Jörg Hinrichs

Incorporation of whey proteins in cheese

In traditional cheese-making casein forms the curd structure while whey proteins are lost in the whey. When whey proteins are integrated into fresh, soft, semi-hard and hard cheese, this not only improves the nutrient value and yield but also causes changes to functional properties. There are several technologies for re-integrating whey proteins into cheese during processing. The application and process adaptations depend mainly on the type of cheese and the desired texture. Whey proteins may be retained by applying high heat treatment in order to affix the whey proteins to caseins or by using membrane technology to reduce the aqueous phase. Alternatively, whey proteins may be removed from drained whey by ultrafiltration and then added to curd after special heat treatment or by recycling into cheese milk.

Characterization of aerobic spore-forming bacteria associated with industrial dairy processing environments and product spoilage

Due to changes in the design of industrial food processing and increasing international trade, highly thermoresistant spore-forming bacteria are an emerging problem in food production. Minimally processed foods and products with extended shelf life, such as milk products, are at special risk for contamination and subsequent product damages, but information about origin and food quality related properties of highly heat-resistant spore-formers is still limited. Therefore, the aim of this study was to determine the biodiversity, heat resistance, and food quality and safety affecting characteristics of aerobic spore-formers in the dairy sector. Thus, a comprehensive panel of strains (n=467), which originated from dairy processing environments, raw materials and processed foods, was compiled. The set included isolates associated with recent food spoilage cases and product damages as well as isolates not linked to product spoilage. Identification of the isolates by means of Fourier-transform infrared spectroscopy and molecular methods revealed a large biodiversity of spore-formers, especially among the spoilage associated isolates. These could be assigned to 43 species, representing 11 genera, with Bacillus cereus s.l. and Bacillus licheniformis being predominant. A screening for isolates forming thermoresistant spores (TRS, surviving 100°C, 20 min) showed that about one third of the tested spore-formers was heat-resistant, with Bacillus subtilis and Geobacillus stearothermophilus being the prevalent species. Strains producing highly thermoresistant spores (HTRS, surviving 125°C, 30 min) were found among mesophilic as well as among thermophilic species. B. subtilis and Bacillus amyloliquefaciens were dominating the group of mesophilic HTRS, while Bacillus smithii and Geobacillus pallidus were dominating the group of thermophilic HTRS. Analysis of spoilage-related enzymes of the TRS isolates showed that mesophilic strains, belonging to the B. subtilis and B. cereus groups, were strongly proteolytic, whereas thermophilic strains displayed generally a low enzymatic activity and thus spoilage potential. Cytotoxicity was only detected in B. cereus, suggesting that the risk of food poisoning by aerobic, thermoresistant spore-formers outside of the B. cereus group is rather low.

Hybrid model of the fouling process in tubular heat exchangers for the dairy industry

A simulation model of the fouling behaviour of an arbitrary heat treatment device for milk, instancing tubular heat exchangers, is described. The final target is to examine new processing technologies in order to lengthen the processing time between two cleaning cycles whilst maintaining product quality. For this purpose a hybrid model of the fouling process in tubular heat exchangers was developed, combining deterministic differential equations with cognitive elements. The model allows the calculation of both processing and product behaviour throughout the whole heat exchanger. Pressure drop, temperature distribution and the chemical and biological effects of the heat treatment on the product can be calculated, so that the fouling behaviour and the expected product quality can be estimated. In order to validate the process model measured data from an industrial UHT plant were used. The calculated temperature profiles and pressure drops were in reasonable agreement with the experimental data. The deviation of calculated to measured values ranges between 10% and 20% for pressure, between 5% and 10% for temperature.

Biodiversity of refrigerated raw milk microbiota and their enzymatic spoilage potential.

The refrigerated storage of raw milk selects for psychrotolerant microorganisms, many of which produce peptidases and lipases. Some of these enzymes are heat resistant and are not sufficiently inactivated by pasteurisation or even ultra-high temperature (UHT) treatment. In the current study, 20 different raw cows milk samples from single farms and dairy bulk tanks were analysed close to delivery to the dairies or close to processing in the dairy for their cultivable microbiota as well as the lipolytic and proteolytic potential of the isolated microorganisms. Altogether, 2906 isolates have been identified and assigned to 169 species and 61 genera. Pseudomonas, Lactococcus and Acinetobacter were the most abundant genera making up 62% of all isolates, whereas 46 genera had an abundance of <1% and represent only 6.6%. Of all isolates, 18% belong to hitherto unknown species, indicating that a large fraction of the milk microbiota is still unexplored. The potential of the isolates to produce lipases or peptidases followed in many cases a genus or group specific pattern. All isolates identified as members of the genus Pseudomonas exhibited mainly lipolytic and proteolytic activity or solely proteolytic activity. On the other hand, nearly all isolates of the genus Acinetobacter were lipolytic but not proteolytic. Only 37% of all tested lactic acid bacteria (LAB) showed enzymatic activity at 6 °C and the type of activity was proteolytic in 97% of these cases.

