CHAPTER 1 INTRODUCTION
PREAMBLE
Alleviating hunger is a part of the first United Nation's
Millennium Development Goal but still malnutrition remains a major
fundamental cause of death among children worldwide. Malnutrition
is responsible, directly or indirectly, for 54 % of the 10.8 million
deaths per year in children under five in developing countries.
Traditional household fermented cereal foods are consumed by large
number of human beings as they provide important sources of
nutrients but have also great potential in maintaining health and
preventing diseases.
This study deals with traditional fermented cereal-based food
“Idli”, in which detailed bacterial flora is analyzed using modern
molecular techniques. The work has followed to find out the role of
the microflora in souring and leavening action in Idli batter.
Selected isolates were also studied for their probiotic role that is
essential in promoting health and preventing disease. It is also
shown that the enteric pathogens like Salmonella cannot survive during Idli fermentation. This study was essential as the field has not been fully explored even though Idli is a staple diet of large number of individuals in India.
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 1
INTRODUCTION
Foods are essential for the vital continued existence of
animals and human beings. Since primeval times, different
techniques have been used to process and preserve food. Discovery
of food fermentation is considered as one of the oldest traditions of
food processing and preservation. Fermented food was consumed
much before mankind had any knowledge regarding microorganisms
and their fermentation capabilities. 1.2.1 Fermented Foods
Fermented foods can be defined as foods that have been
subjected to the action of microorganisms to bring useful
biochemical changes leading to major desirable alterations in the
raw material (Campbell-Platt, 1987). During the process of fermentation, microorganisms are not only involved in the preparation and preservation of food products but also give the flavor and aroma to the food (Steinkraus, 2002). Change in texture is one of the important qualities associated with fermented foodstuff. Improvement of nutritional quality after food fermentation occurs due to enrichment of essential amino acids, fatty acids and vitamins. As compared to the raw material, fermented foods are preferred since they are easy to assimilate.
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Fermented food replenishes necessary human gut microflora
that is lost during long term antibiotic treatment. Another important aspect is the requirement of less cooking time for fermented foods. This saves heat energy. In almost all over the world, fermented foods and beverages contribute approximately 20-
40 % of the person’s dietary requirements. Fermented foods are geographically different and selective due to the differences in climate, social patterns, consumption practices and availability of raw materials (Nout, 2009). Fermented foods can be classified roughly based on the initial raw material used for preparation. The raw material can be cereals, legumes, milk, fish and meat, fruits, vegetables and starchy tubers. Various fermented foods [Table 1] prepared from different raw materials are consumed all over the world (Scott and Sullivan, 2008).
Cereals and pulses are used globally as staple foods.
Digestibility of conventional pulses and cereals is considerably lower compared to the foods made from fish and animal sources. In most developing countries belonging to Asia and Africa, pulses and cereals constitute the major dietary constituents. Difficulty in digestion of complex proteins, presence of high levels of insoluble fiber and anti-nutritional factors make plant based diets less nutritive. It is of interest to mention here that these difficult-to-
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 3 digest cereals are converted to nutrition rich food by fermentation, by the people of Africa and Asia (Nout, 2009).
RAW FOOD ORGANISM MATERIAL Beer Grain malt Saccharomyces cerevisiae Bread Grain flour S. cerevisiae S. cerevisiae ; Candida rugosa ; Chocolate Cacao bean Kluyveromyces marxianus Coffee Coffee bean Erwinia dissolvens Soy Sauce Soy bean Aspergillus oryzae Miso Soy bean A. oryzae Lactobacillus plantarum ; L. brevis ; Kimchi Streptococcus faecalis ; Leuconostoc Daikon Napa mesenteroides ; Pediococcus pentosaceus Tempeh Soy bean Rhyzopus oligosporus Candida sp. ; Cryptococcus sp. ; Olives Olives Debaryomyces hanseii; Lactobacillus sp.; Saccharomyces sp. Leuconostoc mesenteroides ; Pickles Cucumber Lactobacillus sp. Coliform sp. ; Lactobacillus sp. ; Sauerkraut Cabbage Leuconostoc plantarum S. cerevisiae ; Gluconobacter sp. ; Vinegar Fruit juice Acetobacter sp. Meat + Sausages Pediococcus sp. ; Lactobacillus sp. spices Wine Grapes Saccharomyces cerevisiae Yogurt Milk L. bulgaricus ; Streptococcus sp. Butter Milk Streptococcus sp. ; Leuconostoc sp. Lactobacillus sp. ; Lactococcus sp. ; Pediococcus sp. ; Streptococcus sp. ; Cheese Milk Leuconostoc mesenteroides ; Propionibacter sp. Kefir Milk Saccharomyces kefir ; Torula kefir
Table 1: Popular Fermented Foods
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1.2.1.1 Fermented Foods in India
India is a vast country which has different climatic conditions
and numerous communities. This has resulted in a diverse array of
fermented foods. The variety of regional fermented foods
supplements the dietary requirements of communities belonging to
different cultures. Fermentation is carried out using cereals, pulses,
milk, vegetables and unripe fruits as initial raw material. Some of
the popular Indian fermented beverages are prepared from rice,
sprouted rice, rice husk, cereals, fruits, flowers, jaggery [unrefined
sugar]. There is a wide variety of fermented foods consumed in India
(Ramakrishnan, 1979). The names of these preparations are mostly
colloquial and few very popular foods are listed in Table 2.
