Electrostatic spray drying of whey protein-carbohydrate systems: Influence of pH, water activity, and storage temperature on Maillard reactions

Nonenzymatic Browning via the Maillard Reaction in Foods

Cellular systems are vulnerable to environmental parameters that impose thermodynamic constraints on metabolic function. These include biophysical challenges and events relating to low water-availability, solute-induced stresses, dehydration-rehydration cycles and extremes of temperature, and these can sometimes be lethal. The concept of a water-availability limit for Earth's biosphere might evoke the Sahara, Atacama and other deserts where water is scarce, or subzero environments where any water is locked up as ice. However, if a cell is dried then, whereas it may remain viable, life processes cease, from an existential viewpoint it is debatable whether life exists/occurs under such conditions at all. Regardless of this, water stress also occurs in microbial habitats that are wet, even within bodies of water. Indeed, it is arguably implausible that any microbial system can ever function in a stress-free mode, and this can often be due oxidative stress caused by reactive oxygen species as well as oscillating suboptimal or supraoptimal water activity (Hallsworth, 2018). Water activity, that is the mole fraction of water molecules in a solution, is a potent stress parameter that is numerically equivalent to relative humidity but divided by 100 (Scott, 1957). Cells respond to low water activity, osmotic stress and other water- and solute-induced stresses using a variety of mechanisms, including production of protein-stabilization proteins, increased generation of cell-available energy, adaptations of plasma-membrane composition and accumulation of soluble stress-metabolites (compatible solutes) that can act in osmotic adjustment and protect macromolecular structures, depending on the microbe and stress(es) experienced. Some microbes, known as xerophiles, are able to function optimally at much lower values of water activity than most other taxa. Here, 'xerophiles' refers to fungi that are capable of growth at low water activity on high-sugar or high-glycerol media (although some xerophilic fungi are also halophilic). Research into this group was historically driven by the food industry, with studies focusing on fungi that spoil high-sugar foods (Gane, 1950; Scott, 1957; Pitt, 1975; Dagnas and Membré, 2013; Biango-Daniels and Hodge, 2018). In recent years, an increasing amount of information has come to light about fungi in high-salt habitats, such as solar salterns (Gunde-Cimerman and Zalar, 2014; Nazareth and Gonsalves, 2014). Although some xerophiles are known to cause indoor contamination of building materials (Fig. 1A) and the formation of brown spots on paper (caused by the Maillard reaction and known as 'foxing': Arai, 2000; Piñar et al., 2015), the surfaces of domestic furniture and artefacts have generally been overlooked as a potential source of extremely xerotolerant microbes. Water availability is a potent determinant for life on Earth, and it is a quirk of history that water activity was designated a maximum value of 1. The parameter is derived using Raoult's Law (Scott, 1957), so we designate water activity in decimal fractions. For 50 years, the water-activity value at which the most-resilient microbe was thought to become non-functional is 0.605 (Pitt and Christian, 1968); equivalent to a relative humidity of 60.5%. In other words, whereas the biophysical window for microbial life on Earth spans a temperature range of approximately 160°C, the entire water-activity window for life is allocated a value of only 0.4 units (Stevenson et al., 2015a). Given that living systems are as sensitive to water stress as they are to temperature, this makes it is easy to overlook the profound impact of water activity on cellular systems. Optimal rates of growth/metabolism, and/or health, occur at different water-activity values, according mainly to the biological system. In humans and most other mammals, this is approximately 0.995 (Pirt and Thackery, 1964; Persons et al., 1987), for most fungi approximately 0.990 and for some extreme xerophiles 0.900–810 (Stevenson et al., 2015b; 2017a). In their study, Pitt and Christian isolated fungi from spoiled fruits, and determined the water-activity minima at which they were able to germinate. Aspergillus, Chrysosporium, Penicillium and other genera were present, but the most xerophilic was a Xeromyces bisporus strain (FRR 0025) that germinated at 0.605 water activity after a four-month incubation. For organismal systems, cellular water-activity tends to be closely regulated, although some plant systems and some invertebrates are able to undergo partial desiccation via anhydrobosis. Many fungi can survive dehydration but for mammals, such as ourselves, relatively small fluctuations of cellular water-activity are lethal. In relation to X. bisporus, 0.605 has been used as the seminal