Effect of temperature and pH on the solubility of caseins: Environmental influences on the dissociation of αS- and β-casein

Selective precipitation is a common method for the isolation of β-casein, using the different calcium sensitivities of the individual caseins and the selective solubility of β-casein at a low temperature. In previous studies, it has been indicated that the β-casein yield depends on the physicochemical characteristics of the casein raw material used for fractionation. The objective of this study was to evaluate and compare the solubility of α(S)- and β-casein in solutions of micellar casein, sodium caseinate, and calcium caseinate as a function of pH and temperature. Additionally, the solubility of isolated α(S)- and β-casein fractions in demineralized water, ultrafiltration permeate, and a calcium-depleted milk salt solution was investigated depending on the pH and temperature. Furthermore, micellar casein, sodium caseinate, and calcium caseinate were subjected to a calcium chloride-precipitation process to determine the solubility of α(S)- and β-casein in calcium chloride precipitate, which is produced during selective precipitation, as a function of temperature and pH. Generally, the temperature had only a marginal influence on the α(S)-casein solubility compared with the β-casein solubility, whereas the solubility was shown to be strongly influenced by the pH. Our results suggest that the yield of β-casein obtained during isolation by means of selective precipitation may be a result of the solubility characteristics of α(S)- and β-casein in calcium chloride precipitate. Manufacturers may consider a simple solubility experiment before the β-casein isolation process by means of selective precipitation to predict β-casein yield.

Relating Creamy Perception of Whey Protein Enriched Yogurt Systems to Instrumental Data by Means of Multivariate Data Analysis

UNLABELLED Yogurts differing in fat content, protein content, and casein to whey protein ratio were produced, and structurally as well as sensorially examined. The objective of the current research was to evaluate the predictive value of rheological and particle size measurements concerning sensory appearance and texture attributes in 13 differently composed stirred yogurt systems, with a focus on graininess, viscosity, and creaminess. Structural and sensory analyses showed large differences in texture properties between the tested yogurt systems. Both data sets were correlated by means of multivariate statistical methods. Sensory graininess was highly correlated with particle size-related parameters, sensory viscosity was highly correlated with destructive rheological parameters, and creamy perception was highly correlated with particle size-related parameters and destructive rheological parameters but was not as well described by any oscillatory parameter. Best predictive ability (r(2) > 0.89) was found for creaminess combining particle size related- and destructive rheological parameters tested within this study. PRACTICAL APPLICATION Knowing the instrumental parameters describing sensory textural attributes provides important information for having a better understanding of the underlying processes during consumers perception. Knowledge about the sensory behavior of a product and its oral processing imparts an opportunity to fasten the product development process. By means of yogurt systems instrumental parameters derived from particle size analysis and rheological measurements were correlated with sensory attributes in order to determine the main factors leading to the mouthfeel sensations grainy, viscous, and creamy of semisolid milk products.

The role of processing and matrix design in development and control of microstructures in dairy food production: a survey

New options to process dairy products by means of new single unit operations or combinations thereof are presented. The innovative possibilities discussed in this paper mainly refer to novel ways of influencing product microstructures or textures as perceived during consumption, by means of contributions of single molecule fractions of complex systems derived from membrane fractionation techniques. In addition, options to integrate physiologically active components which also have a structure forming effect in fermented or other dairy products are highlighted. Alternatives derived from thermal, mechanical and enzymatic processing and from fractionation techniques by means of membranes are presented which can be exploited for fractionation and compositional matrix design of dairy products.

Apparent voluminosity of casein micelles determined by rheometry

The voluminosity of casein micelles was studied by means of static rheometry. In concentrated casein micelle suspensions with fluid-like flow properties to random-close packing, the reduced viscosity was obtained and linked via the Krieger-Dougherty model of volume fraction effect. The temperature dependency of hydration was fitted in a wide temperature (5°C≤θ≤35°C) and mass fraction range (0.01≤w≤0.16). The results of our study suggested that the voluminosity of casein micelles decreased with increasing temperature and asymptotically reached a plateau (θ>30°C) as a consequence of the protein swelling and decreasing water immobilization. The obtained apparent voluminosity of native casein micelles dispersed in UF permeate was 5.0 ml g(-1) at 5°C, 4.1 ml g(-1) at 20°C, and 3.7 ml g(-1) at 35°C.

Kinetics of the thermal inactivation of the Lactococcus lactis bacteriophage P008

The thermal resistance of the lactococcal bacteriophage P008 was investigated between 55 and 80 degrees C. Inactivation kinetics revealed an order of reaction above 1 and could be determined by a non-1st-order regression model. Phage inactivation was influenced by the medium (milk and Ca-M17-broth). Within the investigated temperature range, milk had a protective effect on phage P008. This was reflected in the rate constant and in the activation energy. Thermal phage inactivation studies reported in literature were re-analysed using non-1st-order regression. The obtained kinetic parameters showed that phage P008 belongs to the most heat resistant lactococcal phages investigated so far.

Firmness of pressure-induced casein and whey protein gels modulated by holding time and rate of pressure release

Abstract The main protein fractions of milk, casein and whey protein, may react differently to processing due to their amino acid sequence and conformation and their ability to build up intermolecular covalent and non-covalent bonds. Gels made from solutions of micellar casein and whey protein isolate were induced by applying ultra-high pressure (600 MPa/30 °C). The pressure built up was held constant at 200 MPa min −1 , while the holding time of 0.15 and 30 min was varied as well as the pressure release rate (20, 200, 600 MPa min −1 ). The firmness of the pressure-induced whey protein gel was essentially influenced by the degree of whey protein denaturation and determined by the amount of disulfide bonds stabilizing the gel microstructure. In contrast, the firmness of pressure-induced casein-based gels was mainly influenced by pressure release rate. A slow pressure release produced a rough and weak gel. A high release rate, however, caused a homogeneous microstructure to be formed that created a high level of firmness.