Transcript fermentation

FE308- Fermentation Technology
Spring 2016
Lecture 2
Biological Agents responsible in Food
Fermentations
Biological agents responible in Food
Fermentations
1. Bacteria
a)Lactic acid bacteria
b)Types of commercial starter cultures
c)Conditions required for bacterial
fermentations
d)Characteristics of important genera
2.Yeasts
3.Molds
Micro-organisms cause changes in
the foods
– Help to preserve the food,
– Extend shelf-life considerably over that of the raw
materials from which they are made,
– Improve aroma and flavour characteristics,
– Increase its vitamin content or its digestibility
compared to the raw materials.
Biological agents responible in Food
Fermentations
Most fermentations require several species, acting
simultaneously and/or sequentially to give product
with desired properties ,including appearance,
aroma, texture and taste.
Vinegar production is a joint effort between yeast
and acetic acid forming bacteria. The yeast convert
sugars to alcohol which is the substrate required by
the Acetobacter to produce acetic acid through
oxidation.
Role of fermenting microorganisms are;
Production of lactic acid, flavor, proteolytic activity, lipolytic
activity, organic compounds, prevention of foodborne disease
and spoilage, and change in texture of food. The most
common groups of microorganisms involved in food
fermentations are bacteria, yeasts and molds. Microbial
enzymes also play important role in food fermentations.
In general, growth will be initiated by bacteria, fallowed by
yeasts and then molds. The smaller microorganisms multiply
and take up nutrients from the surrounding area most rapidly.
Bacteria are the smallest of microorganisms, fallowed by
yeasts and molds. The smaller bacteria, such as Leuconostoc
and Streptcoccus grow and ferment more rapidly than their
close relatives.
Bacteria
a)Lactic acid Bacteria
i)Groups of LAB depending on glucose
metabolism
ii)Groups of LAB depending on growth
temperature
b)Types of commercial bacterial starter culture
c)Conditions required for bacterial
fermentations
Lactic Acid Bacteria(LAB)
• İt is loosely defined as all members of fermenting
bacteria producing lactic acid from hexoses and
lack functional heme-linked electron transport
system or cytochromes(no krebs cycle).
• Lactic acid bacteria compose a group of bacteria
that degrade carbohydrate (e.g., fermentation )
with the production of lactic acid.
• The principle genera of LAB are
Lactobacillus,Lactococcus,Leuconostoc,Pediococc
us, and Streptoccus(Table 2.2)
Lactic Acid Bacteria
• While this is a loosely defined group with no precise
boundaries all members share the property of producing
lactic acid from hexoses.
• As fermenting organisms, they lack functional heme-linked
electron transport systems or cytochromes, they do not
have a functional Krebs cycle.
• Energy is obtained by substrate-level phosphorylation while
oxidising carbohydrates.
Table 2.2.Principle genera of the lactic acid bacteria
Genus
Cell
Morphology
Fermentation
Lactate isomer
Lactococcus
Pediococcus
Steptococcus
Lactobacillus
Cocci in chains
cocci
Cocci in chains
rods
L
DL
L
DL,D,L
Leuconostoc
cocci
homo
homo
homo
Homo,
heteroferm
heteroferm
D
Microorganisms
Characteristics
Reactions
Acetobacter spp
A. aceti
A. pasteurianum
A. peroxydans
Aerobic Gram(-)
Rods,grow at aw
≥
0.9
Oxidase organic compounds (such as
alcohols)to organic acids (acetic acids)
Streptoccus spp
S. bovis
S. thermophilus
Ent. faecalis
Gram(+)
Tolerant
acid,grow at aw
≥0.9
Homofermentative. Common in dairy
fermentations, but E. faecalis is in vegetable
products.
They can grow in high pH media
Leuconostoc spp
L. mesenteroides
L. dextranicum
L. paramesenteroides
L. oenos
Gram(+)
cocci
Heterofermentative. Produce lactic acid,plus
acetic acid, ethanol and CO2 from glucose. L.
oenos utilises malic acid and other organic
acids in wine.