value upon which methodologies to preserve foods, museum specimens, artworks, documents and books have been based. In addition, the COSPAR Planetary Protection Policy, recognized by the United Nations, is based this value. This policy minimizes the risk of contamination events on extraterrestrial bodies with terrestrial microbes during space-exploration missions (Kminek et al., 2010; Rummel et al., 2014). Whereas X. bisporus has held its position as the most-extreme xerophile for five decades, there was little systematic research carried out during this time to find microbes that might be more xerophilic. It seemed difficult, therefore, to accept that strain FRR 0025, which originated from a prune, might not one day be dislodged from its number-one position. So, I set about trying to coax various microbes to multiply below this value. Optimistically, and with some naivety, we expected that achieving this would take several months. It transpired, however, that this scientific journey which began in 2001 threaded its way through several generations of research students and the three domains of microbial life; involved 126 collaborators/coauthors (from 22 countries), and sampling campaigns on two different continents; and spanned a period of almost 20 years. Working as a PhD student with Naresh Magan (Cranfield University, England, UK; 1991–1994), we exploited the phenotypic plasticity of entomopathogenic fungi to enhance intracellular accumulation of the compatible solutes trehalose, mannitol, arabitol, erythritol and glycerol. We found that the lowest molecular-weight polyols, especially glycerol, increased the vigour of, and reduced the water-activity minimum for, fungal germination and growth in vitro, and on the insect host (Hallsworth and Magan, 1994; 1995). After this, I took several postdoctoral positions, at Heriot-Watt University (Scotland, UK), Kumamoto Institute of Technology (Japan), Stellenbosch University (South Africa) and then – in the group of Kenneth N. Timmis – at University of Essex (England). The microbial model system(s) and their applications differed in each location, but the underlying theme was consistent; to identify cellular stress mechanisms and responses. This included stresses imposed by low-temperature and low water-activity, and that imposed by ethanol, urea and other chaotropic substances; that is those that entropically disordering macromolecular systems (i.e. those that are chaotropic). Whereas chaotropicity and water activity are mechanistically distinct stress parameters, the chaotrope-stress work impacted our search for microbes that can tolerate low water-activity. During the time in Essex, I worked on several projects, including the EU-funded Biotechnologies from the Deep (BIODEEP; 2001–2004), alongside halophile expert Terry J. McGenity. BIODEEP focused on the microbial ecology of the Mediterranean deep-sea anoxic brine lake Discovery that lies 3.58 km below the ocean surface. The brine of the lake body is saturated with MgCl2, and the lake's interface with the overlying seawater is a 1.5-m deep halocline with a Mg2+ gradient from 50 mM to 5.05 M (Hallsworth et al., 2007). Our study was carried out in collaboration with Michail M. Yakimov (Institute for Coastal Marine Environment, Italy), Peter N. Golyshin (Helmholtz Centre for Infection Research, Germany) and others, and the main scientific finding was that the chaotropicity of MgCl2 constrained life to the upper layers of the interface. There was no metabolic activity in evidence in the lower interface at MgCl2 concentrations of > 2.3 M. Furthermore, disparate lines of evidence indicated that the presence of kosmotropic (macromolecule-stabilizing) salts would enable microbial activity at slightly higher MgCl2 concentrations, by mitigating against the chaotropicity of the latter; a phenomenon that was confirmed in a number of other studies (Williams and Hallsworth, 2009; de Lima Alves et al., 2015; Cray et al., 2015; Yakimov et al., 2015). We also worked on NaCl-saturated deep-sea systems (Daffonchio et al., 2006), and noticed that some halophilic bacteria and Archaea exhibit very high growth rates – and even optimal growth – at NaCl saturation (0.755 water activity). However, proliferation has not been observed at lower water activity due to the finite solubility of NaCl. During the Lake Discovery study, we also worked on synthetic, MgCl2-dominated substrates and found that no halophiles can retain function in such brines even at 0.755 water activity (Hallsworth et al., 2007). So, we set about looking into how we might manufacture brines with a water-activity of < 0.755, yet a sufficiently low chaotropic activity to permit halophile metabolism. At the time, one of our colleagues commented that this kind of work 'seems a bit like breaking records'. This was an amiable colleague, and the comment was meant to be helpful, but we didn't share that view. For me, working with life at the point where the cellular system interfaces with