Determining the physical stability and water–solid interactions responsible for caking during storage of glucose monohydrate

A free flowing crystalline powder can develop severe caking if held under humid and/or high temperature storage. In addition, a crystalline hydrate material can experience compositional changes due to hydrate formation or loss if held at too high or low of a storage RH, respectively. Thus, the critical RH values for caking and compositional changes of glucose monohydrate (GM) and GM partitioned into three particle sizes were assessed using saturated salt slurries ranging from 0 to 84 % RH at 25 °C for 20 weeks. Caking was measured using a five-point visual physical stability scale, from free flowing to fully caked, and sample composition was determined using X-ray powder diffraction. Caking was observed in GM during storage at 53–84 % RH at 25 °C and fine particle GM caked at lower RH values than medium and large particle GM. For all GM samples, hydrate loss (via conversion of GM to alpha-anhydrous glucose) occurred at 0 and 11 % RH and hydrate formation (via mutarotation of beta-anhydrous glucose to alpha-anhydrous glucose and conversion to GM) occurred at 53–84 % RH at 25 °C. Particle size did not affect compositional changes during GM storage, but greatly affected caking. Neither deliquescence nor amorphous content were detected in this study and hydrate formation and β-AG content did not cause caking in GM, therefore, decreased flowability was the result of capillary condensation caking. At 25 °C, GM should be stored above 11 % RH to avoid hydrate loss and below 53 % RH to avoid caking.     

Determining the physical stability and water–solid interactions responsible for caking during storage of alpha-anhydrous glucose

Typically, a crystalline powder is considered reasonably stable below it deliquescence point (RH₀), however, caking has been reported for some materials below their RH₀. The critical relative humidity (RH) values for caking and hydrate formation in alpha-anhydrous glucose (α-AG) and α-AG partitioned into three particle sizes were assessed using saturated salt slurries ranging from 0 to 84 % RH at 25 °C for 20 weeks. The degree of caking was determined by a five-point visual physical stability scale, from free flowing with minimal clumping (1) to fully caked (5), and X-ray powder diffraction was used to determine the composition of the samples. Caking was observed in α-AG during storage at 68 % RH at 25 °C and the severity of caking increased with increasing RH. Fine particle α-AG caked during storage at 64 % RH, whereas medium and large particle α-AG caked at 68 and 75 % RH, respectively, at 25 °C. Caking was observed in the absence of deliquescence, amorphous content, and hydrate formation; therefore, it is proposed that capillary condensation leads to caking in α-AG below its RH₀. Capillary condensation caking occurs at a specific RH (termed RH_cc) where direct condensation of moisture into confined spaces, such as particle contact points or surface defects, causes the formation of liquid bridges, which may solidify over time without changes in RH or temperature. To avoid caking, α-AG should be stored below its RH_cc, which is highly dependent on particle size; and to avoid conversion to glucose monohydrate, α-AG, regardless of particle size, should be stored below 64 % RH at 25 °C.     

The Stability of Poly(lactic acid) Packaging Films as Influenced by Humidity and Temperature

The effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food‐packaging conditions, obtained by different humidities (11% to 98% RH) and temperatures (5 °C and 25 °C), was investigated by decrease in number average molecular weight (M_n) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 °C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 °C to 25 °C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 °C and 25 °C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 °C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.     

Kinetic Study on Peptide‐Bound Pyrraline Formation and Elimination in the Maillard Reaction Using Single‐ and Multiple‐Response Models

