CALIBRATION AND EVALUATION OF HAZE METERS

A survey of haze meters that are currently available has been carried out to find out whether an instrument(s) can be recommended for use by the brewing industry. There is a marked difference between values measured by instruments reading at 13° and 90° scatter. There are very minor differences in the haze values obtained using the various 90° instruments. Overall the Hach meter is recommended as a replacement for the Radiometer. Suspensions of styrene divinylbenzene beads were judged to be suitable as an alternative to Formazin for standardising haze meters.     

A preliminary study of the quality attributes of a cloudy wheat beer treated by flash pasteurization

Flash pasteurization (37 and 100 pasteurization units, PU) and conventional tunnel pasteurization (15 PU) processing of wheat beers were evaluated by examining their impacts on microorganisms, colour, colloidal haze and flavour stability during 84 days of storage at 20°C. The results revealed that the microbiological stability of 37 and 100 PU flash‐pasteurized beers was comparable with that of the 15 PU sample, and the development of both yeast and lactic acid bacteria was inhibited for 84 days of storage. The conventional tunnel‐pasteurized wheat beer resulted in a higher thermal load relative to the flash‐pasteurized samples based on the results of oxidative stability. These three pasteurized beers showed a similar decrease in haze intensity throughout the storage period. Meanwhile, flash‐pasteurized beers had better colour and colloidal haze stability than the tunnel‐pasteurized beer. It was also found by dynamic light scattering analysis that the temperature in the flash pasteurizer has the desired effect on the protein denaturation and particle size distribution. Therefore, flash pasteurization is a promising method to increase the shelf‐life of wheat beers instead of conventional tunnel pasteurization. Copyright © 2017 The Institute of Brewing & Distilling     

A preliminary study about the influence of high hydrostatic pressure processing on the physicochemical and sensorial properties of a cloudy wheat beer

High hydrostatic pressure (HHP) (400 MPa/15 min, 500 MPa/10 min, 600 MPa/5 min at 20 °C) and heat (60 °C/15 min) processing of wheat beers were evaluated by examining their impacts on microorganisms, colloidal haze, flavour, foam stability and shelf‐life prediction during 84 days of storage at 20 °C. The results obtained showed that the microbiological stability of HHP beers was comparable with heat‐treated samples, and the development of both aerobic bacteria and lactic acid bacteria was inhibited for 84 days of storage. The main parameters of the wheat beer, such as ethanol content, original extract, pH, bitterness and viscosity, were scarcely affected by either treatment compared with the control samples; however, heat pasteurization increased the colour value. Heat‐pasteurized beer resulted in an increase in the phenethyl alcohol concentration and a decrease in isoamyl acetate and ethyl acetate levels compared with the HHP samples. These treatments did not affect the amount of 4‐vinylguaiacol and 4‐vinylphenol in the beer. The HHP‐treated beers had higher colloidal haze and foam stability values than the heat‐pasteurized beers. Dynamic light scattering analysis showed that HHP treatments at 500 MPa/10 min resulted in smaller and more uniform particle sizes, which had a positive effect on beer haze stability during storage. Copyright © 2016 The Institute of Brewing & Distilling     

Application of an inline particle size device to microgel particles during post-processing of fresh cheese

The aim was to apply a mechanical treatment to tempered fresh cheese and study the inline particle size by 3-fold dynamical optical reflectance measurement (3D ORM). Particle size measured in a beaker using 3D ORM correlated well with static laser light scattering (R² = 0.8250). Differences may arise from different measuring principles and sample preparation. Consistently, particle size increased by tempering (45–54 °C, 1–300 min) due to particle rearrangement and decreased by shearing with a rotor/stator device (250–500 L h⁻¹, 300–3000 rpm), which showed that shear conditions need to be adapted to the sample, e.g., amount, size, and voluminosity of particle clusters. An experimental set-up was constructed to analyse particle size using 3D ORM inline that correlated well with the beaker values (R² = 0.9659). A proposed production line combines shearing and inline analysis and may enable manufacturers to adjust particle size and properties with shorter response time giving potential to reduce product losses.     