extreme, thermodynamic constraints is in itself motivating, and even fascinating. Understanding system failure at the biophysical limit can potentially elucidate aspects of ecophysiology even for non-extremophilic microbes. We also believed that water plays a key role under the extreme (solute-induced) conditions where even the most-resilient microbes fail (Hallsworth et al., 2003; Stevenson et al., 2015a; Ball, 2017). We recruited MSc student Richa Sahay (2003–2004) for the study of halophiles at low water-activity. Richa cultured some of the most halophilic microbes known, and determined ability to grow in synthetic brines that contained NaCl+MgCl2 and NaCl+MgCl2 + either glycerol or ethylene glycol (and some nutrients). In this way, we found that some strains can indeed proliferate below 0.755 water activity, and even down to 0.681. Analyses of data from published sources (e.g. Javor, 1984; Yoshida et al., 1991; Antón et al., 2000; Bolhuis et al., 2004; Deole et al., 2013) were later carried out by PhD student Andrew Stevenson from 2013 to 2016, who worked with me once based in Belfast. To ensure that our study was as comprehensive as possible, we asked a number of experts to join us: Ailsa D. Hocking (fungal xerophiles; CSIRO Food and Nutrition, Australia), Nina Gunde-Cimerman (fungal halophiles; University of Ljubljana, Slovenia) Josefa Antón and Aharon Oren (halophilic bacteria and Archaea; University of Alicante, Spain and The Hebrew University of Jerusalem, Israel respectively) and others. Andy's analyses revealed that some prokaryotes function at even lower water-activity values; that is down to 0.635 (Fig. 1B). Collectively, the findings showed that the respective limits for the three domains-of-life actually converge close to a common water-activity value (Stevenson et al., 2015b). Additional studies, carried out by undergraduate student Callum J. D. Lee et al., confirmed that NaCl-saturated environments are moderate rather than thermodynamically extreme habitats for microbes; that is given that microbial ecosystems can function at < 0.755, saturated NaCl does not represent a water-activity barrier to the microbial biosphere (Lee et al., 2018). Jonathan A. Cray (PhD student from 2012 to 2015) became involved in our water-activity studies through his analyses of deep-sea brines (Yakimov et al., 2015). The scientific journey also wove its way through the stress biology of pathogenic aspergilli (Paulussen et al., 2017), and the biophysics of high-sugar ecosystems (Lievens et al., 2015). We also examined the evidence for ecosystem function, based on the functionality of the most-extreme xerophiles and halophiles at < 0.690 water activity (Stevenson et al., 2015a). Whereas there is an active international research community working on halophiles (this term gives 449 hits on the Web-of-Science database for the past five years; at 5 November 2018), fungal xerophiles are less-extensively studied (the term 'xerophile*' yields only 22 hits). The relatively low level of interest in xerophiles however, seems paradoxical given the important applications of fungal xerophiles, and the insights they offer into biophysics of life. Some of our other studies at the time of Richa's halophile study were focused on fungi and a Brazilian postdoc., Flávia de Lima Alves, joined us at University of Essex to work on this topic (2003–2004). Flávia's studies of solute-stress tolerance in Aspergillus wentii indicated that glycerol was the most biologically permissive solute that can be used to reduce the water activity of nutrient media (de Lima Alves et al., 2015). They also revealed that glycerol induces an osmotic change only momentarily, and then quickly equilibrates across the plasma membrane. At the same time as Richa and Flávia were working on solute-induced stresses, I made a recreational trip to Paris, visited a street market there, and purchased two wooden (mother-and-baby) owls that, according to the vendor, had been made in Thailand (Fig. 1C). This trip to the Parisian market, it turned out later, impacted our research trajectory. I began setting up a research group in Queen's University Belfast (Northern Ireland, UK) from 2006, and recruited PhD student Jim P. Williams at this time (2006–2009). He is an experiment-driven scientist with deep interest in cellular biology, and his sponsor provided blue-skies funding for the project. So, we were able to focus on the (arguably esoteric) search for microbial proliferation below 0.605 water-activity. We obtained xerophile strains by scouring the literature for extreme xerophiles and obtaining these from commercial culture collections, and via sampling campaigns in three humid climates: cool Northern Ireland and relatively hot regions of India and Japan. We began sampling activities by swabbing the surfaces of wooden structures located outdoors, and surfaces of furniture and domestic artefacts; some of these in my own home. The collection we amassed, 157 isolates in total, also