1.3 Microorganisms and Food Fermentations
Fermentation is an anaerobic cellular process in which organic compounds are converted into simpler compounds, and chemical energy is produced (Frazier and Westhoff, 2008).
Fermentation is thought to have been the prime means of energy production in primitive organisms when oxygen was at low concentration in the atmosphere. Food fermentation is the process in which biochemical modification of primary food products are brought about by the action of microorganisms and their enzymes. A variety of bacteria and fungi are involved in the fermentation of
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foods (Nout, 2009) [Table 1-3].
RAW FOOD ORGANISM MATERIAL Rice + Adai Lactic acid bacteria Legume Streptococcus faecalis, Pediococcus Fermented Rice acidilactici, Bacillus sp., ; rice Microbacterium flavum Leuconostoc mesenteroides, Rice + Idli Streptococcus faecalis, pulse Pediococcus cerevisiae Lactobacillus fermentum, Cereal + Dhokla L. mesenteroides, Pichia silvicola, ; pulse Streptococcus faecalis, ; Torulopsis sp. L. mesenteroides, L. fermentum, ; Ambali Cereal Streptococcus faecalis Lactic acid bacteria Nan wheat Saccharomyces cerevisiae Taotjo Cereal Aspergillus oryzae Table 2: Popular Indian [sub-continental] Fermented Foods
GRAM GRAM NEGATIVE FILAMENTOU POSITIVE YEAST BACTERIA S FUNGI BACTERIA Acetobacter Arthrobacter Aspergillus Candida Acinetobacter Bacillus Aureobasidium Cryptococcus Alcaligenes Bifidobacterium Fusarium Debaromyces Flavobacterium Lactobacillus Mucor Hansenula Gluconobacter Leuconostoc Neurospora Kluyveromyces Klebsiela Micrococcus Penicillium Pichia Methylococcus Pediococcus Rhizopus Rhodotorula Propionibacterium Streptococci Trichoderma Saccharomyces Xanthomonas Streptomyces Yarrowia Zygosacchar- Zymomonas Weissella omyces Table 3: Various Microorganisms [Genus] involved in Food Fermentation
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Most of these facultative anaerobic microorganisms have catabolic activities to oxidize sugars to yield various acids, alcohols and carbon dioxide. Homo-fermentative microorganisms utilize
Embden-Meyerhof-Parnas [EMP] and Entener Doudoroff [ED] pathways to metabolize hexose to obtain ATP.
In EMP pathway, one mole of glucose is converted to two moles of pyruvate and it is the most important catabolic pathway in fermentative microorganisms. Conversion of pyruvate to lactic acid or ethanol [Figure 1] balances the redox reaction.
Glucose Glycolysis
D-Glyceraldehyde-3-phosphate
NAD NADH + H+
Pyruvate
NAD NADH + H+ Lactic acid
Figure 1: Formation of lactate by Homo-fermentative bacteria
Two ATP molecules are generated during this reaction, proving
EMP pathway as most efficient energy generating pathway in ferme-
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tative microorganisms (Gottschalk, 1986). In dairy fermentations,
galactose catabolism from milk sugar “lactose” is essentially done
by enzymes involved in ED pathway and during this only one ATP molecule is generated (Montville and Matthews, 2008).
