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ThesisItem Open Access Qualitative changes of yoghurt prepared from milk preserved by different methods(Department of Dairy Science, College of Veterinary and Animal Sciences,Mannuthy, 1990) Prasad, V; KAU; Sukumaran, M VAn experiment was conducted to study the qualitative changes of yoghurt prepared from milk preserved by different methods. An attempt was also made to study the efficiency of LP system in controlling psychrotrops in refrigerated milk thereby extending the keeping quality of such stored milk. The efficacy of the system was compared with pasteurized milk and raw milk stored under similar conditions. An exhaustive review of literature has been presented on the use of various preservation methods employed in milk, quality of yoghurt and other related aspects. The methods of analyses of some important components of milk and yoghurt has been detailed. The milk after collection were divided into three portions and used for various treatments A (raw milk as such), B (laboratory pasteurized) and C )LP activated). Samples in each treatment were again divided into four parts and stored under refrigeration for 0, 24, 48 and 72 hours for further analysis and yoghurt preparation. When raw milk was stored under refrigeration, acidity developed to a significantly high level (P < 0.05) at the end of 72 hours of storage whereas no significant increase in activity was noticed in treatments B and C. This result was corroborated by a decrease in both psychrotrophic and total bacterial counts in milk under treatments B and C. So it was concluded that the development of acidity in treatment A could be due to bultiplication of microbes particularly psychrotrophs. In B and C its growth was arrested by the treatments. Hydrogen peroxide and thiocyanate were detected in all raw milk samples at a level of 3.78 and 7.33 ppm respectively. The level of H2 O2 and SCN – used for the activation of LP system for the study were found to be adequate, since the psychrotrophic count in milk at the end of 72 hours in treatment C was less than that found in treatment B. The residual H2 O2 and SCN – contents at the end of 72 hours were found to be within the normal level found in milk thus having no health hazards, by this method of preservation. When yoghurt samples were prepared from stored milk no significant differences between treatments were noticed in the values of fermentation period, acidity, pH, total proteins and total solids. A significant increase in NPN and tyrosine values were noticed in yoghurt prepared from milk under treatment A indicating extensive proteolysis in milk during storage under this treatment. However, no difference was noticed between treatments B and C. Diacetyl and acetaldehyde were produced at a desirable level in yoghurt samples under all the three treatments. A proper ratio of Str. Thermophiles – 6 and L. bulgaricus – 4 was found to be maintained in all yoghurt samples. On organoleptic evaluation the yoghurt prepared from milk under treatment C could not be distinguished from other two treatments. In fact, yoghurt under C got a higher total score on organoleptic evaluation than A and B. Low score for body and texture, and falvour was observed under treatment A. This may be attributed to the effect of growth of psychrotrophs in raw milk during refrigeration. From the results, it was concluded that good quality yoghurt can be prepared from milk stored under refrigeration following pasteurization or LP activation. Yoghurt samples prepared from milk stored under treatment A was found to be of inferior quality when compared to B and C. The result also confirmed that LP system can be recommended as a safe preservative for extending storage life of refrigerated milk. When such stored milk was used for yoghurt production, no significant difference in the quality was noticed when compared to yoghurt under treatment B. Suggesting that LP activated milk can be conveniently and economically used for the production of fermented milk products like yoghurt without any apparent harmful effect.ThesisItem Open Access Preparation of mozzarella cheese using skim milk filled with coconut milk(Department of Dairy Science, College of Veterinary and Animal Sciences, Mannuthy, 1994) Gnana Selva, Johnson; KAU; Mukundan, MA detailed study was carried out to determine the quality of coconut fat filled milk for the preparation of Mozzarella cheese and why drinks. Literatures based on filled milk products has been reviewed, apart from the preparation of cheese and why drinks. The control samples of Mozzarella cheese and whey drinks were prepared using cow’s milk. Experiment I products were prepared from milk in which 50 per cent of milk fat was replaced with coconut fat. Experiment II products were prepared from cheese milk in which 100 per cent of milk fat was replaced with coconut fat. All the samples of milk were standardized to 4 per cent fat. A total of 6 trials were carried out to obtain reliable data for statistical analysis. The acidity, pH, stretchbility and FDM content were found to be similar in control, experiment I and II Mozzarella cheese. Eventhough, the control Mozzarella cheese were found to have slightly higher yield protein, fat and lower moisture content, the experimental I and II. Mozzarella cheese also satisfied the requirements for good quality Mozzarella cheese. The control Mozzarella cheese got maximum score on sensory evaluation than the experiment I and II Mozzarella cheese. Pineapple and Lemon falvoured control, experiment I and II whey drinks were found to be equally acceptable with nodifference on storage studies ar 5 + loC. Total bacterial count on whey drinks were also made. The studies revealed that the cow milk in which the milk fat replaced to the extend of 50 per cent and 100 per cent with coconut fat can be effectively utilised for preparation of Mozzarella cheese. The quality of such cheese is comparable with that made from cow milk.ThesisItem Open Access Use of condensed coconut water in yoghurt(Department of Dairy Science, College of Veterinary and Animal Sciences, Mannuthy, 1996) Malarkannan, S P; KAU; Geevarghese, P IAn attempt was made to incorporate condensed coconut water in partial replacement of MSNF at 25 and 50 per cent level in yoghurt and to study the properties of the product which were compared with normal yoghurt. An exhaustive review of literature on the various physico – chemical properties of yoghurt and other fermented milk products has been presented. The procedure for the analysis of coconut water and condensed coconut water for its chemical composition, mineral profile and method of condensation has been described. The quantity of ingredients for yoghurt preparation was derived by linear programming model. The treatments were divided into TC (control), T2 (25 per cent replacement of MSNF using condensed coconut water without gelatin), T3 (T2 + gelatin at 0.5 per cent level), T4 (50 per cent replacement of MSNF using condensed coconut water without gelatin) and T5 (T4 + 0.5 per cent gelatin). A pre – trial was conducted to find out the ideal combination of starter culture and gelatin to be added to give good quality yoghurt. A combination of four per cent starter culture with 0.5 per cent gelatin produced good quality yohurt and this combination was used in the subsequent trials. A pilot heat stability test was conducted in treatment mixes to find out the amount of trisodium citrate required to provide sufficient heat stability. Yoghurt mixes prepared were analysed for titratable acidity, pH and total solids. Statistical analysis revealed no significant difference between control and treatments for the above. No significant difference was observed in pH and fat between the control and treatments. A significant difference (P < 0.01) in titratable acidity, protein and NPN percentage was observed between control and treatments. The curd tension and viscosity showed a decreasing trend with increasing level of replacement but this properties improved to certain extent by addition of gelatin. The setting time and NPN content showed an increasing trend as replacement level increased and this may be due to high mineral and NPN content in coconut water. There was no significant difference in tyrosine value between the control and treatments T2 and T3. No significant difference was observed in L. bulgaricus count and coliform count between control and treatments, whereas but S. thermophiles and yeast and mould count showed significant difference between control and treatments which may be due to a stimulatory factor in coconut water for yeast and mould and inhibitory factor for S. thermophiles resulting in slow growth. Organoleptic quality revealed that 25 per cent replacement of MSNF with or without addition of gelatin produced comparable scores as that of control yoghurt. A savings of 13.95 per cent and 8.14 per cent in cost can be achieved by 25 per cent replacement of MSNF with or without addition of gelatin respectively. The results of the experiment revealed that 25 per cent replacement of MSNF with condensed coconut water can be successfully tried in preparing yoghurt without affecting the physic – chemical and organoleptic properties together with considerable reduction in cost.
