L12 - Texture Flashcards

1
Q

Texture. Where does it come from?

A

Texture declines over time

Maturation, ripening, senescence

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2
Q

Tomato firmness

A

Variation in time of harvest

  • Skin color
  • No effect on process

Ripening on and off the plant

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3
Q

Mango firmness

A

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

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4
Q

Tomato and mango difference (1/2)

A

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 (!)
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5
Q

Tomato and mango difference (2/2)

A

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

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6
Q

Maturation vs Ripening vs Senescence

A

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

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7
Q

Cell wall and texture

A
  • Primary cell walls main origin of texture (sometime also secondary cell wall)
  • Middle lamella (glue between cells) also important
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8
Q

Primary cell wall

A
  • Cellulose coated with hemicellulose
  • Pectin form interlocking matrix gel
  • Interaction with proteins
  • Outer parts contain cutin and waxes
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9
Q

Cell wall

A

contains pectin which are polysaccharides mostly galacturonic acid and are complex

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10
Q

Secondary cell wall

A

Pectin is replaced by lignin (super long molecule)

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11
Q

Middle lamella

A

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

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12
Q

Pectin breakdown

A

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)
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13
Q

PG action in mango

A
  • Ethylene is produced autocatalytically during climacteric
  • Ethylene induces PG action
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14
Q

Hemicellulose

A
  • 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
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15
Q

Cellulose

A

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

  • Exception: avocado
    cellulases affected by ethylene
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16
Q

Cell wall hydrolases and hormones

A

ABA is involved leading to climacteric ethylene production

  • CK= control
  • NDGA= ABA blocker
  • ACC= ethylene precursors
  • ACS and ACO ethylene precursor enzymes
17
Q

Softening

A

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

Affected by:

  • Auxin (IAA)
  • Polyamines from S-adenosylmethionine decarboxylase (SAMDC
18
Q

Cell wall turgor pressure

A

Water loss
Cells become flaccid
Loss of firmness

(Check picture in slide 12, different scenarios)

19
Q

PG and turgor

A

PG suppressed apple genotypes

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