Pyrraline, an advanced glycation end product (AGE), is related to some chronic diseases and can be employed as an indicator for heat damage in food processing. In this study, the impact of changing the reactant concentration and ratio on the kinetic parameters describing peptide‐bound pyrraline (pep‐pyr) formation and elimination was evaluated in the Lys‐Gly/glucose model systems, with microwave heating treatment ranging from 120 to 200 °C. The maximum pep‐pyr concentration increased as follows: 200 °C ? 180 °C ? 160 °C ? 120 °C ? 140 °C. First, the pep‐pyr formation and elimination was modeled by using a single‐response modelling. The formation rate constant (k_F) of pep‐pyr was independent of the initial concentration of the reactants and ratios. However, the elimination rate constant of pep‐pyr (k_E) increased with increasing reactant concentrations. Second, a multiresponse modelling was performed to illustrate the pathways of pep‐pyr formation and elimination. Two adapted models can fit to the experimental data with the goodness‐of‐fit ranging from 0.663 to 0.920. Glucose‐to‐fructose isomerization rather than glucose‐to‐mannose epimerization was detected in an equimolar model system and the model system with an excess of any of the reactants. The caramelization reaction was negligible in the equimolar systems and the model systems with an excess of peptide. The reaction rate constant of glucose‐to‐fructose isomerization was independent of the initial reactant ratios. It was more difficult for pep‐pyr elimination in the model system with an excess of peptide than that in the other 2 model systems (the equimolar system and the system with an excess of glucose), whereas a reverse result in pep‐pyr formation was obtained.     

Sorption and Diffusional Studies of Extruded Waxy Maize Starch‐Glycerol Systems

It is believed that glycerol decreases the water activity of food systems due to its hygroscopic nature. The work presented here focuses on water vapour sorption and diffusion characteristics of thermomechanically extruded waxy maize starch (WMS) and glycerol samples. The different mixtures were prepared with similar specific mechanical energies (SME ∼ 50 Wh/kg). The levels of glycerol ranged from 0–20% dry weight basis. At equilibrium relative humidities RH > 70% at 25°C, glycerol contributed to an increase in moisture but, for RH < 70% the moisture content decreased. The values of the monolayer (m_o) and heat of sorption (C) from Brunauer‐Emmett‐Teller (BET) and Guggenheim‐Anderson‐de Boer (GAB) equations significantly decreased in the presence of the polyol, suggesting a reduction in sorption sites availability. The diffusivities (D) of these mixtures were estimated, assuming a Fickian mechanism. The D values increased with RH but, there was an apparent reduction in this value for the RH > 60% when glycerol was present. Microscopic observations indicated formation of agglomerates and loss of particle integrity, which coincided with the marked change in the diffusivity value and the mixture's transition from the glassy to rubbery state. Therefore understanding of the amount and speed of water uptake into complex systems is important if their shelf life properties and texture are to be understood.     

Atmospheric Pressure Plasma Treatment of Black Peppercorns Inoculated with Salmonella and Held Under Controlled Storage

Spices, including black pepper, are a source of microbial contamination and have been linked to outbreaks of salmonellosis when added to products that undergo no further processing. Traditional thermal processing employed to reduce microbial contamination can lead to losses of heat‐sensitive compounds. Thus, alternative processes such as atmospheric pressure plasma (APP) are desirable. The purpose of this research was to determine the efficacy of APP in the destruction of Salmonella inoculated on the surface of peppercorns. Secondarily, we examined the effect of storage on the subsequent inactivation of Salmonella on the surfaces of black peppercorns by APP. Black peppercorns inoculated with a cocktail of Salmonella enterica serotypes Oranienburg, Tennessee, Anatum, and Enteritidis were stored at 25 °C, 33% relative humidity (RH); 25 °C, 97% RH; and, 37 °C, 33% RH for 10 d and additionally at 25 °C, 33% RH for 1 and 30 d then treated with APP. Results showed that Salmonella populations decreased significantly (P < 0.05) with respect to the treatment time, but where not related to previous storage conditions (P > 0.05). Approximately a 4.5‐ to 5.5‐log₁₀ reduction in population was achieved after 60 to 80 s treatment. A combination of treatments, storage and 80 s of plasma, may achieve a total reduction on the order of 7‐log₁₀CFU/g. These findings support the potential of APP to decontaminate Salmonella on the surfaces of black peppercorns and other dry foods and illustrate that a multiple hurdle approach may prove effective for achieving significant reductions of Salmonella in many low‐moisture foods.     