Pediococcus spp
P. cerevisia
P. acidilactici
P. pentosaceus
Gram(+)
Cocci pairs in
tetrads
Saprophytic organisms present in fermenting
vegetables, mashes, beer and wort. They are
important in sucuk fermentation.
Microorganisms
Characteristics
Reactions
Lactobacillus spp
Homofermentative
Hereformentative
Gram(+)
Rods, Tolerate
acid,grow at aw
≥0.9
Metabolize sugars to lactic and acetic acid
,ethyl alcohol, CO2 .
Produce lactic acid
Produce lactic and acetic acid ,ethyl alcohol,
CO2 , partially
Reduces fructose to mannitol
Yeasts
Sac. cerevisia
Sac. pombe
Tolerate
S. Cerevisiae can metabolize sugars from a
acid,40% sugar, fermentative to an oxidative
grow at aw≥0.85 pathway,depending on oxygen avalibility.
Tolerate high salt concentrations and low aw.
Candida,Geot. candidum
Molds
P. roquefortii
P. camembertii
Many
aerobic,some
anerobes
Aerobic,tolerate
acid,grow at
aw≥0.85
Metabolize sugars through extracellular
enzymes and oxidation
Groups of LAB on glucose metabolism
• Homofermenters
• Heterofermenters
Groups of LAB on tempertaures
• Mesophilic starter cultures(optimum growth
temp range 20-30 ˚C)
• Thermophilic starter cultures
cultures(cultures(optimum growth temp range
40-45 ˚C)
• Miscellaneus bacterial starter cultures
cultures(optimum growth temp range 37-41
˚C)
Mesophilic starter cultures
They are used for production of fermented milk
products such as fresh cheese, semi-hard cheese,
butter and sucuk. Optimum growth temp. range
from 20-30˚C.
Mesophilic starter cultures
Lac. lactis subsp. lactis
Lac. lactis subsp. cremoris
Mesophilic aroma cultures
Lac. lactis subsp. lactis biovar diacetylactis
Leu. mesenteroides subsp. cremoris
Thermophilic starter cultures
They are mainly used for the production of yogurt,
hard cheese and soft cheese. Optimum growth
temp. range from 40-45˚C.Examples:
Str. thermophilus
Lb. bulgaricus
Lb. helveticus
Lb. lactis
Lb. casei
Lb. acidophilus
Miscellaneus bacterial starter cultures
Bifidobacterium longum
Bifidobacterium infantis
Propionibacterium shermanii
and they have optiumum temperature range
from 37 C to 41 ˚C.
Bifidobacterium ssp.are used as probiotic
cultures and Propionibacterium in the
production of some type of cheese.
Types of commercial starter culture
• Liquid, for propagation of mother culture
• Deep frozen, concentrated cultures for
propagation of bulk starter
• Freeze dried, concentrated cultures in powder
form, for propagation of bulk starter culture.
• Deep superfrozen, superconcentrated cultures
in readily soluble form, for direct inoculation
of the product.
Conditions required for bacterial
fermentations
•
•
•
•
•
•
Temperature
Salt concentration
Water activity
Hydrogen ion concentration(pH)
Oxygen avalibilty
Nutrients
Lactococcus
The genus grouped from N group Streptoccus and includes
several species
used in dairy
Lac. lactis subsp. lactis
fermentation
Lac. lactis subsp. cremoris
Lac. lactis subsp. hordniae
Lac. garviae
Lac. raffinolactis
Thety are ovoid,about 0.5 to 1.0 µm in diameter ,present in
pairs or short chains, nonmotile, nonsporulating,
homofermentative, facultative anaerobic to microaerophilic
and catalase negative. They grow well between 20-30 C,do not
grow in 6.5% NaCl and at pH 9.6.In suitable medium they can
produce about 1%L(+)-lactic acid and reduce pH to about 4.5.
Natural habitats are green vegetation, silage,dairy
environments, and raw milk. They are used in the production
of Cottage cheese and white cheeses and butter.
