Application of edible coatings to

maintain postharvest quality of

pomegranate fruit

Presented by

Tatenda Kawhena

Advisors : Prof. U.L Opara, Prof. O.A Fawole & Dr A.A Tsige

Internal decay External decay

ShrivellingChilling injury Scalding

Major causes of postharvest quality losses

Mould

3

Application of edible coatings

An alternative postharvest strategy

Volatile compounds aroma

Coating layer

Moisture

Gases (O2, CO2,

Ethylene)

Fresh produce(Water, Carbohydrates,

Proteins, Pigments and Aroma)

Adapted from Raghav, Agarwal and Saini, 2016

4

Types of edible coatings

5

Bioactive edible coatings

Active

compounds

Examples

Antimicrobials Organic acids, metals (silver), Bacteriocins (nisin, lacticin) and

enzymes (lysozyme, lactoperoxidase), peptides and natural

antimicrobials (spices and essentials oil)

Antioxidants Ascorbic acid, carotenoids, and flavonoids

Nutraceuticals Vitamins, phytosterols, lutein, fatty acids and lycopene

Flavours Thymol, geraniol, Limonene and β-unsaturated aldehydes

((E)-2-hexenal, (E)-cinnamaldehyde, citral)

Edible coatings can be utilized as encapsulating matrices to many bioactive

compounds that improve the quality of food products

6

Soluble chitosan

Gum arabic

Lemongrass oil

Pomegranate peel extract

Our approach

Edible coatings

Active ingredients

Pomegranate(cv. Wonderful)

Bioactive edible coatings

Endura-Fresh 6100

OR

7

Chitosan(1 g) 100 ml distilled water

Glycerol (1 %)

Tween 80 (0.05 %)

Chitosan

(1 %)

Preparation of edible coatings

Gum arabic

(1.5 g)

Homogenization

2 500 r.p.m. for 30 min

magnetic stirring

(90 ºC)-45 min

100 ml distilled water

Gum arabic

(1.5 %)Tween 80 (0.05 %)

Glycerol (1 %)

Lemongrass oil

(0.5%)magnetic stirring

(90 ºC)-45 min

Pomegranate peel

extract (1 %)

±

8

Storage conditions: 5 ± 0.7 °C and 95 ± 2 % RH

Evaluation period : 2 w, 4 w, 6 w, 8 w, 3 mon and 4 mon

Quality assessments of fruit were carried out prior to packaging

and storage as a baseline on day 0

CH CH + PP

GA

CH + LM

GA + LM GA + PP UNCOATED

CONTROL

Storage conditions and evaluation periods

CH + LM+ PP

GA + LM + PP

GA = Gum arabic

CH = Chitosan

LM = Lemongrass oil

PP = Pomegranate peel extract

LAC-RESIN

9

Storage and packaging of fruit

Phytosanitization(600 ppm Fludioxinil solution

for 10 min) Dipping (1 min) Drying –Growth/Humidity chamber

(20 ± 2 °C and 65 ± 5 % RH)

Edible coating

(5 L)

1 2

4

3

5

Packaging10 fruit/box, 10 boxes per treatment

SIMULATED STORAGE5 ± 0.7 °C and 95 ± 2 % RH

10

Postharvest evaluation of fruit

Parameter Relevance

Physical properties Weight loss Moisture loss in fruit

Colour Visual appeal/appearance

Headspace gas

composition

Respiration rate (CO2

production)

Fermentation/off flavour

Chemical

properties

Titratable acidity, total

soluble solids and pH

Sugar, acid and overall flavour

Results

12

Cumulative weight loss

0

0,962

2,934

4,812

0

0,677

3,81

8,402

0

0,396

1,82,901

0

1

2

3

4

5

6

7

8

9

0 2 4 6

%

Storage duration (weeks)

LAC-RESIN CONTROL GA + LM + PP

GA = Gum arabic

LM = Lemongrass oil

PP = Pomegranate peel extract

13

Scanning Electron Micrographs

Uncoated peel

Open lenticels

CHITOSAN (2 Weeks)

GUM ARABIC (2 Weeks @ 5 ºC)