The Possibilities of Particle Analysis Demonstrated by the Measurement of the Colloidal Stability of Filtered Beer

Long‐term stability is one of the most important quality criteria of beer. Three groups of measuring methods are available for its determination: real time tests, predictive tests and indicative tests. One of the most common methods is the predictive forcing test, which is a time‐consuming method for accelerating beer ageing, e.g., at 0°C and 60°C. Two ways exist to perform this test: (1) follow‐up of haze development and determination of the lag phase or (2) the measurement of haze values after several days. The first option was evaluated by performing a long‐term Forcing test over a period of 4 months by analyzing a bottom‐fermented beer. It was shown that the haze curve followed a typical course with a lag phase, an increase phase and a stationary phase. Significant differences between the measurement after the cooling and the warm period were shown. In search of quicker methods and more accurate predictive indicators, the charge titration method was developed as an alternative to determine the particle charge of filtered beers, whereupon the relationship was elucidated between the increase in hazing and decrease of potential along with the advanced aging of beer. The results showed that with increased particle size due to agglomeration, the total charge decreased. In this array of trials, two differently stabilized beers were examined. Although both beers showed different haze values in the beginning (0.32 EBC and 1.30 EBC), the less stabilized beer had only 10 warm days and in contrast the beer with the good stabilization had over 20 warm days. With the help of the total charge, predictions were possible regarding the long‐term stability of the beer.     

Effect of extraction temperature on cream and extractability of black tea [Camellia sinensis (L.) O. Kuntze]

Summary Tea cream and haze in black tea infusions increased with the rise in the tea extraction temperature. The temperature at which substances involved in cream and haze formation began to be extensively extracted into the tea infusion was between 50 and 60 °C. The tea cream particle volume concentration in infusions extracted at 50 °C or below formed less tea cream particles, and their particle sizes were larger and more heterogeneous than those extracted at 60 °C and second infusions extracted at 90 °C from the residual leaves that were previously extracted at 40–50 °C. High‐performance liquid chromatography confirmed that constituents with pyrogallol groups are involved in tea creaming, and the effect of caffeine on tea cream and haze depends on whether these constituents are sufficiently present. The extractability of tea increased with the rise in extraction temperature. Two‐stage extraction of tea in ready‐to‐drink tea processing and its effects on colorimetric indicators were also examined.     

Factors Affecting Separation of Low Fat Flesh from Fatty Fish by Cryo-shattering

Our previous report on separating low fat flesh from fatty fish by cryo-shattering indicated that at appropriate temperatures, fat content in particles increased with particle size. The effect was temperature dependent; that effect of low temperature on fracture stress and elastic modulus of model fish flesh was further examined at - 60°C to - 196°C. The fish flesh showed abrupt changes in compression and tensile fracture stress at about - 90°C and - 150°C; such changes strongly affected fat content-particle size relations (FCPSR). Using measured fracture stress and elastic modulus values, FCPSR was successfully simulated when Bond's equation was linked with an empirical equation to estimate work index values.     

Evaluating haze formation in flavoured lager beers using a range of forcing methods

Haze formation is a quality problem that can affect a wide range of drinks for a number of different reasons. Although well‐characterized in traditional beers, the emergence of novel beer‐based beverages has led to the potential for chemical interactions that can result in the precipitation of haze material. In this study, the haze formation in 19 commercially available flavoured lager beers was investigated. The chemical parameters of each of the drinks were measured and haze formation was induced through three forcing tests, developed for use in both the beer and wine industries, as well as using a novel forcing test, designed for this study. Several of the products were particularly susceptible to a number of haze forcing tests and the EBC temperature cycling and the Wine Forcing (70°C) tests were found to generate the most forced haze (measured at 90 and 13° scatter angles, respectively) in these products. There was no overall correlation between the drinks' chemical parameters and their susceptibility to haze formation. However, a weak, but statistically significant, correlation (p  = 0.044) was observed between the concentration of polyphenols in the products and the presence of haze measured by 90° scatter angle. Copyright © 2017 The Institute of Brewing & Distilling     

Influence of heat treatment of goat milk on casein micelle size,rheological and textural properties of acid gels and set type yoghurts

