L12 - Texture

Question 1

Texture. Where does it come from?

Answer 1

Texture declines over time

Maturation, ripening, senescence

Question 2

Tomato firmness

Answer 2

Variation in time of harvest

• Skin color
• No effect on process

Ripening on and off the plant

Question 3

Mango firmness

Answer 3

Before harvest: hardly firmness loss

Variation in initial firmness (not skin color difference)

Softening has to start
‘tree factor’. Tropical fruits mature on the plant

Question 4

Tomato and mango difference (1/2)

Answer 4

Mango shows slow (on tree) maturation, but no ripening. Tomato on the other hand, ripens on the hand

Mango:

• 0.5% increase of starch every week on tree
• More potential sweetness
• Higher firmness (!)

Question 5

Tomato and mango difference (2/2)

Answer 5

Tomato:
Already ripening on the plant
Already cell wall hydrolases present at harvest

Mango:
Not ripening on the plant only maturation
No cell wall hydrolases at harvest

Question 6

Maturation vs Ripening vs Senescence

Answer 6

Maturation = NO expression of cell wall hydrolases

Ripening = expression of cell wall hydrolases

Senescence = NO expression of cell wall hydrolases
PCD (programmed cell death) -> necrosis

Question 7

Cell wall and texture

Answer 7

• Primary cell walls main origin of texture (sometime also secondary cell wall)
• Middle lamella (glue between cells) also important

Question 8

Primary cell wall

Answer 8

• Cellulose coated with hemicellulose
• Pectin form interlocking matrix gel
• Interaction with proteins
• Outer parts contain cutin and waxes

Question 9

Cell wall

Answer 9

contains pectin which are polysaccharides mostly galacturonic acid and are complex

Question 10

Secondary cell wall

Answer 10

Pectin is replaced by lignin (super long molecule)

Question 11

Middle lamella

Answer 11

-Pectin and proteins are the main components.
-No cellulose. Can be dissolved completely
(Happens in cold storage -> High porosity- meailiness)

Question 12

Pectin breakdown

Answer 12

By PME and PG (cell wall hydrolases)

• PME (pectin methylesterase)de-esterifies by removing methyl groups of galacturonic acid
• Demethylation of pectin changes the pH that makes pectin more susceptible to degradation by PG (polygaracturonse)

Question 13

PG action in mango

Answer 13

• Ethylene is produced autocatalytically during climacteric
• Ethylene induces PG action

Question 14

Hemicellulose

Answer 14

• linear xyloglucans connecting to cellulose strands via hydrogen bridges
• covalent bonds between hemicellulose and pectin (glue between cellulose and pectin in the primary cell wall)
• But also between lignin and cellulose in the secondary cell wall

Question 15

Cellulose

Answer 15

NO cellulases in fruits
-Cellulose backbone is the final firmness after ripening

• Exception: avocado
  cellulases affected by ethylene

Question 16

Cell wall hydrolases and hormones

Answer 16

ABA is involved leading to climacteric ethylene production

• CK= control
• NDGA= ABA blocker
• ACC= ethylene precursors
• ACS and ACO ethylene precursor enzymes

Question 17

Softening

Answer 17

Regulated by hormones:
- Can be stopped by 1-MCP

Affected by:

• Auxin (IAA)
• Polyamines from S-adenosylmethionine decarboxylase (SAMDC

Question 18

Cell wall turgor pressure

Answer 18

Water loss
Cells become flaccid
Loss of firmness

(Check picture in slide 12, different scenarios)

Question 19

PG and turgor

Answer 19

PG suppressed apple genotypes

• Firmer
• Intercellular adhesion - - higher (middle lamella!)
• Higher turgor
• Reduced transpiration