included the X. bisporus strain (FRR 0025; i.e. ATCC 28298) that was isolated by John I. Pitt and used in the study by Pitt and Christian (1968). For all xerophile isolates, Jim began by assessing ability to grow at low water-activity using ethanol, NaCl, urea, ethylene glycol, KCl, ammonium nitrate, glycerol, MgCl2, guanidine hydrochloride, CaCl2, glucose and sorbitol as stressors, and established that the majority of strains grew at their lowest water-activity on glycerol-supplemented media. Jim assayed xerophile growth rates over a matrix of conditions (water activity, temperature, pH) and selected the 25 most-xerophilic strains, each capable of growth at ≤ 0.750 water activity. These included Aspergillus penicillioides JH06THH and JH06THJ (isolated from the mother owl, Fig. 1C), JH06GBM and JH06GBO (from the underside of an antique sycamore from the Fig. FRR (from dried (from an antique wooden purchased in Fig. FRR (from a Xeromyces bisporus FRR (from a FRR (from and FRR (from a (Williams and Hallsworth, strains isolated during our own sampling campaigns JH06GBO and were using a of and Aspergillus penicillioides strains JH06GBM and and strains and were isolated from wooden (Fig. that had been in the which is located close to the Northern Ireland of and on and with a wooden (and or It may be that such habitats for xerophile In to the water-activity minimum for Jim selected xerophiles a range of nutrient media with glycerol or glycerol kosmotropic solutes (e.g. NaCl, KCl, These studies some strains capable of growth at lower water-activity values that had been (i.e. in the range (Williams and Hallsworth, 2009; Stevenson et al., 2015b). These at water activity, A. penicillioides JH06THJ and X. bisporus strains FRR and FRR (Stevenson et al., at A. penicillioides strains JH06THH and FRR and at X. bisporus strains FRR (Williams and Hallsworth, We were by the finding that impacted water-activity minima for xerophile function, but at the same time not to have observed activity at ≤ The finding that X. bisporus can at 0.605 had not been or during studies of fungal Furthermore, whereas of growth a minimum for some halophiles of down to there are no of activity of halophilic bacteria or Archaea at ≤ 0.635 (Stevenson et al., 2015b). studies have high of microbial and growth at low water-activity growth of at et al., et al., germination of the fungal xerophile at and and data in the deep-sea brine lake at and to be evidence of and active such as and et al., 2018). data have not been and have either been (Pitt and Christian, Stevenson and Hallsworth, or data any cellular or activity et al., M. M. Yakimov et al., in We carried out analyses of growth for X. bisporus and A. penicillioides strains with the xerotolerant and found that the fungal cell is sensitive to of water activity of at (Stevenson et al., 2015a). We the for water-activity based on to be to an equivalent level of (Hallsworth and Stevenson et al., 2015b). on a wooden might water from and and may also water via cellular metabolism. that the mole fraction of water in and the are in (i.e. water activity and relative humidity are not the fungal cell would water from the with the but little work has been on this to the which I was a was et al., and we whether microbes proliferate by water from the The that microbes may be able to grow any source of water was a to some on and at our by Institute of and was the of that can on surfaces So, microbes on surfaces not known to may potentially a of water via formation that is to the This me to a with of a out studies into on plant We used a of formation on a plant to how can act as sources of water for (Stevenson et al., 2015a). are known to water from the and to water through metabolic but whether or not an source of water is for microbial proliferation Stevenson was in the of his PhD work at Queen's we to have a to the water-activity limit for via studies of germination on a range of media with glycerol or glycerol other number of xerophiles were selected for this X. bisporus strains FRR 0025, FRR (from spoiled FRR and FRR strain FRR strain FRR (from strain FRR (from strain FRR (from spoiled from the CSIRO Food and and A. penicillioides strains JH06THH and JH06THJ and strain (Stevenson et al., that contained high of intracellular glycerol were obtained from on glycerol-supplemented media. They were in of glycerol, or glycerol other solutes and these were used to the range of low water-activity media. this high-glycerol study system to of germination vigour at low water-activity, and reduced the water-activity minima for germination of to our however, germination not occur at ≤ X. bisporus germinated down to A. penicillioides to and to water activity. So, once our to microbial activity at ≤ 0.605 had been indicated a water-activity minimum for germination of X. bisporus and A. penicillioides of colleagues to us that are and that there may be no activity in below I the such but also that these extreme xerophiles were capable of more