Streptococcus
• Only one species Str. Thermophilus is used in
dairy fermenetation(such as in yogurt and cheese
production)
Gram positive,spherical to ovoid,0.7 to 0.9 µ in
diameter,homofermentative,facultative anaerobes
and exist in pairs and in long chains.
The cells grow well from 37 to 44 ˚C. But can also
grow at 52 ˚ C(thermoduric),do not grow at 10 ˚ C
and in 6.5% NaCl, can reduce pH 4.0 with L(+) lactic
acid production.
It presentin raw milk and dairy environment
Leuconostoc
Leu. mesenteroides
• They are Gr(+),spherical or ovoid ,arranged in pairs or
chains, nonmotile, nonsporulating,catalase negative
mesophilic. heterofermantative,faculative anaerobes.
• Grow well 20 to 30 C.
• Ferment glucose to produce D(-) lactic acid,CO2,
ethanol and acetic acid with pH reduction to 5.0-4.5.
• Leuconostoc species associates with plants,
vegetables,silage,milk,some milk products, and raw
and processed meats. One species, Leuconostoc oenos
may associate with wine.
• Example species: Leu. mesenteroides,
Leu.paramesenteroides,Leu. oenos, Leu. galidium.
Pediococcus
They are spherical and form tetrads, pairs and single cells or forming
short and long chains.
Gram positive, catalase negative, nonmotile,nonspore forming,
microaerophilic and facultative anerobic.
Grow well between 25-32 C.
Grow in the presence of 5%NaCl.
Ferment glucose to produce L(+) or DL-lactic acid and reducing the pH
to about 3.6.
The associate with plant, vegetable,silage,beer, milk,fermented
vegetables, meats, and fish.
Ped. pentosaceus, Ped. acidilactici and Ped.halophilus are used in
vegetable, meal, cereal and other types of fermented food production.
The are also responsible in the ripening and flavor production of
pickles and sausages.
Lactobacillus
The genus includes a large number of Gram positive, rod shaped,
usually nonmotile, nonsporulating,bcatalase and oxidase negative
and facultative anaerobic species. Dependingg on species they can
produce either only lactic acid(L(+),D(-),or DL) or a mixture of lactic
acid, acetic acid, ethanol and CO2.Lactobacillus used as starters in
controlled fermentation grow well between 25-44 C.pH can be
reduced from 3.5 to 5.0.
They can associate with plants, vegetables,grains,seeds,raw milk,
meat, fermented meat,and milk products, and fermented
vegetables. Some are prsent in digestive tract.
The species can be divided into 3 groups
1.GroupI-Thermobacterium(Obligately homofermentative)
Ex: Lb. bulgaricus,Lb. lactis,Lb. helveticus)
2.Group II-Streptobacterium(Facultatively heterofermentative)
Ex: Lb. casei,Lb. plantarum,Lb. curvatus
3.GroupIII-Betabacterium(Obligately heterofermentative)
(Ex: Lb. fermentum,Lb. kefir,Lb. sanfirancisco,Lb. reuteri)
Lb. casei
Lb. plantarum
Lb. rhamnasus
Lb. bulgaricus
Bifidobacterium
They are morpholgically similar to Lactobacillus spp. And are previously included in
this gnus.
They are Gram positive,rods of various shapes and sizes, present in single cells or in
chain.
They are nonspore forming,nonmotile,mesophilic,anaerobic and some can tolerate O2
in the presence of CO2.They grow optimally from 37 to 41 C with grow temp. 25-45
C.They usulally do not grow at pH above 8.0 or below 4.5.
They ferment glucose to lactic acid and acetic acid in 2:3 molar ratio without
production CO2 .
They associate in feces of humans,animals and birds are beneficial for the normal
health of the digestive tract. Bifidobacterium called as probiotics are used in the
production of fermented milk products such as yogurt,cheese and kefir.
They are present in large numbers in the feces of infants within the 2-3 days after
birth.
