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Theses

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1996 - 19983
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Subject: Dairy Technology × Author: KAU × End date: 1999 × Start date: 1996 ×
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    ThesisItemOpen Access
    Immobilization of Beta Galactosidase for production of fermented milk products with low lactose
    (Department of Dairy Science, College of Veterinary and Animal Sciences, Mannuthy, 1996) Geetha, R; KAU; Prasad, V
    An immobilized β – galactosidase enzyme system was developed using permeabilized cells of K. fragilis as an enzyme source and food grade agar as the immobilizing agent. This was utilised for hydrolysing lactose content present in milk, which in turn was used for preparing selected fermented products with low lactose content. An attempt was also made to assess the possibility of utilisation of whey as a medium for culture maintenance with a view to utilise the by – product. A detailed review of literature has been presented about β – galactosidase specific activity of different organisms, various immobilization techniques,influence of lactose hydrolysis on physico chemical properties of the product and also about the utilisation of whey as a media for culture maintenance. The experiment comprised of determination of β – galactosidase specific activity of permeabilized cells of three selected organisms and assessing the suitability of agar and sodium alginate as immobilizing agents. Since β – galactosidase specific activity was found to be the highest for K. fragilis, it was selected as the best enzyme source. Agar was selected as the suitable immobilizing agent because it was found to be safe, economical and comparatively more efficient. Using these two raw materials an efficient immobilized enzyme system was developed and its efficiency was assessed by estimating the rate of lactose hydrolysis at fixed time intervals. Selected strains of starter bacteria were screened for their performance in four different media viz. Skim milk, 50 per cent lactose hydrolysed skim milk, condensed whey, and 50 per cent lactose hydrolysed condensed whey. Two media were selected from among the four, which stimulated the starter activity and used for further studies. Three different products viz., yogurt, bifidus yogurt and acidophilus milk were prepared using 50 per cent lactose hydrolysed milk obtained by passing through the immobilized enzyme system and cultures maintained separately in lactose hydrolysed milk and lactose hydrolysed whey. Two control products were prepared with ordinary milk and above described cultures. All the three products under different treatments were analysed for acidity, pH, tyrosine value, total lactic count and sensory evaluation. The results obtained in the study were compared with similar reported findings and the following conclusions were made. 1. Permeabilized cells of K. fraglis possessed better B – galactosidase specific activity than the cells of S. thermophiles and L. delbrueckii sub sp. bulgaricus. 2. Food grade agar was found to be an efficient immobilizing agent than sodium alginate. 3. The immobilized enzyme prepared with 10 g of K. fragilis could hydrolyse 50 per cent of lactose content present in 250 ml of milk, after holding in the column for four hours at room temperature (300 C). 4. The rate of lactose hydrolysis was found to be the maximum within first half an hour, thereafter a decline in the rate of hydrolysis was observed. 5. This system was repeatedly used in five batches without any change in its efficiency or mechanical stability of the beads but after which a reduction in activity was noticed. 6. A slight brownish discolouration was observed on the beads when the column was stored for a long period. 7. Repalcement of skim milk with whey was a starter media slightly enhanced the activity of cultures, especially, S. thermophilus, L. lactis and B. bifidum whereas L. acidophilus and L. delbrueckii sub sp. bulgaricus performed better in skim milk, especially when the media was subjected to lactose hydrolysis. 8. The utilisation of lactose hydrolysed milk for preparation of products slightly enhanced the acidity, proteolytic activity and viable cell count of yogurt, bifidus yogurt and acidophilus milk. 9. In the case of treatment yogurts (Y1 and Y2) prepared with lactose hydrolysed milk, a significantly higher protolytic activity was observed. 10. Organoleptic evaluation indicated that the utilisation of lactose hydrolysed milk and cultures maintained in lactose hydrolysed skim milk and whey did not affect the flavour and textural characteristics of yogurt. On the contrary the flavour as well as body and texture scores of bifidus yogurt and acidophilus milk were slightly improved by this technique.
