Surimi (SF 2)

surimi is defined as __

a wet protein concentrate made of fish myofibrillar proteins obtained from mechanically deboned fish flesh , that is processed through mincing > washing > mixing w GRAS cryoprotectant > freezing

a surimi gel have __ that holds __ & __

inter-connected protein chains that form a matrix

holds water + low molecular weight particles

surimi develops higher quality products from __

under-utilized species

overview of desirable properties of fish to make surimi (4-5)

1. strong gel-forming ability

   • varies across species

   • marine > freshwater ,, white-fleshed > dark-fleshed

2. good organoleptic quality

   • good flavour, no odour

3. abundant supply, available all yr round

4. reasonable price

marine fishes form better gel networks compared to freshwater as freshwater are more prone to __ during __

protein denaturation, during frozen storage

why does protein denaturation affect gel forming abilities

• proteins are aggregated tgt w formation of chemical bonds

• proteins → unavailable for gel formation / inferior gel network in freshwater

reasons why dark-fleshed species r not preferred (compared to white-fleshed)

1. poor gel formation

   • due to more sacroplasmic proteins + higher proteolytic activity

   • lower pH → faster protein denaturation

2. higher amts of polyunsat lipids + iron

   • polyunsat lipids → lipid peroxidation leading to off-flavours && denaturation of proteins

   • iron → facilitates peroxidation

3. colour

   • visually more appealing + easier to colour

key outline of surimi manufacture process

1. removal of unwanted stuffs

2. lots of washing

3. adding cryoprotectants

4. frozen storage

what are removed during the fish processing

head, scales, bones, viscera

the main point of removing these unwanted parts of fish is to get __ , and also to remove __ __ __ so that …

: get fish muscle for surimi production

• remove viscera → contain proteolytic enzymes that can interrupt gel network

• remove polyunsat fats from viscera → prevent lipid peroxidation

• remove dark muscles (from pelagic species) → colour

why is there so much washing of fish muscle

ultimately → enhance gel-forming abilities

1. to concentrate the raw material

2. remove undesirable compounds in fish muscle

how does washing w water concentrate raw material

• desirable myofibrillar protein for surimi is water-insoluble

• some stroma proteins consisting of water-insoluble collagen present ,, but will turn into gelatin when heated → X affect gelling

• sarcoplasmic proteins ; water-soluble → removed

what are the undesirable compounds removed w washing

lipid fraction, heme proteins, TMAO demethylase, nitrogenous compounds, proteolytic enzymes

lipid fraction including __ will be washed away because they __

fats, oils, membrane phospholipids

float

heme proteins removed are __ & __

haemoglobin & myoglobin

why are heme proteins removed & how are they removed

1. cause undesirable pigmentation

2. causes off-flavours

   • hv iron ions that catalyse lipid peroxidation from residual lipids + denature myofibrillar p.

use of Na4P2O7

TMAO demethylase is removed as it forms __ that will __

forms formaldehydes that can denature proteins → undesirable cross-linking of myofibrillar p.

how is TMAO demethylase removed

most → evisceration step

• washing → remove any remaining from fish muscles

nitrogenous compounds are removed because they __. examples of nitrogenous compounds are …

undesirable odour

• TMA & DMA

how are nitrogenous compounds removed

from washing, they r water-soluble

why and how are proteolytic enzymes removed

• removed cus they can destroy protein network formed during gelation ,, leads to undesired texture (mushy)

• most removed during evisceration, washing removes any remaining from fish muscles

considerations of water quality

• temperature

  • tropical fishes → use warm water

  • temperate fishes → use cooler water

  • more cost effective to use tropical fishes for surimi as they require less cooling

• pH

  • ideal 6.8-7.0

  • reduce protein denaturation for H water retention in surimi

• use of soft water (i.e low in dissolved minerals)

  • hard water affects texture + colour during frozen storage

• chlorine

  • remove odours + bleaching

• salt concentration

  • X too high as actomyosin (myofibrillar p.) are salt-soluble

what do cryoprotectants do

stabilise fish muscle protein → prevent protein denaturation in surimi during frozen storage

mechanism behind cryoprotectants

interact w FGs on protein molecule → increased hydration prevents protein chains from aggregating & forming cross-linkages so that gelling ability is X compromised

examples of cryoprotectants

sucrose, sorbitol, salt

• sucrose & sorbitol → sweetness

cryoprotectants are always added to __ surimi

frozen surimi

• prone to protein denaturation & damage from ice crystals during frozen storage

how are surimi frozem

• packed in freezing pans

• frozen quickly to below -25 degrees using a contact freezer

making imitation fish products from surimi

1. salt added to dissociate actomyosin complex

2. surawi takes place (from sol → gel) at 40 degrees

   • p. molecules unfold → interact w nearby proteins → 3D gel-like network

3. set the shape

4. cook (80-90 degrees) → rigid ; irreversible

modori phenomenon is __

a structural degradation that occurs at 50-70 degrees

why does modori phenomenon occur

some endogenous & heat-stable proteinases left behind even after washing

• degrade myofibrillar proteins rapidly, esp myosin

environmental impact of surimi production

lots of washing → waste water

• waste water could be recovered & utilised due to components in it

  • contains lots of sarcoplasmic proteins (h2o soluble) & lipids

• or can be treated for safe discharge