Acid gels and yoghurts were made from goat milk that was heated at 72°C/30 s, 85°C/5 min, and 95°C/5 min, followed by acidification with starter culture at 43C until pH 4.6. The rheological and textural properties of acid gels and yoghurts were analyzed using dynamic low amplitude oscillatory rheology and back extrusion texture analysis, respectively. The effect of goat milk heat treatment on the mean casein micelle diameter and protein profile was also determined by dynamic light scattering and SDS PAGE electrophoresis, respectively. The shortest gelation and fermentation time was recorded for yoghurt prepared from milk heated at 85°C/5 min. Also, the pH of gelation, the storage moduli (G′) and yield stress were higher for this yoghurt, compared with the other two. Textural properties of goat milk yoghurts such as firmness and consistency were strongly affected by milk heat treatment, and the highest values were recorded for yoghurt produced from milk preheated at 85°C/5 min, as well. The largest casein micelles were measured after 85°C/5 min treatment and their size decreased at higher temperature, despite higher denaturation of whey proteins at the most intense heat regime, indicating the structure changes that influence on the acid gelation.     

FLUID to PARTICLE CONVECTIVE HEAT TRANSFER COEFFICIENT IN A HORIZONTAL SCRAPED SURFACE HEAT EXCHANGER DETERMINED FROM RELATIVE VELOCITY MEASUREMENT1

Liquid-to-particle convective heat transfer coefficient (h_fp) between fluid and particle was investigated in continuous flow through a horizontal scraped surface heat exchanger. the relative velocities between fluid and particle were measured, and h_fp calculated from well known correlations. Heat transfer coefficients increased with increasing flow rate, rotational speed, and decreased with increasing carrier medium viscosity and particle size. the measured relative velocities during flow visualization studies ranged from 0.04 to 0.29 m/s with corresponding h_fp values of 597 W/m²°K and 1975 W/m²°K, respectively. Even with the most conservative correlation, Nusselt numbers ranged from 12.1 to 49.7; significantly greater than the value of 2.0 for a sphere in a stagnant fluid.     

Fast optical sizing without dilution

Particle size is a key characteristic of colloidal dispersions. Small-angle light scattering, the standard measurement method, requires extensive sample dilution before size measurement. This process may change the sample. It is also time-consuming and makes on-line process control difficult. We present a new method of particle sizing that does not require dilution. It is based on the static (steady) scattering of incoherent light in the multiple scattering limit. We call it steady light transport (SLT). We focus a laser onto the sample and measure the halo of backscattered light. The technique is fast, robust, inexpensive and non-invasive. Diameters between tens of nanometers and several micrometers can be measured reliably. We first describe a simple technique that does not use the polarization of light. It gives the average size when the particle volume fraction and optical contrast are known. A second, more sophisticated version measures the full light-polarizing properties of the sample. This method can give both average particle size and volume fraction. Only the optical contrast needs to be measured independently. We demonstrate the use of SLT to size emulsions and to measure emulsification in real time.     

Analytical Characterization of the Hydrolysis of Barley Malt Macromolecules During Enzymatic Degradation Over Time Using AF4/MALS/RI

The changes on the molecular weight distribution (MWD) and particle size distribution (PSD) during hydrolysis of barley malt in isothermal mashing procedures were determined using asymmetrical flow field flow fractionation coupled to multiangle laser light scattering and refractive index (AF4/MALS/RI). Mash/trials were focused on amylolytic starch degradation. Therefore, temperatures (65, 70, and 75 °C) were selected according to α‐ and β‐amylases range of activity. Samples were produced by triplicate, tracking amylolytic processes over time periods from 10 to 90 min in each mash/trial. AF4/MALS/RI analysis demonstrated significant differences on the values of the MWD and PSD according to the temperature/time profile used. At mashing times over 30 min at a temperature of 65 °C, when α‐ and β‐amylase are both active, the decrease over time of the MWD and PSD was significantly higher (P < 0.005) than at 70 °C when mainly α‐amylase is active. At 75 °C, also the activity of α‐amylase decreased and the MWD and PSD were significantly lower (P < 0.005) than at 70 or 65 °C at any time of the procedure. The MWD and PSD of beer components influence beer palate fullness, thus AF4/ MALS/RI would be a powerful tool for breweries to adapt their technological processes to obtain beers with particular sensorial attributes.     

Are disulphide bonds formed during acid gelation of preheated milk?

