Hydrolysis Of Lactose In Permeate From The Ultrafiltration Of Cottage Cheese Whey Using Immobilized Beta Galsctosidase

Author : Victor Manuel Bernal Olivera
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (143 download)

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Download or read book Whey Protein Stabilization and Lactose Hydrolysis for the Production of Whey-based Beverages written by Victor Manuel Bernal Olivera and published by . This book was released on 1984 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The major objectives of this research were related to two technical problems found when considering the manufacture of a non-fermented beverage from lactose-hydrolyzed whey: 1) to prevent the formation of a protein sediment in the drink as a consequence of the heat treatment applied to these products; and 2) to evaluate several commercial lactase preparations for the hydrolysis of lactose in cottage cheese whey and to select the best enzyme among those preparations to be used in the manufacture of the drink. In the first part of the study, several factors affecting the thermal stability of the proteins present in whey were studied over 2.5-6.5 pH range using Differential Scanning Calorimetry (DSC) and heat precipitation studies. The highest denaturation temperature for an acid whey protein concentrate prepared by ultrafiltration was 88°C at pH 3.5, while for pure /3-lactoglobul in (/3 - 1 g) the highest denaturation temperature, obtained at pH 3.5, was 81.9°C. Presence of milk sugars (lactose, glucose and galactose) appeared to increase the resistance of /3-lg against thermal denaturation. In bovine serum albumin preparations, denaturation temperature varied with fatty acid contents. The importance of calcium for the thermal stability of a-lactalbumin was proven by a 20-22°C decrease in the denaturation temperature upon the addition of 0.1 M EDTA. Heating of whey at 95°C for 5 minutes above pH 3.8-3.9 produced extensive protein precipitation. When the same heat treatment was applied below pH range 3.7, protein precipitation was prevented. In a preliminary hydrolysis experiment, the effectiveness of lactose hydrolysis by a soluble /3-galactosidase from K1 uyveromyces 1 act is was compared in skim milk, KOH-treated cottage cheese whey, KOH-treated ultrafiltration permeate, and model lactose solutions. Of the three possible industrial substrates, the highest /3-galactosidase activity was observed in whey, followed by ultrafiltration permeate and milk. The addition of /3-lactoglobulin, bovine serum albumin and ovalbumin to buffered lactose solutions had no effect on the activity of the enzyme. The hydrolysis of lactose seemed to be dependent upon the amount of potassium present. The Km of the enzyme for lactose in 0.025 M KH2P04 was 76.9 mM. Comparison between NaOH and KOH-treated whey confirmed the suitability of potassium as neutralizing agent when this enzyme is used. In the main hydrolysis study, six commercial /3-galactosidase (E.C. 3.2.1.23) preparations were compared for the hydrolysis of lactose in cottage cheese whey. The comparison was based on parameters obtained from the kinetic characteristics of the enzymes in lactose solutions (Michaelis-Menten constants, apparent turnover numbers, initial reaction rates and integrated equations derived from the Michaelis-Menten expression), and on experimental progress curves for the hydrolysis of lactose in whey. The conversion data were used to predict optimum enzyme dosage/hydrolysis time combinations to attain a fixed degree of lactose conversion. The Km values for lactose varied from 24.0 to 150.2 mM. The lactose hydrolysis efficiency in cottage cheese whey was different for each enzyme. The use of acid /3-galactosidases did not impart any undesirable sensory characteristics to a grapefruit flavoured prototype product developed in the laboratory. Sensory evaluation experiments (triangle tests) showed no significant difference in bitterness (1.0% confidence level) between a protoype product sweetened with sucrose and several drinks made from whey treated with any of the three best acid /3-galactosidases to an 80% lactose hydrolysis level. Based on the results obtained and including an economic evaluation of the commercial preparations, the most suitable /3-galactosidase preparations available for use in cottage cheese whey were identified. This study demonstrated that it should be possible to manufacture a lactose hydrolyzed whey beverage without protein sedimentation problems and with acceptable organoleptic characteristics. The cost of the enzyme required to carried out the lactose hydrolysis would be only about 3 or 4 cents per litre of whey, under the conditions described in this work.