than we had observed within our system. In the of his PhD by this time, I with to one Many xerotolerant species were obtained from our sampling including from the of a dried in Fig. Aspergillus from an antique Fig. Penicillium and from a wooden in Fig. A. from the of a dried of in Fig. and Aspergillus and from (Fig. in India (Williams and Hallsworth, 2009; The most xerophilic isolates, however, from the surfaces of wooden (Fig. (Williams and Hallsworth, studies that were carried out to parameters such as temperature and established that A. penicillioides strain may be the most xerophilic strain in our collection (Fig. and it had germinated and growth at (Stevenson et al., 2015b; Furthermore, A. penicillioides has an and and is a that is (Stevenson et al., and J. Hallsworth, in more xerophilic than X. bisporus that is well known for an extreme et al., 2015). So, for our we focused on the obtained by swabbing the owls from the Parisian street market (Fig. 1C). We the germination slightly to water from the culture and were to to any in the rather than assessing + or – a of the was obtained by rates and of during the of production of germination structures, formation of and of and/or of by production of and/or production of and For this a range of media were a water-activity range from to (Stevenson et al., The germination in our study indicated that JH06THJ be capable of germination on most of these even the three at < 0.605 water activity (Stevenson et al., Whereas there were lower water-activity of germination indicated that these would not permit germination at their respective water-activity We to work with the The who has as a to the Institute with the of strain JH06THJ his low water-activity culture media. The to had been with the of the of germination as the it became that the had not yet the after Andy's to Belfast. the to on nutrient media at then on some other and then by – day – there was at glycerol-supplemented that is production of germination day cell had at had been (Fig. and JH06THJ well to of but the water-activity germination had on a with glycerol after so of we had observed and cell of a microbe at < 0.605 water activity. in Stevenson et this finding a in the water-activity window for microbial and this is to an of the temperature window for life. It seems paradoxical that the most xerophilic activity was observed on a high-glycerol although it may be that within the this In of data indicated an even lower water-activity of we up the study in which the high-glycerol system was found to be fungal germination at the water-activity limit for Stevenson et al., we focused on the biophysical role of glycerol. up the water-activity study, we the finding from an The finding has some interest from the and including to the COSPAR for the on the Planetary Protection for in and Planetary and to join the and and the of research The study fungi to conditions on the of the during a study et al., 2018). The has been to the research to A. penicillioides JH06THJ and other microbes to conditions during a in the This is level on the and thought to be the on Earth, with an temperature of and et al., et al., 2014). this may on to a study of for strain JH06THJ on the So, the search for an extreme xerophile was an and in to the wooden these provided an extremely this fungal strain to a of and and a number of the A. penicillioides JH06THJ was at values of water activity or relative humidity than or the humidity within a can often this value. However, such xerophiles can survive of and there may have been of water was once a of microbial on the of their water-activity minima that had been by J. I. Pitt Food and which to an focused on microbes, and has been and by (e.g. a recent trip to I was the of a whereas the microbial community was there was of based on position on the that was determined by water To me, this a living of with the microbial biosphere in – and in relation to water activity – across a of environmental of water activity also occur on to such as where water is from or other including those of the The water-activity for life in of a yet one that can be and For the water of some microbial habitats that (e.g. et al., 2013; et al., 2015) can and profound in water activity. The same phenomenon occurs in on surfaces and brine systems et al., et al., 2018). microbes within may in water (water activity and as the the cell may be water et al., et al., This how the of a limit for life can It also that the of Earth's biosphere is all us as the owls also sampling in can microbes and The is based on work by the and Research United and of and Northern and of and Northern was provided by and Andrew Stevenson University of UK), of The University, University of Australia), of Ailsa D. Hocking Food and Nutrition, Australia), Naresh Magan (Cranfield University, England, UK), Research Research University, of N. of J. of England, UK), Kenneth N. Timmis University and Michail M. Yakimov (Institute for Coastal Marine Environment,

