1.
Rheological And Microstructural Study Of Commercial Cheddar And Mozzarella Cheeses By Using Farinograph
by Saima Inayat | Prof. Dr. Muhammad Ayaz | Prof. Dr | Prof. Dr. Talat Naseer Pasha.
Material type: ; Format:
print
; Literary form:
drama
Publisher: 2012Dissertation note: A series of five experiments were conducted using Brabender Farinograph-E to study rheological properties of different brands of cheeses. This is a computerized machine having data recording capacity. It was found that Farinograph was a use full machine for preparing cheese and studying its rheology. The data recorded in the form of Farinogram showed that torque (resistance against flow of farinograph paddles) depended on fat content, temperature employed and time given to cheese formation. Also, the texture of cheese was influenced by these factors.
Sensory tests are not capable of measuring results more accurately as compared to Instrumental tests. To study cheese properties and effects of many manufacturing factors the fundamental methods will help researchers to develop cheeses with required and persistent textural and rheological properties. The instrument most frequently used all over the world for determining water absorption and mixing characteristics of wheat and rye flour in baking industry is Brabender Farinograph®. The present study was conducted by using Farinograph-E as a major tool to measure rheology of cheeses. In this study cheeses of different ages, and kinds e.g., Mozzarella, medium Cheddar, mild Cheddar, old Cheddar, extra old Cheddar, Ricotta and Parmesan were included. The parameters for operating Farinograph-E were developed and initial trials were conducted in various directions to finalize the procedure. Farinograph-E (Brabender GmbH, Duisburg, Germany) was used in this study by using its bowl W-50.
The tests were performed by cutting whole cheese bars into small pieces and shifted into air tight containers. The grated cheese was loaded with the help of spatula into Farinograph bowl. Water bath was adjusted at various temperatures like 20, 30, 40, 50 and 60°C. The temperature was continuously monitored through a temperature probe, inserted into the bowl contained cheese sample. The speed of paddles/ spindles was fixed in Newton meters (Nm) and was kept as constant for all the trials. The lid was closed after filling the bowl and clamped in order to avoid any disturbance. The test was allowed to run for specified time for 35 and 60 minutes. After completion of time durations the test was stopped automatically. The readings were recorded in the form of a graph (torque, time and temperature) of cheese dough resistance over mixing time.
Besides Farinographic studies, the results of Mozzarella and medium Cheddar Farinographic samples of (brand No name) were examined through Cryo-scanning electron microscopy and Fluorescence microscopy to study their microstructure at different stages and their relationship with quality of cheeses. The present study revealed that temperature, time and different fat percentages of different cheese brands shows significant effects on torque values. The results indicated that by increasing fat percentage the torques value decreases.
Cryo-scanning electron microscopy revealed finer details of cheeses. Shape, size and distribution of fat globules were observed through fluorescence microscopy. The changes in globule sizes and their interaction with casein matrix was also observed. Size of globule was estimated using image analysis technique. Aggregation of globules and their rupture was also observed. These changes in fat globules shape and sizes affected flowability, meltability and viscosity of cheeses and thus affected production of torques which were observed in graphs produced by Farinographs.
By studying microstructure it was obvious from micrographs that Stage 1 showed smaller fat globules in large numbers. In Stage 2 the globules became larger in size and lesser in number and like bubbles in shape, as shown in plates. At stage 3, there was no particular change from Stage 2 texture, except slight change in colour. The same changes are depicted in the shape of curve, that moved up and downwards and then upwards.
Full fats at stage 1, showed smaller fat globules those enlarged at stage 2. In stage 3, only enlarged globules were observed, and the resistance increased against paddles of farinograph and sharp increase was seen in the slope of graph. Globules retained their features at next stage and slope in graph became horizontal to x-axis after reaching maximum value.
These results suggest that size distribution of fat globules tended to impose influence on Farinographic results. Overall it is indicated that Farinograph is a suitable instrument for measuring rheology of cheeses.
Availability: Items available for loan: UVAS Library [Call number: 1578,T] (1).
3.
Survival Of Probiotics In Yogurt Ice Cream
by Hafiz Shahzad Muzammil | Dr. Imran Javed | Dr.Muhammad Ayaz | Prof. Dr.
Material type: ; Format:
print
; Literary form:
not fiction
Publisher: 2013Dissertation note: This study was designed to produce the yogurt ice cream containing probiotic
microorganisms with the recommended levels (106-107) of live cells at the time
consumption. The mixture was supplemented before freezing with prebiotics (inulin
and oligofructose) and cryoprotectant (glycerol) to see their (prebiotics and glycerol)
effects on the survival of Streptococcus thermophilus, Lactobacillus bulgaricus,
Lactobacillus acidophilus and Bifidobacterium lactis during freezing process and in
storage period. Along with bacterial population, the effects of prebiotics and glycerol
supplementation on physicochemical properties like air holding capacity, fat
components, protein contents, total solids, hardness, stickiness, melting rate, glass
transition, air cell size and ice crystal size were also investigated. Glass transition
temperature was analyzed in each treatment mixture before freezing with differential
scanning calorimeter. The results from the data obtained at various stages of study
have shown different variation pattern for each property.
The initial count of each bacterium before freezing in all treatments with in
experiment was similar and during the freezing process there was non-significant
change in bacterial population. During the storage period at -20°C in the first three
weeks there was less loss in all the samples (P<0.05). With the passage of time the
death rate is increased in all the samples but this decrease was very less with
supplementation as compared to control samples (P<0.05). In the prebiotic yogurt ice
cream the greatest loss was observed in L. acidophilus (P<0.05), while the S.
thermophilus concentration was the maximum among all the bacteria (P<0.05). At the
Summary
110
end of 12 weeks storage period all the bacteria maintained the minimum required
(106-107 CFU/g) concentration (P<0.05). The addition of prebiotics and glycerol has
increased the total solids of all the samples (P<0.05) that would ultimately led to
more overrun percentage. The supplementation of prebiotics and glycerol have shown
non-significant effect on the fat quantity while decreased the protein concentration
significantly (P<0.05). Fat and protein contents remained unchanged during the
storage period of 90 days (P<0.05). The hardness increased with prebiotics and
decreased with glycerol supplementation, while the stickiness increased with the
increasing prebiotics and glycerol concentration (P<0.05). The melting rate has
shown different behavior although the dry matter contents increased with prebiotics
and glycerol but it did not support the slow melting (P<0.05). Prebiotics show less
effect on glass transition temperature, the increase was very less almost to 1°C.
Glycerol has shown most of the effect and it decreased Tg to near about 10°C in 4%
supplemented samples (P<0.05). The overrun percentage show most of its effect on
probiotics as these bacteria are anaerobic and grow best in absence of oxygen, but the
addition of glycerol minimized its effect on survival rate of the bacteria. The overrun
have shown no effect on total solids, fat and protein level but it decreased the melting
rate at 22 °C. The air act as insulator and prevent the melting of yogurt ice cream
(P<0.05). The hardness and stickiness also decreased with increasing level of overrun
(P<0.05). The prebiotics and glycerol supplementation have shown non- significant
change in air cell size and ice crystal size while overrun percentage has significantly
decreased the air cell and ice crystal sizes (P<0.05).
Summary
111
In conclusion, the addition of prebiotics and glycerol increased the survival
rate by decreasing the freeze damage caused by large ice crystal formation and also
improved the physicochemical properties of yogurt ice cream.
Availability: Items available for loan: UVAS Library [Call number: 1769,T] (1).
