive processes: Convection, Radiation, Ventilation
- Avoid water loss
- Avoid air stratification
- Parameters: Air recirculation number and Air velocity
What are the main functions of the storage factor air humidity?
- Prevent weight loss through water evaporation (ca. 5percent due to respiration and ca. 95 due to transpiration)
- No transpiration at RH>98 percent- equilibrium between turgor of the fruit and partial preassure gradient of the air
- Transpiration influenced by: Specific permeability of the fruit, Developing stage, Maturity stage, Storage conditions
- Problem: Too high RH= Accumulation of phytotoxic metabolites (ethanol) and risk of pyhsiological disorders (internal browning or sclad)
- Ideal RH between 92-98% = min. weight loss and no free water on fruits
What are potential ways to passively control transpiration?
- COATINGS with: mineral oil, wax, polymers
But: uncontrollable interactions with respiration and Additional costs
- Advantage: senescence delay
What are the main functions of the storage factor controlled atmosphare (CA)?
- Delay of ripening processes by partial inhibition respiratory activity
- By modification of atmoshpere composition: Decrease of O2>
- CA conditions reduce: Organic Acid conversion, Mitochondria activity (respiration) and Ethylene turnover
What are the effects of a controlled atmosphere on fruit?
CA delays:
- Chlorophyll-degradation
- Pectin degradation
- Org. acid degradation
- Starch, sugar, protein degradation
- Activation of climacteric metabolism
- Ethylene, VOCs (aroma)
What are potential problems related to CA storage and how can they be prevented?
Induced fruit damage:
- Phytotoxicity
- skin injuries
- cavities formation (Pyruvat)
- internal tissue browning
Prevention:
- automated gas control
- additional gas checking/calibrating
- fruit checking
- additional analytics, alarm sensors
- post-storage
What is dynmaic CA?
- The atmospheric composition is not static anymore , i.e. set at specific, ‘optimal’, constant gas levels
- But dynamically modified according to the plant product´s physiological stage and current its requiremnts
- CA levels respond to actual fruit needs
What do the right DCA conditions depend upon?
- Cultivar
- Maturity
- Seasonal quality variation
- Location influence
- Ripening during storage
Why does DCA focus on achieving LOL (lowest O2 level)?
- Slows down the aerobic respiratory metabolism
- Inhibits oxidative processes
- Reduceds respiratory driven catabolism
- Reduces ethylene related ripening processes
- Reduces physiological disorders
Explain the LOL value and draw the graph?
- The LOL represents the O2 level where respiration changes: from predominantely aerobic to fermentative
- The Fermentation Threshold (FT): The O2 level at which fermentation is induced
- The Anaerobic Compensation Point (ACP): The O2 concentration at which the CO2 evolution is minimum
- The Respiratory Quotient Breaking Point (RQB): the increase of RQ in response to lowering the O2
- The respiratory quotient RQ is the ratio of CO2 respired over O2 consumed.
How are the O2 levels dinamically controlled?
- A Chlorophyll Fluorescence (CF) sensor responds to low O2 levels with fluorescence spike signals
- Large surface measurement on the fruit skin
- Non-destructive
- Always on same sample
- Real-time monitoring
- Frequent, rapid and robust measurements
- Not averaging the response from whole room/fruit content, instead giving a sample specific signal
What are the ways of action of 1-MCP (1-Methylcyclopropen)
- Influences the ripening hormon ethylene by binding at the ethylene receptors of the cell membrane
- Inhibits the signalling by exogenous ethylene
- Inhibits the production of endogenous ethylene
What´s the difference between desease and disorder?
What different types of controlled atmosphere?
How can we reduce the effects of Ethylen?
- 1-MCP
- Scrubbers
- Temperature
