Practical 5 – Ethylene production and sensitivity of produce-Lab Report

Practical 5 – Ethylene production and sensitivity of produce

Ethylene is a colourless gas with a faint, sweetish smell that is naturally produced by certain fruit and vegetables.  It is also produced as an exhaust gas from petrol combustion engines.  Despite the fact that ethylene is a gas, it is also a major plant hormone and plays a major role in the ripening of many fruit and most vegetables.  For some fruit, there is a rise in respiration as they ripen that is accompanied by a similar increase in ethylene production.  These rises are called the climacterics, and their magnitude varies among species.  However, some fruit (non-climacteric fruit) do not increase their ethylene production during ripening.

Some fruits such as bananas are gassed with ethylene so that their ripening is controlled.  While ethylene can used under controlled conditions as a ripening agent, even small amounts of ethylene during shipping and storage causes most fresh produce to deteriorate faster.  Ethylene gas and its removal are both important in giving the consumer the best possible product.  Ethylene production and perception are affected by temperature and this practical will try to illustrate these effects.

Experiment 1

1. Each group will weigh and place into 6 or 8 L containers the commodities assigned to them:

• 9 green bananas                                   (Groups 1 & 5)
• 9 ripe bananas                                    (Groups 2 & 6)
• 2 ripe apples                                   (Groups 3 & 7)
• 2 bunches of grapes (Groups 4 & 8)
• 9 green bananas cut into slices (Groups 4 & 8)

Seal the containers and keep them at 20°C.

2. Measure ethylene concentrations in the containers after ~2 h by injecting 1 mL aliquots of air from the containers into a gas-liquid chromatograph (GC).
3. Inject an ethylene standard into the GC and calculate the mL ethylene produced per kg per hour using the following formula:

C₂H₄ (mL.kg^-1.h^-1) =    PH_Sam  x     0.001         x     60    x    1000   x  (CV – Wt)

PH_Std                 T            Wt

Where:             PH_Sam   =          Peak height sample

PH_Std    =          Peak height standard

T    =          Time (in min) since lid was sealed

CV   =          Container volume (in mL)

Wt    =          Weight of produce (in g)

0.001   =          mL.mL^-1 ethylene in standard

5. Place your ethylene concentrations in an EXCEL spreadsheet and collect the class data from the Postharvest website.

Experiment 1

Commodity                                                     =

Peak height sample (PH_Sam)                                     =

Peak height standard (PH_Std)                                   =

Time (in min) since lid was sealed (T)            =

Container volume (in mL) (CV)                     =

Weight of produce (in g) (Wt )                       =

 

Experiment 2

 

6. Each group will place an equal number of green bananas (3 to 6 depending on size) in to a 6 or 8 L container.

 

7. The groups specified will set up the following treatments:

 

• Groups 1 & 5 – nothing else added to container – stored at 12°C
• Groups 1 & 5 – nothing else added to container – stored at 20°C
• Groups 1 & 5 – ethylene (10 ppm final concentration) – stored at 12°C
• Groups 1 & 5 – ethylene (10 ppm final concentration) – stored at 20°C
• Groups 2 & 6 – 4 ripe bananas added to container – stored at 12°C
• Groups 2 & 6 – 4 ripe bananas added to container – stored at 20°C
• Groups 3 & 7 – 2 ripe apples added to container – stored at 12°C
• Groups 3 & 7 – 2 ripe apples added to container – stored at 20°C
• Groups 4 & 8 – 1 bunch of grapes added to container – stored at 12°C
• Groups 4 & 8 – 1 bunch of grapes added to container – stored at 20°C

 

 

8. The containers will be opened 3 days later and the bananas allowed to ripen at 20°C.

 Assessment – Experiment 2

 

9. One week after treatment and ripening, look at the bananas from each group and record their appearance.

 

Addition	Temperature	Description
Nothing	12°C
Nothing	20°C
Ethylene (10 ppm)	12°C
Ethylene (10 ppm)	20°C
Ripe bananas	12°C
Ripe bananas	20°C
Ripe apples	12°C
Ripe apples	20°C
Grapes	12°C
Grapes	20°C

 

 

 

 

 

 

 

 

 

Changes in the angularity of the cross-sections of banana fruit as they ripen (from von Loesecke (1949) Bananas, Wiley Inter-sciences London).

 

 

 

1. Each group should assess the colour of one of the bananas from each treatment using a colourimeter and place the hue angle (h), a* and b* values the EXCEL spreadsheet.

 

Addition	Treatment Temperature	Colourimeter Readings
		h	a*	b*
Nothing	12°C
Nothing	20°C
Ethylene (10 ppm)	12°C
Ethylene (10 ppm)	20°C
Ripe bananas	12°C
Ripe bananas	20°C
Ripe apples	12°C
Ripe apples	20°C
Grapes	12°C
Grapes	20°C

 Write-up

 

Before you write up the practical, read through the relevant pages of your textbook and your lecture notes.  Also, perform a literature review using the facilities provided to you by the UWS library.  For this practical you do not need to write an abstract, introduction or methods section.

 

For Experiment 1, calculate the average ethylene production rates and their standard errors from the class data.  Draw an appropriately labelled graph of the data and describe any patterns, trends, relationships or differences you can see in the data for the four commodities.  Assign means to groups.  Explain any manipulation of the data you may have performed to remove any outlying values. (14 marks)

 

For Experiment 2, calculate the average h, a* and b* values and their standard errors from the class data for the test bananas.  Draw three appropriately labelled graphs of the data and describe any patterns, trends, relationships or differences you can see in the data.  Assign means to groups.  Explain any manipulation of the data you may have performed to remove any outlying values. (20 marks per graph)

 

Produce a table describing the appearance of the bananas after treatment and ripening.  Describe any trends or differences you see in the data.  (10 marks)

 

Now answer the following questions (use the questions as headers):

 

(A) Why were the treatments with ethylene and the “nothing added” treatment included in this experiment? (4 marks)

 

(B) Why were differences found in ethylene production by the apples, the green and ripe bananas, and the grapes found? (8 marks)

 

(C) Why were differences found in ethylene production between the wounded and unwounded bananas? (4 marks)

 

(D) What were the relationships between ethylene production by the apples, the ripe bananas, and the grapes on the ripening of the test bananas? (6 marks)

 

(E) What implications do the results from this practical have for the storage of fresh produce? (10 marks)

 

(F) Why did temperature have an affect on the ripening of the test bananas? (10 marks)

 

(G) How is colour measured and assessed using a colourimeter and what parameters can be measured using this instrument? (10 marks)

 

(H) What changes in biochemistry caused the changes in colouration that can be seen in the test bananas? (6 marks)

 

 

 

It is expected that all lab reports will be word-processed, using computer graphics where necessary.  Ensure that any figures or tables you use have legends and that the figures and tables are referred to in the text.  The practical report should be submitted via Turnitin.  Guidelines for submission are provided on the Postharvest vUWS website.  Ensure you read and understand the Turnitin guidelines before you submit your work.  The practical will be marked and handed back the following week.  Include a completed Assignment Cover Sheet as the first page.

Solution for the Lab Reoport