This study investigates the influence of pH, temperature, and water activity on the occurrence of covalent adduct formation between select flavor compounds and a model food protein (β-lactoglobulin). These reactions potentially result in the loss of flavor during processing and storage, reducing consumer acceptability. Foods present a diverse reaction environment encompassing a wide range of aw, pH, and storage temperature, which potentially influence protein: flavor reaction rates. Liquid chromatography/mass spectrometry (LC/MS) data showed that covalent adducts were formed more slowly at low pHs (3) than basic pHs (8) (for citral, allyl isothiocyanate, and dimethyl trisulfide). No reactivity was observed for benzaldehyde at pH 3, but substantial reactivity was found at pHs 7 and 8. The amount of adducts formed increased with an increase in storage temperature. Higher temperatures (45 °C) led to the formation of products that were not observed at lower temperatures (4 and 20 °C). An increase in water activity (0.11-0.75) led to an increase in formation of adducts for allyl isothiocyanate. There were no observable differences in adduct formation as a function of aw for benzaldehyde, citral, and dimethyl disulfide. However, this lack of observed effect may be due to the rate of reaction being too slow to be detected in the timeframe of this study.

Quality and flavor evolution of infant formula during simulated secondary shelf-life storage: Focus on volatile compounds at different storage temperatures.

<span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">This research was conducted to study the chemical and microbiogical properties of goat milk kefir stored under different temperatures and storage time. A completely randomized design, factorial pattern 3 x 3 was used in this study. The first factor was storage temperature (-1 to -5; 1 to 5 and 6 to 10</span></span></span></span><span style="color: #000000;">^{<span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">o</span></span></span>}</span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">C) and the second factor was storage time (10; 20 and 30 day</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">s</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">). Each treatment has three replicates. Variables observed included pH, water activity (aw), total lactic acid bacteria (LAB), and total yeast. Data were subject to analysis of variance and Duncan’s multiple range t</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">est</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">. Results showed that storage time and temperature had significant effects on pH. The lowest pH of Kefir was obtained by storing it for 10 days at 6 to 10</span></span></span></span><span style="color: #000000;">^{<span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">o</span></span></span>}</span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">C. Titratable acidity was significantly affected by temperature, and kefir stored at 6 to 10</span></span></span></span><span style="color: #000000;">^{<span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">o</span></span></span>}</span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">C has the highest titratable acidity. Storage time and temperature had no significant effects on water activity, and the average water activity of kefir was 0.875±0.028. Total LAB and total yeast were significantly affected by temperature, but not by storage time. In average, total LAB and total yeast in kefir were 7.17± 0.92 log cfu/ml and 6.76± 0.39 log cfu/ml</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="id-ID">, respectively</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB">. In conclusion, this study confirmed that temperature of storage has a major contribution to the characteristics of kefir made from goat milk; hence it has to be considered when handling kefir for a</span></span></span></span><span style="color: #000000;"><span style="font-family: 'Times New Roman', serif;"><span><span lang="en-GB"> longer period of time.</span></span></span></span>

Effect of heat treatment, water activity and storage temperature on the oxidative stability of whole milk powder

The influence of controlled atmosphere storage on the flavor and texture profiles of display-ready pork cuts

Harpadon nehereus is a high-protein marine fish. A valuable way to add value to H. nehereus is to convert it into protein hydrolysate. The Maillard reaction is an effective way to improve the functional properties of peptides and proteins, which are affected by many factors such as reactant concentration, water activity, pH, temperature, and heating time. However, the traditional Maillard reaction method is inefficient. The purpose of this study was therefore to explore the effect of the ultrasound-assisted wet heating method on the Maillard reaction of H. nehereus protein hydrolysate (HNPH) in a new-type green solvent - a natural hypereutectic solvent (NADES). Harpadon nehereus protein hydrolysate-xylose (Xy) conjugates were prepared via a Maillard reaction in a NADES system using an ultrasound-assisted wet heating method. The effects of different treatment conditions on the Maillard reaction were studied. The optimized glycation degree (DG) of HNPH-Xy conjugates was obtained with a water content of 10%, a reaction temperature of 80 °C, a reaction time of 35 min, and an ultrasonic power level of 300 W. Compared with HNPH, the structure of HNPH-Xy conjugates were significantly changed. Moreover, the functional properties and antioxidant activity of HNPH-Xy were all superior to the HNPH. An ultrasound-assisted wet-heating Maillard reaction between HNPH and Xy in the NADES system could be a promising way to improve the functional properties of HNPH. © 2023 Society of Chemical Industry.

