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Theses

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1996 - 19982
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Subject: Dairy Technology × Author: KAU × End date: 2000 × Start date: 1996 × Type: Thesis × Thesis Type: M.V.Sc. ×
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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.