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    ThesisItemOpen Access
    Use of coconut cream in flavoured filled yoghurt
    (Department of Dairy Science, College of Veterinary and Animal Sciences, Mannuthy, 1998) Pandiyan, C; KAU; Geevarghese, P I
    A trial was conducted to assess the suitability of incorporating coconut fat as coconut cream in flavoured yoghurt at various levels and the properties of the product were studied. A detailed review of literature on the various physico-chernical properties of yoghurt has been presented. The treatments were divided in to TC ( control without stabiliser) T2, T3, T4,T5 (25, 50, 75 and 100 per cent replacement level of milk fat respectively using coconut cream, without stabiliser), T6, T7, T8, T9 (25, 50, 75 and 100 per cent replacement level of milk fat respectively using coconut cream, with stabiliser 0.2 per cent) and the physico - chemical, micro-biological and organoleptic properties of the treatments were studied. Experimental yoghurt mixes prepared were analysed for titratable acidity, pH and total solids. Statistical analysis revealed no significant difference between control and treatments of the above characters. No significant difference was noticed in pH and fat between the control and treatment yoghurt samples whereas a significant difference (p< 0.01) in titratable acidity, protein, NPN, curd tension and viscosity was observed between control and treatments. Protein, NPN, curd tension and viscosity showed an increasing trend with increasing level of replacement. In treatments T6, T7, T8 and T9 sodium alginate produced slight improvement in curd tension and viscosity but it was not statistically significant. Tyrosine value increased at replacement level of 50 per cent onwards as compared to control. Coliform and yeast/ mould count showed no significant difference between control and treatments. Organoleptic quality of the products revealed no significant difference between control and treatments except for body and texture scores which showed a significant (p< 0.05) difference. Stabiliser sodium alginate produced little improvement in the body and texture score but was statistically not significant as compared to their corresponding pair. The results of the experiment revealed that coconut fat can be replaced upto 100 per cent level in the yoghurt preparation with an advantage of cost saving, increased protein, NPN, curd tension and tyrosine value. Even upto 100 per cent replacement level overall total organoleptic scores were comparable with control.
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    ThesisItemOpen Access
    Technological evaluation of Kera ice cream
    (Department of Dairy Science, College of Veterinary and Animal Sciences, Mannuthy, 1996) Geevarghese, P I; KAU; Francis, U T
    An experiment was conducted to assess the suitability of incorporating coconut fat in the form of coconut cream in preparing ice cream and ice cream mix powder replacing milk fat at 25, 50, 75 and 100 per cent levels (treatments) so as to reduce the cost of preparation of ice cream. The product developed was named as kera ice cream and the qualities were compared with normal ice cream (control). Kera ice cream was prepared with pineapple flavour and a combination of sodium alginate and glyceryl monosterate as stabilizer since it was found to be the most suitable. It was found that replacement of milk fat with coconut fat at any level does not influence the acidity, pH and specific gravity of kera ice cream mix. The relative viscosity of kera ice cream was increased as fat substitution level increased. Higher surface tension was observed for the control, and among treatments it showed a gradual increase as replacement level increased. It was observed that the overrun percentage increased as replacement with coconut fat increased. Contrary to this a decreasing trend in meltdown time was observed as percentage replacement with coconut fat increased. Whipping ability was lowest for the control during the first 5 min of freezing but it significantly increased during the second five min of freezing. Structural details of the ice cream revealed that as replacement level increased the air cell diameter and cell wall thickness increased. Organoleptic quality of kera ice cream were comparable to normal ice cream. The savings in cost of production for kera ice cream with 100 per cent replacement was calculated as 40.57 per cent compared to control. The properties of the reconstituted ice cream revealed more or less similar trend in characters like acidity, pH, specific gravity, overrun, meltdown time and organoleptic properties as that of the freshly prepared ice cream. The ultra structure of the kera ice cream mix powder particle were studied and it revealed that as replacement level increased the particle size also increased. Clumping of the particles and irregular surface were more evident at 75 and 100 per cent level whereas particles of the control and 25 per cent had smooth surface. Solubility index of the powder increased as percentage replacement increased. Significant difference could be noted with regard to bulk density and percent volume occupied by the powder particle. Storage studies were conducted with different packaging material and metallised polyester polyethylene was found to be the best. The moisture and titratable acidity of kera ice cream mix powder with and without antioxidant were significantly higher at any replacement level at 180 days of storage. The thiobarbituric acid value showed a significant difference for the powder without antioxidant at 120 days of storage and with antioxidant the difference could be noted at 180 days of storage. Peroxide value was recorded as zero at different periods of storage upto 180 days of storage. At 180 days of storage, powder without BHA at any replacement level showed significant difference whereas in antioxidant added powder difference could be noted at 75 and 100 per cent replacement levels. Nutritional qualities of kera ice cream was evaluated by rat feeding trials and was found that protein efficiency value and feed efficiency were comparable to ice cream diet. The cholesterol and triglyceride level in animals fed with kera ice cream and ice cream were also not different. Pathological examination of carcases and tissues of animals under treatment and control groups did not reveal significant changes indicating that incorporation of coconut fat cannot cause any untoward effect in organs and tissues of animals. It can be concluded that coconut fat can be incorporated in the prepartation of ice cream and mix powder with out any noticeable changes in the quality. Addition of antioxidant prolongs the keeping quality of the powder by two months. There is no health hazard in consuming the kera ice cream as revealed by the pathological examination of tissues from the experimental animals fed with kera ice cream.