Film tearing off

Not evenly spread

CLOSED LENTICEL

Lenticel NOT

FULLY CLOSED

UNTREATED CONTROL

Lac-resin wax

FUNGI HYPHAE ON FRUIT SURFACE

CRACK ON LENTICEL

16

15,315,6333

16,2333

15,2

14,8333

13,4667

15

14,2667

13,2667

13,8

13,1

14,166713,9

12,6

13,3667

10

11

12

13

14

15

16

17

2 4 6

˚Bri

x

Storage duration (weeks)

GA GA + LM GA + LM + PP LAC-RESIN WAX CONTROL

GA = Gum arabic

LM = Lemongrass oil

PP = Pomegranate peel extract

How ‘sweet’ were the arils?

17

0,8

0,9

1

1,1

1,2

1,3

1,4

2 4 6

Citri

c ac

id

(g/1

00g)

GA GA + LM + PP LAC-RESIN WAX CONTROL

GA = Gum arabic

LM = Lemongrass oil

PP = Pomegranate peel extract

How ‘bitter’ were the arils?

18

Lac-resin waxChitosan + LM + PP extract

Fruit appearance (8 weeks + 5 days shelf life)

1

0 = without scald; 1 = 1-25 %; 2 = 25-50 %; 3 = 50-75 %; 4 = 100 %

2 3 4

Scalding and chilling injury

20

Scalding and chilling injury

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0 2 4 6

Chill

ing

inju

ry (

1-5

)

Storage duration (months)

CH CH + LM CH + PP CH + LM + PP

LAC-RESIN CONTROL GA GA + LM

GA + PP GA + LM + PP

0

0,1

0,2

0,3

0,4

0,5

0,6

0 2 4 6

Sca

ldin

g (1

-5)

Storage duration (months)

CH CH + LM CH + PP CH + LM + PPLAC-RESIN CONTROL GA GA + LMGA + PP GA + LM + PP

SCALDING CHILLING INJURY

21

Mould development

0

0,05

0,1

0,15

0,2

0,25

0 2 4 6

(1-5

)

Storage duration (months)

CH CH + LM CH + PP CH + LM + PP LAC-RESIN

CONTROL GA GA + LM GA + PP GA + LM + PP0 = without mould; 1 = 1-25 %; 2 = 25-50 %; 3 = 50-

75 %; 4 = 100 %

3

2

1

22

Fruit applied with Gum Arabic + lemon grass oil + pomegranate peel extract (GA+LM+PP)

recorded the least cumulative weight loss (2.9 %) after 6 weeks of cold storage at 5 ºC

compared with Endura-Fresh 6100 (4.8 %). This may have financial implication on exported fruit,

as fruit is marketed on weight basis

Fruit coated with chitosan and gum arabic with or without lemongrass oil (LM) and/or

pomegranate peel extract (PP) developed the least incidence of scald (50 % for uncoated and 0 %

for GA+LM+PP) and chilling injury (2.5 % for CH+LM+PP and UNCOATED-34 %)

Mould incidence was mostly prevalent in uncoated control and Endura-Fresh 6100 coated fruit

(11 % for UNCOATED and 0 % for GA+LM, GA+PP, CH+LM & CH+LM+PP)

We continue to investigate the effect of various coating formulations on postharvest quality of

pomegranate fruit. In 2019/2020 season, we will explore the possibility of eliminating use of liners

inside packaging with the goal to minimize cost and provide a biodegradable packaging system for

postharvest handling of pomegranates

Summary and future prospects

Acknowledgements

This work is based on the research supported by the South African Research Chairs Initiative (SARChI) of the

Departments of Science and Technology and National Research Foundation

We thank Pomegranate Association of South Africa for research and bursary funding

Prof. Umezuruike Linus Opara, SARChI Postharvest Technology, Department of Horticultural Science

Prof. Olaniyi Amos Fawole, SARChI Postharvest Technology, Department of Horticultural Science

Dr Alemayehu Ambaw, SARChI Postharvest Technology, Department of Horticultural Science

DISCLAIMER : Information shared in this presentation is for research purposes and is subject to change during the course of the PhD study. Under no

circumstances shall we be held accountable for any damage or loss of any kind incurred in the adoption of the findings communicated

John 3: 16