The Maillard reaction, also known as non-enzymatic browning reaction between reducing sugars and amino groups. This reaction is responsible for the formation of several compounds, called MRP (Maillard Reaction Products) for food products. The Maillard reaction produces undesirable effects during the processing and storage of different liquid foods such as milk or fruit juices whereas for other solid foods the changes are favorable (in the case of bread, breakfast cereals, candies, coffee, chocolate, etc.). The Maillard reaction is a complex reaction, since it is influenced by many factors such as temperature, pH, time, water activity, type and concentration of reactant source and sugar involved. In heated food products, two carcinogenic compounds are produced during maillard reactions, acrylamide and imidazoquinoline. Furosine and HMF are two compounds that indicate the extent of the maillard reaction related to the type and intensity of the food processing conditions. Keywords: Maillard reaction, melanoidin, furfural, amadori rearrangement

Chemical changes during cooking of wheat

The moisture sorption isotherms of a commercial potato powder were investigated at 20 degrees C for water activities ranging from 0.11 to 0.97. The sorption isotherms were typical type-II sigmoidal curves, with a steep increase in moisture content for water activities above 0.9 and exhibiting hysteresis over the whole water activity range. On the basis of the isotherms, the influence of the initial water activity and moisture content on both Maillard browning and acrylamide formation was determined by heating oil containing potato powder mixtures in a closed stainless-steel tubular reactor. The Maillard browning, as determined spectrophotometrically, showed an optimum at intermediate water activities. The yields of acrylamide, expressed relatively to the molar amount of asparagine, remained constant below 0.8 aw and below moisture contents of about 20% (on a dry basis). For the more intense heat treatments, an increased acrylamide yield was however observed at higher moisture contents, with an optimum at water contents of about 100% (on a dry basis). However, this increase and optimum was not observed at less intense heat treatments. At moisture contents above 100%, a significant decrease in acrylamide yields was assessed, although the water activity increased only marginally in this area of the sorption isotherms. It was thus observed that the acrylamide content was rather dependent upon the moisture content than upon the water activity in the high-moisture potato powder model system.

Influence of temperature, water activity and time on cookability and color of a stored Rwandan dry bean ( Phaseolus vulgaris) mixture

Propofol is an intravenous anesthetic commonly used due to its favorable pharmacokinetic and pharmacodynamic profile. There are discrepancies in the literature about the most appropriate sample for determining propofol concentrations. Although plasma has been used for determining propofol concentrations, whole blood has been the preferred sample. There is also a lack of consistency in the literature on the effect of storage time and temperature on propofol concentrations and this may lead to errors in the design of pharmacokinetic/pharmacodynamics studies. The purpose of this study was to determine the difference in propofol concentrations in whole blood versus plasma and to evaluate the influence of storage time (56 days) and temperature (4 °C, −20 °C, −80 °C) on the stability of propofol concentrations in blood and plasma samples. Results from the study indicate that whole blood and plasma samples containing propofol stored at −80 °C have concentrations as high as or higher than those stored at 4 °C or −20 °C for 56 days; thus, −80 °C is an appropriate temperature for propofol sample storage. Plasma propofol concentrations were consistently higher than whole blood for all three storage temperatures. Consequently, plasma is the most appropriate sample for propofol analysis due to its consistent determinations.

Propofol is an intravenous anesthetic commonly used due to its favorable pharmacokinetic and pharmacodynamic profile. There are discrepancies in the literature about the most appropriate sample for determining propofol concentrations. Although plasma has been used for determining propofol concentrations, whole blood has been the preferred sample because propofol is significantly bound to erythrocytes. There is also a lack of consistency in the literature on the effect of storage time and temperature on propofol concentrations and this may lead to errors in the design of pharmacokinetic/pharmacodynamics studies. The purpose of this study was to determine the difference in propofol concentrations in whole blood versus plasma and to evaluate the influence of storage time (56 days) and temperature (4°C, -20°C, -80°C) on the stability of propofol concentrations in blood and plasma samples. Results from the study indicate that whole blood and plasma samples containing propofol were stable for at least 56 days when stored at -80°C; thus, -80°C is the most appropriate temperature for propofol sample storage out of the three temperatures evaluated. Plasma propofol concentrations were consistently higher than whole blood for all 3 storage temperatures. Consequently, plasma is the most appropriate sample for propofol analysis due to its consistent determinations.

Redness generation via Maillard reactions of whey protein isolate (WPI) and ascorbic acid (vitamin C) in spray-dried powders