Biochemical changes in plant food raw material and products

a) Natural, in vivo, processes – tissue maturation and senescence

Cell wall and middle lamella structure degradation

Intracellular processes

b) Stress - cold, drought, injury, infection….

Oxidative burst

A ccumulation of phytoalexines, polyamines, phenolic

componds

Enzyme activation (PPO, LOX, PLases …)

c) Post harvest processes – tissue demage

Mechanical processing

Physiological processes – PCD, necrotization

Zrání a stárnutí pletiv

1. Iniciace

- Dosažení metabolického prahu

- Utlumení fotosynthesy

- Změny redox stavu buňky

- Signální dráhy

Iniciátory:

Vliv prostředí,vývojové vlivy (počátek

kvetení, tvorba plodů nebo semen),

hormony, patologické stavy

2. Reorganizace / degenerativní fáze

- Aktivace metabolických drah,

utlumení jiných

- autotrofní met. → heterotrofní

- detoxifikace

Akcelerátory a inhibitory:

Hormony, prostředí, vývoj

Terminální fáze

- akumulace antibiotik

- volné radikály

- eliminace metabolitů

- ztráta b. integrity, buněčná smrt

Autotrophic metab to

heterotrophic

Autotrophic metab. to

heterotrophic

Hormonal

regulation

Ethylene,

cytokinin

Maturation and senescence

Gene regulation SAG – senescence associated genes B. napus

Proteases, ubiqvitinylation factors, enzymes of Krebs cycle, PLD, gln synthase,

metalothionein, GST, catalase, cytP450, PR1, chitinase, ACC oxidase, NADH oxidase

Ethylene

Indukce synthesy pathogeny, poraněním

Hormonal regulation:

Ethylene signalling pathway

Cytokinin and its derivatives

riboside

riboside phosphate

Isopentenyl

aromate

glycosyl

Cis-, trans-

OE of IPT –

isopentenyltransferase

Delayed senescence

Changes in the cell wall texture in peach

Biochemical processes during ripening and senescence

Metabolism of pigments, phenolic compounds (PAL)

Protein metabolism

photosynthesis

Oxidative metabolism

lipids → saccharides (glyoxalate cycle)

ROS production

Metabolismus chlorofylu a ostatních barviv

Degradací chl se

„odhalí“ ostatní barviva

- karotenoidy

Synthesis of carotenoids

Protein degradation

Changes in basal metabolis

– peroxisomes conversion to glyoxysomes (lipids→sacharides)

Změny redox stavu buněk – produkce ROS

Membrane deterioration

Biochemical changes in plant food raw material and products

a) Natural, in vivo, processes – tissue maturation and senescence

Cell wall and middle lamella structure degradation

Intracellular processes

b) Stress - cold, drought, injury, infection….

Oxidative burst

A ccumulation of phytoalexines, polyamines, phenolic

componds

Enzyme activation (PPO, LOX, PLases …)

c) Post harvest processes – tissue demage

Mechanical processing

Physiological processes – PCD, necrotization

Abiotic stress

Buchanan, 2002

Biotic stress – patogens, herbivores

Tomatoes – frequent research subject

Affecting the texture of tomatoes (Lycopersicon esculentum)

PG in unripe fruits non-detectable, de novo synthesis, coded by 1 gene - 2 isoforms

(1% of mRNA in ripening fruits!!!!)

PE constituvely expressed, more isoforms, anti-PE2 tomatoes

Effect on pectins:

Tomato juice from antiPG tomatoes

Ethylene – influences ripening of fruits

Lycopersicon esculentum:

Antisense - ACC synthasa, ACC oxidasa

GMO - ACC deaminasa bakteriální

Biochemical changes in plant food raw material and products

a) Natural, in vivo, processes – tissue maturation and senescence

Cell wall and middle lamella structure degradation

Intracellular processes

b) Stress - cold, drought, injury, infection….

Oxidative burst

A ccumulation of phytoalexines, polyamines, phenolic

componds

Enzyme activation (PPO, LOX, PLases …)

c) Post harvest processes – tissue demage

Mechanical processing

Physiological processes – PCD, necrotization

Enzymes involved in the processing of plant raw materials

1. Changes in sensoric properties

- LOX, lipases, fosfolipases, proteases

2. Changes in texture and consistence

- pectolytic and celulolytic enzymes

3. Changes in colour

- Polyphenol oxidases, peroxidases

4. Decrease of nutritional value

- Ascorbate oxidase, ascorbate peroxidase, thiaminase…

Enzymatic browning

Animals

Crustacea Plants

(fruits, vegetables)

Reactionsce catalysed by polyphenol oxidase

Monophenoloxide reaction

Diphenol oxidase reaction

Enzymatic browning

Substrates of PPO - Products of phenylpropanoid pathway

Principle of enzyme browning

Oranžovo- hnědo-černé látky

Very complex process …..

Prevention of enzyme browning

1. Breeding of varieties with lower content of

phenolics

2. Inactivation of PPO – physical methods

- inhibition

3. Combined

Ad 2) physical methods

a) Temperature or pH change

b) Limitation of O2

- Packaging without O2 access

- Packagin in the inert atmosphere

- High sucrose content

Inhibition

a) Chelating agents

b) Anorganic ions - halides (NaCl. NaF)

c) Kompetitive inhibitors – benzoic acid,

cinnamic acid

d) Quinone reducing agents (askorbic acid,

HSO3-, thiols)