Heterofermentative pathway [Figure 2] is characterized by generation of carbon dioxide from hexose sugar. It generates one
ATP molecule. Enzymes in this pathway allow the utilization of five and three carbon sugars (Gottschalk, 1986).
Glucose
Glucose 6-phosphate
6-phospho gluconic acid
Carbon dioxide
Ribulose 5-phosphate
Xylulose 5-phosphate
Glyceraldehyde 3-phosphate Acetyl phosphate
Acetaldehyde
Lactic acid Ethanol
Figure 2: Fermentation of glucose by Heterofermentative bacteria
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Cereals are fermented all over the world. Due to this reason, there exists a wide variety of both raw materials and conditions of different fermentations. Cereals in their dry state are not fermented but are soaked in water which increases enzymatic and microbial activity on cereals. As a general rule, most traditional fermentations are brought about spontaneously by lactic acid bacteria [LAB] as predominant bacteria and in many cases yeasts carry out the fermentations (Font de Valdez et al, 2010; Nout and Sarkar, 1999).
LAB are a functionally related group of bacteria belonging to order
Lactobacillales [Table 4], identified mainly for fermentative role in food and beverages (Axelsson, 2004).
The largest varieties of metabolic properties are found in LAB which have been isolated in cereal environments. LAB plays a role ranging from sporadic contaminants to major fermentative flora in fermented foods (Gänzle et al, 2009).
Most of the cereals fermenting LAB are hetero-fermentative with rapid utilization of maltose as preferred carbon source. These
LAB produce lactate, carbon dioxide, and the alternative end products ethanol and acetate. Utilization of maltose also leads to exo-polysaccharide production by cereal-associated LAB (Welman and Maddox, 2003).
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¾ Aerococcaceae Abiotrophia Aerococcus Dolosicoccus Eremococcus Facklamia Globicatella Ignavigranum ¾ Carnobacteriaceae Alkalibacterium Allofustis Atopococcus Atopobacter Atopostipes Carnobacterium Desemzia Dolosigranulum Granulicatella Isobaculum Lacticigenium Marinilactibacillus Trichococcus ¾ Enterococcaceae Bavariicoccus Catellicoccus Enterococcus Pilibacter Tetragenococcus Vagococcus ¾ Lactobacillaceae Lactobacillus Paralactobacillus Sharpea Pediococcus ¾ Leuconostocaceae Fructobacillus Leuconostoc Oenococcus Weissella ¾ Streptococcaceae Lactococcus Lactovum Okadaella Streptococcus Aerosphaera Carnococcus
Table 4: Phylogeny of the Order Lactobacillales
The formation of oligosaccharides is catalyzed by
glycansucrases, disaccharide hydrolases and disaccharide
phosphorylases enzymes from LAB. These oligosaccharides
stimulate intestinal normal flora, preventing pathogen adhesion to
gut epithelium. This is typical prebiotic activity of oligosaccharides
synthesized by LAB (Tieking et al, 2003).
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The fermentative microbial flora of food utilizes nutrients
causing their depletion, generate organic acids lowering the pH of
batter and reduce redox potential. They also synthesize
antimicrobial compounds like ethanol, diacetal, hydrogen peroxide
and different bacteriocins. These environmental changes in food
inhibit the growth of pathogens during fermentation (Adams, 2001).
Most bacteria isolated from cereal fermentation have shown to
possess probiotic characters. Fermented probiotic cereal products
made from oats, maize and, malted barley having Lactobacillus and
Bifidobacterium as probiotic constituents (Rivera-Espinoza and
Gallardo-Navarro, 2010) are available.
1.3.1 Idli and its Preparation
In India, the semitropical humid climate is ideal for rice
cultivation. An average Indian consumes 2400 calories per day and
rice supplements nearly 30 % of caloric needs. Rice is fermented by
several methods in India to obtain different fermented foodstuffs
and beverages. Idli is one of the important fermented South Indian
dish prepared from rice. It is savored all over India today. It is
popular because of its soft and spongy texture and organoleptic
attributes such as sour taste and aroma. Idli is presented as a small, white, acid leavened steam cake.
The initial mention of the name 'Idli' occurs in the Kannada
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writing of Shivakotiacharya in 920 AD. The earliest available
Kannada encyclopedia describes that Idli was prepared by soaking
black gram in butter milk, ground to a fine paste (Achaya, 1994).