Assessment of changes in hop resins and polyphenols during long‐term storage

Changes in the content and composition of hop secondary metabolites during storage are reflected in beer quality and in the economics of beer production. A 12‐month storage experiment with T90 pellets of four hop varieties showed different dynamics of hop aging in relation to both storage conditions and hop variety. Negligible effects on the α‐ and β‐acids were detected during storage without air access at +2°C. Storage at +20°C resulted in a final loss of 20–25% α‐acids, but the content of β‐acids did not change significantly. Large decreases in α‐acids (64–88%) and in β‐acids (51–83%) were found in hops stored with access to air at +20°C. The rate of decline accelerated markedly after 6 months of storage. In terms of hop resin changes, Premiant and Sládek were the most and the least stable varieties, respectively. After 12 months, the content of the total polyphenols and flavonoids decreased by 30–40% and by 20–30%, respectively, irrespective of storage conditions. The rate of decline accelerated strongly after 6 months. The DPPH (1,1‐diphenyl‐2‐picrylhydrazyl) antiradical potential decrease was significant only in hops stored under aerobic conditions. The depletion was 9–25% after 1 year; Saaz was the most stable variety. Copyright © 2012 The Institute of Brewing & Distilling     

Effect of substrate ratios and temperatures on development of Maillard reaction and antioxidant activity of silver carp (Hypophthalmichthys molitrix) protein hydrolysate–glucose system

The study of antioxidant activity of the hydrolysates is necessary during its processing in which Maillard reaction would often occur. To understand the effect of Maillard reaction on antioxidant activity of silver carp protein hydrolysates (SPH), the Maillard reaction products (MRPs) were prepared at different ratios between SPH and glucose by Maillard reaction in powdered state, respectively. MRPs possessed a strong 2, 2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity and reducing power (P < 0.05). The hydrolysate and glucose heated with the ratio of 2:1 at 60 °C showed high browning intensity and good antioxidant properties (P < 0.05). According to the correlation coefficients of variables included in the hydrolysate–glucose system, good correlations were observed among the antioxidant activities, the absorbance at 294 nm and the loss of free amino groups. The results suggested that Maillard reaction has a good potential to improve the antioxidant activity of SPH.     

Spray drying of red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit juices: physicochemical and antioxidant properties of the powder

This study aims to investigate physical stability and antioxidant properties of spray‐dried red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit powder upon storage at various relative humidity (RH). Inlet air temperatures of 120 °C (red dragon fruit) and 110 °C (white dragon fruit) as well as maltodextrin concentration of 30% (w/v) were selected as the spray drying conditions as powder was obtained at these minimum conditions. The powder was ranging from 3 to 7 μm in particle size with spherical morphology. The powder had lower antioxidant content and antioxidant activities compared with the control before spray drying. Storage of powder at 43%, 54% or 75% RH at 25 °C for 25 days resulted in structural changes correlating to the depression of glass transition temperatures (T_g) to below storage temperature. At 33% RH, no visible structural changes were observed. Antioxidant properties of the powder remained unchanged after 25 days' storage at the studied RHs.     

Purification and enzymatic identification of an acid stable and thermostable α‐amylase from Rhizopus microsporus

Rhizopus microsporus, recently isolated from a solid culture of Heng‐Shui Lao‐Bai‐Gan (HSLBG, a famous distilled liquor in Northern China) was found to produce a novel extracellular acid stable and thermostable α‐amylase. This fungal α‐amylase was purified using ammonium precipitation, Sephadex G‐25 desalination and DEAE‐52 cellulose chromatography. Its molecular weight was estimated to be 75 kDa by SDS–PAGE. The optimum pH and temperature of this enzyme was pH 5.0 and 70°C respectively. Thermostability and kinetic analysis through the Arrhenius and Michaelis–Menten equations revealed that this enzyme showed an exceptional activity at low pH and high temperature. A combination of this thermostability and acid stability could be a valuable trait for the efficient hydrolysis of amylose to glucose in large‐scale biotechnology applications. Copyright © 2012 The Institute of Brewing & Distilling     

