gellan gum

Gellan gum: an alternative to carrageenan in heat-processed petfood products?

(Rowena) Jane Newton

Supervisors: Dr C Speirs (Masterfoods)Dr S Hill and Dr C Dodd (University of Nottingham)

Gellan : the vision

Manufacture of gelled petfoods

In-house fermentation process to produce semi-refined gellan

Direct supply to the factory, eliminating need to buy seaweed from Far East

Result: control of gelling agent supply and cost savings

Project objectives•To show that gelled petfood can be made from gellan gum

•To determine if this has any advantages over carrageenan mixed gels

•To produce gellan by fermentation

•Development of downstream processing of fermentation broth to give a crude material for direct use in petfood products

Work carried out so far•Use of commercial gellan to study:

•Viscosity properties

•Gelling properties

•Different pHs

•Effect of different cations and anions

•Fermentation behaviour in 1l culture vessel

•Choice of starting culture

•Today will talk on:

Overview

•History of gellan gum

•Properties

•Benefits

•Could gellan work as a replacement for carrageenan?

Gellan: discovery

•Discovered 1981

•Search for environmental microorganism which could make an exopolysaccharide resembling agar

•Found a strain of P. elodea (now called S. paucimobilis) growing on plants collected in Pennsylvania

•Developed by Kelco

Gellan: how they grew it

•Kang et al (1982). Appl. Env. Micro. 43 (5), 1086-1091.

•Grew bacteria on a medium containing 30g/l glucose, K2HPO4, MgSO4 and soy protein isolate as a nitrogen source

•Also added a solution of salts to provide necessary metals

•Grown at 30OC in a 30 litre fermentor at pH6.5 for 3 days

•After this time, the fermentation broth was treated to precipitate any polysaccharide present:

Gellan: how they collected it

Boiling waterbath, 10mins

Then: native or deacetylated?

native

3 volumes ice cold isopropanol, overnight

Dry to constant weight at 80OC

deacetylated

adjust pH to 10

Heat to 90OC, 15 mins

Lower pH to 7

Gellan: how they analysed it

•Use of Brookfield to measure fermentation liquor viscosity

•GC for analysis of sugars

•Heating gum in presence of cations and performing texture analysis

•Using the gum to try and solidify microbiological media

Gellan: the findings

Contains glucose, rhamnose and glucoronic acid. Later shown to be present in a 2: 1: 1 ratio;

-Glucose- -glucoronic acid- -glucose- -rhamnose-

Gellan: the findings

•One of the glucose residues carries substitutions. Either a glycerate group (occurring every repeat unit) or an acetate group (occurring once in every 2 repeat units)

•Treatment with alkali removes the substitutions and creates a more brittle gel

•Fermentation process is over in ~50 hours, and at this point the liquor has a viscosity of 4,000-8,000cP

•Gum can withstand several cycles of autoclaving. Addition of cations produces stronger gels. These could be mono- or divalent.

Gellan: desirable properties

•Taken from Sanderson and Clark (1984). ‘Gellan gum, a new gelling polysaccharide. In Gums and Stabilisers for the Food Industry 2.

•Can be used at considerably lower levels than most other gelling polysaccharides

•Can be used in the high acyl form to give viscous solutions and in the presence of salts to give somewhat elastic thermoreversible gels

•Can be cooled in the presence of cations in the low acetyl form to give brittle gels

•Can combine the two forms to modify texture

Gellan: desirable properties

Gellan: desirable properties

•Low acetyl gellan can function in many protein-based foods, including acidified milk products

•Can be used in the deacetylated form to solidify bacteriological media at 25% of the level of agar used

•Has applications in a variety of products including: confectionery (jellies,fillings), jams, processed vegetables, dessert gels, instant puddings, icings, dairy-based desserts and drinks

•PETFOOD

Gellan and petfoods

•Currently all CIL and CIJ products gelled with kappa carrageenan in synergy with other gums, such as LBG, cassia, konjac

•Synergists are interchangeable, but there is nothing to replace carrageenan at present

•Carrageenan is a seaweed; its seasonal availability changes

•It is expensive due to an ongoing seaweed shortage

•Real need to find an alternative to carrageenan

•Gellan is the alternative.

Gellan and petfoods

•Gellan is currently commercially available from Kelco

•Due to its high level of purification, it is costly

•Project aims to therefore develop a semi-refined grade of gellan gum

•Idea is to cultivate this material in-house to maintain control over the gum supply, and not to depend on buying carrageenan from the Far East.

Making petfood jelly with gellan

•Needs to function in a phosphate buffered system at low pH, and in the presence of meat

•Must also be resistant to the sterilisation process

•Must perform better than carrageenan under similar conditions, in terms of gel texture

•Have performed studies using low acetyl gellan

•Currently products cannot be made below pH 6.0 because of carrageenan degradation. Will gellan work at lower pH?

Making petfood jelly with gellan

•The best way to measure gel strength is by texture analysis

•Look at the force required to break a gel by penetrating it with a probe

•Plot force applied versus distance of penetration

•Usually produces an initial peak of force, which is the point at which the gel breaks:

Making petfood jelly with gellan

Force/g

Distance/mm

Force at first fracture: force required to break the gel. The higher the force, the harder the gel.

The influence of pH and salt on non-autoclaved aqueous gellan gels

Making petfood jelly with gellan•The more acid the environment in the absence of added salts, the stronger the low acetyl gellan gel in an unprocessed gel

•Related to how the glucoronic acid reacts to the changes in pH:

The effect of pH on force at first fracture of 1% gellan gels

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pH

forc

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e/g

1% gellanfit

Making petfood jelly with gellan•The presence of additional salts can also have an impact on the gel strength

•For example, increasing amounts of NaCl will increase the strength of an unprocessed 1% gellan gel:

The effect of NaCl on gellan gel breakstrength

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NaCl molarity/mM

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ture

/g 0.5% gellan1.0% gellan1.5% gellan

Making petfood jelly with gellan•But in petfood we have:

•Harsh process

•Complex system containing meats

•Buffer system based around phosphates and containing a mixture of salts

•How does gellan behave as compared to carrageenan in these circumstances?