There is no known record of rice being added until sometime in the
17th century.
Nowadays, Idli is mainly prepared from fermentation of mixture of cereal and legume. This mixture is nutritionally preferred as it supplies an improved balance of calories and proteins containing proper proportions of essential amino acids. This mixture typically consists of dehulled cotyledons of black gram
[Phaseolus mungo L. now known as Vigna mango], a legume, and
rice [Oryza sativa L.], a cereal (Joshi, 2009).
Parboiled rice which has higher B-complex vitamins in
endosperm or rice grits can also be used for making Idli. It is seen
that the characteristics of Idli were influenced by the variety of rice
and the degree of polishing (Kumar et al, 2005). Fermentation and
preparation of Idli [Figure 3] is relatively simple. Black gram and
rice are washed to remove dirt, dust and surface microflora and
separately soaked in water for 4-6 hours. The soaked material is
pulverized in a blender or stone grinder to obtain a coarse to smooth
batter. The combined mixture is allowed to ferment for 20-22 hours
at room temperature (Steinkraus et al, 1967). Different proportions
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 12 of black gram to rice i.e. from 4:l to 1:4 w/w can be used for making
Idli (Desikachar et al, 1960). The amount of water added to the mixture can also vary from 1.5-2.0 times over the dry weight of the raw material. Several other condiments and ingredients are added to the batter to enhance the Idli taste and flavor.
Rice Dehulled black gram
Soak separately for 4-6 hours
Grind separately in a blender
Mix and allow to ferment at ~30oC for ~20 hours
Mix well/Add seasonings
Steam in cake mold cast
Nutritious/Tasty Idli
Figure 3: Process of Preparation of Idli
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1.3.2 Microorganisms and Idli fermentation
The most important microbial analysis of Idli fermentation is
reported from Prof. K. H. Steinkraus’s laboratory. Leavening leading
to dough rising and lowering of batter pH due to acid production are
two major changes that occur in Idli batter during fermentation.
After 20-24 hours of fermentation, the volume of batter increases
by approximately 50-60 % as compared to the initial quantity and
after 24 hours, the volume decreases rapidly even below the starting
volume with a concomitant decrease in pH from 6.0 to 4.3. Total
acidity increased fourfold in 20 hours and was 3.14 gram of lactic
acid per gram of dry batter. Although there is no external microbial
inoculum to initiate the fermentation, within 20 hours the bacterial
number increases by approximately 2.5 x 105 fold indicating very
high growth rate of bacteria during soaking and batter fermentation.
The number of bacteria decreases as the fermentation proceeds
beyond 24 hours.
Idli is closely related to sourdough and the leavening is
carried out by bacteria rather than yeast. The acid and gas required
for leavening of batter are generated solely by the action of
heterofermentative Leuconostoc mesenteroides (Mukherjee et al,
1965) These LAB could ferment glucose, fructose, galactose,
mannose, sucrose, maltose, and xylose with normal amount of acid
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 14
production. In addition, Streptococcus faecalis [now Enterococcus
faecalis] could be isolated from Idli batter which would then produce acid with no carbon dioxide gas. E. faecalis have capacity to ferment glucose, fructose, galactose, mannose, arabinose, sucrose, maltose, lactose, raffinose, and mannitol.
In addition to the above two isolates, another major isolate was Pediococcus cerevisae, which grew in typical tetrad formation, produced acid but not carbon dioxide. L. mesenteroides and S. faecalis were present during the early part of fermentation, followed by the high acid-producing P. cerevisiae. Pediococci start growing only after 28 hours, a stage when the batter is highly acidic and hypo-leavened (Mukherjee et al, 1965). L. mesenteroides has been found to be naturally present on black gram.
Two yeast species Torulopsis candida and Trichosporan pullulans also have been isolated from Idli batter. These are responsible for its fermentation and flavor. Saccharomyces cerevisiae, Debaryomyces hansenii, Pichia anomala, and
Guehomyces pullulans are also isolated from Idli batter (Soni and
Sandhu, 1991). However the role of yeast isolates in Idli fermentation is not well defined.