Effect of relative humidity and temperature on absorption kinetics of two types of oxygen scavengers for packaged food

To investigate the effect of temperature and relative humidity (RH) on the absorption kinetics of self‐activated and moisture‐activated O₂ scavengers for packaged food, kinetic parameters of each O₂ scavenger were evaluated at 43%, 75% or 100% RH and at 10, 25 and 40 °C respectively. Absorption kinetics was well described by a first‐order reaction with an Arrhenius type behaviour. For moisture‐activated O₂ scavengers, a proper high RH was needed to ensure a high O₂ absorption capacity, as average O₂ absorption capacity was 3.82 mL at 43% RH and 43.40 mL at 75% RH. When the temperature increased, O₂ absorption rate constant ascended from 10 °C to 40 °C on an average of 0.153 and 0.306 h^?1 in moisture‐activated and self‐activated O₂ scavengers respectively. We could take the effect of temperature and RH into account when we chose different types of iron‐based O₂ scavengers for packaged food.     

Histamine Production by Morganella morganii in Mackerel, Albacore, Mahi-mahi, and Salmon at Various Storage Temperatures

Morganella morganii was studied for its growth and histamine formation in mackerel, albacore, mahi‐mahi, and salmon stored at various temperatures from ‐30 °C to 37 °C. The optimal temperature for histamine formation was 25 °C. Mackerel, albacore, and mahi‐mahi were shown as good substrates for histidine decarboxylation by M. morganii at elevated temperatures (> 15 °C). M. morganii inoculated in all fish species including salmon formed histamine above the FDA guideline. Their growth was controlled by cold storage of the fish at 4 °C or below, but histamine formation was controlled only by frozen storage. Although histamine was not detected in any frozen samples, it accumulated rapidly in the previously frozen fish stored at 25 °C.     

A Rapid In‐vitro Digestibility Assay Based on Glucometry for Investigating Kinetics of Starch Digestion

The potential of glucometry in in‐vitro starch digestion was investigated for developing a rapid procedure to understand kinetics of digestion. A hand‐held glucometer, intended for testing of plasma glucose levels, was used for the assay of glucose released by the combined action of α‐amylase and amyloglucosidase on a range of starch substrates. The glucometer was sensitive to glucose concentrations in water, and its readings were independent of pH (7.7 and 3.9) and temperature (37°C and 25°C) of the glucose solution, but dependent on lactose and maltose concentrations. Neither fructose nor sucrose affected the readings. Digested starch calculated from the glucometer was not significantly (p > 0.05) different from that calculated from spectrophotometry. Particle size of substrate, sample formulation, grain genotype, and processing affected the glucometer readings as expected from how these factors influence starch digestibility. Corrections are required when samples containing lactose and maltose prior to in‐vitro digestion analysis are studied. The developed rapid procedure can be used to collect large numbers of data points per sample per analysis for better understanding the kinetics of starch digestion, and increased confidence level in modelling the digestogram. The glucose detection method is robust and could be adapted for non‐laboratory use. Single‐point data can also be extracted from digestograms for comparative analysis.     

Properties of Cast Films Made of HCl‐Methanol Modified Corn Starch

The molecular and physicochemical properties of the studied starches modified with 0.36% HCl in methanol at 25 °C and 45 °C were related to the film properties of these starches. The weight‐averaged molecular weight (M_w) and the number of long‐chain branches (DP 13‐36) of HCl‐methanol modified starch decreased with increasing degree of acid modification, but the number of short‐chain branches (DP < 6) increased. HCl‐methanol modification significantly decreased the ghost formation in gelatinized starch dispersions and the viscosity of starch film‐forming dispersions. Thus, the homogeneity of the produced starch films was improved and their opacity reduced. Proper HCl‐methanol modification produced corn starch films with lower moisture absorption rate and maximum moisture content under high relative humidity (RH = 97%) condition.     