Some of the species are Bif. bifidum,Bif. longum,Bif. İnfantis, and Bif. adolescentia.
Propionibacterium
• They belongs to Propionibacteriacae family and responsible
for flavor and texture of some fermented food
products(especially Swiss cheese-eyes and holes formation)
• They break down lactic acid into acetic acid and propionic
acid and CO2.
• The cells are Gr(+),pleomorphic thick rods or coccoids ,11.5µm.occur as in single cells,pairs,or short chainswith
different configurations.
• They are nonmotile,nonsporulating,anerobic and
aerotolerant,catalase positive.
• They grow optimally fro 30-37 Cwith pH 6.0-7.0.
• Some species form pigment.
• Species in dairy industry are Pro. freudenreichii,Pro.
jensenii,Pro. thoeni,Pro. acidopropionia.
Acetic Acid Bacteria
Acetobacter aceti
Acetobacter and Gluconabactera important two
genera producing acetic acid.They are in the family
They oxidaze alcohol to actic acid in the presence of
excess oxygen.
They are Gr(-),obligate aerobic,catalase
positive,rods(0.5-1.5 µm),occuring single cells,pairs
or chains or chains.motile or non motile.
They grow between 25-30 ˚C.
They present naturally in fruits,sake,alcoholic
beverages,cane juice and soil.
Yeast
A small number of yeasts is able to grow
anaerobically and utilizes sugar to generate energy.
The majority of these yeasts also grow aerobically.
They have beneficial and non-beneficial effects on
foods.
Yeasts are unicellular organisms that reproduce
asexulally by budding.
Yeasts play important role in food industry as they
produce enzymes that cause desirable chemical
reactions such as leaving of bread and the
production of alcohol and inverting sugar
S. cerevisia and its subspecies are used for producing
bread,beer,wine,distilled liquor,industrial
alcohol,invertase,and give flavor to some foods(e.g.soups).All
Saccharomyce strains ferment glucose and many ferment
plant associated carbohydrates such as sucrose, maltose and
raffinose but not ferment the lactose.
Yeasts associate w,th fermentation of foods to produce
alcohol ,enzymes,single cell proteins and additives.
A restricted number of yeasts are used in the fermentation.
Saccharamyces spp. are used in the production of bread,
wine, champania, alcohol,distilled licor and invertase enzyme.
• Kluyveromyces marxianus,K.
marxianus var. lactis hydrolyse
lactose and associate with natural
fermentation along with other yeasts
and lactic acid bacteria in alcoholic
dairy products such as kefir and
kımız.
• Yeasts grow at low water activities in
the presence of high concentrations
of salt and sugar.
Candida utiis used to produce single cell
proteins.They can cause spoilage in foods.
Some candida spp are functional in the
production of kefir, cacao,beer and fruit
fermented juices.
Molds
• They are aerobic organisms therefore they can nor carry out
fermentation but produce extracellular enzymes. These enzymes
hydrolyze large organic compounds to smaller units. These
smaller compounds are utilized by fermentative bacteria and
yeasts.
• Molds are important n food industry with respect to enzyme
producers, spoilers and preservers of foods. Certain molds
produce undesirable toxins and cause food spoilage.(The
Aspergillus spp)
• The genus Penicillium associate with ripening and flavor of
cheeses.
• A. niger is used in the production of citric and gluconic
acid,,pectinase and amylase enzymes from glucose,sucrose and
starch.
• Rhizopus oligosporum is used in te production of tempe.
• P. roqufortiii is used for ripening of Roquefort,Gorgonzola and
Blue Cheeses, P. camabertii for Camemberti cheese and P.
caseicolum for brine cheese.
Roquefort
Gorgonzola
Camemberti
Tempe
Enzymes
Microbial enzymes play a role in the fermentation
of food. They are complex proteins produced by
living organisms to carry out specific biochemical
reactions. They are sensitive to change in
temperature, pH, moisture content, ionic strength,
concentrations of substrate and inhibitors.