Traditionally, the batter is fermented naturally without any external inoculum as microorganisms present on rice and black
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 15
gram act as inoculum for this fermentation. Sometimes, sour
buttermilk or yeasts are added to enhance the fermentation. Batter
prepared using starter cultures like Pediococcus pentosaceus and
Enterococcus faecium, individually and along with Candida versatilis yielded better quality batter with respect to volume, level of gas produced, titratable acidity, and Idli as judged by sensory profile acceptance and shelf life (Sridevi et al, 2010).
1.3.3 Physico-chemical properties of Idli batter
After steaming, the texture of Idli becomes a soft and spongy
[porous crumb] solid from semisolid viscous batter. The air voids
and fine network [spongy texture] of the Idli is important for its
scrumptiousness. The soft spongy texture of steamed Idli is due to presence of two important components in black gram. One of them is surface active protein [globulin] with high molecular component having foam forming activity. The second component is an arabinogalactan [polysaccharide] which is mucilaginous viscogenic compound containing arabinose and galactose sugars at 3:2 ratio respectively. The viscosity of black gram polysaccharide is 10 times more than standard larch Arabinogalactan (Susheelamma and Rao,
1979; Susheelamma and Rao, 1978). This polymer stabilizes the network of foam formed by the surface active protein and is
essential for leavening of batters and for sponginess of the Idli even
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 16
after steam treatment.
Rheological performance relates to food consistency which
also appeals to sensory organs. Since Idli batter contains insoluble
material, soluble polymeric proteins and carbohydrates from grains
and entrapped gas, its rheological character is most important to
yield final spongy Idli. The Idli batter has been shown to exhibit shear thinning behavior prior to and after fermentation.
Fermentation increases the batter viscosity and degree of shear thinning (Castel-Perez and Mishra, 1995).
Rheological properties of individual components namely black gram (Bhattacharya et al, 2004) and rice (Xue and Nagadi, 2006) also have been reported. After fermentation of black gram flour the apparent viscosities of the batter increased significantly over that of native flour. Addition of salts causes considerable decrease in apparent viscosities of the flour but only marginal decrease in fermented flour. Peak viscosity decreases by both sodium chloride and fermentation. Intrinsic viscosity of starch isolated from black gram flour increases considerably while solubility and swelling power increased only marginally after fermentation.
The quality of steamed Idli is a subject of interest, to judge and optimize the production method of good textured Idli with the selection and adoption of the ingredients and its process. The
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 17
firmness value positively correlates with gumminess, chewiness,
cohesiveness and springiness which depict the soft nature of Idli.
Resilience is not correlated with other textural parameters. The first
principal component is highly positively correlated with gumminess,
chewiness and cohesiveness. The second principal component is
positively correlated with firmness and negatively correlated with
springiness (Ghosh and Chattopadhyay, 2011b).
1.3.4 Nutritional Benefits of Idli Fermentation
Sprouting is one way to increase the nutritional value of
cereals but the increase has its own limitations. Therefore,
fermentation of cereals is the preferred way of improving nutritional
quality of food as it contains live microorganisms that ferment food
and also their metabolites produced during fermentation.
Fermentation is deliberately carried out to improve the nutritional
property of the food. Major changes in Idli batter after fermentation are shown in Table 5.
Soaking and microbial fermentation of Idli raw material leads to a decrease in the level of carbohydrates and complex indigestible oligosaccharides such as verbascose, stachyose, raffinose in legumes. A decrease in oligosaccharide levels reduces abdominal distention and flatulence (Reddy et al, 2006).
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% CHANGE AFTER INGREDIENT FERMENTATION STUDY-I STUDY-II Protein 0.7 ND Protein Efficiency Ratio 11 33.3 (PER) Choline 33.9 Folic acid 58.7 Thiamine 176 Riboflavin 116 Vitamin B-12 -5.1 Total phosphorus -8 Phytic acid -35 Oligosaccharides ND Sucrose -32.5 Stachyose -28.9 Verbascose -18 Amino acids Cysteine -90.8 Lysine 29.1 Arginine 28.9 Tryptophan -8.3 Methionine 10.5 18.6 ND = Not determined
Table 5: Changes in major nutritionally important ingredients after Fermentation of Idli batter
Fermentation followed by steaming results in further substantial reduction in these oligosaccharides. Fermentation of black-gram slurry reduces the levels of phytic acid and polyphenols significantly (Rajalakshmi and Vanaja, 1967). In vitro digestibility of
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starch and protein improves significantly with increase in
temperature and fermentation period. This may be due to
elimination of chymotrypsin inhibitor during Idli preparation
(Padhye and Salunkhe, 1978).