Effect of microbial transglutaminase on autolysis and gelation of lizardfish surimi

In the absence of microbial transglutaminase (MTGase), the textural properties of lizardfish surimi (Saurida spp) improved when pre‐incubated at 4 and 25 °C for 24 and 4 h, respectively. MTGase optimally catalyzed incorporation of monodansylcadaverine (MDC) into surimi at 40 °C. Addition of MTGase appeared to reduce autolytic activity at 25 and 40 °C, but had no effect on autolytic activity at 65 °C. Breaking force and deformation of lizardfish surimi significantly improved when 0.1 unit MTGase g^?1 surimi (1.8 g kg^?1) was added and pre‐incubated at either 25 or 40 °C. Textural properties improved concomitant with cross‐linked polymers of myosin heavy chain and tropomyosin, but not actin. Addition of MTGase also improved the storage modulus (G′). The gel network of surimi mixed with MTGase and pre‐incubated at 40 °C readily formed during the pre‐incubation period, while formation of the gel network began at 48.1 °C in the absence of MTGase. Copyright © 2005 Society of Chemical Industry     

Optimizing red sorghum malt quality when Bacillus subtilis is used during steeping to control mould growth

Previous work has shown that Bacillus subtilis‐S499‐based biocontrol treatments applied without aeration at the steeping stage of red sorghum malting offer good mould reduction, but yield malts with low levels of key hydrolytic enzymes. Thus we attempted to raise these levels by aerating the steeping liquor, varying the steeping time (from 8 to 40 h) and temperature (from 25 to 35 °C), and combining a biocontrol treatment with prior steeping in 0.2% NaOH. Aeration proved particularly important whenever B. subtilis cells were present in the steep liquor. The optimal temperatures for α‐ and β‐amylase were 30 and 25 °C, respectively. By increasing the steeping time, it was possible to improve the α‐amylase activity, but the β‐amylase activity peaked sharply between 16 and 20 h, depending on the steeping medium. A good compromise was steeping in a biocontrol medium for 14–16 h at 30 °C. Combination steeping treatments (0.2% NaOH for 8 h followed by biocontrol for 8 h) yielded malts of a quality approaching that afforded by dilute alkaline treatment. Copyright © 2012 The Institute of Brewing & Distilling     

Crystallisation and moisture sorption properties of selected Australian unifloral honeys

The sorption properties of yapunyah (Eucalyptus ochropholia) and yellow box (Eucalyptus melliodora) honeys (Australian unifloral honeys) were investigated in a controlled relative humidity (RH) environment at 30 °C for 71 days. The original water activity of the honeys affected the sorption properties. These two honeys absorbed moisture at and above 67.9% RH and desorbed moisture at and below 51.4% RH. The crystallisation behaviour of tea tree (Melaleuca quinquenervia) and yapunyah honeys was studied during storage at 13 and 23 °C. The degree of crystallisation was monitored by measuring the absorbance at 660 and 665 nm using a spectrophotometer. The heat‐treated honeys did not show any sign of crystallisation after 5 months, whereas a seeding with precrystallised honey induced crystallisation of the same honeys. This crystallisation was more rapid at 13 than at 23 °C. Copyright © 2003 Society of Chemical Industry     

GABA shunt mediates thermotolerance in Saccharomyces cerevisiae by reducing reactive oxygen production