The role of thiol/disulphide exchanges during acid gelation of preheated milk was studied with milk samples with or without N‐ethylmaleimide (NEM), a thiol‐blocking agent, and acidified to pH 4 by the addition of glucono‐delta‐lactone at 20 °C. Active or total thiol groups, particle size with light scattering measurements in a dissociating solvent or by SDS‐agarose electrophoresis were determined on acidified milk samples. Diffusing wave spectroscopy and rheology in low strain were applied during acidification of sample, while rheology in large strain was applied on final acid gels. The only effect of the presence of NEM was a reduced firmness of acid gels as measured at large strain and a reduced tendency to form large aggregates at pH<5.5. In conclusions, thiol/disulphide exchanges during acidification of milk played only a minor role in the building of acid gel networks from heated milk.     

THE INFLUENCE of FIELD STRENGTH, SUGAR and SOLID CONTENT ON ELECTRICAL CONDUCTIVITY of STRAWBERRY PRODUCTS

The effects of field strength, soluble solids (from 14 to 59.5 °Brix) and particle size (using two size distributions) on electrical conductivity were investigated. Electrical conductivity increased with temperature for all the products and conditions tested following linear or quadratic relations. Electrical conductivity was found to vary greatly between strawberry‐based products. an increase of electrical conductivity with field strength was obvious for fresh strawberries and strawberry jelly but not for strawberry pulp, probably due to the presence of texturizing agents. This parameter decreases with the increase of solids and sugar content. For some of the formulations tested (solid content over 20% w/w and over 40 °Brix) a different design of ohmic heater may be necessary because of the low values of electrical conductivity.     

Influence of Soybean Variety and the Method of Processing in Tofu Manufacturing: Comparison of Methods For Measuring Soluble Solids in Soymilk

The measurement of percent solids in soymilk was compared by three methods: light scattering, refractive index, and hydrometry. Soymilks were prepared from Vinton, Amsoy 71, and Weber variety soybeans by grinding the hydrated soybeans in (A) 20-25°C water, (B) 100°C water, and holding the slurry temperature above 90°C for 10 min or (C) soaking the soybeans in 45°C 15% ethanol solution for 12 hr and grinding in 20-25° water. Hydrometer readings at 80-90°C showed no correlation with soymilk percent solids. Light scattering was found more accurate at measuring percent solids compared with refractive index. Significant differences were found between the standard curves of percent solids vs light scattering due to the variety of soybeans and the processing conditions.     

Elimination of aggregates of (1→3) (1→4)-β-D-glucan in dilute solutions for light scattering and size exclusion chromatography study

Methods for eliminating aggregates of cereal (1→3) (1→4)-β-D-glucan in dilute solutions were investigated using dynamic light scattering and size exclusion chromatography. Wheat β-D-glucan samples were selected and dissolved in various solvents under different preparation conditions. The molecular size distribution was monitored by dynamic light scattering measurement. In most of the solutions, there were two well separated species of different average sizes. It appeared that the specie with smaller average size represented the un-aggregated molecules (unimers) and the specie with larger particle size corresponded to the aggregates. The results showed that heat treatment, filtration, ultrasonication, and the use of urea solution (up to 6 M) could not eliminate aggregates completely. However, the percentage of aggregates in aqueous NaOH solution decreased significantly with the increase of NaOH concentration. In 0.5 M NaOH solution, no aggregation was detectable by dynamic light scattering measurement. Both dynamic light scattering and HPSEC data showed that wheat β-D-glucan was stable in 0.5 M NaOH solution without any noticeable degradation when stored at 25 °C for 12 h. The results of present study suggested that 0.5 M NaOH solution is a suitable solvent for cereal β-D-glucans. Using this solvent, the molecular characteristics of wheat β-D-glucan was studied by both dynamic and static light scattering. The weight average molecular weight (M_w), radius of gyration (R_g), hydrodynamic radius (R_h), and the second virial coefficient (A₂) were obtained with the values of 3.29×10⁵ g/mol, 45.6 nm, 26.2 nm, and 1.04×10⁻³ cm³ mol/g² respectively. This study also confirmed that wheat β-glucan in solution exhibited a random coil conformation.     