Easy digestibility of Idli is controversial as some reports
suggest that it is the same as that of the unfermented mixture (Van
Veen et al, 1967). These differences could be due in part to utilization of different proportions of rice to black gram in preparation of Idli.
Fermentation also improves the Protein Efficiency Ratio [PER]
and Biological Value [BV] of Idli over the unfermented batter
(Padhye and Salunkhe, 1978; Rajalakshmi and Vanaja, 1967). The
Idli contained 15.3 % protein, with a PER of 1.84 as compared to
1.79 for the same unfermented ingredients but this increase in PER
is also contradictory (Van Veen et al, 1967). In the final fermented
steamed product, there was considerable increase in some
important vitamins and essential amino acids. Increase in vitamins
like thiamine, riboflavin, choline and folic acid contents as a result
of fermentation was seen. It is reported that the methionine content
of Idli was 18.6 % greater than that of the unfermented batter while
other two studies reported increase of 10.6 % (Steinkraus et al,
1967) and 60.0 % (Padhye and Salunkhe, 1978) of methionine in
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fermented batters. An increase in methionine during fermentation is
of importance as most legumes have very meager quantity of
methionine.
Weanling rats fed on fermented Idli were found to be superior to those fed on unfermented product with regard to weight gain,
nitrogen retention, thiamine and riboflavin contents of the liver and
the activities of liver xanthine oxidase and succinic dehydrogenase
and haemoglobin content of blood. It was observed that feeding of
Idli to rats resulted in a better red blood cells production.
Accumulation of fat in rat liver due to low protein diet could be
reversed by feeding Idli to experimental animals and this was significant as compared with feeding the same batter before fermentation (Rao, 1961).
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 21
1.4 AIMS OF THE STUDY
Staple foods worldwide are cereals and pulses that are
consumed after cooking. But large amounts of cereals are fermented
to improve its biological value prior to consumption (Nout, 2009).
Idli is one such fermented cereal preparation and the quality of
steamed product is a subject of interest being a very popular
breakfast foodstuff in India.
Idli batter fermentation has been the subject of quite a few
research investigations involving many aspects. These studies
include optimization of ingredients (Steinkraus et al, 1967),
microbiological aspects of batter fermentation (Mukherjee et al,
1965), physico-chemical changes during batter incubation
(Bhattacharya and Bhat, 1997) and nutritional improvement after
fermentation (Soni and Sandhu, 1989).
The only fundamental work describing the fermentation of Idli
batter was published in 1965 (Mukherjee et al, 1965). The paper
ascribed role of acid and gas production to L. mesenteroides, S. faecalis and P. pentosaceus during fermentation. The isolates from batter were identified mainly by colony characters, morphology and sugar fermentations. Isolation of yeast species was not reported by these authors although some studies have reported involvement of yeast in Idli batter fermentation (Aidoo et al, 2006). Many reviews
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 22 and book chapters written on cereal fermentation and fermented food quote this single paper for microbial involvement in making of
Idli. This single study was carried out by Mukherjee et al in laboratory conditions.
In the light of this situation, the aims of this study include:
¾ Isolation of bacteria and yeasts from samples of Idli batter
from vendors where Idli fermentations are routinely carried
out on large scale and laboratory made Idli batter.
¾ Identification of these isolates using routine biochemical tests
as well as by 16S ribosomal RNA gene sequence analysis which
would impart the idea regarding the diverse microbial flora
present during fermentation.
¾ Most isolates from cereal fermentations play an important role
as probiotic microorganisms. For this reason characterization
of isolates based on different probiotic criteria such as non-
pathogenicity, bile tolerance, adhesion to intestinal cells and
inhibition of pathogens.
¾ Characterization of Rheological changes during Idli
fermentation.
Lokesh P. Sharma, Ph. D. Thesis, 2011 Page 23
¾ Establish the correlation between microbial activity and the
changes in Rheology.
¾ Many conventional fermented foods from Asia have been
upgraded to high technology production methods. This could
happen because of the strong research traditions in fermented
food technology. This research component is minimal in Idli
manufacturing. Therefore, attempt has been made in this
thesis to throw light on type of microorganisms and their role
in making of Idli.
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