The GABA shunt pathway involves three enzymes, glutamate decarboxylase (GAD), GABA aminotransferase (GAT) and succinate semialdehyde dehydrogenase (SSADH). These enzymes act in concert to convert glutamate (α‐ketoglutarate) to succinate. Deletion mutations in each of these genes in Saccharomyces cerevisiae resulted in growth defects at 45°C. Double and triple mutation constructs were compared for thermotolerance with the wild‐type and single mutant strains. Although wild‐type and all mutant strains were highly susceptible to brief heat stress at 50°C, a non‐lethal 30 min at 40°C temperature pretreatment induced tolerance of the wild‐type and all of the mutants to 50°C. The mutant strains collectively exhibited similar susceptibility at 45°C to the induced 50°C treatments. Intracellular reactive oxygen intermediate (ROI) accumulation was measured in wild‐type and each of the mutant strains. ROI accumulation in each of the mutants and in various stress conditions was correlated to heat susceptibility of the mutant strains. The addition of ROI scavenger N‐tert‐butyl‐α‐phenylnitrone (PBN) enhanced survival of the mutants and strongly inhibited the accumulation of ROI, but did not have significant effect on the wild‐type. Measurement of intracellular GABA, glutamate and α‐ketoglutarate during lethal heat exposure at 45°C showed higher levels of accumulation of GABA and α‐ketoglutarate in the uga1 and uga2 mutants, while glutamate accumulated at higher level in the gad1 mutant. These results suggest that the GABA shunt pathway plays a crucial role in protecting yeast cells from heat damage by restricting ROI production involving the flux of carbon from α‐ketoglutarate to succinate during heat stress. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of par‐baking and frozen storage time on the quality of cup cake

The effects of frozen storage and initial baking time of par‐baked cake on baking loss, volume, moisture, colour and textural properties of cake obtained after thawing and rebaking were investigated. Cakes, par‐baked at 175 °C for 15, 20 and 25 min, were stored at ?18 °C for 3, 6 and 9 months. After storage, par‐baked cakes were thawed and rebaked at 175 °C for 10, 15 and 20 min. Baking loss, moisture content, L and +b colour values, firmness, gumminess and chewiness of the resulting full‐baked cakes were significantly affected by both par‐baking and frozen storage time, while specific volume, cohesiveness, springiness and resilience values were significantly affected by frozen storage time. The increase in the time of frozen storage of the par‐baked cake leads to a decrease in the quality of the rebaked cake, namely an increase of baking loss and cake crumb firmness, and a loss in the moisture content and specific volume. Moisture of cake crumb, L and +b colour values, firmness, gumminess and chewiness significantly increased as the par‐baking time increased. However, regarding baking loss, specific volume, moisture content and textural properties, 3‐month intermediate storage at ?18 °C and 20‐min initial baking time gave the best result among the cakes produced by using the two‐step baking procedure.     

Maltose Transport by Brewer's Yeasts in Brewer's Wort

The kinetics of maltose transport by two industrial yeasts were studied. The ale and lager strain each showed both high and low affinity transport. For the lager strain, maltose transport was only weakly inhibited by maltotriose, sucrose and trehalose, suggesting that its dominant maltose transporter is the maltose‐specific type coded by MALx1 genes. For the ale strain, maltose transport was strongly inhibited by maltotriose, sucrose and trehalose, suggesting that its dominant maltose transporter may be the AGT1‐encoded type that also carries these sugars. Also glucose inhibited transport by the ale strain more than that by the lager strain. Instantaneous inhibition by ethanol at concentrations met in brewery fermentations was moderate (about 25% at 50 g ethanol · L^?1). The apparent Vmax for high affinity transport increased about 100‐fold between 0 and 30°C, whereas the Km (3 ± 1 mM) was constant. Standard activities of maltose transport and maltase were followed through pilot fermentations of 11–24°P worts. Rapid (20 s) measurements of the zero‐trans‐rate of maltose uptake were also made with each day's yeast (rapidly harvested and washed) in reaction mixtures containing the same day's wort labelled with tracer ¹⁴C‐maltose. Results suggested that maltose uptake is the dominant factor controlling the rate of maltose utilization in these wort fermentations.