Functional hydrogel microspheres: Parameters affecting electrostatic assembly of biopolymer particles fabricated from gelatin and pectin

Hydrogel microspheres may be used for various applications within foods, cosmetics, and pharmaceuticals, such as texture modification, encapsulation, or controlled release. The aim of this research was to examine the key parameters affecting the formation and properties of hydrogel microspheres fabricated by electrostatic complexation of gelatin and pectin. Hydrogel microspheres were formed by mixing 0.5 wt% gelatin and 0.01 wt% pectin at pH 10.0 and 30 °C, and then acidifying to pH 5.0 with continuous stirring. The effects of salt content (0–100 mM NaCl), shear rate (150–600 rpm), and acidification rate (fast, medium, and slow) on the formation and properties of the hydrogel microspheres were investigated. Increased salt content perturbed the complexation process due to electrostatic screening and ion-binding effects, which meant that lower pH values were needed to induce complexation. Optical microscopy and static light scattering showed that salt content also altered hydrogel particle microstructure. The largest particles were formed at an intermediate shear rate (300 rpm), which was attributed to the influence of shearing on mixing, particle disruption, and particle coalescence. Hydrogel microsphere size decreased as the acidification rate increased, which was attributed to an alteration in the balance of particle formation and particle growth. The parameters identified in this study facilitate the design of hydrogel microspheres with specific sizes and morphologies, which might be useful for tailoring their functional properties for different commercial applications.     

Size distribution, sources, and seasonality of suspended particles in southern California marine bathing waters

In this paper we define seasonal and along-shore variations in suspended particle size distributions (PSDs) at two marine bathing beaches in southern California, using a low-angle light scattering instrument (LISST). Empirical Orthogonal Function (EOF) analysis of the LISST data set (n = 55 651) identified three particle size modes that collectively account for > 90% of the variance in the de-meaned PSD data at six sites along the shoreline at Huntington Beach and Newport Beach: a dinoflagellate mode, a large particle mode, and a small particle mode. These three modes exhibit distinct seasonal patterns, and along-shore distributions, reflecting both the sources of particles and environmental factors that trigger their occurrence. Comparison of volume-based PSDs generated from the LISST and from image analysis of optical micrographs indicates that the LISST performs well when measuring the size distribution of particles associated with dinoflagellate blooms. However, LISST measurements on stormwater-impacted samples consistently yield a rising tail at small particle sizes that may be an artifact arising from the non-spherical nature of inorganic particles in terrestrial runoff. The results presented here demonstrate that PSDs measured by light scattering instruments such as the LISST represent a new data resource for assessing water quality, and managing human health risk, at marine bathing beaches.     

Kiwifruit Juice Clarification using a Fungal Proteolytic Enzyme

A commercial fungal proteolytic enzyme from Aspergillus niger was used in kiwifruit juice as a replacement for conventional fining agents to produce a stable clarified juice. Reductions in detectable protein levels of 73% and 82% were achieved using 500 mg/kg of enzyme and incubating at 60°C for 20 and 60 min respectively. Concentrates prepared from proteolytic enzyme-treated juice had reduced browning and haze formation compared to a control, without affecting ascorbic acid level. When stored at 20°C, proteolytic enzyme treated concentrates (60 min) remained clear up to 90 days and had minimal haze (A_{650 nm}= 0.047) and browning (A_{420 nm}= 0.93) after 6 mo storage. The molecular size of the protein as well as protein concentration are important factors in haze formation.     

Kinetics of haze formation and factors influencing the development of haze in clarified apple juice

The rate of haze formation in commercial clarified apple juice stored at 4, 25 and 37°C was monitored over a 16 to 35-week storage period. Changes in turbidity, tannin content and browning index were evaluated. The juice appeared virtually clear and had very little colloidal particles during the initial stages of storage. After 24 weeks, an increase in turbidity of 2.32 NTU was observed for juice samples stored at 37°C. An increase of 0.58 and 0.95 NTU was observed for samples stored at 25 and 4°C, respectively. There was a general decrease in tannin content and an increase in browning index with storage; this effect was most pronounced for samples stored at 37°C. The rate of haze formation and tannin depletion in juice samples followed first-order reaction kinetics. Light and headspace did not affect haze formation. NaCl and CaCl₂ increased haze development while sucrose (up to 60%), urea (0.5 M), and EDTA (up to 0.01 M) had little effect. Addition of sodium dodecyl sulfate retarded haze formation.