Making petfood jelly with gellan•Have made gellan and carrageenan gels in a petfood type buffer (Na phosphate for gellan, K for carrageenan but containing equal numbers of moles of salt)

•Have processed the gels at 121OC for 15 minutes in cans

•Have subjected the gels to texture analysis

•Can compare the forces at first fracture at each concentration of gum

•Have studied two pH levels:5.5 and 6.5

Petfood gels at pH5.5•At every concentration, gellan forms a stronger gel than carrageenan:

Average force at first fracture versus polysaccharide concentration of gellan and carrageenan gels (made up in

pH5.5 buffer, processed at 121OC for 15 mins)

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gel composition

aver

age

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0.3% gellan0.3% carrageenan0.45% gellan0.45% carrageenan0.6% gellan0.6% carrageenan

Petfood gels at pH6.5•The same is true at pH6.5:

Average force at first fracture of polysaccharide gels in relation to polysaccharide concentration (made up in pH6.5

buffer, and processed at 121OC for 15 minutes)

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gel composition

aver

age

forc

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t fra

ctur

e/g

0.3% gellan0.3% carrageenan0.45% gellan0.45% carrageenan0.6% gellan0.6% carrageenan

Petfood gels :more texture analysis•As well as giving info on gel strength, texture analysis graphs tell us about whether a gel is brittle or elastic

•If a gel is brittle, it breaks quickly. The initial force/distance gradient is high

•If elastic, it takes a greater penetration distance to break. The initial slope is much lower:

Force/g

Distance/mm

Brittle

Elastic

Petfood gels :more texture analysis

•The data from before can be re-plotted to show the initial force/distance gradients, which show us that:

•Gellan survives processing and can gel in a petfood buffer system

•Gellan gels are much more brittle than carrageenan gels

•At the same concentration, gellan is stronger at the more acid pH than carrageenan. The difference between the gels strengths is more pronounced at pH5.5

Petfood gels :pH5.5Changes in the average initial force/distance gradient when gels are made up at different polysaccharide concentrations

in petfood buffer pH5.5 (processed at 121OC for 15mins)

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gel composition

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age

initi

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rce/

dist

ance

gra

dien

t (g

/mm

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0.3%gellan0.3% carrageenan0.45% gellan0.45% carrageenan0.6% gellan0.6% carrageenan

Petfood gels :pH6.5Changes in average initial force/distance gradient when

gels are made up at different polysaccharide concentrations in petfood buffer pH 6.5

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gel composition

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age

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rce/

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t (g

/mm

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0.3% gellan0.3% carrageenan0.45% gellan0.45% carrageenan0.6% gellan0.6% carrageenan

All force dataA comparison of the average forces at first fracture of

polysaccharide gels made up in phosphate petfood buffer at pH5.5 or 6.5 and processed at 121OC for 15 minutes

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gel composition

aver

age

forc

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0.3% gellan Ph5.5

0.3% gellan Ph6.5

0.3% carrageenanPh5.50.3% carrageenanpH6.50.45% gellan Ph5.5

0.45% gellan Ph6.5

0.45% carrageenanPh5.50.45% carrageenanPh6.50.6% gellan pH5.5

0.6% gellan pH6.5

0.6% carrageenanpH5.50.6% carrageenanpH6.5

All gradient dataA comparison of the average initial force/distance gradients

of polysaccharide gels made up in phosphate petfood buffer at pH5.5 and 6.5 and processed at 121OC for 15

minutes

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gel compositionaver

age

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t (g

/mm

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0.3% gellan Ph5.50.3% gellan Ph6.50.3% carrageenan Ph5.50.3% carrageenan Ph6.50.45% gellan Ph5.50.45% gellan Ph6.50.45% carrageenan Ph5.50.45% carrageenan Ph6.50.6% gellan ph5.50.6% gellan Ph6.50.6% carrageenan Ph5.50.6% carrageenan Ph6.5

Products made up at pH6.5•Chunks in jelly made up in the appropriate pH6.5 buffer

•0.45% gum concentration

•Gellan is more brittle, carrageenan is more mushy

•Brittleness = BETTER FLAVOUR RELEASE.

Products made up at pH6.5

Gellan jelly Carrageenan jelly

Product made up at pH5.50.3% gellan forms a very firm gel

Texture comparison, 0.3% gelsChanges in force with distance of compression of product

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distance/mm

forc

e/g carrageenan Ph5.5

carrageenan Ph6.5gellan ph6.5gellan ph5.5

Texture comparison, 0.3% gelsComparison of the forces at first fracture of petfood

products made up in phosphate buffered polysaccharide gels

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gel composition

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0.3% carrageenan Ph5.50.3% gellan Ph5.50.3% carrageenan Ph6.50.3% gellan Ph6.5

Conclusions:

•Need to replace carrageenan due to shortages and problems with supply and cost

•Gellan is a good candidate to do this

•But commercial gellan is very pure and therefore expensive

•Solution is to grow semi-refined material at the plant and use it as a carrageenan replacement

Conclusions:

•Using a semi-refined grade would resolve cost issues

•We would have control over the supply of the main gelling agent, price and availability

•Gellan matches or betters the performance of carrageenan in canned products

•Gellan gels are more brittle than carrageenan gels, resulting in potentially better flavour release.

•What is the lowest possible gellan level producing an acceptable gelled product?