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Alkaline phosphatase as an indicator for the heat treatment of the milk for cheesemaking
Malínská, Hana ; Potůčková, Miroslava (advisor) ; Lidmila, Lidmila (referee)
Alkaline phosphatase as an indicator for the heat treatment of the milk for cheesemaking
Summary
The aim of this diploma thesis was to summarize current knowledge about the evaluation of alkaline phosphatase activity as an indicator of heat treatment of milk for production of dairy products in theoretical part. In experimental part were comparised 2 methods for this enzyme activity determination, the original according to ČSN EN ISO 11816-2 (2003), using pasteurized milk as an extracting agent, and ISO 11816-2/IDF 155-2 (2010), using extraction buffer. For comparison were used 110 cheese samples, 8 quarg products, 49 fresh cheese products, 9 spiced fresh cheese products, 7 white-brined cheese products, 7 Penicillium sp. flora cheese products, 5 coryneform flora cheese products and 25 semi-hard and hard cheese products.
Alkaline phosphatase (EC 3.1.3.1) is a hydrolase cleaving phosphate groups at the 5th and 3rdposition of many molecules including especially nucleotides and proteins. The enzyme has a pH optimum in the alkaline range (pH 10), their cofactors are ions Zn2+and inhibitors Cu2+. Dairy alkaline phosphatase derived from mammary epithelium and other cellular residua in milk. In this medium is the enzyme localized on the membrane of fat globules. Their amount depends on the stage of lactation (the highest concentration is in colostrum) and animal health (their concentration increases when disease, especially mastitis, starts). Due to its specific thermostability is alkaline phosphatase used for proof of milk and milk products pasteurization.
In the experimental part of the diploma thesis was found that the recommended substitution of pasteurized milk for buffer improves enzyme extraction process from cheese matrix and so enhances method sensitivity (p > 0.05). Method unsuitability for Penicillium sp. flora cheese (especially for blue-veined ones) was also confirmed (p > 0.05). This unsuitability could be explained by content of microbial alkaline phosphatase. For the same reason might not be this method suitable also for coryneform flora cheese. On the contrary, this analysis is suitable (p > 0.05) for white-brined cheese. For spiced fresh cheese were the results in terms of evaluation suitability ambiguous. Based on the obtained data was also confirmed the suitability of proposed limit (10 mU/g) for residual enzyme activity in products from pasteurized milk.
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Ice cream with additional value
Melicharová, Barbora ; Potůčková, Miroslava (advisor) ; Lidmila, Lidmila (referee)
The aim of this bachelor thesis is to summarise current knowledge about production and properties of ice cream with an additional value. Nowadays, incorporation of probiotics is considered as the most intensively studied possibility for functional ice cream manufacture. Their viability depends on the kind of a microorganism, for example bifidobacteria are mostly less stable than lactobacilli in ice cream matrix. Lactobacillus acidophilus AB518, AK414, Lactobacillus agilis AA1773, AC1888 and Lactobacillus rhamnosus AB2010 were chosen as suitable strains for ice cream production because of their stability during manufacture and storage processes and also digestion.
Viability of probiotic cultures in ice cream matrix can be negatively influenced by lethal damage of living cells during manufacture processes and storage. Critical points are freezing of ice cream mixture and temperature fluctuation during storage. The basic ingredients (milk fat, proteins, lactose, sweeteners, hydrocolloids, air bubbles, fruit ingredients) naturally protect starters against these impacts. Survival of probiotics can be also supported by prebiotics inuline and oligofructose (> 9 %) addition, by microorganisms incorporation into chocolate chips (> 23 %) or by starter microencapsulation into calcium alginate (> 30 %).
Probiotic microorganisms addition influences also sensory profile of the final product. To minimize their effect is recommended to incorporate them before the freezing step. Good sensory profile had for example ice cream containing Lactobacillus reuteri and Bifidobacterium bifidum. Probiotic ice-creams could have poorer aroma, yoghurt taste or unpleasant probiotic taste, but on the other hand pleasant fresh sauer taste, higher viscosity, homogenity, smoothness and resistance to melting. Their sensory quality can be also positively influenced by adding milk fat, hydrocolloids (guar gum, xanthan) and sauer fruit ingredients (strawberries) or by overrun (60 90 vol. %).
Moreover, probiotic ice cream is possible to use as a carrier of other health beneficial ingedients, for example essential substances (fatty acids, minerals, vitamins particularly calcium and vitamin D), fibre and antioxidants. It was observed that probiotic ice cream containing Bifidobacterium lactis and Lactobacillus acidophilus had anticariogenic effect.
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