Gerd Konrad

A large-scale isolation of native β-lactoglobulin: characterization of physicochemical properties and comparison with other methods

A novel method for β-lactoglobulin (β-lg) isolation from whey was investigated. The method comprised a peptic treatment of whey and membrane filtration under gentle conditions for isolation of native β-lg. The method was applied to 10,000 L batches of processed whey and the product quality obtained was compared with pilot-scale results of three other procedures: 3% trichloroacetic acid (TCA) precipitation, a salting-out procedure and a selective thermal precipitation. The calculated yields of native β-lg were 67.3, 44.9, 46.7 and 49.6% of the β-lg present in whey using the four methods, respectively. The composition of the different β-lg preparations was found to be comparable, however, analysis of purity revealed slight differences as indicated by electrophoresis and fast protein liquid chromatography (FPLC). The isolated β-lg retained a high degree of purity and native properties. The new method for isolation of native β-lg was found to be reproducible, selective and robust as processing of three 10,000 L batches did not indicate any technical problems or variations in the purity of the isolated β-lg.

Physico-chemical and functional properties of whey protein as affected by limited papain proteolysis and selective ultrafiltration

Abstract Limited proteolysis of whey protein by papain at pH 6.5 and subsequent thermal unfolding at acidic pH were studied and correlations between physico-functional (solubility, foaming, emulsifying) and physico-chemical properties were determined. The optimal degree of hydrolysis (DH) for functionality was about 3.0%, characterized by a significant reduction of aggregated whey protein present in commercial ultrafiltered whey protein concentrates. From Chromatographic and electrophoretic results it may by concluded that peptidic fragments are derived from bovine serum albumin and molecular unfolded β-lactoglobulin whereas α-lactalbumin remained unaffected. Liberated peptidic fragments were found to support foaming but not emulsiflcation as determined by a selective ultrafiltration. The beneficial effects of proteolytic and thermal modification of proteins can be maximized with each protein requiring a particular protease to develop a desirable functionality at well-defined DH.

Protein hydrolysis—the key to meat flavoring systems

Abstract The flavors produced by stewing, broiling, or roasting make meat one of the most popular items in the human diet. No “key” compounds are responsible for meat flavors. However, protein degradation appears essential to the development of meat flavor precursors whose interactions are responsible for characteristic meat flavors. This review examines simulated meat flavor systems based on the protein degradation products produced by acid hydrolysis using strong mineral acids, yeast autolysis, and enzyme degradation of natural meat proteins by pure proteinases. In addition, the contributions to meat flavor made by heating protein hydrolysates in the presence of sugars and organic sulfur compounds are reviewed. This paper also describes the work in applied meat flavor research carried out in the former East Germany.

Microparticulation of whey protein: related factors affecting the solubility

ZusammenfassungSimplesse 100, Fettsubstitut auf Molkenbasis, zeigt ein gutes Lösungsverhalten. Da die Entstehung von Mikropartikeln mit thermischen Verfahrensschritten verbunden ist, ist ein solches Verhalten ungewöhnlich. Zur Klärung dieses Phänomens wurden gelchromatographische Trennungen an Sephadex G-100 bzw. an Sephacryl S-1000 sowie die SDS-PAGE herangezogen, unterstützt durch UV-Studien, analytische Techniken und Zentrifugation bei 23.000g. Die Ergebnisse lassen den Schluß zu, daß das Lösungsverhalten mikropartikulierten Molkenproteins im wesentlichen von zwei Effekten bestimmt wird, (1) der optimalen Entfaltung der Proteinmoleküle und (2) der Stabilisierung der entfalteten Proteinmoleküle durch Kohlenhydrate. Beide Effekte favorisieren nicht-kovalente Bindungsmechanismen im mikropartikulierten Protein und sind verantwortlich für physiko-funktionelle und nutritive Eigenschaften.AbstractSolubility of Simplesse 100, the only wheybased fat substitute, was found to be good, considering the fact that technology for preparation of Simplesse 100 is a sequence of thermal steps. To characterize this phenomen, gel chromatography on Sephadex G-100, Sephacryl S-1000 and SDS-PAGE were used, supported by high-speed separation, UV studies and analytical procedures. Results show that the unusual solubility characteristic of microparticulated whey protein is related to two molecular effects: (1) optimal defolding of protein molecules and (2) stabilization of the defolded status by carbohydrate. Both effects were considered to favour non-covalent bonds, which contribute to the outstanding physico-functional and nutritive properties of microparticles.

Interrelation between pH and availability of α-lactalbumin and β-lactoglobulin for proteolysis by papain

Abstract The enzymic hydrolysis of α-lactalbumin and β-lactoglobulin by papain was studied on pure whey protein fractions and on a commercial whey protein concentrate (Lacprodan 80). The effect of pH on substrate specificity of papain was indicated by the increase in proteolytic fragments as free α-amino nitrogen, by the decrease in proteinaceous matter using the BIO-RAD protein assay, by gel permeation chromatography (Sephadex G-100) and FPLC anion-exchange chromatography. Enzymic availability of β-lactoglobulin was determined in view of its pH-dependent molecular association status and was best at pH > 7.5, favouring the monomeric structure, whereas α-lactalbumin was hydrolysed without limitation only at acidic pH. The binding of calcium protected completely native α-lactalbumin against proteolytic degradation at pH 6.0 and 8.0. This protective effect was lower for α-lactalbumin in the commercial whey protein concentrate and was absent in calcium-depleted α-lactalbumin.

Eine verbesserte Methode zur Bestimmung der maximalen Emulgierkapazität von Proteinlösungen

SummaryA method for the examination of the maximum value of emulsifying capacity was optimized using milk proteins. This method is based on a sudden increase in the electrical resistance at the inversion point of the emulsion. The following parameters were tested: protein concentration, pH value, rate of oil dosage, speed of the Ultra-Turrax, time needed for one experiment, and the requirements for preparing the blank. By fixing these parameters it is possible to minimize the coefficient of variation of about 2.0%. This method is successfully applicable for all soluble proteins and meets all the requirements for standardisation.ZusammenfassungAm Beispiel der Milchproteine wird die Methode zur Bestimmung der maximalen Emulgierkapazität optimiert. Die Methode beruht darauf, daß am Inversionspunkt einer Emulsion der elektrische Widerstand sprunghaft ansteigt. Experimentell überprüft wurden die Parameter Proteinkonzentration, pH-Wert, Öl-Dosierungsrate, Ultra-Turrax-Drehzahl und Versuchsdauer. Ferner wurden Forderungen an die Ermittlungdes Leerwertes begründet. Durch Festlegen der stofflich und methodisch bedingten Einflußgrößen gelingt es, den Variationskoeffizienten auf Werte um 2,0% zu minimieren. Die vorgestellte Methode ist mit gutem Erfolg auf alle löslichen Proteine übertragbar und erfüllt die Anforderungen einer Standardisierung.